HomeMy WebLinkAbout5ALateDocument23663 9 Human Health Effects 9. Human Health Effects 9.1. Diseases 9.2. Nutrition 9.3. Human Longevity 9.4. Food vs. Nature 9.5. Biofuels The idea that CO2-induced global warming is harmful
to people’s health has become entrenched in popular culture, with the reports of the Intergovernmental Panel on Climate Change (IPCC) being the source of much of this concern. In the
Working Group II contribution to the Fourth Assessment Report, the authors claim to have “very high confidence” that “climate change currently contributes to the global burden of disease
and premature deaths” (IPCC, 2007-II, p. 393). They also claim climate change will “increase malnutrition and consequent disorders … increase the number of people suffering from death,
disease and injury from heatwaves, floods, storms, fires and droughts … continue to change the range of some infectious disease vectors … increase the burden of diarrhoeal diseases …
increase cardiorespiratory morbidity and mortality associated with ground-level ozone … [and] inc?rease the number of people at risk of dengue.” The IPCC admits that warming weather
would “bring some benefits to health, including fewer deaths from cold,” but says those benefits “will be outweighed by the negative effects of rising temperatures worldwide, especially
in developing countries” (Ibid.). Some of these claims have been shown in previous chapters to be counterfactual. For example, research cited in Chapter 6 showed the global warming that
occurred in the twentieth century did not cause more “heatwaves, floods, storms, fires and droughts,” and that a warmer world is likely to see fewer episodes of these extreme weather
events than a cooler world. We will not repeat that analysis in this chapter. This chapter reviews data on the relationships between temperature and CO2 and diseases, heatrelated mortality,
nutrition, and human longevity. We find in each case that global warming is likely to improve human health. Section 9.4 explains how rising CO2 concentrations in the air will play a
positive role in solving the conflict between the need to raise food for a growing population and the need to protect natural ecosystems. Section 9.5 describes the negative role played
by increased use of biofuels, which the IPCC advocates in the Working Group III contribution to the Fourth Assessment Report (IPCC, 2007-III), in this same conflict. References IPCC.
2007-II. Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change,
M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden and C.E. Hanson (Eds.) Cambridge University Press, Cambridge, UK. IPCC. 2007-III. Climate Change 2007: Mitigation. Contribution
of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. B. Metz, O.R. Davidson, P.R. Bosch, R. Dave, L.A. Meyer (Eds.) Cambridge University
Press, Cambridge, UK.
Climate Change Reconsidered 664 9.1. Diseases Which is more deadly: heat or cold? Rising temperatures or falling temperatures? The IPCC claims warming is the primary danger to be avoided
at all costs. Real-world data, however, indicate the opposite. Systematic research on the relationship between heat and human health dates back to the 1930s (Gover, 1938; Kutschenreuter,
1950; Kutschenreuter, 1960; Oechsli and Buechley, 1970). Early studies by Bull (1973) and Bull and Morton (1975a,b) in England and Wales, for example, demonstrated that normal changes
in temperature typically are inversely associated with death rates, especially in older subjects. That is, when temperatures rise, death rates fall; when temperatures fall, death rates
rise. Bull and Morton (1978) concluded “there is a close association between temperature and death rates from most diseases at all temperatures,” and it is “very likely that changes
in external temperature cause changes in death rates.” Since this early research was published, a a large number of studies have confirmed the original findings. Contrary to the IPCC’s
highly selective reading of the literature, the overwhelming majority of researchers in the field have found that warmer weather reduces rather than increases the spread and severity
of many diseases and weather-related mortality rates. We review this literature in the following order: cardiovascular diseases, respiratory diseases, malaria, tick-borne diseases, and
finally cold-and heat-related mortality from all diseases. Additional information on this topic, including reviews on the health effects of CO2 not discussed here, can be found at http://www.co2
science.org/subject/h/subject_h.php under the heading Health Effects. References Bull, G.M. 1973. Meteorological correlates with myocardial and cerebral infarction and respiratory disease.
British Journal of Preventive and Social Medicine 27: 108. Bull, G.M. and Morton, J. 1975a. Seasonal and short-term relationships of temperature with deaths from myocardial and cerebral
infarction. Age and Ageing 4: 19-31. Bull, G.M. and Morton, J. 1975b. Relationships of temperature with death rates from all causes and from certain respiratory and arteriosclerotic
diseases in different age groups. Age and Ageing 4: 232-246. Bull, G.M. and Morton, J. 1978. Environment, temperature and death rates. Age and Ageing 7: 210-224. Gover, J. 1938. Mortality
during periods of excessive temperatures. Public Health Rep. 53: 1122-1143. Kutschenreuter, P.H. 1950. Weather does affect mortality. Amer. Soc. Heat. Refrig. Air-Cond. Eng. 2: 39-43.
Kutschenreuter, P.H. 1960. A study of the effect of weather on mortality in New York City. M.S. Thesis. Rutgers University, New Jersey, USA. Oechsli, F.W. and Buechley, R.W. 1970. Excess
mortality associated with three Los Angeles September hot spells. Environmental Research 3: 277-284. 9.1.1. Cardiovascular Diseases A good place to begin a review of temperature-related
mortality is a cold location … like Siberia. Feigin et al. (2000) examined the relationship between stroke occurrence and weather parameters in the Russian city of Novosibirsk, which
has one of the highest incidence rates of stroke in the world. Analyzing the health records of 2,208 patients with a sex and age distribution similar to that of the whole of Russia over
the period 1982-93, they found a statistically significant association between stroke occurrence and low ambient temperature. For ischemic stroke (IS), which accounted for 87 percent
of all strokes recorded, they report that the risk of IS occurrence on days with low ambient temperature is 32 percent higher than on days with high ambient temperature. They recommend
implementing “preventive measures … such as avoiding low temperature.” Hong et al. (2003) studied weather-related death rates in Incheon, Korea over the period January 1998 to December
2000, reporting that “decreased ambient temperature was associated with risk of acute ischemic stroke,” with the strongest effect being seen on the day after exposure to cold weather.
They found found that “even a moderate decrease in temperature can increase the risk of ischemic stroke.” In addition, “risk estimates associated with decreased temperature were greater
in winter than in the summer,” suggesting that “low temperatures as well as temperature changes are associated with the onset of ischemic stroke.” Nafstad et al. (2001) studied weather-related
death rates in Oslo, Norway. Thanks to a Norwegian
Human Health Effects 665 law requiring all deaths to be examined by a physician who diagnoses cause and reports it on the death certificate, they were able to examine the effects of
temperature on mortality due to all forms of cardiovascular disease for citizens of the country’s capital over the period 1990 to 1995. They found that the average daily number of cardiovascular-rela
ed deaths was 15 percent higher in the winter months (October-March) than in the summer months (April-September), leading them to conclude that “a milder climate would lead to a substantial
reduction in average daily number of deaths.” Hajat and Haines (2002) set out to determine if cardiovascular-related doctor visits by the elderly bore a similar relationship to cold
temperatures. Based on data obtained for registered patients aged 65 and older from several London, England practices between January 1992 and September 1995, they found the mean number
of general practitioner consultations was higher in the cool-season months (October-March) than in the warm-season months (April-September) for all cardiovascular diseases. Of course,
one might say, such findings are only to be expected in cold climates. What about warm climates, where summer maximum temperatures are often extreme, but summer minimum temperatures
are typically mild? Research conducted by Green et al. (1994) in Israel revealed that between 1976 and 1985, mortality from cardiovascular disease was 50 percent higher in mid-winter
than in mid-summer, both in men and women and in different age groups, in spite of the fact that summer temperatures in the Negev, where much of the work was conducted, often exceed
30°C, while winter temperatures typically do not drop below 10°C. These findings were substantiated by other Israeli studies reviewed by Behar (2000), who states that “most of the recent
papers on this topic have concluded that a peak of sudden cardiac death, acute myocardial infarction and other cardiovascular conditions is usually observed in low temperature weather
during winter.” Evidence of a seasonal variation in cardiacrelated mortality has been found in the mild climate of southern California in the United States. In a study of all 222,265
death certificates issued by Los Angeles County for deaths caused by coronary artery disease from 1985 through 1996, Kloner et al. (1999) found that death rates in December and January
were 33 percent higher than those observed in the period June through September. Likewise, based on a study of the Hunter region of New South Wales, Australia that covered the period
1 July 1985 to 30 June 1990, Enquselassie et al. (1993) determined that “fatal coronary events and non-fatal definite myocardial infarction were 20-40 percent more common in winter and
spring than at other times of year.” Regarding daily temperature effects, they found that “rate ratios for deaths were significantly higher for low temperatures,” noting that “on cold
days coronary deaths were up to 40 percent more likely to occur than at moderate temperatures.” In a study study of “hot” and “cold” cities in the United States—where Atlanta, Georgia;
Birmingham, Alabama; and Houston, Texas comprised the “hot” group, and Canton, Ohio; Chicago, Illinois; Colorado Springs, Colorado; Detroit, Michigan; Minneapolis-St. Paul, Minnesota;
New Haven, Connecticut; Pittsburgh, Pennsylvania; and Seattle and Spokane, Washington comprised the “cold” group—Braga et al. (2002) determined the acute effects and lagged influence
of temperature on cardiovascular-related deaths. They found that in the hot cities, neither hot nor cold temperatures had much impact on mortality related to cardiovascular disease (CVD).
In the cold cities, on the other hand, they report that both high and low temperatures were associated with increased CVD deaths, with the effect of cold temperatures persisting for
days but the effect of high temperatures restricted to the day of the death or the day before. Of particular interest was the finding that for all CVD deaths the hot-day effect was five
times smaller than the cold-day effect. In addition, the hot-day effect included some “harvesting,” where the authors observed a deficit of deaths a few days later, which they did not
observe for the cold-day effect. Gouveia et al. (2003), in a study conducted in Sao Paulo, Brazil using data from 1991-1994, found that the number of cardiovascular-related deaths in
adults (15-64 years of age) increased by 2.6 percent for each 1°C decrease in temperature below 20°C, while there was no evidence for any heat-induced deaths due to temperatures rising
above 20°C. In the elderly (65 years of age and above), however, a 1°C warming above 20°C led to a 2 percent increase in deaths; but a 1°C cooling below 20°C led to a 6.3 percent increase
in deaths, or more than three times as many cardiovascular-related deaths due to cooling than to warming in the elderly. Similar results have been found in Australia (Enquselassie et
al., 1993), Brazil (Sharovsky et al., 2004), England (McGregor, 2005; Carder et al., 2005; McGregor et al., 2004; and Kovats et al., 2004), Greece (Bartzokas et al., 2004), Japan (Nakaji
et al., 2004), the United States (Cagle and Hubbard, 2005),
Climate Change Reconsidered 666 and parts of Africa, Asia, Europe, Latin America and the Caribbean (Chang et al., 2004). These studies demonstrate that global warming reduces the incidence
of cardiovascular disease related to low temperatures and wintry weather by a much greater degree than it increases the incidence associated with high temperatures and summer heat waves.
Additional information on this topic, including reviews of newer publications as they become available, can be found at http://www.co2 science.org/subject/h/healtheffectscardio.php.
References Bartzokas, A., Kassomenos, P., Petrakis, M. and Celessides, C. 2004. The effect of meteorological and pollution parameters on the frequency of hospital admissions for cardiovascular
and respiratory problems in Athens. Indoor and Built Environment 13: 271-275. Behar, S. 2000. Out-of-hospital death in Israel -Should we blame the weather? Israel Medical Association
Journal 2: 56-57. Braga, A.L.F., Zanobetti, A. and Schwartz, J. 2002. The effect of weather on respiratory and cardiovascular deaths in 12 U.S. cities. Environmental Health Perspectives
110: 859-863. Cagle, A. and Hubbard, R. 2005. Cold-related cardiac mortality in King County, Washington, USA 1980-2001. Annals of Human Biology 32: 525-537. Carder, M., McNamee, R.,
Beverland, I., Elton, R., Cohen, G.R., Boyd, J. and Agius, R.M. 2005. The lagged effect of cold temperature and wind chill on cardiorespiratory mortality in Scotland. Occupational and
Environmental Medicine 62: 702-710. Chang, C.L., Shipley, M., Marmot, M. and Poulter, N. 2004. Lower ambient temperature was associated with an increased risk of hospitalization for
stroke and acute myocardial infarction in young women. Journal of Clinical Epidemiology 57: 749-757. Enquselassie, F., Dobson, A.J., Alexander, H.M. and Steele, P.L. 1993. Seasons, temperature
and coronary disease. International Journal of Epidemiology 22: 632-636. Feigin, V.L., Nikitin, Yu.P., Bots, M.L., Vinogradova, T.E. and Grobbee, D.E. 2000. A population-based study
of of the associations of stroke occurrence with weather parameters in Siberia, Russia (1982-92). European Journal of Neurology 7: 171-178. Gouveia, N., Hajat, S. and Armstrong, B. 2003.
Socioeconomic differentials in the temperature-mortality relationship in Sao Paulo, Brazil. International Journal of Epidemiology 32: 390-397. Green, M.S., Harari, G., Kristal-Boneh,
E. 1994. Excess winter mortality from ischaemic heart disease and stroke during colder and warmer years in Israel. European Journal of Public Health 4: 3-11. Hajat, S. and Haines, A.
2002. Associations of cold temperatures with GP consultations for respiratory and cardiovascular disease amongst the elderly in London. International Journal of Epidemiology 31: 825-830.
Hong, Y-C., Rha, J-H., Lee, J-T., Ha, E-H., Kwon, H-J. and Kim, H. 2003. Ischemic stroke associated with decrease in temperature. Epidemiology 14: 473-478. Kloner, R.A., Poole, W.K.
and Perritt, R.L. 1999. When throughout the year is coronary death most likely to occur? A 12-year population-based analysis of more than 220,000 cases. Circulation 100: 1630-1634. Kovats,
R.S., Hajat, S. and Wilkinson, P. 2004. Contrasting patterns of mortality and hospital admissions during hot weather and heat waves in Greater London, UK. Occupational and Environmental
Medicine 61: 893-898. McGregor, G.R. 2005. Winter North Atlantic Oscillation, temperature and ischaemic heart disease mortality in three English counties. International Journal of Biometeorology
49: 197-204. McGregor, G.R., Watkin, H.A. and Cox, M. 2004. Relationships between the seasonality of temperature and ischaemic heart disease mortality: implications for climate based
health forecasting. Climate Research 25: 253-263. Nafstad, P., Skrondal, A. and Bjertness, E. 2001. Mortality and temperature in Oslo, Norway. 1990-1995. European Journal of Epidemiology
17: 621-627. Nakaji, S., Parodi, S., Fontana, V., Umeda, T., Suzuki, K., Sakamoto, J., Fukuda, S., Wada, S. and Sugawara, K. 2004. Seasonal changes in mortality rates from main causes
of of death in Japan (1970-1999). European Journal of Epidemiology 19: 905-913. Sharovsky, R., Cesar, L.A.M. and Ramires, J.A.F. 2004. Temperature, air pollution, and mortality from
myocardial infarction in Sao Paulo, Brazil. Brazilian Journal of Medical and Biological Research 37: 1651-1657.
Human Health Effects 667 9.1.2. Respiratory Diseases As was true of cardiovascular-related mortality, deaths due to respiratory diseases are more likely to be associated with cold conditions
in cold countries. In Oslo, where Nafstad et al. (2001) found winter deaths due to cardiovascular problems to be 15 percent more numerous than similar summer deaths, they also determined
that deaths due to respiratory diseases were fully 47 percent more numerous in winter than in summer. Likewise, the London study of Hajat and Haines (2002) revealed that the number of
doctor visits by the elderly was higher in coolseason than warm-season months for all respiratory diseases. At mean temperatures below 5°C, in fact, the relationship between respiratory
disease consultations and temperature was linear, and stronger at a time lag of six to 15 days, such that a 1°C decrease in mean temperature below 5°C was associated with a 10.5 percent
increase in all respiratory disease consultations. Gouveia et al. (2003) found that death rates in Sao Paulo, Brazil due to a 1°C cooling were twice as great as death rates due to a
1°C warming in adults, and 2.8 times greater in the elderly. Donaldson (2006) studied the effect of annual mean daily air temperature on the length of the yearly respiratory syncytial
virus (RSV) season in England and Wales for 1981-2004 and found “emergency department admissions (for 1990-2004) ended 3.1 and 2.5 weeks earlier, respectively, per 1°C increase in annual
central England temperature (P = 0.002 and 0.043, respectively).” He concludes that “the RSV season has become shorter” and “these findings imply a health benefit of global warming in
England and Wales associated with a reduction in the duration of the RSV season and its consequent impact on the health service.” The study of hot and cold cities in the United States
by Braga et al. (2002) found that increased temperature variability is the most significant aspect of climate change with respect to respiratory-related deaths in the U.S. Why is this
finding important? Because Robeson (2002) has clearly demonstrated, from a 50-year study of daily temperatures at more than 1,000 U.S. weather stations, that temperature variability
declines with warming, and at a very substantial rate. The reduced temperature variability in a warmer world would lead to reductions in temperature-related deaths at both the high and
low ends of the daily temperature spectrum at all times of the year. These studies show that a warming world would improve people’s health by reducing deaths related to respiratory disease.
Additional information on this topic, including reviews of newer publications as they become available, can be found at http://www.co2 science.org/subject/h/healtheffectsresp.php. References
Braga, A.L.F., Zanobetti, A. and Schwartz, J. 2002. The effect of weather on respiratory and cardiovascular deaths in 12 U.S. cities. Environmental Health Perspectives 110: 859-863.
Donaldson, G.C. 2006. Climate change and the end of the respiratory syncytial virus season. Clinical Infectious Diseases 42: 677-679. Gouveia, N., Hajat, S. and Armstrong, B. 2003. Socioeconomic
differentials in the temperaturemortality relationship in Sao Paulo, Brazil. International Journal of Epidemiology 32: 390-397. Hajat, S. and Haines, A. 2002. Associations of cold temperatures
with GP consultations for respiratory and cardiovascular disease amongst the elderly in London. International Journal of Epidemiology 31: 825-830. Nafstad, P., Skrondal, A. and Bjertness,
E. 2001. Mortality and temperature in Oslo, Norway. 1990-1995. European Journal of Epidemiology 17: 621-627. Robeson, S.M. 2002. Relationships between mean and standard deviation of
air temperature: implications for global warming. Climate Research 22: 205-213. 9.1.3. Malaria Rogers and Randolph (2000) note that “predictions of global climate change have stimulated
forecasts that vector-borne diseases will spread into regions that are at present too cool for their persistence.” Such predictions are a standard part of the narrative of those who
believe global warming would have catastrophic effects. However, even the IPCC states “there is still much uncertainty about the potential impact of climate change on malaria in local
and global scales” and “further research is warranted” (IPCC, 2007-II, p. 404). According to Reiter (2000), claims that malaria resurgence is the product of CO2-induced global warming
ignore the disease’s history and an extensive literature showing factors other than climate are
Climate Change Reconsidered 668 known to play more important roles in the disease’s spread. For example, historical analysis reveals that malaria was an important cause of illness and
death in England during the Little Ice Age. Its transmission began to decline only in the nineteenth century, during a warming phase when, according to Reiter, “temperatures were already
much higher than in the Little Ice Age.” Why was malaria prevalent in Europe during some of the coldest centuries of the past millennium? And why have we only recently witnessed malaria’s
widespread decline at a time when temperatures are warming? Other factors are at work, such as the quality of public health services, irrigation and agricultural activities, land use
practices, civil strife, natural disasters, ecological change, population change, use of insecticides, and the movement of people (Reiter, 2000; Reiter, 2001; Hay et al., 2002). Models
employed by the IPCC predict widespread future increases in malaria because nearly all of the analyses they cite used only one, or at most two, climate variables to make predictions
of the future distribution of the disease over the earth, and they generally do not include any non-climatic factors. In one modeling study that used more than just one or two variables,
Rogers and Randolph (2000) employed five climate variables and obtained very different results. Briefly, they used the present-day distribution of malaria to determine the specific climatic
constraints that best define that distribution, after which the multivariate relationship they derived from this exercise was applied to future climate scenarios derived from state-of-the-art
climate models, in order to map potential future geographical distributions of the disease. They found only a 0.84 percent increase in potential malaria exposure under the “medium-high”
scenario of global warming and a 0.92 percent decrease under the “high” scenario. They state that their quantitative model “contradicts prevailing forecasts of global malaria expansion”
and “highlights the use [we would say superiority] of multivariate rather than univariate constraints in such applications.” This study undercuts the claim that any future warming of
the globe will allow malaria to spread into currently malaria-free regions. Hay et al. (2002) investigated long-term trends in meteorological data at four East African highland sites
that experienced significant increases in malaria cases over the past couple decades, reporting that “temperature, rainfall, vapour pressure and the number of months suitable for P.
falciparum transmission have not changed significantly during the past century or during the period of reported malaria resurgence.” Therefore, these factors could not be responsible
for the observed increases in malaria cases. Likewise, Shanks et al. (2000) examined trends in temperature, precipitation, and malaria rates in western Kenya over the period 1965-1997,
finding no linkages among the variables. Also working in Africa, Small et al. (2003) examined trends in a climate-driven model of malaria transmission between 1911 and 1995, using a
spatially and temporally extensive gridded climate data set to identify locations where the malaria transmission climate suitability index had changed significantly over this time interval.
Then, after determining areas of change, they more closely examined the underlying climate forcing of malaria transmission suitability for those localities. This protocol revealed that
malaria transmission suitability did increase because of climate change in specific locations of limited extent, but in Southern Mozambique, which was the only region for which climatic
suitability consistently increased, the cause of the increase was increased precipitation, not temperature. In fact, Small et al. say that “climate warming, expressed as a systematic
temperature increase over the 85-year period, does not appear to be responsible for an increase in malaria suitability over any region in Africa.” They concluded that “research on the
links between climate change and the recent resurgence of malaria across Africa would be best served through refinements in maps and models of precipitation patterns and through closer
examination of the role of nonclimatic influences.” The great significance of this has recently been demonstrated by Reiter et al. (2003) for dengue fever, another important mosquito-borne
disease. Examining the reemergence of malaria in the East African highlands, Zhou et al. (2004) conducted a nonlinear mixed-regression model study that focused on the numbers of monthly
malaria outpatients of the past 10-20 years in seven East African highland sites and their relationships to the numbers of malaria outpatients during the previous time period, seasonality
and climate variability. They say that “for all seven study sites, we found highly significant nonlinear, synergistic effects of the interaction between rainfall and temperature on malaria
incidence, indicating that the use of either temperature or rainfall alone is not sensitive enough
Human Health Effects 669 for the detection of anomalies that are associated with malaria epidemics.” This has also been found by Githeko and Ndegwa (2001), Shanks et al. (2002) and Hay
et al. (2002). Climate variability—not just temperature or warming—contributed less than 20 percent of the temporal variance in the number of malaria outpatients, and at only two of
the seven sites studied. In light of their findings, Zhou et al. concluded that “malaria dynamics are largely driven by autoregression and/or seasonality in these sites” and that “the
observed large among-site variation in the sensitivity to climate fluctuations may be governed by complex interactions between climate and biological and social factors.” This includes
“land use, topography, P. falciparum genotypes, malaria vector species composition, availability of vector control and healthcare programs, drug resistance, and other socioeconomic factors.”
Among these are “failure to seek treatment or delayed treatment of malaria patients, and HIV infections in the human population,” which they say have “become increasingly prevalent.”
Kuhn et al. (2003) say “there has been much recent speculation that global warming may allow the reestablishment of malaria transmission in previously endemic areas such as Europe and
the United States.” To investigate the robustness of this hypothesis, they analyzed the determinants of temporal trends in malaria deaths within England and Wales from 1840-1910. Their
analysis found that “a 1°C increase or decrease was responsible for an increase in malaria deaths of 8.3 percent or a decrease of 6.5 percent, respectively,” which explains “the malaria
epidemics in the ‘unusually hot summers’ of 1848 and 1859.” Nevertheless, the long-term near-linear temporal decline in malaria deaths over the period of study, in the words of the researchers,
“was probably driven by nonclimatic factors.” Among these they list increasing
livestock populations (which tend to divert mosquito biting from humans), decreasing acreages of marsh wetlands (where mosquitoes breed), as well as “improved housing, better access
to health care and medication, and improved nutrition, sanitation, and hygiene.” They additionally note that the number of secondary cases arising from each primary imported case “is
currently minuscule,” as demonstrated by the absence of any secondary malaria cases in the UK since 1953. Although simplistic model simulations may suggest that the increase in temperature
predicted for Britain by 2050 is likely to cause an 8-14 percent increase in the potential for malaria transmission, Kuhn et al. say “the projected increase in proportional risk is clearly
insufficient to lead to the reestablishment of endemicity.” Expanding on this statement, they note that “the national health system ensures that imported malaria infections are detected
and effectively treated and that gametocytes are cleared from the blood in less than a week.” For Britain, they conclude that “a 15 percent rise in risk might have been important in
the 19th century, but such a rise is now highly unlikely to lead to the reestablishment of indigenous malaria,” since “socioeconomic and agricultural changes” have greatly altered the
cause-and-effect relationships of the past. Zell (2004) states that many people “assume a correlation between increasing disease incidence and global warming.” However, “the factors
responsible for the emergence/reemergence of vector-borne diseases are complex and mutually influence each other.” He cites as an example the fact that “the incidence and spread of parasites
and arboviruses are affected by insecticide and drug resistance, deforestation, irrigation systems and dams, changes in public health policy (decreased resources of surveillance, prevention,
and vector control), demographic changes (population growth, migration, urbanization), and societal changes (inadequate housing conditions, water deterioration, sewage, waste management).”
Therefore, as he continues, “it may be over-simplistic to attribute emergent/reemergent diseases to climate change and sketch the menace of devastating epidemics in a warmer world.”
Indeed, Zell states that “variations in public health practices and lifestyle can easily outweigh changes in disease biology,” especially those that might be caused by global warming.
Rogers and Randolph (2006) ask if climate change could be responsible for recent upsurges of malaria in Africa. They demonstrate that “evidence for increasing malaria in many parts of
Africa is overwhelming, but the more likely causes for most of these changes to date include land-cover and land-use changes and, most importantly, drug resistance rather than any effect
of climate,” noting that “the recrudescence of malaria in the tea estates near Kericho, Kenya, in East Africa, where temperature has not changed significantly, shows all the signs of
a disease that has escaped drug control following the evolution of chloroquine resistance by the malarial parasite.” They then go on to explain that “malaria waxes and wanes to the beat
of two rhythms: an
Climate Change Reconsidered 670 annual one dominated by local, seasonal weather conditions and a ca. 3-yearly one dominated by herd immunity,” noting that “effective drugs suppress both
cycles before they can be expressed,” but that “this produces a population which is mainly or entirely dependent on drug effectiveness, and which suffers the consequence of eventual
drug failure, during which the rhythms reestablish themselves, as they appear to have done in Kericho.” Childs et al. (2006) present a detailed analysis of malaria incidence in northern
Thailand from January 1977 through January 2002 in the country’s 13 northern provinces. Over this time period, when the IPCC claims the world warmed at a rate and to a level that were
unprecedented over the prior two millennia, Childs et al. report a decline in total malaria incidence (from a mean monthly incidence of 41.5 to 6.72 cases per hundred thousand people.
Noting “there has been a steady reduction through time of total malaria incidence in northern Thailand, with an average decline of 6.45 percent per year,” they say this result “reflects
changing agronomic practices and patterns of immigration, as well as the success of interventions such as vector control programs, improved availability of treatment and changing drug
policies.” Finally, some researchers have studied the effect of rising CO2 concentrations on the mosquitos that transmit malaria. Tuchman et al. (2003) took leaf litter from Populus
tremuloides (Michaux) trees that had been grown out-of-doors in open-bottom root boxes located within open-top above-ground chambers maintained at atmospheric CO2 concentrations of either
360 or 720 ppm for an entire growing season, incubated the leaf litter for 14 days in a nearby stream, and fed the incubated litter to four species of detritivorous mosquito larvae to
assess its effect on their development rates and survivorship. This work revealed that larval mortality was 2.2 times higher for Aedes albopictus (Skuse) mosquitos that were fed leaf
litter that had been produced in the high-CO2 chambers than it was for those fed litter that had been produced in the ambient-air chambers. In addition, Tuchman et al. found that larval
development rates of Aedes triseriatus (Say), Aedes aegypti (L.), and Armigeres subalbatus (Coquillett) were slowed by 78 percent, 25 percent, and 27 percent, respectively, when fed
litter produced in the high-CO2 as opposed to the ambient-CO2 chambers, so that mosquitoes of these species spent 20, 11, and nine days longer in their respective larval stages when
feeding on litter produced in the CO2-enriched as compared to the ambient-CO2 chambers. As for the reason behind these observations, the researchers suggest that “increases in lignin
coupled with decreases in leaf nitrogen induced by elevated CO2 and subsequent lower bacterial productivity [on the leaf litter in the water] were probably responsible for [the] decreases
in survivorship and/or development rate of the four species of mosquitoes.” What is the significance of these findings? In the words of Tuchman et al., “the indirect impacts of an elevated
CO2 atmosphere on mosquito larval survivorship and development time could potentially be great,” because longer larval development times could result in fewer cohorts of mosquitoes surviving
to adulthood; and with fewer mosquitoes around, there should be lower levels of mosquito-borne diseases. In conclusion, research that takes into account more than one or two variables
typically shows little or no relationship between the incidence of malaria and temperature. Many factors are more important than temperature, and those that are subject to human control
are being used to steadily reduce the incidence of deaths from this disease. In the words of Dye and Reiter (2000), “given adequate funding, technology, and, above all, commitment, the
campaign to ‘Roll Back Malaria,’ spearheaded by the World Health Organization, will have halved deaths related to [malaria] by 2010” -independent of whatever tack earth’s climate might
take in the interim. Additional information on this topic, including reviews of newer publications as they become available, can be found at at http://www.co2 science.org/subject/m/malaria.php
References Childs, D.Z., Cattadori, I.M., Suwonkerd, W., Prajakwong, S. and Boots, M. 2006. Spatiotemporal patterns of malaria incidence in northern Thailand. Transactions of the Royal
Society of Tropical Medicine and Hygiene 100: 623-631. Dye, C. and Reiter, P. 2000. Temperatures without fevers? Science 289: 1697-1698. Githeko, A.K. and Ndegwa, W. 2001. Predicting
malaria epidemics in the Kenyan highlands using climate data: A tool for decision makers. Global Change and Human Health 2: 54-63. Hay, S.I., Cox, J., Rogers, D.J., Randolph, S.E., Stern,
D.I., Shanks, G.D., Myers, M.F. and Snow, R.W. 2002. Climate
Human Health Effects 671 change and the resurgence of malaria in the East African highlands. Nature 415: 905-909. IPCC, 2007-II. Climate Change 2007: Impacts, Adaptation and Vulnerability.
Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden and
C.E. Hanson (Eds.) Cambridge University Press, Cambridge, UK. Kuhn, K.G., Campbell-Lendrum, D.H., Armstrong, B. and Davies, C.R. 2003. Malaria in Britain: Past, present, and future.
Proceedings of the National Academy of Science, USA 100: 9997-10001. Reiter, P. 2000. From Shakespeare to Defoe: Malaria in England in the Little Ice Age. Emerging Infectious Diseases
6: 1-11. Reiter, P. 2001. Climate change and mosquito-borne disease. Environmental Health Perspectives 109: 141-161. Reiter, P., Lathrop, S., Bunning, M., Biggerstaff, B., Singer, D.,
Tiwari, T., Baber, L., Amador, M., Thirion, J., Hayes, J., Seca, C., Mendez, J., Ramirez, B., Robinson, J., Rawlings, J., Vorndam, V., Waterman, S., Gubier, D., Clark, G. and Hayes,
E. 2003. Texas lifestyle limits transmission of Dengue virus. Emerging Infectious Diseases 9: 86-89. Rogers, D.J. and Randolph, S.E. 2000. The global spread of malaria in a future, warmer
world. Science 289: 1763-1766. Rogers, D.J. and Randolph, S.E. 2006. Climate change and vector-borne diseases. Advances in Parasitology 62: 345-381. Shanks, G.D., Biomndo, K., Hay, S.I.
and Snow, R.W. 2000. Changing patterns of clinical malaria since 1965 among a tea estate population located in the Kenyan highlands. Transactions of the Royal Society of Tropical Medicine
and Hygiene 94: 253-255. Shanks, G.D., Hay, S.I., Stern, D.I., Biomndo, K. and Snow, R.W. 2002. Meteorologic influences on Plasmodium falciparum malaria in the highland tea estates of
Kericho, Western Kenya. Emerging Infectious Diseases 8: 1404-1408. Small, J., Goetz, S.J. and Hay, S.I. 2003. Climatic suitability for malaria transmission in Africa, 1911-1995. Proceedings
of the the National Academy of Sciences USA 100: 15,341-15,345. Tuchman, N.C., Wahtera, K.A., Wetzel, R.G., Russo, N.M., Kilbane, G.M., Sasso, L.M. and Teeri, J.A. 2003. Nutritional
quality of leaf detritus altered by elevated atmospheric CO2: effects on development of mosquito larvae. Freshwater Biology 48: 1432-1439. Zell, R. 2004. Global climate change and the
emergence/reemergence of infectious diseases. International Journal of Medical Microbiology 293 Suppl. 37: 16-26. Zhou, G., Minakawa, N., Githeko, A.K. and Yan, G. 2004. Association
between climate variability and malaria epidemics in the East African highlands. Proceedings of the National Academy of Sciences, USA 101: 2375-2380. 9.1.4. Tick-Borne Diseases The IPCC
claims that one of the likely consequences of the increase in temperature would be expanded geographic ranges of tick-borne diseases, although once again this prediction is highly qualified.
“Climate change alone is unlikely to explain recent increases in the incidences of tick-borne disease in in Europe or North America,” the IPCC admits, and “other explanations cannot
be ruled out” (IPCC 2007-II, p. 403). Randolph and Rogers (2000) reported that tickborne encephalitis (TBE) “is the most significant vector-borne disease in Europe and Eurasia,” having
“a case morbidity rate of 10-30 percent and a case mortality rate of typically 1-2 percent but as high as 24 percent in the Far East.” The disease is caused by a flavivirus (TBEV), which
is maintained in natural rodent-tick cycles; humans may be infected with it if bitten by an infected tick or by drinking untreated milk from infected sheep or goats. Early writings on
the relationship of TBE to global warming predicted it would expand its range and become more of a threat to humans in a warmer world. However, Randolph and Rogers indicate that “like
many vector-borne pathogen cycles that depend on the interaction of so many biotic agents with each other and with their abiotic environment, enzootic cycles of TBEV have an inherent
fragility,” so that “their continuing survival or expansion cannot be predicted from simple univariate correlations.” The two researchers decided to explore the subject in greater detail
than had ever been done before. Confining their analysis to Europe, Randolph and Rogers first correlated the present-day distribution of TBEV to the present-day distributions of five
climatic variables: monthly mean, maximum, and minimum temperatures, rainfall and saturation vapor pressure, “to provide a multivariate description of present-day areas of disease risk.”
Then, they applied this understanding to outputs of a general circulation model of the atmosphere that predicted how these five climatic variables may change in the future. The results
of these operations indicated that the
Climate Change Reconsidered 672 distribution of TBEV might expand both north and west of Stockholm, Sweden in a warming world. For most other parts of Europe, however, the two researchers
say “fears for increased extent of risk from TBEV caused by global climate change appear to be unfounded.” They found that “the precise conditions required for enzootic cycles of TBEV
are predicted to be disrupted” in response to global warming, and that the new climatic state “appears to be lethal for TBEV.” This finding, in their words, “gives the lie to the common
perception that a warmer world will necessarily be a world under greater threat from vector-borne diseases.” In the case of TBEV, in fact, they report that the predicted change “appears
to be to our advantage.” Similarly, Estrada-Peña (2003) evaluated the effects of various abiotic factors on the habitat suitability of four tick species that are major vectors of livestock
pathogens in South Africa. This work revealed “year-to-year variations in the forecasted habitat suitability over the period 1983-2000 show a clear decrease in habitat availability,
which is attributed primarily to increasing temperature in the region over this period.” In addition, when climate variables were projected to the year 2015, Estrada-Peña found that
“the simulations show a trend toward the destruction of the habitats of the four tick species.” This is the opposite of what is predicted by those who warn of catastrophic consequences
from global warming. Zell (2004) determined that “the factors responsible for the emergence/reemergence of vectorborne diseases are complex and mutually influence each other,” citing
as an example that “the incidence and spread of parasites and arboviruses are affected by insecticide and drug resistance, deforestation, irrigation systems and dams, changes in public
health policy (decreased resources of surveillance, prevention, and vector control), demographic changes (population growth, migration, urbanization), and societal changes (inadequate
housing conditions, water deterioration, sewage, waste management).” In light of these many complicating factors, Zell says “it may be over-simplistic to attribute emergent/re-emergent
diseases to climate change and sketch the menace of devastating epidemics in a warmer world.” Indeed, he concludes that “variations in public health practices and lifestyle can easily
outweigh changes in disease biology,” especially those that might be caused by global warming. References Estrada-Peña, A. 2003. Climate change decreases habitat suitability for some
tick species (Acari: Ixodidae) in South Africa. Onderstepoort Journal of Veterinary Research 70: 79-93. IPCC, 2007-II. Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution
of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden and C.E. Hanson (Eds.)
Cambridge University Press, Cambridge, UK. Randolph, S.E. and Rogers, D.J. 2000. Fragile transmission cycles of tick-borne encephalitis virus may be disrupted by predicted climate change.
Proceedings of the Royal Society of London Series B 267: 1741-1744. Zell, R. 2004. Global climate change and the emergence/reemergence of infectious diseases. International Journal of
Medical Microbiology 293 Suppl. 37: 16-26. 9.1.5. Heat-related Mortality Keatinge and Donaldson (2001) analyzed the effects of temperature, wind, rain, humidity, and sunshine during
high pollution days in the greater London area over the period 1976-1995 to determine what weather and/or pollution factors have the biggest influence on human mortality. Their most
prominent finding was that simple plots of mortality rate versus daily air temperature revealed a linear increase in deaths as temperatures fell from 15°C to near 0°C. Mortality rates
at temperatures above 15°C were, in the words of the researchers, “grossly alinear,” showing no trend. Days with high pollutant concentrations were colder than average, but a multiple
regression analysis revealed that no pollutant was associated with a significant increase in mortality among people over 50 years of age. Indeed, only low temperatures were shown to
have a significant effect on both immediate (one day after the temperature perturbation) and longterm (up to 24 days after the temperature perturbation) mortality rates. Keatinge et
al. (2000) examined heat-and coldrelated mortality in north Finland, south Finland, southwest Germany, the Netherlands, Greater London, north Italy, and Athens, Greece in people aged
65-74. For each of these regions, they determined the 3°C temperature interval of lowest mortality and then evaluated mortality deviations
Human Health Effects 673 from that base level as temperatures rose and fell by 0.1°C increments. The result, according to the researchers, was that “all regions showed more annual cold
related mortality than heat related mortality.” Over the seven regions studied, annual cold-related deaths were nearly 10 times greater than annual-heat related deaths. The scientists
also note that the very successful adjustment of the different populations they studied to widely different summer temperatures “gives grounds for confidence that they would adjust successfully,
with little increase in heat related mortality, to the global warming of around 2°C predicted to occur in the next half century.” Indeed, they say their data suggest “any increases in
mortality due to increased temperatures would be outweighed by much larger short term declines in cold related mortalities.” For the population of Europe, therefore, an increase in temperature
would appear to be a climate change for the better. Gouveia et al. (2003) conducted a similar study in Sao Paulo, Brazil, where they tabulated the numbers of daily deaths from all causes
(excepting violent deaths and deaths of infants up to one month of age), which they obtained from the city’s mortality information system for the period 1991-1994. They then analyzed
these data for children (less than 15 years of age), adults (ages 15-64), and the elderly (age 65 and above) with respect to the impacts of warming and cooling. For each 1°C increase
above the minimum-death temperature of 20°C for a given and prior day’s mean temperature, there was a 2.6 percent increase in deaths from all causes in children, a 1.5 percent increase
in deaths from all causes in adults, and a 2.5 percent increase in deaths from all causes in the elderly. For each 1°C decrease below the 20°C minimum-death temperature, however, the
cold effect was greater, with increases in deaths from all causes in children, adults, and the elderly registering 4.0 percent, 2.6 percent, and 5.5 percent, respectively. These cooling-induced
death rates are 54 percent, 73 percent, and 120 percent greater than those attributable to warming. Kan et al. (2003), in a study conducted in Shanghai, China from June 1, 2000 to December
31, 2001, found a V-like relationship between total mortality and temperature that had a minimum mortality risk at 26.7°C. Above this temperature, they note that “total mortality increased
by 0.73 percent for each degree Celsius increase; while for temperatures below the optimum value, total mortality decreased by 1.21 percent for each degree Celsius increase.” The net
effect of a warming of the climate of Shanghai, therefore, would likely be reduced mortality on the order of 0.5 percent per degree Celsius increase in temperature, or perhaps even more,
in light of the fact that the warming of the past few decades has been primarily due to increases in daily minimum temperatures. Goklany and Straja (2000) studied deaths in the United
States due to all causes over the period 1979-97. They found deaths due to extreme cold exceeded those due to extreme heat by 80 percent to 125 percent. No trends were found due to either
extreme heat or cold in the entire population or, remarkably, in the older, more susceptible, age groups, i.e., those aged 65 and over, 75 and over, and 85 and over. Goklany and Straja
say the absence of any trend “suggests that adaptation and technological change may be just as important determinants of such trends as more obvious meteorological and demographic factors.”
Davis et al. (2003) examined daily mortality rates for 28 major U.S. cities over 29 years between 1964 and 1998. In order to control for changes in the age structure of each city’s population
that might bias temporal comparisons, they standardized each day’s mortality count relative to a hypothetical standard city with a population of one million people, with the demographics
of that city based on the age distribution of the entire U.S. population in the year 2000. They found “heat-related mortality rates declined significantly over time in 19 of the 28 cities.
For the 28-city average, there were 41.0+/-4.8 (mean +/-SE) excess heat-related deaths per year (per standard million) in the 1960s and 1970s, 17.3 +/-2.7 in the 1980s, and 10.5 +/-2.0
in the 1990s.” This 74 percent drop in heat-related deaths occurred despite an average increase in temperature of 1.0°C during the same period. They interpret this to mean that “the
U.S. populace has become systematically less affected by hot and humid weather conditions,” and they say this “calls into question the utility of efforts linking climate change forecasts
to future mortality responses in the United States,” something the IPCC explicitly does. The four scientists conclude that “there is no simple association between increased heat wave
duration or intensity and higher mortality rates in the United States.” Donaldson et al. (2003) determined the mean daily May-August 3°C temperature bands in which deaths of people aged
55 and above were at a minimum for three areas of the world—North Carolina, USA; South Finland; and Southeast England. They then compared heat-and cold-related
Climate Change Reconsidered 674 deaths that occurred at temperatures above and below this optimum temperature interval for each region, after which they determined how heat-related deaths
in the three areas changed between 1971 and 1997 in response to: (1) the 1.0°C temperature rise that was experienced in North Carolina over this period (from an initial temperature of
23.5°C), (2) the 2.1°C temperature rise experienced in Southeast England (from an initial temperature of 14.9°C), and (3) the unchanging 13.5°C temperature of South Finland. First, it
was determined that the 3°C temperature band at which mortality was at its local minimum was lowest for the coolest region (South Finland), highest for the warmest region (North Carolina),
and intermediate for the region of intermediate temperature (Southeast England). This suggests these three populations were somewhat acclimated to their respective thermal regimes. Second,
in each region, cold-related mortality (expressed as excess mortality at temperatures below the region’s optimum 3°C temperature band) was greater than heat-related mortality (expressed
as excess mortality at temperatures above the region’s optimum 3°C temperature band). Third, the researchers found that in the coldest of the three regions (South Finland, where there
was no change in temperature over the study period), heatrelated deaths per million inhabitants in the 55-andabove age group declined from 382 to 99. In somewhat warmer Southeast England,
where it warmed by 2.1°C over the study period, heat-related deaths declined but much less, from 111 to 108. In the warmest of the three regions (North Carolina, USA, where mean daily
May-August temperature rose by 1.0°C over the study period), heat-related deaths fell most dramatically, from 228 to a mere 16 per million. From these observations we learn that most
people can adapt to both warmer and cooler climates and that cooling tends to produce many more deaths than warming, irrespective of the initial temperature regime. As for the reason
behind the third observation—the dramatic decline in heat-related deaths in response to warming in the hottest region of the study (North Carolina)—Donaldson et al. attribute it to the
increase in the availability of air conditioning in the South Atlantic region of the United States, where they note that the percentage of households with some form of air conditioning
rose from 57 percent in 1978 to 72 percent in 1997. With respect to the declining heat-related deaths in the other two areas, they say “the explanation is likely to lie in the fact that
both regions shared with North Carolina an increase in prosperity, which could be expected to increase opportunities for avoiding heat stress.” Huynen et al. (2001) analyzed mortality
rates in the entire population of Holland. For the 19-year period from January 1979 through December 1997, the group of five scientists compared the numbers of deaths in people of all
ages that occurred during welldefined heat waves and cold spells. They found a total excess mortality of 39.8 deaths per day during heat waves and 46.6 deaths per day during cold spells.
These numbers indicate that a typical cold-spell day kills at a rate that is 17 percent greater than a typical heat-wave day in the Netherlands. The researchers note that the heat waves
they studied ranged from 6 to 13 days in length, while the cold spells lasted 9 to 17 days, making the average cold spell approximately 37 percent longer than the average heat wave.
Adjusting for this duration differential makes the number of deaths per cold spell in the Netherlands fully 60 percent greater than the number of deaths per heat wave. What is more,
excess mortality continued during the whole month after the cold spells, leading to even more deaths, while there appeared to be mortality deficits in the month following heat waves,
suggesting, in the words of the authors, “that some of the heat-induced increase in mortality can be attributed to those whose health was already compromised” or “who would have died
in the short term anyway.” This same conclusion has been reached in a number of other studies (Kunst et al., 1993; Alberdi et al., 1998; Eng and Mercer, 1998; Rooney et al., 1998). It
is highly likely, therefore, that the 60 percent greater death toll we have calculated for cold spells in the Netherlands as compared to heat waves is an underestimate of the true differential
killing power of these two extreme weather phenomena. The Dutch could well ask themselves, therefore, “Will global climate change reduce climate-related mortalities in the Netherlands?”
... which is exactly what the senior and second authors of the Huynen et al. paper did in a letter to the editor of Epidemiology (Martens and Huynen, 2001). Based on the predictions
of nine different GCMs for an atmospheric CO2 concentration of 550 ppm in the year 2050—which implied a 50 percent increase in Dutch heat waves and a 67 percent drop in Dutch cold spells—they
calculated a total mortality decrease for Holland of approximately 1,100 people per year at that point in tim
e. Human Health Effects 675 Data from Germany tell much the same story. Laschewski and Jendritzky (2002) analyzed daily mortality rates of the population of Baden-Wurttemberg, Germany
(10.5 million inhabitants) over the 30-year period 1958-1997 to determine the sensitivity of the people living in this moderate climatic zone of southwest Germany to long-and short-term
episodes of heat and cold. They found the mortality data “show a marked seasonal pattern with a minimum in summer and a maximum in winter” and “cold spells lead to excess mortality to
a relatively small degree, which lasts for weeks,” and that “the mortality increase during heat waves is more pronounced, but is followed by lower than average values in subsequent weeks.”
The authors’
data demonstrate that the mean duration of above-normal mortality for the 51 heat episodes that occurred from 1968 to 1997 was 10 days, with a mean increase in mortality of 3.9 percent,
after which there was a mean decrease in mortality of 2.3 percent for 19 days. Hence, the net effect of the heat waves was a calculated overall decrease in mortality of 0.2 percent over
the full 29-day period. We end with the work of Thomas Gale Moore, an economist at Stanford University USA. In his first publication reviewed here (Moore, 1998), Moore reported the results
of two regression analyses he conducted to estimate the effect on the U.S. death rate of a 4.5°F increase in average termperature, the IPCC’s “best estimate” at the time (1992) of likely
warming over the course of the next century. For the first analysis, Moore “regressed various measures of warmth on deaths in Washington, DC, from January 1987 through December 1989,”
a period of 36 months, and then extrapolated the results for the entire country. He used Washington, DC because termperatures are recorded for major urban areas, not states, while monthly
data on deaths is available from the National Center for Health Statistics only for states, but the center treats the nation’s capital as a state. This analysis found a 4.5°F rise “would
cut deaths for the country as a whole by about 37,000 annually.” For his second analysis, Moore regressed the death rates in 89 large U.S. counties with various weather variables, including
actual average temperatures in 1979, highest summer temperature, lowest winter temperature, number of heating degree days, and number of cooling degree days, and several other variables
known to affect death rates (percent of the population over age 65, percent black, percent with 16 years or more of schooling, median household income, per-capita income, air pollution,
and health care inputs such as number of hospital beds and physicians per 100,000 population.) He found “the coefficient for average temperature implies that if the United States were
enjoying temperatures 4.5 degrees warmer than today, mortality would be 41,000 less. This savings in lives is quite close to the number estimated based on the Washington, DC data, for
the period 1987 through 1989.” Moore notes that “a warmer climate would reduce mortality by about the magnitude of highway deaths.” Two years later, in a report published by the Hoover
Institution, Moore estimated the number of deaths that would be caused by the costs associated with reducing U.S. greenhouse gas emissions (Moore, 2000). “Economists studying the relationship
of income and earnings to mortality have found that the loss of $5 million to $10 million in the U.S. GDP [gross domestic product] leads to one extra death,” Moore writes. Since the
Energy Information Administration (EIA) estimated that meeting the Kyoto Protocol’s goal of reducing greenhouse gas emissions to 7 percent below 1990 levels by 2010-2012 would cost $338
billion annually (without emissions trading), “the EIA estimates imply that somewhere between 33,800 and 67,000 more Americans will die annually between 2008 and 2012.” These studies
of the effects of temperature on human mortality show that cooling, not warming, kills the largest number of people each year. The number of lives saved by warmer weather, if the IPCC’s
forecasts of future warming are correct (and we doubt that they are), would far exceed the number of lives lost. The margin in the United States is enormous, with the number of prevented
deaths exceeding the number of deaths that occur on the nation’s highways each year. Conversely, attempting to stop global warming by reducing emissions would cost lives—between 33,800
and 67,000 a year in the U.S. alone, according to Moore (2000). These staggering numbers leave little doubt that global warming does not pose a threat to human health. References Alberdi,
J.C., Diaz, J., Montero, J.C. and Miron, I. 1998. Daily mortality in Madrid community 1986-1992: relationship with meteorological variables. European Journal of Epidemiology 14: 571-578.
Climate Change Reconsidered 676 Davis, D.E., Knappenberger, P.C., Michaels, P.J. and Novicoff, W.M. 2003. Changing heat-related mortality in the United States. Environmental Health Perspectives
111 (14): 1712-1718. Donaldson, G.C., Keatinge, W.R. and Nayha, S. 2003. Changes in summer temperature and heat-related mortality since 1971 in North Carolina, South Finland, and Southeast
England. Environmental Research 91: 1-7. Eng, H. and Mercer, J.B. 1998. Seasonal variations in mortality caused by cardiovascular diseases in Norway and Ireland. Journal of Cardiovascular
Risk 5: 89-95. Goklany, I.M. and Straja, S.R. 2000. U.S. trends in crude death rates due to extreme heat and cold ascribed to weather, 1979-97. Technology 7S: 165-173. Gouveia, N., Hajat,
S. and Armstrong, B. 2003. Socioeconomic differentials in the temperaturemortality relationship in Sao Paulo, Brazil. International Journal of Epidemiology 32: 390-397. Huynen, M.M.T.E.,
Martens, P., Schram, D., Weijenberg, M.P. and Kunst, A.E. 2001. The impact of heat waves and cold spells on mortality rates in the Dutch population. Environmental Health Perspectives
109: 463-470. Kan, H-D., Jia, J. and Chen, B-H. 2003. Temperature and daily mortality in Shanghai: A time-series study. Biomedical and Environmental Sciences 16: 133-139. Keatinge, W.R.
and Donaldson, G.C. 2001. Mortality related to cold and air pollution in London after allowance for effects of associated weather patterns. Environmental Research 86A: 209-216. Keatinge,
W.R., Donaldson, G.C., Cordioli, E., Martinelli, M., Kunst, A.E., Mackenbach, J.P., Nayha, S. and Vuori, I. 2000. Heat related mortality in warm and cold regions of Europe: Observational
study. British Medical Journal 321: 670-673. Kunst, A.E., Looman, W.N.C. and Mackenbach, J.P. 1993. Outdoor temperature and mortality in the Netherlands: a time-series analysis. American
Journal of Epidemiology 137: 331-341. Laschewski, G. and Jendritzky, G. 2002. Effects of the thermal environment on human health: an investigation of 30 years of daily mortality data
from SW Germany. Climate Research 21: 91-103. Martens, P. and Huynen, M. 2001. Will global climate change reduce thermal stress in the Netherlands? Epidemiology 12: 753-754. Moore, T.G.
1998. “Health and amenity effects of global warming.” Economic Inquiry 36: 471–488. Moore, T.G. 2000. In sickness or in health: The Kyoto protocol vs global warming. Essays in Public
Policy Hoover Press #104. Stanford, CA. Rooney, C., McMichael, A.J., Kovats, R.S. and Coleman, M.P. 1998. Excess mortality in England and Wales, and in greater London, during the 1995
heat wave. Journal of Epidemiology and Community Health 52: 482-486. 9.2. Nutrition Rising concentrations of CO2 in the atmosphere affect human health indirectly by enhancing plant productivity,
a topic examined at length in Chapter 7. In this section we review the scientific literature on CO2-induced changes to the quantity and quality of food crops—in particular the protein
and antioxidants present in grains and fruits—and on the medicinal properties properties of some plants. We find the overwhelming weight of evidence indicates a positive effect of global
warming on human health. 9.2.1. Food Quantity The concentration of CO2 in the earth’s atmosphere has risen approximately 100 ppm since the inception of the Industrial Revolution. To
measure the effect this increase had on wheat, Mayeux et al. (1997) grew two cultivars of commercial wheat in a 38-meter-long soil container topped with a transparent tunnel-like polyethylene
cover within which a CO2 gradient was created that varied from approximately 350 ppm at one end of the tunnel to about 200 ppm at the other end. Both wheat cultivars were irrigated weekly
over the first half of the 100-day growing season, to maintain soil water contents near optimum conditions. Over the last half of the season, this regimen was maintained on only half
of the wheat of each cultivar, in order to create both water-stressed and wellwatered treatments. At the conclusion of the experiment, the scientists determined that the growth response
of the wheat was a linear function of atmospheric CO2 concentration in both cultivars under both adequate and less-thanadequate soil water regimes. Based on the linear regression equations
they developed for grain yield in these situations, we calculate that the 100-ppm increase in atmospheric CO2 concentration experienced over the past century-and-a-half probably
Human Health Effects 677 increased the mean grain yield of the two wheat cultivars by about 72 percent under well-watered conditions and 48 percent under water-stressed conditions, for
a mean yield increase on the order of 60 percent under the full range of moisture conditions likely to have existed in the real world. In other words, the historical rise in CO2 concentrations
may have increased wheat yields by 60 percent, clearly a benefit to a growing population. This CO2-induced yield enhancement to wheat production also has been documented by Alexandrov
and Hoogenboom, 2000a; Brown and Rosenberg, 1999; Cuculeanu et al., 1999; Dijkstra et al., 1999; Eitzinger et al., 2001; Harrison and Butterfield, 1996; Masle, 2000; Southworth et al.,
2002; and van Ittersum et al., 2003. Nor is wheat the only food crop that benefits from CO2-fertilization. Research reviewed in Chapter 7 showing increased production by other crops
exposed to enhanced CO2, includes the following: • Alfalfa (De Luis et al., 1999; Luscher et al., 2000; Morgan et al., 2001; Sgherri et al., 1998) • Cotton (Booker, 2000; Booker et al.,
2000; Leavitt et al., 1994; Reddy et al., 1999; Reddy et al., 1998. Tischler et al., 2000) • Corn (maize) (Baczek-Kwinta and Koscielniak, 2003; Bootsma et al., 2005; Conway and Toenniessen,
2003; Leakey et al., 2004; Magrin et al., 2005; Maroco et al., 1999; Shen et al., 2005; Watling and Press, 1997; Watling and Press, 2000) • Peanuts (Alexandrov and Hoogenboom, 2000b;
Prasad et al., 2003; Stanciel et al., 2000; Vu, 2005) • Potatoes (Bunce, 2003; Chen and Setter, 2003; Fangmeier and Bender, 2002; Kauder et al., 2000; Lawson et al., 2001; Louche-Tessandier
et al., 1999; Ludewig et al., 1998; Magliulo et al., 2003; Miglietta et al., 1998; Olivo et al., 2002; Pruski et al., 2002; Schapendonk, et al., 2000; Sicher and Bunce, 1999; Wolf and
van Oijen, 2002; Wolf and van Oijen, 2003) • Rice (Baker et al., 2000; De Costa et al., 2003a; De Costa et al., 2003b; Gesch et al., 2002; Kim et al., 2003; Kim et al., 2001; Kobayashi
et al., 2001; Tako, et al., 2001; Watling and Press, 2000; Weerakoon et al., 2000; Widodo et al., 2003; Ziska et al., 1997) • Sorgham (Ainsworth and Long, 2005; Ottman et al., 2001;
Prior et al., 2005; Watling and Press, 1997) • Soybeans (Alexandrov and Hoogenboom, 2000b; Allen et al., 1998; Bernacchi et al., 2005; Birt et al., 2001; Bunce, 2005; Caldwell et al.,
2005; Ferris et al., 1999; Heagle et al., 1998; Messina, 1999; Nakamura et al., 1999; Rogers et al., 2004; Serraj et al., 1999; Thomas et al., 2003; Wittwer, 1995; Ziska, 1998; Ziska
and Bunce, 2000; Ziska et al., 2001a; Ziska et al., 2001b) • Strawberries (Bunce, 2001; Bushway and Pritts, 2002; Deng and Woodward, 1998) Based on this voluminous data and much more,
Idso and Idso (2000) calculated that the increase in atmospheric CO2 concentration during the past 150 years probably caused mean yield increases on the order of 70 percent for wheat
and other C3 cereals, 28 percent for C4 cereals, 33 percent for fruits and melons, 62 percent for legumes, 67 percent for root and tuber crops, and 51 percent for vegetables. Such major
increases in production by important food plants due to the historical increase in the air’s CO2 content have undoubtedly benefitted human health. In fact, it is safe to say that some
of the people reading these words would not be alive today were it not for the CO2 enrichment caused by human industry since the beginning of the Industrial Revolution. What does the
IPCC say about this extraordinary benefit to human health made possible by rising CO2 levels? Incredibly, it is not mentioned anywhere in the contribution of Working Group I to the Fourth
Assessment Report of the IPCC (IPCC 2007-I) or in the chapter on the impact of global warming on human health in the contribution of Working Group II (IPCC 2007-II). It is treated dismissively
in the chapter on agriculture in the contribution of Working Group III (IPCC 2007-III), even though the proposals justified in the first two volumes and advanced in the third would reduce
CO2 emissions and therefore have a negative impact on crop yields. To call this a gross oversight is to be kind to the authors of these reports. In view of these observations, it is
indisputable that the ongoing rise in the air’s CO2 content has bestowed a huge benefit to human health by expanding the yields of food crops. Additional information on this topic, including
reviews of newer publications as they become available, can be found at http://www.co2 science.org/subject/a/agriculture.php.
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CO2 increases sorghum biomass under drought conditions. New Phytologist 150: 261-273. Prasad, P.V.V., Boote, K.J., Allen Jr., L.H. and Thomas, J.M.G. 2003. Super-optimal temperatures
are detrimental to peanut (Arachis hypogaea L.) reproductive processes and yield at both ambient and elevated carbon dioxide. Global Change Biology 9: 1775-1787. Prior, S.A., Runion,
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rice to increasing carbon dioxide and air temperature. Agronomy Journal 89: 45-53. 9.2.2. Food Quality The quantity of food is mankind’s primary concern when it comes to survival. But
after survival is assured, the quality of food rises to the fore. What role does the ongoing rise in the air’s CO2 content play here? In this section we survey the literature on the
effects of higher CO2 air concentration on plant protein and antioxidant content. 9.2.2.1. Protein Content Idso and Idso (2001) and Idso et al. (2001) cited studies where elevated levels
of atmospheric CO2 either increased, decreased, or had no effect on the protein concentrations of various agricultural crops.
Climate Change Reconsidered 682 The relationship, as we will see, is complex, though in the end it appears that enhanced atmospheric CO2 has a positive effect on the protein content
of most crops. Pleijel et al. (1999) analyzed the results of 16 open-top chamber experiments that had been conducted on spring wheat in Denmark, Finland, Sweden, and Switzerland between
1986 and 1996. In addition to CO2 enrichment of the air, these experiments included increases and decreases in atmospheric ozone (O3). The scientists found that while increasing O3 pollution
reduced wheat grain yield it simultaneously increased the protein concentration of the grain. Removing O3 from the air led to higher grain yield but lower protein concentration. The
opposite relationship was found for atmospheric CO2 enrichment, which increased grain yield but lowered protein concentration. Water stress, which was also a variable in one of the experiments,
reduced yield and increased grain protein concentrations. In an earlier study of CO2 and O3 effects on wheat grain yield and quality, Rudorff et al. (1996) found that “flour protein
contents were increased by enhanced O3 exposure and reduced by elevated CO2” but that “the combined effect of these gases was minor.” They conclude that “the concomitant increase of
CO2 and O3 in the troposphere will have no significant impact on wheat grain quality.” Earlier, Evans (1993) had found several other crops to be greatly affected by soil nitrogen availability.
Rogers et al. (1996) observed CO2-induced reductions in the protein concentration of flour derived from wheat plants growing at low soil nitrogen concentrations, but no such reductions
were evident when the soil nitrogen supply was increased. Pleijel et al. concluded that the oft-observed negative impact of atmospheric CO2 enrichment on grain protein concentration
would probably be alleviated by higher applications of nitrogen fertilizers. The study of Kimball et al. (2001) confirmed their hypothesis. Kimball et al. studied the effects of a 50
percent increase in atmospheric CO2 concentration on wheat grain nitrogen concentration and the baking properties of the flour derived from that grain throughout four years of free-air
CO2 enrichment experiments. In the first two years of their study, soil water content was an additional variable; in the last two years, soil nitrogen content was a variable. The most
influential factor in reducing grain nitrogen concentration was determined to be low soil nitrogen. Under this condition, atmospheric CO2 enrichment further reduced grain nitrogen and
protein concentrations, although the change was much less than that caused by low soil nitrogen. When soil nitrogen was not limiting, however, increases in the air’s CO2 concentration
did not affect grain nitrogen and protein concentrations; neither did they reduce the baking properties of the flour derived from the grain. Hence, it would appear that given sufficient
water and nitrogen, atmospheric CO2 enrichment can significantly increase wheat grain yield without sacrificing grain protein concentration in the process. There are some situations
where atmospheric CO2 enrichment has been found to increase the protein concentration of wheat. Agrawal and Deepak (2003), for example, grew two cultivars of wheat (Triticum aestivum
L. cv. Malviya 234 and HP1209) in opentop chambers maintained at atmospheric CO2 concentrations of 350 and 600 ppm alone and in combination with 60 ppb SO2 to study the interactive effects
of elevated CO2 and this major air pollutant on crop growth. They found that exposure to the elevated SO2 caused a 13 percent decrease in foliar protein concentrations in both cultivars;
but when the plants were concomitantly exposed to an atmospheric CO2 concentration of 600 ppm, leaf protein levels decreased only by 3 percent in HP1209, while they actually increased
by 4 percent in Malviya 234. In the case of rice—which according to Wittwer (1995) is “the basic food for more than half the world’s population,” supplying “more dietary energy than
any other single food”—Jablonski et al. (2002) conducted a wide-ranging review of the scientific literature, finding that it too appeared to suffer no reduction in grain nitrogen (protein)
concentration in response to atmospheric CO2 enrichment. Likewise, they found no CO2-induced decrease in seed nitrogen concentration in the studies of legumes they reviewed. This finding
is also encouraging, since according to Wittwer (1995) legumes “are a direct food resource providing 20 percent of the world’s protein for human consumption,” as well as “about two thirds
of the world’s protein concentrate for livestock feeding.” What is more, the biomass of the CO2-enriched wheat, rice, and legumes was found by Jablonski et al. to be significantly increased
above that of the same crops grown in normal air. Hence, there will likely be a large increase in the total amount of protein made available to humanity in a future CO2-enriched world,
both directly via food crops and indirectly via livestock.
Human Health Effects 683 With respect to the leguminous soybean, Thomas et al. (2003) additionally note that “oil and protein comprise ~20 and 40 percent, respectively, of the dry weight
of soybean seed,” which “unique chemical composition,” in their words, “has made it one of the most valuable agronomic crops worldwide.” In addition, they say “the intrinsic value of
soybean seed is in its supply of essential fatty acids and amino acids in the oil and protein, respectively,” and they report that Heagle et al. (1998) “observed a positive significant
effect of CO2 enrichment on soybean seed oil and oleic acid concentration.” Legumes and their responses to atmospheric CO2 enrichment also figure prominently in a number of studies of
mixed forage crops. In a study of nitrogen cycling in grazed pastures on the North Island of New Zealand, for example, Allard et al. (2003) report that under elevated CO2, leaves of
the individual species exhibited lower nitrogen concentrations but higher water-soluble carbohydrate ((WSC) concentrations. They also say “there was a significantly greater proportion
of legume in the diet at elevated CO2,” and that this “shift in the botanical composition towards a higher proportion of legumes counterbalanced the nitrogen decrease observed at the
single species scale, resulting in a nitrogen concentration of the overall diet that was unaffected by elevated CO2.” They further report that “changes at the species level and at the
sward level appeared to combine additively in relation to WSC,” and “as there was a significant correlation between WSC and digestibility (as previously observed by Dent and Aldrich,
1963 and Humphreys, 1989), there was also an increase in digestibility of the high CO2 forage,” which result, in their words, “matches that found in a Mini-FACE experiment under cutting
(Teyssonneyre, 2002; Picon-Cochard et al., 2004),” where “digestibility also increased in response to CO2 despite reduced crude protein concentration.” These data, plus the strong relationship
between soluble sugars (rather than nitrogen) and digestibility, led them to suggest that “the widespread response to CO2 of increased soluble sugars might lead to an increase in forage
digestibility.” Luscher et al. (2004) found much the same thing in their review of the subject, which was based primarily on studies conducted at the Swiss FACE facility that hosts what
has become the world’s longest continuous atmospheric CO2 enrichment study of a naturally occurring grassland. In response to an approximate two-thirds increase in the air’s CO2 concentration,
leaf nitrogen (N) concentrations of white clover (Trifolium repens L.) and perennial ryegrass (Lolium perenne L.) were reduced by 7 percent and 18 percent, respectively, when they were
grown separately in pure stands. However, as Luscher et al. report, “the considerably lower concentration of N under elevated CO2, observed for L. perenne leaves in pure stands, was
found to a much lesser extent for L. perenne leaves in the bi-species mixture with T. repens (Zanetti et al., 1997; Hartwig et al., 2000).” Furthermore, as they continue, “under elevated
CO2 the proportion of N-rich T. repens (40 mg N g-1 dry matter) increased in the mixture at the expense of the N-poor L. perenne (24 mg N g-1 dry matter when grown in monoculture),”
the end result being that “the concentration of N in the harvested biomass of the mixture showed no significant reduction.” Campbell et al. (2000) analyzed research conducted between
1994 and 1999 by a worldwide network of 83 scientists associated with the Global Change and Terrestrial Ecosystems (GCTE) Pastures and Rangelands Core Research Project 1 (CRP1) that
resulted in the publication of more than 165 peerreviewed scientific journal articles. Campbell et al. determined from this massive collection of data that the legume content of grass-legume
swards was typically increased by approximately 10 percent in response to a doubling of the air’s CO2 content. Luscher et al. (2004) state that “the nutritive value of herbage from intensively
managed managed grassland dominated by L. perenne and T. repens ... is well above the minimum range of the concentration of crude protein necessary for efficient digestion by ruminants
(Barney et al., 1981).” They conclude that “a small decrease in the concentration of crude protein in intensively managed forage production systems [which may never occur, as noted above]
is not likely to have a negative effect on the nutritive value or on the intake of forage.” One final forage study is Newman et al. (2003), who investigated the effects of two levels
of nitrogen fertilization and an approximate doubling of the air’s CO2 content on the growth and chemical composition of tall fescue (Festuca arundinacea Schreber cv. KY-31), both when
infected and uninfected with a mutualistic fungal endophyte (Neotyphodium coenophialum Morgan-Jones and Gams). They found that the elevated CO2 reduced the crude protein content of the
forage by an average of 21 percent in three of the four situations studied: non-endophyteinfected plants plants in both the low and high nitrogen treatments, and endophyte-infected plants
in the high nitrogen treatment. However, there was no protein
Climate Change Reconsidered 684 reduction for endophyte-infected plants in the low nitrogen treatment. As noted by Newman et al., “the endophyte is present in many native and naturalized
populations and the most widely sown cultivars of F. arundinacea,” so the first two situations in which the CO2-induced protein reduction occurred (those involving non-endophyte-infected
plants) are not typical of the real world. In addition, since the dryweight biomass yield of the forage was increased by fully 53 percent under the low nitrogen regime, and since the
10-times-greater high nitrogen regime boosted yields only by an additional 8 percent, there would appear to be no need to apply any extra nitrogen to F. arundinacea in a CO2-enriched
environment. Consequently, under best management practices in a doubled-CO2 world of the future, little to no nitrogen would be added to the soil and there would be little to no reduction
in the crude protein content of F. arundinacea, but there would be more than 50 percent more of it produced on the same amount of land. With respect to the final plant quality studied
by Newman et al.—i.e., forage digestibility— increasing soil nitrogen lowered in vitro neutral detergent fiber digestibility in both ambient and CO2-enriched air; this phenomenon was
most pronounced in the elevated CO2 treatment. Again, however, under low nitrogen conditions there was no decline in plant digestibility. Hence, there is a second good reason not to
apply extra nitrogen to F. arundinacea in a high CO2 world of the future and, of course, little to no need to do so. Under best management practices in a future CO2-enriched atmosphere,
therefore, the results of this study suggest much greater quantities of goodquality forage could be produced without the addition of any, or very little, extra nitrogen to the soil.
But what about the unmanaged world of nature? Increases in the air’s CO2 content often—but not always (Goverde et al., 1999)—lead to greater decreases in the concentrations of nitrogen
and protein in the foliage of C3 as compared to C4 grasses (Wand et al., 1999); as a result, in the words of Barbehenn et al. (2004a), “it has been predicted that insect herbivores will
increase their feeding damage on C3 plants to a greater extent than on C4 plants” (Lincoln et al., 1984, 1986; Lambers, 1993). To test this hypothesis, Barbehenn et al. (2004a) grew
Lolium multiflorum Lam. (Italian ryegrass, a common C3 pasture grass) and Bouteloua curtipendula (Michx.) Torr. (sideoats gramma, a native C4 rangeland grass) in chambers maintained
at either the ambient atmospheric CO2 concentration of 370 ppm or the doubled CO2 concentration of 740 ppm for two months, after which newly molted sixthinstar larvae of Pseudaletia
unipuncta (a grassspecialist noctuid) and Spodoptera frugiperda (a generalist noctuid) were allowed to feed upon the grasses. As expected, foliage protein concentration decreased by
20 percent in the C3 grass, but by only 1 percent in the C4 grass, when grown in the CO2-enriched air. However, and “contrary to our expectations,” according to Barbehenn et al., “neither
caterpillar species significantly increased its consumption rate to compensate for the lower concentration of protein in [the] C3 grass,” noting that “this result does not support the
hypothesis that C3 plants will be subject to greater rates of herbivory relative to C4 plants in future [high-CO2] atmospheric conditions (Lincoln et al., 1984).” In addition, and “despite
significant changes in the nutritional quality of L. multiflorum under elevated CO2,” they report that “no effect on the relative growth rate of either caterpillar species on either
grass species resulted” and there were “no significant differences in insect performance between CO2 levels.” In a similar study with the same two plants, Barbehenn et al. (2004b) allowed
grasshopper (Melanoplus sanguinipes) nymphs that had been reared to the fourth instar stage to feed upon the grasses; once again, “contrary to the hypothesis that insect herbivores will
increase their feeding rates disproportionately in C3 plants under elevated atmospheric CO2,” they found that “M. sanguinipes did not significantly increase its consumption rate when
feeding on the C3 grass grown under elevated CO2,” suggesting this observation implies that “postingestive mechanisms enable these grasshoppers to compensate for variable nutritional
quality in their host plants,” and noting that some of these postingestive responses may include “changes in gut size, food residence time, digestive enzyme levels, and nutrient metabolism
(Simpson and Simpson, 1990; Bernays and Simpson, 1990; Hinks et al., 1991; Zanotto et al., 1993; Yang and Joern, 1994a,b).” In fact, their data indicated that M. sanguinipes growth rates
may have actually increased, perhaps by as much as 12 percent, when feeding upon the C3 foliage that had been produced in the CO2-enriched air. In conclusion, the ongoing rise of the
air’s CO2 concentration is not reducing the protein concentration in, or digestibility of, most important
Human Health Effects 685 plant crops. In cases where protein concentration might by reduced, the addition of nitrogen fertilizer appears to offset the effect. Additional information
on this topic, including reviews of newer publications as they become available, can be found at http://www.co2 science.org/subject/p/protein.php. References Agrawal, M. and Deepak,
S.S. 2003. Physiological and biochemical responses of two cultivars of wheat to elevated levels of CO2 and SO2, singly and in combination. Environmental Pollution 121: 189-197. Allard,
V., Newton, P.C.D., Lieffering, M., Clark, H., Matthew, C., Soussana, J.-F. and Gray, Y.S. 2003. Nitrogen cycling in grazed pastures at elevated CO2: N returns by ruminants. Global Change
Biology 9: 1731-1742. Barbehenn, R.V., Karowe, D.N. and Chen, Z. 2004b. Performance of a generalist grasshopper on a C3 and a C4 grass: compensation for the effects of elevated CO2 on
plant nutritional quality. Oecologia 140: 96-103. Barbehenn, R.V., Karowe, D.N. and Spickard, A. 2004a. Effects of elevated atmospheric CO2 on the nutritional ecology of C3 and C4 grass-feeding
caterpillars. Oecologia 140: 86-95. Barney, D.J., Grieve, D.G., Macleod, G.K. and Young, L.G. 1981. Response of cows to a reduction in dietary crude protein from 17 to 13 percent during
early lactation. Journal of Dairy Science 64: 25-33. Bernays, E.A. and Simpson, S.J. 1990. Nutrition. In: Chapman, R.F. and Joern, A. (Eds.) Biology of Grasshoppers. Wiley, New York,
NY, pp. 105-127. Campbell, B.D., Stafford Smith, D.M., Ash, A.J., Fuhrer, J., Gifford, R.M., Hiernaux, P., Howden, S.M., Jones, M.B., Ludwig, J.A., Manderscheid, R., Morgan, J.A., Newton,
P.C.D., Nosberger, J., Owensby, C.E., Soussana, J.F., Tuba, Z. and ZuoZhong, C. 2000. A synthesis of recent global change research on pasture and rangeland production: reduced uncertainties
and their management implications. Agriculture, Ecosystems and Environment 82: 39-55. Dent, J.W. and Aldrich, D.T.A. 1963. The interrelationships between heading date, yield, chemical
chemical composition and digestibility in varieties of perennial ryegrass, timothy, cooksfoot and meadow fescue. Journal of the National Institute of Agricultural Botany 9: 261-281.
Evans, L.T. 1993. Crop Evolution, Adaptation and Yield. Cambridge University Press, Cambridge, UK. Goverde, M., Bazin, A., Shykoff, J.A. and Erhardt, A. 1999. Influence of leaf chemistry
of Lotus corniculatus (Fabaceae) on larval development of Polyommatus icarus (Lepidoptera, Lycaenidae): effects of elevated CO2 and plant genotype. Functional Ecology 13: 801-810. Hartwig,
U.A., Luscher, A., Daepp, M., Blum, H., Soussana, J.F. and Nosberger, J. 2000. Due to symbiotic N2 fixation, five years of elevated atmospheric pCO2 had no effect on litter N concentration
in a fertile grassland ecosystem. Plant and Soil 224: 43-50. Heagle, A.S., Miller, J.E. and Pursley, W.A. 1998. Influence of ozone stress on soybean response to carbon dioxide enrichment:
III. Yield and seed quality. Crop Science 38: 128-134. Hinks, C.R., Cheeseman, M.T., Erlandson, M.A., Olfert, O. and Westcott, N.D. 1991. The effects of kochia, wheat and oats on digestive
proteinases and the protein economy of adult grasshoppers, Malanoplus sanguinipes. Journal of Insect Physiology 37: 417-430. Humphreys, M.O. 1989. Water-soluble carbohydrates in perennial
ryegrass breeding. III. Relationships with herbage production, digestibility and crude protein content. Grass and Forage Science 44: 423-430. Idso, C.D. and Idso, K.E. 2000. Forecasting
world food supplies: The impact of the rising atmospheric CO2 concentration. Technology 7S: 33-56. Idso, K.E., Hoober, J.K., Idso, S.B., Wall, G.W. and Kimball, B.A. 2001. Atmospheric
CO2 enrichment influences the synthesis and mobilization of putative vacuolar storage proteins in sour orange tree leaves. Environmental and Experimental Botany 48: 199-211. Jablonski,
L.M., Wang, X. and Curtis, P.S. 2002. Plant reproduction under elevated CO2 conditions: a metaanalysis of reports on 79 crop and wild species. New Phytologist 156: 9-26. Kimball, Kimball,
B.A., Morris, C.F., Pinter Jr., P.J., Wall, G.W., Hunsaker, D.J., Adamsen, F.J., LaMorte, R.L., Leavitt, S.W., Thompson, T.L., Matthias, A.D. and Brooks, T.J. 2001. Elevated CO2, drought
and soil nitrogen effects on wheat grain quality. New Phytologist 150: 295-303. Lambers, H. 1993. Rising CO2, secondary plant metabolism, plant-herbivore interactions and litter decomposition.
Theoretical considerations. Vegetatio 104/105: 263-271. Lincoln, D.E., Couvet, D. and Sionit, N. 1986. Responses of an insect herbivore to host plants grown in carbon dioxide enriched
atmospheres. Oecologia 69: 556-560. Lincoln, D.E., Sionit, N. and Strain, B.R. 1984. Growth and feeding response of Pseudoplusia includens (Lepidoptera: Noctuidae) to host plants grown
in controlled
Climate Change Reconsidered 686 carbon dioxide atmospheres. Environmental Entomology 13: 1527-1530. Luscher, A., Daepp, M., Blum, H., Hartwig, U.A. and Nosberger, J. 2004. Fertile temperate
grassland under elevated atmospheric CO2—role of feed-back mechanisms and availability of growth resources. European Journal of Agronomy 21: 379-398. Newman, J.A., Abner, M.L., Dado,
R.G., Gibson, D.J., Brookings, A. and Parsons, A.J. 2003. Effects of elevated CO2, nitrogen and fungal endophyte-infection on tall fescue: growth, photosynthesis, chemical composition
and digestibility. Global Change Biology 9: 425-437. Picon-Cochard, C., Teyssonneyre, F., Besle, J.M. et al. 2004. Effects of elevated CO2 and cutting frequency on the productivity and
herbage quality of a semi-natural grassland. European Journal of Agronomy 20: 363-377 Pleijel, H., Mortensen, L., Fuhrer, J., Ojanpera, K. and Danielsson, H. 1999. Grain protein accumulation
in relation to grain yield of spring wheat (Triticum aestivum L.) grown in open-top chambers with different concentrations of ozone, carbon dioxide and water availability. Agriculture,
Ecosystems and Environment 72: 265-270. Rogers, G.S., Milham, P.J., Gillings, M. and Conroy, J.P. 1996. Sink strength may be the key to growth and nitrogen responses in N-deficient wheat
at elevated CO2. Australian Journal of Plant Physiology 23: 253-264. Rudorff, B.F.T., Mulchi, C.L., Fenny, P., Lee, E.H., Rowland, R. 1996. Wheat grain quality under enhanced tropospheric
CO2 and O3 concentrations. Journal of Environmental Quality 25: 1384-1388. Simpson, S.J. and Simpson, C.L. 1990. The mechanisms of nutritional compensation by phytophagous insects. In:
Bernays, E.A. (Ed.) Insect-Plant Interactions, Vol. 2. CRC Press, Boca Raton, FL, pp. 111-160. Teyssonneyre, F. 2002. Effet d’une augmentation de la concentration atmospherique en CO2
sur la prairie permanete et sur la competition entre especes prairiales associees. Ph.D. thesis, Orsay, Paris XI, France. Thomas, J.M.G., Boote, K.J., Allen Jr., L.H., Gallo-Meagher,
M. and Davis, J.M. 2003. Elevated temperature and carbon dioxide effects on soybean seed composition and transcript abundance. Crop Science 43: 1548-1557. Wand, S.J.E., Midgley, G.F.,
Jones, M.H. and Curtis, P.S. 1999. Responses of wild C4 and C3 grass (Poaceae) species to elevated atmospheric CO2 concentration: a meta-analytic test of current theories and perceptions.
Global Change Biology 5: 723-741. Wittwer, S.H. 1995. Food, Climate, and Carbon Dioxide: The Global Environment and World Food Production. CRC Press, Boca Raton, FL. Yang, Y. and Joern,
A. 1994a. Gut size changes in relation to variable food quality and body size in grasshoppers. Functional Ecology 8: 36-45. Yang, Y. and Joern, A. 1994b. Influence of diet quality, developmental
stage, and temperature on food residence time in the grasshopper Melanoplus differentialis. Physiological Zoology 67: 598-616. Zanetti, S., Hartwig, U.A., Van Kessel, C., Luscher, A.,
Bebeisen, T., Frehner, M., Fischer, B.U., Hendrey, G.R., Blum, G. and Nosberger, J. 1997. Does nitrogen nutrition restrict the CO2 response of fertile grassland lacking legumes? Oecologia
112: 17-25. Zanotto, F.P., Simpson, S.J. and Raubenheimer, D. 1993. The regulation of growth by locusts through post-ingestive compensation for variation in the levels of dietary protein
and carbohydrate. Physiological Entomology 18: 425-434. 9.2.2.2. Antioxidant Content Antioxidants are chemical compounds that inhibit oxidation. Some antioxidants found in the human
diet, such as vitamin E, vitamin C, and beta carotene, are thought to protect body cells from the damaging effects of oxidation. Scurvy—a condition characterized by general weakness,
anemia, gum disease (gingivitis), and skin hemorrhages—is induced by low intake of vitamin C. There is some evidence that the condition may be resurgent in industrial countries, especially
among children (Dickinson et al., 1994; Ramar et al., 1993; Gomez-Carrasco et al., 1994). Hampl et al. (1999) found that 12-20 percent of 12-to 18-year-old school children in the United
States “drastically under-consume” foods that supply vitamin C. Johnston et al. (1998) determined that 12-16 percent of U.S. college students have marginal plasma concentrations of vitamin
C. Since vitamin C intake correlates strongly with the consumption of citrus juice (Dennison et al., 1998), and since the only high-vitamin-C juice consumed in any quantity by children
is orange juice (Hampl et al., 1999), even a modest role played by the ongoing rise in the air’s CO2 content in increasing the vitamin C concentration of orange juice could prove to
be of considerable significance for public health in the United States and elsewhere. Thus, determining if rising CO2 concentrations increase or
Human Health Effects 687 hinder the production of antioxidants in human food is relevant to the issue of what effect the historical rise in CO2 concentrations is having
on human health. Antioxidant concentrations in plants are generally observed to be high when environmental stresses are present, such as exposure to pollutants, drought, intense solar
radiation, and high air or water temperatures. Stress generates highly reactive oxygenated compounds that damage plants, and ameliorating these stresses typically involves the production
of antioxidant enzymes that scavenge and detoxify the highly reactive oxygenated compounds. In a study of two soybean genotypes, Pritchard et al. (2000) reported that three months’ exposure
to twiceambient CO2 concentrations reduced the activities of superoxide dismutase and catalase by an average of 23 and 39 percent, respectively. Likewise, Polle et al. (1997) showed
that two years of atmospheric CO2 enrichment reduced the activities of several key antioxidative enzymes, including catalase and superoxide dismutase, in beech seedlings. Moreover, Schwanz
and Polle (1998) demonstrated this phenomenon can persist indefinitely, as they discovered similar reductions in these same enzymes in mature oak trees that had been growing near natural
CO2-emitting springs for 30 to 50 years. The standard interpretation of these results is that the observed reductions in the activities of antioxidative enzymes under CO2-enriched conditions
imply that plants exposed to higher-than-current atmospheric CO2 concentrations experience less oxidative stress and thus have a reduced need for antioxidant protection. This conclusion
further suggests that “CO2-advantaged” plants will be able to funnel more of their limited resources into the production of other plant tissues or processes essential to their continued
growth and development. On the other hand, when oxidative stresses do occur under high CO2 conditions, the enhanced rates of photosynthesis and carbohydrate production resulting from
atmospheric atmospheric CO2 enrichment generally enable plants to better deal with such stresses by providing more of the raw materials needed for antioxidant enzyme synthesis. Thus,
when CO2-enriched sugar maple seedlings were subjected to an additional 200 ppb of ozone, Niewiadomska et al. (1999) reported that ascorbate peroxidase, which is the first line of enzymatic
defense against ozone, significantly increased. Likewise, Schwanz and Polle (2001) noted that poplar clones grown at 700 ppm CO2 exhibited a much greater increase in superoxide dismutase
activity upon chilling induction than clones grown in ambient air. In addition, Lin and Wang (2002) observed that activities of superoxide dismutase and catalase were much higher in
CO2-enriched wheat than in ambiently grown wheat following the induction of water stress. In some cases, the additional carbon fixed during CO2-enrichment is invested in antioxidative
compounds, rather than enzymes. One of the most prominent of these plant products is ascorbate or vitamin C. C. In the early studies of Barbale (1970) and Madsen (1971, 1975), a tripling
of the atmospheric CO2 concentration produced a modest (7 percent) increase in this antioxidant in the fruit of tomato plants. Kimball and Mitchell (1981), however, could find no effect
of a similar CO2 increase on the same species, although the extra CO2 of their study stimulated the production of vitamin A. In bean sprouts, on the other hand, a mere one-hour-per-day
doubling of the atmospheric CO2 concentration actually doubled plant vitamin C contents over a seven-day period (Tajiri, 1985). Probably the most comprehensive investigation of CO2 effects
on vitamin C production in an agricultural plant—a tree crop (sour orange)—was conducted by Idso et al. (2002). In an atmospheric CO2 enrichment experiment begun in 1987 and still ongoing,
a 75 percent increase in the air’s CO2 content was observed to increase sour orange juice vitamin C concentration by approximately 5 percent in run-ofthe-mill years when total fruit
production was typically enhanced by about 80 percent. In aberrant years when the CO2-induced increase in fruit production was much greater, however, the increase in fruit vitamin C
concentration also was greater, rising to a CO2-induced enhancement of 15 percent when fruit production on the CO2-enriched trees was 3.6 times greater than it was on the ambient-treatment
trees. Wang et al. (2003) evaluated the effects of elevated CO2 on the antioxidant activity and flavonoid content of strawberry fruit in field plots at the U.S. Department of Agriculture’s
Beltsville Agricultural Research Center in Beltsville, Maryland, where they grew strawberry plants (Fragaria x ananassa Duchesne cv. Honeoye) in six clear-acrylic open-top chambers,
two of which were maintained at the ambient atmospheric CO2 concentration, two of which were maintained at ambient + 300 ppm CO2, and two of which were maintained at ambient + 600 ppm
CO2 for a period of 28 months (from early spring of 1998 through June 2000). The scientists harvested the strawberry fruit, in their words, “at the
Climate Change Reconsidered 688 commercially ripe stage” in both 1999 and 2000, after which they analyzed them for a number of different antioxidant properties and flavonol contents.
Before reporting what they found, Wang et al. provide some background by noting that “strawberries are good sources of natural antioxidants (Wang et al., 1996; Heinonen et al., 1998).”
They further report that “in addition to the usual nutrients, such as vitamins and minerals, strawberries are also rich in anthocyanins, flavonoids, and phenolic acids,” and that “strawberries
have shown a remarkably high scavenging activity toward chemically generated radicals, thus making them effective in inhibiting oxidation of human low-density lipoproteins (Heinonen
et al., 1998).” In this regard, they note that previous studies (Wang and Jiao, 2000; Wang and Lin, 2000) “have shown that strawberries have high oxygen radical absorbance activity against
peroxyl radicals, superoxide radicals, hydrogen peroxide, hydroxyl radicals, and singlet oxygen.” They determined, first, that strawberries had higher concentrations of ascorbic acid
(AsA) and glutathione (GSH) “when grown under enriched CO2 environments.” In going from ambient to ambient + 300 ppm CO2 and ambient + 600 ppm CO2, for example, AsA concentrations increased
by 10 and 13 percent, respectively, while GSH concentrations increased by 3 and 171 percent, respectively. They also learned that “an enriched CO2 environment resulted in an increase
in phenolic acid, flavonol, and anthocyanin contents of fruit.” For nine different flavonoids, for example, there was a mean concentration increase of 55 ± 23 percent in going from the
ambient atmospheric CO2 concentration to ambient + 300 ppm CO2, and a mean concentration increase of 112 ± 35 percent in going from ambient to ambient + 600 ppm CO2. In addition, they
report that the “high flavonol content was associated with high antioxidant activity.” As for the significance of these findings, Wang et al. note that “anthocyanins have been reported
to help reduce damage caused by free radical activity, such as low-density lipoprotein oxidation, platelet aggregation, and endotheliumdependent vasodilation of arteries (Heinonen et
al., 1998; Rice-Evans and Miller, 1996).” In summarizing their findings, Wang et al. say “strawberry fruit contain flavonoids with potent antioxidant properties, and under CO2 enrichment
conditions, increased the[ir] AsA, GSH, phenolic acid, flavonol, and anthocyanin concentrations,” further noting that “plants grown under CO2 enrichment conditions also had higher oxygen
radical absorbance activity against [many types of oxygen] radicals in the fruit.” Deng and Woodward (1998) reported that after growing strawberry plants in air containing an additional
170 ppm of CO2, total fresh fruit weights were 42 and 17 percent greater than weights displayed by control plants grown at high and low soil nitrogen contents, respectively. Bushway
and Pritts (2002) reported that a two-to three-fold increase in the air’s CO2 content boosted strawberry fruit yield by an average of 62 percent. In addition, Campbell and Young (1986),
Keutgen et al. (1997), and Bunce (2001) reported positive strawberry photosynthetic responses to an extra 300 ppm of CO2 ranging from 9 percent to 197 percent (mean of 76 percent ± 15
percent); and Desjardins et al. (1987) reported a 118 percent increase in photosynthesis in response to a 600 ppm increase in the air’s CO2 concentration. Other researchers have found
similar enhancements of antioxidative compounds under enriched levels of atmospheric CO2. Estiarte et al. (1999), for example, reported that a 180-ppm increase in the air’s CO2 content
increased the foliar concentrations of flavonoids, which protect against UV-B radiation damage, in field-grown spring wheat by 11 to 14 percent. Caldwell et al. (2005) found that an
~75 percent increase in the air’s CO2 content increased the total isoflavone content of soybean seeds by 8 percent when the air temperature during seed fill was 18°C, by 104 percent
when the air temperature during seed fill was 23°C, by 101 percent when the air temperature was 28°C, and by 186 percent and 38 percent, respectively, when a droughtstress treatment
was added to the latter two temperature treatments. Lastly, in an experiment conducted under very high atmospheric CO2 concentrations, Ali et al. (2005) found that CO2 levels of 10,000
ppm, 25,000 ppm, and 50,000 ppm increased total flavonoid concentrations of ginseng roots by 228 percent, 383 percent, and 232 percent, respectively, total phenolic concentrations by
58 percent, 153 percent, and 105 percent, cysteine contents by 27 percent, 65 percent, and 100 percent, and non-protein thiol contents by 12 percent, 43 percent, and 62 percent, all
of which substances are potent antioxidants. In summary, as the CO2 content of the air rises, plants typically experience less oxidative stress, and since they thus need fewer antioxidants
for protection, antioxidant levels in their leaves decline, which
Human Health Effects 689 enables them to use more of their valuable resources for other purposes. However, elevated CO2 also provides more of the raw materials needed for oxidant enzyme
synthesis, leading to higher levels of antioxidative compounds—such as ascorbate, or vitamin C. Research shows this happens with enough frequency that higher CO2 levels will lead to
higher concentrations of antioxidants, leading to better health. Additional information on this topic, including reviews of newer publications as they become available, can be found
at http://www.co2 science.org/subject/a/antioxidants.php. References Ali, M.B., Hahn, E.J. and Paek, K.-Y. 2005. CO2-induced total phenolics in suspension cultures of Panax ginseng C.A.
Mayer roots: role of antioxidants and enzymes. Plant Physiology and Biochemistry 43: 449-457. Barbale, D. 1970. The influence of the carbon dioxide on the yield and quality of cucumber
and tomato in the covered areas. Augsne un Raza (Riga) 16: 66-73. Bunce, J.A. 2001. Seasonal patterns patterns of photosynthetic response and acclimation to elevated carbon dioxide in
field-grown strawberry. Photosynthesis Research 68: 237-245. Bushway, L.J. and Pritts, M.P. 2002. Enhancing early spring microclimate to increase carbon resources and productivity in
June-bearing strawberry. Journal of the American Society for Horticultural Science 127: 415-422. Caldwell, C.R., Britz, S.J. and Mirecki, R.M. 2005. Effect of temperature, elevated carbon
dioxide, and drought during seed development on the isoflavone content of dwarf soybean [Glycine max (L.) Merrill] grown in controlled environments. Journal of Agricultural and Food
Chemistry 53: 1125-1129. Campbell, D.E. and Young, R. 1986. Short-term CO2 exchange response to temperature, irradiance, and CO2 concentration in strawberry. Photosynthesis Research
8: 31-40. Deng, X. and Woodward, F.I. 1998. The growth and yield responses of Fragaria ananassa to elevated CO2 and N supply. Annals of Botany 81: 67-71. Dennison, B.A., Rockwell, H.L.,
Baker, S.L. 1998. Fruit and vegetable intake in young children. J. Amer. Coll. Nutr. 17: 371-378. Desjardins, Y., Gosselin, A. and Yelle, S. 1987. Acclimatization of ex vitro strawberry
plantlets in CO2-enriched environments and supplementary lighting. Journal of the American Society for Horticultural Science 112: 846-851. Dickinson, V.A., Block, G., Russek-Cohen, E.
1994. Supplement use, other dietary and demographic variables, and serum vitamin C in NHANES II. J. Amer. Coll. Nutr. 13: 22-32. Estiarte, M., Penuelas, J., Kimball, B.A., Hendrix, D.L.,
Pinter Jr., P.J., Wall, G.W., LaMorte, R.L. and Hunsaker, D.J. 1999. Free-air CO2 enrichment of wheat: leaf flavonoid concentration throughout the growth cycle. Physiologia Plantarum
105: 423-433. Gomez-Carrasco, J.A., Cid, J.L.-H., de Frutos, C.B., Ripalda-Crespo, M.J., de Frias, J.E.G. 1994. Scurvy in adolescence. J. Pediatr. Gastroenterol. Nutr. 19: 118-120. Hampl,
J.S., Taylor, C.A., Johnston, C.S. 1999. Intakes of vitamin C, vegetables and fruits: Which schoolchildren are at risk? J. Amer. Coll. Nutr. 18: 582-590. Heinonen, I.M., Meyer, A.S.
and Frankel, E.N. 1998. Antioxidant activity of berry phenolics on human lowdensity lipoprotein and liposome oxidation. Journal of Agricultural and Food Chemistry 46: 4107-4112. Idso,
S.B., Kimball, B.A., Shaw, P.E., Widmer, W., Vanderslice, J.T., Higgs, D.J., Montanari, A. and Clark, W.D. 2002. The effect of elevated atmospheric CO2 on the vitamin C concentration
of (sour) orange juice. Agriculture, Ecosystems and Environment 90: 1-7. Johnston, C.S., Solomon, R.E., Corte, C. 1998. Vitamin C status of a campus population: College students get
a C minus. J. Amer. Coll. Health 46: 209-213. Keutgen, N., Chen, K. and Lenz, F. 1997. Responses of strawberry leaf photosynthesis, chlorophyll fluorescence and macronutrient contents
to elevated CO2. Journal of Plant Physiology 150: 395-400. Kimball, B.A., Mitchell, S.T. 1981. Effects of CO2 enrichment, ventilation, and nutrient concentration on the flavor and vitamin
C content of tomato fruit. HortScience 16: 665-666. Lin, J.-S and Wang, G.-X. 2002. Doubled CO2 could improve the drought tolerance better in sensitive cultivars than in tolerant cultivars
in spring wheat. Plant Science 163: 627-637. Madsen, E. 1971. The influence of CO2-concentration on the content of ascorbic acid in tomato leaves. Ugeskr. Agron. 116: 592-594. Madsen,
E. 1975. Effect of CO2 environment on growth, development, fruit production and fruit quality of tomato from a physiological viewpoint. In: Chouard, P. and de Bilderling, N. (Eds.) Phytotronics
in Agricultural and Horticultural Research. Bordas, Paris, pp. 318-330.
Climate Change Reconsidered 690 Niewiadomska, E., Gaucher-Veilleux, C., Chevrier, N., Mauffette, Y. and Dizengremel, P. 1999. Elevated CO2 does not provide protection against ozone considering
the activity of several antioxidant enzymes in the leaves of sugar maple. Journal of Plant Physiology 155: 70-77. Polle, A., Eiblmeier, M., Sheppard, L. and Murray, M. 1997. Responses
of antioxidative enzymes to elevated CO2 in leaves of beech (Fagus sylvatica L.) seedlings grown under a range of nutrient regimes. Plant, Cell and Environment 20: 1317-1321. Pritchard,
S.G., Ju, Z., van Santen, E., Qiu, J., Weaver, D.B., Prior, S.A. and Rogers, H.H. 2000. The influence of elevated CO2 on the activities of antioxidative enzymes in two soybean genotypes.
Australian Journal of Plant Physiology 27: 1061-1068. Ramar, S., Sivaramakrishman, V., Manoharan, K. 1993. Scurvy—a forgotten disease. Arch. Phys. Med. Rehabil. 74: 92-95. Rice-Evans,
C.A. and Miller, N.J. 1996. Antioxidant activities of flavonoids as bioactive components components of food. Biochemical Society Transactions 24: 790-795. Schwanz, P. and Polle, A. 2001.
Growth under elevated CO2 ameliorates defenses against photo-oxidative stress in poplar (Populus alba x tremula). Environmental and Experimental Botany 45: 43-53. Schwanz, P. and Polle,
A. 1998. Antioxidative systems, pigment and protein contents in leaves of adult mediterranean oak species (Quercus pubescens and Q. ilex) with lifetime exposure to elevated CO2. New
Phytologist 140: 411-423. Tajiri, T. 1985. Improvement of bean sprouts production by intermittent treatment with carbon dioxide. Nippon Shokuhin Kogyo Gakkaishi 32(3): 159-169. Wang,
H., Cao, G. and Prior, R.L. 1996. Total antioxidant capacity of fruits. Journal of Agricultural and Food Chemistry 44: 701-705. Wang, S.Y., Bunce, J.A. and Maas, J.L. 2003. Elevated
carbon dioxide increases contents of antioxidant compounds in field-grown strawberries. Journal of Agricultural and Food Chemistry 51: 4315-4320. Wang, S.Y. and Jiao, H. 2000. Scavenging
capacity of berry crops on superoxide radicals, hydrogen peroxide, hydroxyl radicals, and singlet oxygen. Journal of Agricultural and Food Chemistry 48: 5677-5684. Wang, S.Y. and Lin,
H.S. 2000. Antioxidant activity in fruit and leaves of blackberry, raspberry, and strawberry is affected by cultivar and maturity. Journal of Agricultural and Food Chemistry 48: 140-146.
9.2.3. Medicinal Constituents Primitive medical records indicate that extracts from many species of plants have been used for treating a variety of human health problems for perhaps
the past 3,500 years (Machlin, 1992; Pettit et al., 1993, 1995). In modern times the practice has continued, with numerous chemotherapeutic agents being isolated (Gabrielsen et al.,
1992a). Until recently, however, no studies had investigated the effects of atmospheric CO2 enrichment on specific plant compounds of direct medicinal value. Stuhlfauth et al. (1987)
studied the individual and combined effects of atmospheric CO2 enrichment and water stress on the production of secondary metabolites in the woolly foxglove (Digitalis lanata EHRH),
which produces the cardiac glycoside digoxin that is used in the treatment of cardiac insufficiency. Under controlled well-watered conditions in a phytotron, a near-tripling of the air’s
CO2 content increased plant dry weight production in this medicinal plant by 63 percent, while under waterstressed conditions the CO2-induced dry weight increase was 83 percent. In addition,
the concentration of digoxin within the plant dry mass was enhanced by 11 percent under well-watered conditions and by 14 percent under conditions of water stress. In a subsequent whole-season
field experiment, Stuhlfauth and Fock (1990) obtained similar results. A near-tripling of the air’s CO2 concentration led to a 75 percent increase in plant dry weight production per
unit land area and a 15 percent increase in digoxin yield per unit dry weight of plant, which combined to produce a doubling of total digoxin yield per hectare of cultivated land. Idso
et al. (2000) evaluated the response of the tropical spider lily (Hymenocallis littoralis Jacq. Salisb.) to elevated levels of atmospheric CO2 over four growing seasons. This plant has
been known since ancient times to possess anti-tumor activity; in modern times it has been shown to contain constituents that are effective against lymphocytic leukemia and ovary sarcoma
(Pettit et al., 1986). These same plant constituents also have been proven to be effective against the U.S. National Cancer Institute’s panel of 60 human cancer cell lines, demonstrating
greatest effectiveness against melanoma, brain, colon, lung, and renal cancers (Pettit et al., 1993). In addition, it exhibits strong antiviral activity against Japanese encephalitis
and
Human Health Effects 691 yellow, dengue, Punta Tora, and Rift Valley fevers (Gabrielsen et al., 1992a,b). Idso et al. determined that a 75 percent increase in the air’s CO2 concentration
produced a 56 percent increase in the spider lily’s below-ground bulb biomass, where the disease-fighting substances are found. In addition, for these specific substances, they observed
a 6 percent increase in the concentration of a two-constituent (1:1) mixture of 7-deoxynarciclasine and 7-deoxy-trans-dihydronarciclasine, an 8 percent increase in pancratistatin, an
8 percent increase in trans-dihydronarciclasine, and a 28 percent increase in narciclasine. Averaged together and combined with the 56 percent increase in bulb biomass, these percentage
concentration increases resulted in a total mean active-ingredient increase of 75 percent for the plants grown in air containing 75 percent more CO2. Other plant constituents that perform
important functions in maintaining human health include sugars, lipids, oils, fatty acids, and macro-and micronutrients. Although concerns have been raised about the availability of
certain of the latter elements in plants growing in a CO2-enriched world (Loladze, 2002), the jury is still out with respect to this subject as a consequence of the paucity of pertinent
data. Literally thousands of studies have assessed the impact of elevated levels of atmospheric CO2 on the quantity of biomass produced by agricultural crops, but only a tiny fraction
of that number have looked at any aspect of food quality. From what has been learned about plant protein, antioxidants, and the few medicinal substances that have been investigated in
this regard, there is no reason to believe these other plant constituents would be present in lower concentrations in a CO2-enriched world and ample evidence that they may be present
in significantly higher concentrations and greater absolute amounts. Additional information on this topic, including reviews of newer publications as they become available, can be found
at http://www.co2 science.org/subject/h/co2healthpromoting.php. References Gabrielsen, B., Monath, T.P., Huggins, J.W., Kefauver, D.F., Pettit, G.R., Groszek, G., Hollingshead, M., Kirsi,
J.J., Shannon, W.F., Schubert, E.M., Dare, J., Ugarkar, B., Ussery, M.A., Phelan, M.J. 1992a. Antiviral (RNA) activity of selected Amaryllidaceae isoquinoline constituents and synthesis
of related substances. Journal of Natural Products 55: 1569-1581. Gabrielsen, B., Monath, T.P., Huggins, J.W., Kirsi, J.J., Hollingshead, M., Shannon, W.M., Pettit, G.R. 1992b. Activity
of selected Amaryllidaceae constituents and related synthetic substances against medically important RNA viruses. In: Chu, C.K. and Cutler, H.G. (Eds.) Natural Products as Antiviral
Agents. Plenum Press, New York, NY, pp. 121-35. Idso, S.B., Kimball, B.A., Pettit III, G.R., Garner, L.C., Pettit, G.R., Backhaus, R.A. 2000. Effects of atmospheric CO2 enrichment on
the growth and development of Hymenocallis littoralis (Amaryllidaceae) and the concentrations of several antineoplastic and antiviral constituents of its bulbs. American Journal of Botany
87: 769-773. Loladze, I. 2002. Rising atmospheric CO2 and human nutrition: toward globally imbalanced plant stoichiometry? Trends in Ecology & Evolution 17: 457-461. Machlin, L.G. 1992.
Introduction. In: Sauberlich, H.E. and Machlin, L.J. (Eds.) Beyond deficiency: New views on the function and health effects of vitamins. Annals of the New York Academy of Science 669:
1-6. Pettit, G.R., Pettit III, G.R., Backhaus, R.A., Boyd, M.R., Meerow, A.W. 1993. Antineoplastic agents, 256. Cell growth inhibitory isocarbostyrils from Hymenocallis. Journal of Natural
Products 56: 1682-1687. Pettit, G.R., Pettit III, G.R., Groszek, G., Backhaus, R.A., Doubek, D.L., Barr, R.J. 1995. Antineoplastic agents, 301. An investigation of the Amaryllidaceae
genus Hymenocallis. Journal of Natural Products 58: 756-759. Stuhlfauth, T. and Fock, H.P. 1990. Effect of whole season CO2 enrichment on the cultivation of a medicinal plant, Digitalis
lanata. Journal Journal of Agronomy and Crop Science 164: 168-173. Stuhlfauth, T., Klug, K. and Fock, H.P. 1987. The production of secondary metabolites by Digitalis lanata during CO2
enrichment and water stress. Phytochemistry 26: 2735-2739. 9.3. Human Longevity The past two centuries have witnessed a significant degree of global warming as the earth recovered from
the Little Ice Age and entered the Current Warm Period. Simultaneously, the planet has seen an increase in its atmospheric CO2 concentration. What effect have these trends had on human
longevity? Although no one can give a precise quantitative answer to this question, it is possible to assess their relative importance by considering the history of human longevity.
Climate Change Reconsidered 692 Tuljapurkar et al. (2000) examined mortality over the period 1950-1994 in Canada, France, Germany (excluding the former East Germany), Italy, Japan, the
United Kingdom, and the United States, finding that “in every country over this period, mortality at each age has declined exponentially at a roughly constant rate.” In discussing these
findings, Horiuchi (2000) notes that the average lifespan of early humans was about 20 years, but that in the major industrialized countries it is now about 80 years, with the bulk of
this increase having come in the past 150 years. He then notes that “it was widely expected that as life expectancy became very high and approached the ‘biological limit of human longevity,’
the rapid ‘mortality decline’ would slow down and eventually level off,” but “such a deceleration has not occurred.” “These findings give rise to two interrelated questions,” says Horiuchi:
(1) “Why has mortality decline not started to slow down?” and (2) “Will it continue into the future?” Some points to note in attempting to answer these questions are the following. First,
in Horiuchi’s words, “in the second half of the nineteenth century and the first half of the twentieth century, there were large decreases in the number of deaths from infectious and
parasitic diseases, and from poor nutrition and disorders associated with pregnancy and childbirth,” which led to large reductions in the deaths of infants, children, and young adults.
In the second half of the twentieth century, however, Horiuchi notes that “mortality from degenerative diseases, most notably heart diseases and stroke, started to fall,” and the reduction
was most pronounced among the elderly. Some suspected this latter drop in mortality might have been achieved “through postponing the deaths of seriously ill people,” but data from the
United States demonstrate, in his words, that “the health of the elderly greatly improved in the 1980s and 1990s, suggesting that the extended length of life in old age is mainly due
to better health rather than prolonged survival in sickness.” Additional support for this conclusion comes from the study of Manton and Gu (2001). With the completion of the latest of
the five National Long-Term Care Surveys of disability in U.S. citizens over 65 years of age—which began in 1982 and extended to 1999 at the time of the writing of their paper— these
researchers were able to discern two trends: (1) disabilities in this age group decreased over the entire period studied, and (2) disabilities decreased at a rate that grew ever larger
with the passing of time. Over the 17-year period of record, the percentage of the group that was disabled dropped 25 percent, from 26.2 percent in 1982 to 19.7 percent in 1999. The
percentage disability decline rate per year for the periods 1982-1989, 1989-1994, and 1994-1999 was 0.26, 0.38, and 0.56 percent per year, respectively. Commenting on the accelerating
rate of this disability decline, the authors say “it is surprising, given the low level of disability in 1994, that the rate of improvement accelerated” over the most recent fiveyear
interval. Looking outside the United States, Oeppen and Vaupel (2002) reported that “world life expectancy more than doubled over the past two centuries, from roughly 25 years to about
65 for men and 70 for women.” They noted that “for 160 years, bestperformance life expectancy has steadily increased by a quarter of a year per year,” and they emphasized that this phenomenal
trend “is so extraordinarily linear that it may be the most remarkable regularity of mass endeavor ever observed.” These observations demonstrate that if the increases in air temperature
and CO2 concentration of the past two centuries were bad for our health, their combined negative influence was minuscule compared to whatever else was at work in promoting this vast
increase in worldwide human longevity. It is that “whatever else” to which we now turn our attention. It is evident that in developed countries, the elderly are living longer with the
passing of time. This phenomenon is likely due to ever-improving health in older people, which in turn is likely the result of continuing improvements in the abilities of their bodies
to repair cellular damage caused by degenerative processes associated with old age, i.e., stresses
caused by the reactive oxygen species that are generated by normal metabolism (Finkel and Holbrook, 2000). Wentworth et al. (2003) report they found “evidence for the production of
ozone in human disease,” specifically noting that “signature products unique to cholesterol ozonolysis are present within atherosclerotic tissue at the time of carotid endarterectomy,
suggesting that ozone production occurred during lesion development.” According to Marx (2003), “researchers think that inflammation of blood vessels is a major instigator of plaque
formation,” that “ozone contributes to plaque formation by oxidizing cholesterol,” and that the new findings “suggest new strategies for preventing
Human Health Effects 693 atherosclerosis.” Also according to Marx, Daniel Steinberg of the University of California, San Diego, says that although it’s still too early to definitively
state whether ozone production in plaques is a major contributor to atherosclerosis, he expresses his confidence that once we know for sure, we’ll know which antioxidants will work in
suppressing plaque formation. Reactive oxygen species (ROS) generated during cellular metabolism or peroxidation of lipids and proteins also play a causative role in the pathogenesis
of cancer, along with coronary heart disease (CHD), as demonstrated by Slaga et al. (1987), Frenkel (1992), Marnett (2000), Zhao et al. (2000) and Wilcox et al. (2004). However, as noted
by Yu et al. (2004), “antioxidant treatments may terminate ROS attacks and reduce the risks of CHD and cancer, as well as other ROS-related diseases such as Parkinson’s disease (Neff,
1997; Chung et al., 1999; Wong et al., 1999; Espin et al., 2000; Merken and Beecher, 2000).” As a result, they say that “developing functional foods rich in natural antioxidants may
improve human nutrition and reduce the risks of ROS-associated health problems.” Consider, in this regard, the common strawberry. Wang et al. (2003) report that strawberries are especially
good sources of natural antioxidants. They say that “in addition to the usual nutrients, such as vitamins and minerals, strawberries are also rich in anthocyanins, flavonoids, and phenolic
acids,” and that “strawberries have shown a remarkably high scavenging activity toward chemically generated radicals, thus making them effective in inhibiting oxidation of human low-density
lipoproteins (Heinonen et al., 1998).” They also note that Wang and Jiao (2000) and Wang and Lin (2000) “have shown that strawberries have high oxygen radical absorbance activity against
peroxyl radicals, superoxide radicals, hydrogen peroxide, hydroxyl radicals, and singlet oxygen.” And they say that “anthocyanins have been reported to help reduce damage caused by free
radical activity, such as lowdensity lipoprotein oxidation, platelet aggregation, and endothelium-dependent vasodilation of arteries (Heinonen et al., 1998; Rice-Evans and Miller, 1996).”
Our reason for citing all of this information is that Wang et al. (2003) have recently demonstrated that enriching the air with carbon dioxide increases both the concentrations and activities
of many of these helpful substances. They determined, for example, that strawberries had higher concentrations of ascorbic acid and glutathione when grown in CO2-enriched environments.
They also learned that “an enriched CO2 environment resulted in an increase in phenolic acid, flavonol, and anthocyanin contents of fruit.” For nine different flavonoids there was a
mean concentration increase of 55 percent in going from the ambient atmospheric CO2 concentration to ambient + 300 ppm CO2, and a mean concentration increase of 112 percent in going
from ambient to ambient + 600 ppm CO2. Also, they report that “high flavonol content was associated with high antioxidant activity.” There is little reason to doubt that similar concentration
and activity increases in the same and additional important phytochemicals in other food crops would occur in response to the same increases in the air’s CO2 concentration. Indeed, the
aerial fertilization effect of atmospheric CO2 enrichment is a near-universal phenomenon that operates among plants of all types, and it is very powerful (e.g., Mayeux et al., 1997;
Idso and Idso, 2000). There must have been significant concomitant increases in the concentrations and activities of the various phytochemicals in these foods that act as described by
Wang et al. (2003). Could some part of the rapid lengthening of human longevity reported by Oeppen and Vaupel (2002) be due to enhanced CO2 in the air putting more antioxidants in our
diets? Two recent experiments showing the positive effects of antioxidants on animal lifespan provide some additional evidence that this may be the case. Melov et al. (2000) examined
the effects of two superoxide dismutase-/catalase-like mimetics (EUK-8 and EUK-134) on the lifespan of normal and mutant Caenorhabditis elegans worms that ingested various concentrations
of the mimetics. In all of their experiments, treatment of normal worms with the antioxidant mimetics significantly increased both mean and maximum lifespan. Treatment of normal worms
with only 0.05 mM EUK-134, for example, increased their mean lifespan by fully 54 percent. In mutant worms whose lifespan had been genetically shortened by 37 percent, treatment with
0.5 mM EUK-134 restored their lifespan to normal by increasing their mutation-reduced lifespan by 67 percent. It also was determined that these effects were not due to a reduction in
worm metabolism, which could have reduced the production of oxygen radicals, but “by augmenting natural antioxidant defenses without having any overt effects on other traits.” In the
words of the authors, “these results suggest that
Climate Change Reconsidered 694 endogenous oxidative stress is a major determinant of the rate of aging,” the significance of which statement resides in the fact that antioxidants tend
to reduce such stresses in animals, including man. Another study addressing the subject was conducted by Larsen and Clarke (2002), who fed diets with and without coenzyme Q to wild-type
Caenorhabditis elegans and several mutants during the adult phases of their lives, while they recorded the lengths of time they survived. This work revealed that “withdrawal of coenzyme
Q from the diet of wildtype nematodes extends adult life-span by ~60 percent.” In addition, they found that the lifespans of the four different mutants they studied were extended by
a Q-less diet. More detailed experiments led them to conclude that the life-span extensions were due to reduced generation and/or increased scavenging of reactive oxygen species, leading
them to conclude in the final sentence of their paper that “the combination of reduced generation and increased scavenging mechanisms are predicted to result in a substantial decrease
in the total cellular ROS and thereby allow for an extended life-span.” In light of these many diverse observations of both plants and animals, there is some reason to believe that the
historical increase of CO2 in the air has helped lengthen human lifespans since the advent of the Industrial Revolution, and that its continued upward trend will provide more of the
same benefit. Additional information on this topic, including reviews of newer publications as they become available, can be found at http://www.co2 science.org/subject/h/humanlifespan.php.
References Chung, H.S., Chang, L.C., Lee, S.K., Shamon, L.A., Breemen, R.B.V., Mehta, R.G., Farnsworth, N.R., Pezzuto, J.M. and Kinghorn, A.D. 1999. Flavonoid constituents of chorizanthe
diffusa with potential cancer chemopreventive activity. Journal of Agricultural and Food Chemistry 47: 36-41. Espin, J.C., Soler-Rivas, C. and Wichers, H.J. 2000. Characterization of
the total free radical scavenger capacity of vegetable oils and oil fractions using 2,2-diphenyl-1-picryhydrazyl radical. Journal of Agricultural and Food Chemistry 48: 648-656. Finkel,
T. and Holbrook, N.J. 2000. Oxidants, oxidative stress and the biology of ageing. Nature 408: 239-247. Frenkel, K. 1992. Carcinogen-mediated oxidant formation and oxidative DNA damage.
Pharmacology and Therapeutics 53: 127-166. Heinonen, I.M., Meyer, A.S. and Frankel, E.N. 1998. Antioxidant activity of berry phenolics on human lowdensity lipoprotein and liposome oxidation.
Journal of Agricultural and Food Chemistry 46: 4107-4112. Horiuchi, S. 2000. Greater lifetime expectations. Nature 405: 744-745. Idso, C.D. and Idso, K.E. 2000. Forecasting world food
supplies: The impact of the rising atmospheric CO2 concentration. Technology 7S: 33-56. Larsen, P.L. and Clarke C.F. 2002. Extension of life-span in Caenorhabditis elegans by a diet
lacking coenzyme Q. Science 295: 120-123. Manton, K.G. and Gu, X.L. 2001. Changes in the prevalence of chronic disability in the United States black and nonblack population above age
65 from 1982 to 1999. Proceedings of the National Academy of Science, USA 98: 6354-6359. Marnett, L.J. 2000. Oxyradicals and DNA damage. Carcinogenesis 21: 361-370. Marx, J. 2003. Ozone
may be secret ingredient in plaques’ inflammatory stew. Science 302: 965. Mayeux, H.S., Johnson, H.B., Polley, H.W. and Malone, S.R. 1997. Yield of wheat across a subambient carbon dioxide
gradient. Global Change Biology 3: 269-278. Melov, S., Ravenscroft, J., Malik, S., Gill, M.S., Walker, D.W., Clayton, P.E., Wallace, D.C., Malfroy, B., Doctrow, S.R. and Lithgow, G.J.
2000. Extension of life-span with superoxide dismutase/catalase mimetics. Science 289: 1567-1569. Merken, H.M. and Beecher, G.R. 2000. Measurement of food flavonoids by high-performance
liquid chromatography: a review. Journal of Agricultural and Food Chemistry 48: 577-599. Neff, J. 1997. Big companies take nutraceuticals to heart. Food Processing 58: 37-42. Oeppen,
J. and Vaupel, J.W. 2002. Broken limits to life expectancy. Science 296: 1029-1030. Rice-Evans, C.A. and Miller, N.J. 1996. Antioxidant activities of flavonoids as bioactive components
of food. Biochemical Society Transactions 24: 790-795. Slaga, T.J., O’Connell, J., Rotstein, J., Patskan, G., Morris, R., Aldaz, M. and Conti, C. 1987. Critical genetic determinants
and molecular events in multistage skin
Human Health Effects 695 carcinogenesis. Symposium on Fundamental Cancer Research 39: 31-34. Tuljapurkar, S., Li, N. and Boe, C. 2000. A universal pattern of mortality decline in the
G7 countries. Nature 405: 789-792. Wang, S.Y., Bunce, J.A. and Maas, J.L. 2003. Elevated carbon dioxide increases contents of antioxidant compounds in field-grown strawberries. Journal
of Agricultural and Food Chemistry 51: 4315-4320. Wang, S.Y. and Jiao, H. 2000. Scavenging capacity of berry crops on superoxide radicals, hydrogen peroxide, hydroxyl radicals, and singlet
oxygen. Journal of Agricultural and Food Chemistry 48: 5677-5684. Wang, S.Y. and Lin, H.S. 2000. Antioxidant activity in fruit and leaves of blackberry, raspberry, and strawberry is
affected by cultivar and maturity. Journal of Agricultural and Food Chemistry 48: 140-146. Wang, S.Y. and Zheng, W. 2001. Effect of plant growth temperature on antioxidant capacity in
strawberry. Journal of Agricultural and Food Chemistry 49: 4977-4982. Wentworth Jr., P., Nieva, J., J., Takeuchi, C., Glave, R., Wentworth, A.D., Dilley, R.B., DeLaria, G.A., Saven,
A., Babior, B.M., Janda, K.D., Eschenmoser, A. and Lerner, R.A. 2003. Evidence for ozone formation in human atherosclerotic arteries. Science 302: 1053-1056. Willcox, J.K., Ash, S.L.
and Catignani, G.L. 2004. Antioxidants and prevention of chronic disease. Critical Reviews in Food Science and Nutrition 44: 275-295. Wong, S.S., Li, R.H.Y. and Stadlin, A. 1999. Oxidative
stress induced by MPTP and MPP+: Selective vulnerability of cultured mouse astocytes. Brain Research 836: 237-244. Yu, L., Haley, S., Perret, J. and Harris, M. 2004. Comparison of wheat
flours grown at different locations for their antioxidant properties. Food Chemistry 86: 11-16. Zhao, J., Lahiri-Chatterjee, M., Sharma, Y. and Agarwal, R. 2000. Inhibitory effect of
a flavonoid antioxidant silymarin on benzoyl peroxide-induced tumor promotion, oxidative stress and inflammatory responses in SENCAR mouse skin. Carcinogenesis 21: 811-816. 9.4. Food
vs. Nature Norman Borlaug, the father of the Green Revolution, recently expressed in a Science editorial his concern over the challenge of “feeding a hungry world” by noting that “some
800 million people still experience chronic and transitory hunger each year,” and that “over the next 50 years, we face the daunting job of feeding 3.5 billion additional people, most
of whom will begin life in poverty” (Borlaug, 2007). He described how the scientific and technological innovations he played a major role in discovering and implementing helped reduce
the proportion of hungry people in the world “from about 60% in 1960 to 17% in 2000.” Had that movement failed, he says, environmentally fragile land would have been brought into agricultural
production and the resulting “soil erosion, loss of forests and grasslands, reduction in biodiversity, and extinction of wildlife species would have been disastrous.” Rising CO2 concentrations
in the air helped make it possible to feed a growing global population in the past without devasting nature, but what of the future? The world’s poulation in 2008 was estimated to be
6.7 billion and is projected to reach between 9.1 and 9.7 billion by 2050 (United Nations, 2009; U.S. Census Bureau, 2008). There is real concern about our ability to feed the world’s
population a mere 50 years hence. Tilman et al. (2001) analyzed the global environmental impacts likely to occur if agriculture is to keep pace with population growth. They report that
“humans currently appropriate more than a third of the production of terrestrial ecosystems and about half of usable freshwaters.” They estimate that the amount of land devoted to agriculture
by the year 2050 will have to increase 18 percent to meet the rising demand for food. Because developed countries are expected to withdraw large areas of land from farming over the next
50 years for recreation, open space, and reforestration, the net loss of natural ecosystems to cropland and pasture in developing countries will amount to about half of all potentially
suitable remaining land, which would “represent the worldwide loss of natural ecosystems larger than the United States.” Similar warnings of a coming food vs. nature conflict have been
expressed by other scientists, for example, Wallace (2000) and Raven (2002). What, if anything, can be done to address this conflict between the need to produce food and the wish to
preserve nature? And what role, if any, will climate change play in averting the crisis or making it even worse? We begin by observing that the fear that there isn’t enough land to support
a growing population’s food needs is a very old one, dating at least to Thomas Malthus (1798) and expressed in our day by popular writers such as Paul Ehrlich (2008) and Al Gore (1992).
Predictions of widespread famine have
Climate Change Reconsidered 696 been wrong before, as trends in food production and daily intake of calories per capita, while not linear in the short term, show long-term positive trends
that are driven primarily by gains in yields per acre, not expansion of the area under cultivation (Alexandratos, 1995; Goklany, 1999; Waggoner and Ausubel, 2001). Malthusian concerns
are misplaced because, as Max Singer once explained, “multiplying food production by five times over the next one hundred or two hundred years will be easier than multiplying it by over
seven times as we did in the last two hundred years. No miracles, no scientific breakthroughs, no unknown lands or unexpected new resources, and no reforms of human character or government
are required. All that is required is a continuing use of current evolutionary processes in technology and in economic dvelopment, and as much peace as we have had in the last century”
(Singer, 1987). We also agree with the sensible assessment of science writer Gregg Easterbrook that “the whole notion that there is a proper level of population for Homo sapiens, or
for any species, would be nonsensical to nature” and “there is no reason in principle that the Earth cannot support vastly more human beings than live upon it today, with other species
preserved and wild habitats remaining intact” (Easterbrook, 1995). Similar sentiments have been expressed by Waggoner (1995, 1996), Waggoner et al. (1996), and Meyer and Ausubel (1999).
Regardless of whether the goal of feeding a growing population while protecting nature is attainable, the question remains about global warming’s role in this very real conflict. Tilman
and a second set of collaborators, writing a year after their previously cited analysis, said “raising yields on existing farmland is essential for ‘saving land for nature’” (Tilman
et al. (2002). They proposed a threepart strategy: (1) increasing crop yield per unit of land area, (2) increasing crop yield per unit of nutrients applied, and (3) increasing crop yield
per unit of water used. With respect to the first of these efforts— increasing crop yield per unit of land area—the researchers note that in many parts of the world the historical rate-of-increase
in crop yield is declining as the genetic ceiling for maximal yield potential is being approached. This “highlights the need for efforts to steadily increase the yield potential ceiling.”
With respect to the second effort—increasing crop yield per unit of nutrients applied—they note that “without the use of synthetic fertilizers, world food production could not have increased
at the rate [that it did in the past] and more natural ecosystems would have been converted to agriculture.” Hence, they say the solution “will require significant increases in nutrient
use efficiency, that is, in cereal production per unit of added nitrogen.” With respect to the third effort—increasing crop yield per unit of water used— Tilman et al. note that “water
is regionally scarce,” and that “many countries in a band from China through India and Pakistan, and the Middle East to North Africa either currently or will soon fail to have adequate
water to maintain per capita food production from irrigated land.” The ongoing rise in the atmosphere’s CO2 concentration will help the world’s farmers achieve all three parts of the
Tilman strategy. First, since atmospheric CO2 is the basic “food” of nearly all plants, the more of it there is in the air, the better they function and the more productive they become.
As discussed in Section 9.2, a 300 ppm increase in the atmosphere’s CO2 concentration would increase the productivity of earth’s herbaceous plants by 30 to 50 percent (Kimball, 1983;
Idso and Idso, 1994) and the productivity of its woody plants by 50 to 80 percent (Saxe et al., 1998; Idso and Kimball, 2001). These increases will be in addition to whatever yield gains
are made possible by advances in plant genetics, pest control, and other agricultural practices. Consequently, as the air’s CO2 content continues to rise, so too will the land-use efficiency
and productive capacity of the planet improve. Regarding the second strategy, of increasing crop yield per unit of nutrients applied, many studies have investigated the effects of an
increase in the air’s CO2 content on plants growing in soils with different nitrogen concentrations. (See Chapter 7, Section 7.3.7, for a thorough review of these studies.) These studies
found that many plants increase their photosynthetic nitrogen-use efficiency when atmospheric CO2 concentration is raised. For example, Smart et al. (1998) found wheat grown in controlled-environment
chambers maintained at an atmospheric CO2 concentration of 1,000 ppm increased average plant biomass by approximately 15 percent, irrespective of soil nitrogen content. Zerihun et al.
(2000) studied the effects of CO2 enrichment on sunflowers using three different soil nitrogen concentrations and found whole plant biomass values that were 44, 13 and 115 percent greater
than those of the plants growing in ambient air at low, medium and high levels of soil nitrogen,
Human Health Effects 697 respectively. Deng and Woodward (1998) found that strawberries grown in high CO2 environments produced 17 percent greater fresh fruit weight even when receiving
the lowest levels of nitrogen fertilization. Newman et al. (2003) investigated the effects of two levels of nitrogen fertilization and an approximate doubling of the air’s CO2 concentration
on the growth of tall fescue, an important forage crop. They found the plants grown in the high-CO2 air and under low N conditions photosynthesized 15 percent more and produced 53 percent
more dry matter (DM). Demmers-Derks et al. (1998) grew sugar beets at atmospheric CO2 concentrations of 360 and 700 ppm and high and low nitrogen treatment levels, and found the extra
CO2 enhanced total plant biomass by 13 percent even in plants receiving the low nitrogen treatments. Also working with sugar beets, Romanova et al. (2002) doubled atmospheric CO2 concentrations
while fertilizing plants with three different levels of nitrate-nitrogen. The plants exhibited rates of net photosynthesis that were approximately 50 percent greater than those displayed
by the plants grown in ambient air, regardless of soil nitrate availability. Fangmeier et al. (2000) grew barley plants in containers at atmospheric CO2 concentrations of either 360
or 650 ppm and either a high or low nitrogen fertilization regime. The elevated CO2 had the greatest relative impact on yield when the plants were grown under the less-than-optimum lownitrogen
regime, i.e., a 48 percent increase vs. 31 percent under high-nitrogen conditions. Finally, the review and analysis of Kimball et al. (2002) of most FACE studies conducted on agricultural
crops since the introduction of that technology back in the late 1980s found that in response to a 300-ppm increase in the air’s CO2 concentration, rates of net photosynthesis in several
C3 grasses were enhanced by an average of 46 percent under conditions of ample soil nitrogen supply and by 44 percent when nitrogen was limiting to growth. Clover experienced a 38 percent
increase in belowground biomass production at ample soil nitrogen, and a 32 percent increase at low soil nitrogen. Wheat and ryegrass experienced an average increase of 18 percent at
ample nitrogen, while wheat experienced only a 10 percent increase at low nitrogen. Other studies have found that many species of plants respond to increases in the air’s CO2 content
by increasing fine-root numbers and surface area, which tends to increase total nutrient uptake under CO2-enriched conditions (Staddon et al., 1999; Rouhier and Read, 1998; BassiriRad
et al., 1998; and Barrett et al., 1998). This once again advances the Tilman strategy of increasing crop yield per unit of available nutrient. (See Chapter 7, Section 7.8.2, for a thorough
review of those studies.) Tilman’s third strategy—increasing crop yield per unit of water used—is also advanced by rising levels of CO2 in the atmosphere. Plants exposed to elevated
levels of atmospheric CO2 generally do not open their leaf stomatal pores—through which they take in carbon dioxide and give off water vapor—as wide as they do at lower CO2 concentrations
and tend to produce fewer of these pores per unit area of leaf surface. Both changes tend to reduce most plants’ rates of water loss by transpiration. The amount of carbon they gain
per unit of water lost—or water-use efficiency—therefore typically rises, increasing their ability to withstand drought. In the study of Serraj et al. (1999), soybeans grown at 700 ppm
CO2 displayed 10 to 25 percent reductions in total water loss while simultaneously exhibiting increases in dry weight of as much as 33 percent. Likewise, Garcia et al. (1998) determined
that spring wheat grown at 550 ppm CO2 exhibited a water-use efficiency that was about one-third greater than that exhibited by plants grown at 370 ppm CO2. Hakala et al. (1999) reported
that twice-ambient CO2 concentrations increased the water-use efficiency of spring wheat by 70 to 100 percent, depending on experimental air temperature. Hunsaker et al. (2000) reported
CO2-induced increases in water-use efficiency for field-grown wheat that were 20 and 10 percent higher than those displayed by ambiently grown wheat subjected to high and low soil nitrogen
regimes, respectively. Also, pea plants grown for two months in growth chambers receiving atmospheric CO2 concentrations of 700 ppm displayed an average water-use efficiency that was
27 percent greater than that exhibited by ambiently grown control plants (Gavito et al., 2000). (See Chapter 7, Section 7.2, for a thorough review of those studies.) An issue related
to water-use efficiency that could become more important in the future is the buildup of soil salinity from repeated irrigations, which can sometimes reduce crop yields. Similarly, in
natural ecosystems where exposure to brackish or salty water is commonplace, saline soils can induce growth stress in plants not normally adapted to coping with this problem. The studies
reported below show that rising atmospheric CO2 concentrations also can help to alleviate this problem.
Climate Change Reconsidered 698 Mavrogianopoulos et al. (1999) reported that atmospheric CO2 concentrations of 800 and 1200 ppm stimulated photosynthesis in parnon melons by 75 and 120
percent, respectively, regardless of soil salinity, which ranged from 0 to 50 mM NaCl. Atmospheric CO2 enrichment also partially alleviated the negative effects of salinity on melon
yield, which increased with elevated CO2 at all salinity levels. Maggio et al. (2002) grew tomatoes at 400 and 900 ppm in combination with varying degrees of soil salinity and noted
that plants grown in elevated CO2 tolerated an average root-zone salinity threshold value that was about 60 percent greater than that exhibited by plants grown at 400 ppm CO2 (51 vs.
32 mmol dm-3 Cl). The review of Poorter and Perez-Soba (2001) found no changes in the effect of elevated CO2 on the growth responses of most plants over a wide range of soil salinities,
in harmony with the earlier findings of Idso and Idso (1994). These various studies suggest that elevated CO2 concentrations will help farmers achieve all three of the strategies Tilman
et al. say are essential to addressing the conflict between feeding a growing human population and preserving space for nature. The actual degree of crop yield enhancement likely to
be provided by the increase in atmospheric CO2 concentration expected to occur between 2000 and 2050 has been calculated by Idso and Idso (2000) to be sufficient—but just barely—to close
the gap between the supply and demand for food some four decades from now. Consequently, letting the evolution of technology take its course—which includes continued emissions of CO2
into the atmosphere by industry—appears to be the only way we can grow enough food to support ourselves in the year 2050 without taking unconscionable amounts of land and freshwater
resources from nature. In spite of the dilemma described above and the fact that enhanced levels of CO2, in the air are a necessary part of the solution, the IPCC calls for strict measures
to reduce anthropogenic CO2 emissions—a strategy that, if it has any effect at all on plant and animal life, would lead to lower land-use efficiency, lower nitrogen-use efficiency, and
lower plant wateruse efficiency, just the opposite of what Tilman et al. called for. One might ask whose predictions are more reliable, the IPCC’s computer-model-generated forecasts
of catastrophic consequences due to rising temperatures a century or longer from now, or our projections of human population growth and agricultural productivity just four decades into
the future? In addition to the obvious time differential between the two sets of predictions, human population growth and agricultural productivity are much better-understood processes
than is global climate change, which involves a host of complex phenomena that span a spatial scale of fully 14 orders of magnitude, ranging from the planetary scale of 107 meters to
the cloud microphysical scale of 10-6 meter. Many of the component processes that comprise today’s state-of-the-art climate models are so far from adequately understood (see Chapters
1 and 2) that even the signs of their impacts on global temperature change (whether positive or negative) are not yet known. Consequently, in light of the much greater confidence that
can realistically be vested in demographic and
agricultural production models, it would seem that much greater credence can be placed in our predictions than in the predictions of climate doom. In conclusion, the aerial fertilization
effect of the increase in the air’s CO2 content that is expected to occur by the year 2050 would boost crop yields by the amounts required to prevent mass starvation in many parts of
the globe, without a large-scale encroachment on the natural world. Acting prematurely to reduce human CO2 emissions, as urged by the IPCC, could interrupt this response, resulting in
the death by starvation of millions of people, loss of irreplaceable natural ecosystems, or both. Additional information on this topic, including reviews of newer publications as they
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Human Health Effects 701 9.5. Biofuels Biofuels are liquid and gaseous fuels made from organic matter. They include ethanol, biodiesel, and methanol. Biofuels may have some advantages
over gasoline and diesel fuels, but they are more expensive to produce and can supply only a small part of the world’s total transportation energy needs. Because they compete with food
crops and nature for land and nutrients, expanding the use of biofuels could negatively affect human health and natural ecosystems. The IPCC does not discuss biofuels in the contributions
of Group I (Science) or Group II (Impacts, Adaptation and Vulnerability) to the Fourth Assessment Report. When it finally does discuss them, in two sections of the contribution of Group
III (Mitigation), it fails to address the likely adverse consequences of increased use of biofuels on human health and the natural environment. We discuss those consequences in this
section. 9.5.1. About Biofuels Biofuels are not new—Henry Ford’s first vehicle was fueled by ethanol—and conversion technologies exist or are in development for converting biomass into
a wide range of biofuels suitable for heating, electric production, and transportation. For example, residues from agriculture and forestry long have been used by the lumber and papermaking
industries to generate heat and power. Methane from animal waste and composting is captured and used locally or sold in commercial markets. Of particular interest, and the focus of this
section, is the biochemical conversion using enzymes of corn, soybeans, sugarcane, and other food crops into ethanol, biodiesel, and other biofuels used mainly for transportation. The
country with the most aggressive biofuels program in the world is Brazil. After the country launched its National Alcohol Program in 1975, ethanol production in Brazil rose dramatically
and now accounts for approximately 40 percent of total fuel consumption in the country’s passenger vehicles (EIA, 2008). Ethanol became popular as a gasoline supplement in the U.S. during
the 1990s, when Congress mandated that oil refiners add oxygenates to their product to reduce some emissions. Congress did not provide liability protection for the makers of methyl tertiary
butyl ether (MTBE), ethanol’s main competitor in the oxygenate business, so most companies quickly switched from MTBE to ethanol (Lehr, 2006). Some states also began to mandate ethanol
use for reasons discussed below. Most ethanol made in the U.S. comes from corn. Its production consumed 13 percent of the U.S. corn crop (1.43 billion bushels of corn grain) in 2005
and an estimated 20 percent of the 2006 crop. E10 (a blend of 10 percent ethanol and 90 percent gasoline) is widely available. E85 is an alternative fuel (85 percent ethanol and 15 percent
gasoline) available mainly in corn-producing states; vehicles must be modified to use this fuel. The Energy Policy Act of 2005 mandated the use of 4 billion gallons of ethanol in 2006.
The 2007 Energy Independence and Security Act (EISA) subsequently mandated the use of 36 billion gallons of renewable fuels by 2022—16 billion gallons of cellulosic ethanol, 15 billion
gallons of corn ethanol, and 5 billion gallons of biodiesel and other advanced biofuels (U.S. Congress, 2007). Federal subsidies to ethanol producers in the U.S. cost taxpayers about
$2 billion a year (Dircksen, 2006). Congress protects domestic ethanol producers by imposing a 2.5 percent tariff and 54 cents per gallon duty on imports. Ethanol producers with plants
of up to 60 million gallons annual production capacity are eligible to receive a production incentive of 10 cents per gallon on the first 15 million gallons of ethanol produced each
year. Ethanol is also subsidized by scores of other countries and by at least 19 U.S. states (Doornbosch and Steenblick, 2007, Annex 1, pp. 45-47). U.S. ethanol output rose from 3.4
billion gallons from 81 facilities in 2004 to 9 billion gallons from 170 facilities in 2008 (RFA, 2009). According to a forecast by the Energy Information Administration (EIA), “total
U.S. biofuel consumption rises from 0.3 quadrillion Btu (3.7 billion gallons) in 2005 to 2.8 quadrillion Btu (29.7 billion gallons) in 2030, when it represents about 11.3 percent of
total U.S. motor vehicle fuel on a Btu basis” (EIA, 2008). In 2005 ethanol represented about 2 percent of total gasoline consumption, and biodiesel less than 0.2 percent of diesel consumption,
in the U.S. Doornbosch and Steenblick (2007), in a report produced for the Organization for Economic Cooperation and Development (OECD), reported that “global production of biofuels
amounted to 0.8 EJ [exajoule] in 2005, or roughly 1% of total road transport fuel consumption. Technically, up to 20 EJ from conventional ethanol and biodiesel, or 11% of
Climate Change Reconsidered 702 total demand for liquid fuels in the transport sector, has been judged possible by 2050.” Also for the world as a whole, EIA predicts “alternative fuels
[will] account for only 9 percent of total world liquids use in 2030, despite an average annual increase of 5.6 percent per year, from 2.5 million barrels per day in 2005 to 9.7 million
barrels per day in 2030” (EIA, 2008). References Dircksen, J. 2006. Ethanol: bumper crop for agribusiness, bitter harvest for taxpayers. Policy Paper #121. National Taxpayers Union.
July 20. Doornbosch, R. and Steenblick, R. 2007. Biofuels: is the cure worse than the disease? Organization for Economic Cooperation and Development. Paris. EIA. 2008. International
energy outlook 2008. Energy Information Administration. Report #:DOE/EIA-0484(2008). Lehr, J.H. 2006. Are the ethanol wars over? PERC Reports, Property and Environment Research Center.
March. RFA. 2009. Growing innovation: America’s energy future starts at home. 2009 ethanol industry outlook. Renewable Fuels Association. Washington, DC. U.S. Congress. 2007. Energy
Independence and Security Act of 2007. 9.5.2. Costs and Benefits Proponents of biofuels say their increased production will increase the supply of transportation fuels and therefore
lead to lower prices. Critics of biofuels point out that ethanol often costs more, not less, than gasoline, either because of production costs or supplies that can’t keep pace with government
mandates, and therefore leads to higher prices at least in the short run. Ethanol has only two-thirds the energy content of gasoline, which makes it a poor value for most consumers.
The production cost of ethanol (which is only one component in determining its price) has fallen as a result of technological innovation and economies of scale, but some properties of
ethanol continue to make it expensive compared to gasoline. Transportation costs for ethanol, for example, are high because it picks up water if it travels through existing pipelines,
diluting the ethanol and corroding the pipelines. Therefore, it is being trucked to the Northeast and along the Gulf Coast. Ethanol must be kept in a different container at the terminal
and is blended into the gasoline in the truck on its way to the retailer from the terminal. This has caused regional shortages, further increasing the retail prices in these areas (Dircksen,
2006). Ethanol also has been promoted as a fuel additive to reduce emissions. It reduces carbon monoxide in older vehicles and dilutes the concentration of aromatics in gasoline, reducing
emissions of toxins such as benzene. Because ethanol has only two-thirds the energy content per volume as gasoline, it increases volumetric fuel use (with small increases in energy efficiency.)
Ethanol increases air emissions such as aldehydes. In some areas, the use of 10 percent ethanol blends may increase ozone due to local atmospheric conditions (Niven, 2004). Ethanol also
is promoted as a “homegrown” and renewable energy source, so using more of it could help reduce a a country’s dependency on foreign oil, which in turn might benefit national security
and international relations. But ethanol used in the U.S. mostly supplants oil from domestic suppliers, which is more expensive than foreign oil, and leaves the country’s dependency
on foreign oil the same or even makes it higher (Yacobucci, 2006). Rural communities benefit from the economic boost that comes from higher prices for corn and the jobs created by ethanol
plants, but those economic benefits come at a high price in terms of higher food prices and tax breaks financed by government debt or higher taxes on other goods and services. Finally,
biofuels are renewable resources, which advocates say makes them environmentally friendlier than fossil fuels. But the energy consumed to make biofuels—to plant, fertilize, irrigate,
and harvest corn and other feedstocks as well as to generate the heat used during the fermentation process and to transport biofuels to markets by train or trucks—is considerable. Fossil
fuels (natural gas or coal) are typically the source of that energy. This environmental impact is the focus of the rest of this section. References Dircksen, J. 2006. Ethanol: bumper
crop for agribusiness, bitter harvest for taxpayers. Policy Paper #121. National Taxpayers Union. July 20.
Human Health Effects 703 Niven, R.K. 2005. Ethanol in gasoline: environmental impacts and sustainability, review article. Renewable & Sustainable Energy Reviews 9(6): 535-555. Yacobucci,
B.D. 2006. Fuel ethanol: background and public policy issues. Congressional Research Service. March 3. 9.5.3. Net Emissions The US 2007 Energy Independence and Security Act (EISA) mandates
that life-cycle greenhouse gas emissions of corn ethanol, cellulosic ethanol, and advanced biofuels achieve 20 percent, 60 percent, and 50 percent greenhouse gas (GHG) emission reductions
relative to gasoline, respectively. But there is considerable controversy over whether these fuels do in fact reduce GHG emissions. Numerous studies of GHG emissions produced during
the life-cycle of ethanol (from the planting of crops to consumption as a fuel) have found them to be less than those of gasoline, with most estimates around 20 percent (Hill et al.,
2006; Wang et al., 2007; CBO, 2009). Emissions vary considerably based on the choice of feedstock, production process, type of fossil fuels used, location, and other factors (ICSU, 2009).
Liska et al. (2009), in their study of life-cycle emissions of corn ethanol systems, found the direct-effect GHG emissions of ethanol (without any offset due to changes in land use)
to be “equivalent to a 48% to 59% reduction compared to gasoline, a twofold to threefold greater reduction than reported in previous studies,” largely because they incorporate a credit
for the commercial use of dry distilled grain (DDG). They report that “in response to the large increase in availability of distillers grains coproduct from ethanol production and the
rise in soybean prices, cattle diets now largely exclude soybean meal and include a larger proportion of distillers grains coproduct (Klopfenstein et al., 2008). Thus, the energy and
GHG credits attributable to feeding distillers grains must be based on current practices for formulating cattle diets.” They give corn ethanol systems DDG credits ranging from 19% to
38% depending on region and type of fossil fuels used. None of these estimates, however, takes into account the emission increases likely to come about from land-use changes. Righelato
and Spracklen (2007) wrote that using ethanol derived from crops as a substitute for gasoline, and vegetable oils in place of diesel fuel, “would require very large areas of land in
order to make a significant contribution to mitigation of fossil fuel emissions and would, directly or indirectly, put further pressure on natural forests and grasslands.” The two British
scientists calculated that a 10 percent substitution of biofuels for gasoline and diesel fuel would require “43% and 38% of current cropland area in the United States and Europe, respectively,”
and that “even this low substitution level cannot be met from existing arable land.” Righelato and Spracklen add that “forests and grasslands would need to be cleared to enable production
of the energy crops,” resulting in “the rapid oxidation of carbon stores in the vegetation and soil, creating a large up-front emissions cost that would, in all cases examined, out-weigh
the avoided emissions.” They report further that individual lifecycle analyses of the conversion of sugar cane, sugar beet, wheat, and corn to ethanol, as well as the conversion of rapeseed
and woody biomass to diesel, indicate that “forestation of an equivalent area of land would sequester two to nine times more carbon over a 30-year period than the emissions avoided by
the use of the biofuel.” They conclude that “the emissions cost of liquid biofuels exceeds that of fossil fuels.” Fargione et al. (2008), writing in Science, said “increasing energy
use, climate change, and carbon dioxide (CO2) emissions from fossil fuels make switching to low-carbon fuels a high priority. Biofuels are a potential low-carbon energy source, but whether
biofuels offer carbon savings depends on how they are produced.” They explain that “converting native habitats to cropland releases CO2 as a result of burning or microbial decomposition
of of organic carbon stored in plant biomass and soils. After a rapid release from fire used to clear land or from the decomposition of leaves and fine roots, there is a prolonged period
of GHG release as coarse roots and branches decay and as wood products decay or burn. We call the amount of CO2 released during the first 50 years of this process the ‘carbon debt’ of
land conversion. Over time, biofuels from converted land can repay this carbon debt if their production and combustion have net GHG emissions that are less than the life-cycle emissions
of the fossil fuels they displace. Until the carbon debt is repaid, biofuels from converted lands have greater GHG impacts than those of the fossil fuels they displace.” Fargione et
al. calculate the number of years required to repay carbon debts for six areas: Brazilian Amazon (319 years), Brazilian Cerrado wooded (17 years), Brazilian Cerrado grassland (37 years),
Indonesian or Malaysian lowland tropical rainforest
Climate Change Reconsidered 704 (86 years), Indonesian or Malaysian peatland tropical rainforest (423 years), and U.S. central grassland (93 years). They observe that no carbon debt
is incurred when abandoned cropland or marginal prairie in the U.S. is used without irrigation to produce ethanol. They conclude that “the net effect of biofuels production via clearing
of carbon-rich habitats is to increase CO2 emissions for decades or centuries relative to the emissions caused by fossil fuel use,” and “at least for current or developing biofuels technologies,
any strategy to reduce GHG emissions that causes land conversion from native ecosystems to cropland is likely to be counterproductive.” In a companion essay in the same issue of Science,
Searchinger et al. (2008) also describe the carbon debt due to land-use conversion, but measure it as the difference between biofuels and gasoline in GHG emissions measured in grams
per MJ (megajoule) of energy. They begin by explaining that “to produce biofuels, farmers can directly plow up more forest or grassland, which releases to the atmosphere much of the
carbon previously stored in plants and soils through decomposition or fire. … Alternatively, farmers can divert existing crops or croplands into biofuels, which causes similar emissions
indirectly. The diversion triggers higher crop prices, and farmers around the world respond by clearing more forest and grassland to replace crops for feed and food.” Searchinger et
al. used the Greenhouse gases Regulated Emissions and Energy use in Transportation (GREET) computer program created by the Center for Transportation Research at Argonne National Laboratory
to calculate the GHGs in grams of CO2 equivalent emissions per MJ of energy consumed over the production and use life-cycles of gasoline, corn ethanol, and biomass ethanol fuels. They
observe that “emissions from corn and cellulosic ethanol emissions exceed or match those from fossil fuels, and therefore produce no greehouse benefits,” unless biofuels are given a
“carbon uptake credit” for the amount of carbon dioxide removed from the air by the growing biofuels feedstocks. When that adjustment is made, they estimate that gasoline (which gets
no carbon uptake credit) produces 92g/MJ; corn ethanol, 74g/MJ; and biomass ethanol, 27g/MJ. Searchinger et al. then calculate the amount of land that would be converted from forest
and grassland into cropland to support the biofuels and, like Fargione et al. (2008), apply the GHG emissions due to land-use change to each type of fuel. The result is that total net
GHG emissions from both kinds of biofuel exceed those from gasoline, 177g vs. 92g in the case of corn ethanol and 138g vs. 92g in the case of biomass ethanol. They conclude that “corn-based
ethanol, instead of producing a 20% savings, nearly doubles greenhouse emissions over 30 years and increases greenhouse gases for 167 years. Biofuels from switchgrass, if grown on U.S.
corn lands, increase emissions by 50%. This result raises concerns about large biofuels mandates and highlights the value of using waste products.” Coming to much the same conclusion,
Laurance (2007) observed that “tropical forests, in particular, are crucial for combating global warming, because of their high capacity to store carbon and their ability to promote
sunlight-reflecting clouds via large-scale evapotranspiration,” which led him to conclude that “such features are key reasons why preserving and restoring tropical forests could be a
better strategy for mitigating the effects of carbon dioxide than dramatically expanding global biofuel production.” Doornbosch and Steenblick (2007), while reporting that biofuels could
provide up to 11 percent of the total world demand for road transport fuel by 2050, say “an expansion on this scale could not be achieved, however, without significant impacts on the
wider global economy. In theory there might be enough land available around the globe to feed an ever increasing world population and produce sufficient biomass feedstock simultaneously,
but it is more likely that land-use constraints will limit the amount of new land that can be brought into production
leading to a ‘food-versus-fuel’ debate.” Looking at a different environmental impact of expanded biofuel production, Crutzen and three collaborators calculated the amount of nitrous
oxide (N2O) that would be released to the atmosphere as a result of using nitrogen fertilizer to produce the crops used for biofuels (Crutzen et al., 2007). Their work revealed that
“all past studies have severely underestimated the release rates of N2O to the atmosphere, with great potential impact on climate warming” because, as they report, N2O “is a ‘greenhouse
gas’ with a 100-year average global warming potential 296 times larger than an equal mass of CO2.” The consequence is that “when the extra N2O emission from biofuel production is calculated
in ‘CO2-equivalent’ global warming terms, and compared with the quasi-cooling effect of ‘saving’ emissions of CO2 derived from fossil fuel,
Human Health Effects 705 the outcome is that the production of commonly used biofuels, such as biodiesel from rapeseed and bioethanol from corn, can contribute as much or more to global
warming by N2O emissions than cooling by fossil fuel savings.” Crutzen et al. concluded that “on a globally averaged basis the use of agricultural crops for energy production … can readily
be detrimental for climate due to the accompanying N2O emissions.” Their concerns were confirmed by a 2009 report from the International Council for Science (ICSU), which found “the
increased N2O flux associated with producing ethanol from corn is likely to more than offset any positive advantage from reduced carbon dioxide fluxes (compared to burning fossil fuels).
Even for ethanol from sugar cane or biodiesel from rapeseed, emissions of nitrous oxide probably make these fuels less effective as an approach for reducing global warming than has been
previously believed” (ICSU, 2009). Producing ethanol from crop residues, or stover, is often often proposed as a way to avoid carbon emissions arising from land conversion. But as Lal
(2007) points out, crop residues perform many vital functions. He reports that “there are severe adverse impacts of residue removal on soil and environmental degradation, and negative
carbon sequestration as is documented by the dwindling soil organic carbon reserves.” He notes that “the severe and widespread problem of soil degradation, and the attendant agrarian
stagnation/deceleration, are caused by indiscriminate removal of crop residues.” Lal concludes that “short-term economic gains from using crop residues for biofuel must be objectively
assessed in relation to adverse changes in soil quality, negative nutrients and carbon budget, accelerated erosion, increase in non-point source pollution, reduction in agronomic production,
and decline in biodiversity.” Finally, while using abandoned or degraded lands to produce biomass, rather than converting existing cropland or forests, is often alleged to reduce carbon
emissions (e.g., Fargione et al., 2008), the ICSU report notes that “of course, if the lands have the potential to revert to forests, conversion to biofuels represents a lost opportunity
for carbon storage. The environmental consequences of inputs (irrigation water, fertilizer) required to make degraded and marginal lands productive must also be considered” (ICSU, 2009).
In conclusion, the production and use of biofuels frequently does not reduce net GHG emissions relative to gasoline, the fossil fuel they are intended to replace. Therefore, there is
no basis from an environmental perspective for preferring them to fossil fuels. References CBO. 2009. The impact of ethanol use on food prices and greenhouse-gas emissions. Congressional
Budget Office. April. Crutzen, P.J., Mosier, A.R., Smith, K.A. and Winiwarter, W. 2007. N2O release from agro-biofuel production negates global warming reduction by replacing fossil
fuels. Atmospheric Chemistry and Physics Discussions 7: 11,191-11,205. Doornbosch, R. and Steenblick, R. 2007. Biofuels: is the cure worse than the disease? Organization for Economic
Cooperation and Development. Paris. Fargione, J., Hill, J., Tilman, D., Polasky, S. and Hawthorne, P. 2008. Land clearing and the biofuels carbon debt. Science 319: 1235-1237. Hill,
J., Nelson, E., Tilman, D., Polasky, S. and Tiffany, D. 2006. Environmental, economic, and energetic costs and benefits of biodiesel and ethanol biofuels. Proceedings of the National
Academy of Sciences 103 (30): 11206-11210. ICSU. 2009. Biofuels: environmental consequences and interactions with changing land use. Proceedings of the Scientific Committee on Problems
of the Environment (SCOPE) International Biofuels Project Rapid Assessment, International Council for Science (ICSU). 22-25 September 2008, Gummersbach, Germany. R.W. Howarth and S.
Bringezu, eds. Lal, R. 2007. Farming carbon. Soil & Tillage Research 96: 1-5. Laurance, W.F. 2007. Forests and floods. Nature 449: 409-410. Liska, A.J, Yang, H.S., Bremer, V.R., Klopfenstein,
T.J., Walters, D.D.T., Galen, E.E. and Cassman, K.G. 2009. Improvements in life cycle energy efficiency and greenhouse gas emissions of corn-ethanol. Journal of Industrial Ecology 13
(1). Righelato, R. and Spracklen, D.V. 2007. Carbon mitigation by biofuels or by saving and restoring forests? Science 317: 902. Searchinger, T., Heimlich, R., Houghton, R.A., Dong,
F., Elobeid, A., Fabiosa, J., Tokgoz, S., Hayes, D. and Yu, TH. 2008. Science 319: 1238-1239. Wang, M., Wu, M., and Huo, H. 2007. Life-cycle energy and greenhouse gas emission impacts
of different corn
Climate Change Reconsidered 706 ethanol plant types. Environmental Research Letters 2 (2): 024001. 9.5.4. Impact on Food Prices Biofuel refineries compete with livestock growers and
food processors for corn, soybeans, and other feedstocks usually used to produce biofuels in the United States, leading to higher animal feed and ingredient costs for farmers, ranchers,
and food manufacturers. Some of that cost is eventually passed on to consumers. A study by the Congressional Budget Office (CBO) found “the demand for corn for ethanol production, along
with other factors, exerted upward pressure on corn prices, which rose by more than 50 percent between April 2007 and April 2008. Rising demand for corn also increased the demand for
cropland and the price of animal feed” (CBO, 2009). The CBO estimated that increased use of ethanol “contributed between 0.5 and 0.8 percentage points of the 5.1 percent increase in
food prices measured by the consumer price index (CPI).” Johansson and Azar (2007) analyzed what they called the “food-fuel competition for bio-productive land,” developing in the process
“a long-term economic optimization model of the U.S. agricultural and energy system,” wherein they found that the competition for land to grow crops for both food and fuel production
leads to a situation where “prices for all crops as well as animal products increase substantially.” Similarly, Doornbosch and Steenblick (2007) say “any diversion of land from food
or feed production to production of energy biomass will influence food prices from the start, as both compete for the same inputs. The effects on farm commodity prices can already be
seen today. The rapid growth of the biofuels industry is likely to keep these prices high and rising throughout at least the next decade (OECD/FAO, 2007).” Runge and Senauer (2007),
writing in Foreign Affairs, reported that the production of corn-based ethanol in the United States “takes so much supply to keep ethanol production going that the price of corn—and
those of other food staples—is shooting up around the world.” The rising prices caused food riots to break out in Haiti, Bangladesh, Egypt, and Mozambique in April 2008, prompting Jean
Ziegler, the United Nations’ “special rapporteur on the right to food,” to call using food crops to create ethanol “a crime against humanity” (CNN, 2008). Jeffrey Sachs, director of
Columbia University’s Earth Institute, said at the time, “We’ve been putting our food into the gas tank—this corn-to-ethanol subsidy which our government is doing really makes little
sense” (Ibid.). Former U.S. President Bill Clinton was quoted by the press as saying “corn is the single most inefficient way to produce ethanol because it uses a lot of energy and because
it drives up the price of food” (Ibid.). Unfortunately, as the CBO report concluded a year later, corn is likely to remain the main source of ethanol for quite some time as “current
technologies for producing cellulosic ethanol are not commercially viable” (CBO, 2009). References CBO. 2009. The impact of ethanol use on food prices and greenhouse-gas emissions. Congressional
Budget Office. April. CNN. 2008. Riots, instability spread as food prices skyrocket. April 14. http://www.cnn.com/2008/WORLD/americas/04/14/world.food.crisis/Accessed 4 May 2009. Doornbosch,
R. and Steenblick, R. 2007. Biofuels: is the cure worse than the disease? Organization for Economic Cooperation and Development. Paris. Johansson, D.J.A. and Azar, C. 2007. A scenario
based analysis of land competition between food and bioenergy production in the US. Climatic Change 82: 267-291. Klopfenstein, T.J., Erickson, G.E. and Bremmer, V.R. 2008. Board-invited
review: use of distillers byproducts in the beef cattle feeding industry. Journal of Animal Science 86 (5): 1223-1231. Lehr, J.H. 2006. Are the ethanol wars over? PERC Reports, Property
and Environment Research Center. March. Liska, A.J, Yang, H.S., Bremer, V.R., Klopfenstein, T.J., Walters, D.T., Galen, E.E. and Cassman, K.G. 2009. Improvements in life cycle energy
efficiency and greenhouse gas emissions of corn-ethanol. Journal of Industrial Ecology 13 (1): OECD/FAO. 2007. Agricultural Outlook 2007-2016. Organization for Economic Cooperation and
Development/Food and Agriculture Organization (United Nations). Paris, Rome. Runge, C.F. and Senauer, B. 2007. How biofuels could starve the poor. Foreign Affairs 86: 41-53.
Human Health Effects 707 9.5.5. Use of Water The third strategy proposed by Tilman et al. (2002) to address the conflict between growing food and preserving natural ecosystems is finding
ways to conserve water. Biofuels, as the following studies demonstrate, fail to advance this objective. Elcock (2008) projects that 12.9 billion gallons per day of water will be consumed
in the manufacture of ethanol by 2030. This “increase accounts for roughly 60% of the total projected nationwide increase in water consumption over the 2005-2030 period, and it is more
than double the amount of water projected to be consumed for industrial and commercial use in 2030 by the entire United States.” A 2009 study by Argonne National Laboratory estimated
life-cycle water consumption for one gallon of four types of fuel: ethanol, gasoline from domestic conventional crude oil, gasoline from Saudi conventional crude oil, and gasoline from
Canadian oil sands (Wu et al., 2009). For ethanol, they estimated an average consumption of 3.0 3.0 gallon of water/gallon of corn ethanol during the production process in a corn dry
mill, a yield of 2.7 gallons of ethanol per bushel of corn, and the average consumptive use of irrigation water for corn farming in three U.S. Department of Agriculture Regions (5, 6,
and 7) representing the vast majority of corn production in the United States. They found “total groundwater and surface water use for corn growing vary significantly across the three
regions, producing 1 gallon of corn-based ethanol consumes a net of 10 to 17 gallon of freshwater when the corn is grown in Regions 5 and 6, as compared with 324 gallon when the corn
is grown in Region 7.” When these figures are adjusted to reflect the lower Btu/gallon of ethanol compared to gasoline (75,700 /115,000, or .66), the amount of water consumed per gallon
of gasoline equivalent ranges from 15.2 to 25.8 gallons in Regions 5 and 6 and 492 gallons in Region 7. Wu et al. (2009) found the amount of water required to create a gallon of gasoline
was dramatically less: 3.4-6.6 gallons of water to make one gallon of gasoline from U.S. conventional crude oil, 2.8-5.8 gallons to make one gallon of gasoline from Saudi conventional
crude, and 2.6-6.2 gallons to make one gallon of gasoline from Canadian oil sands. An even more recent review of the literature conducted by the International Council for Science (ICSU)
found “the water requirements of biofuelderived energy are 70 to 400 times larger than other energy sources such as fossil fuels, wind or solar. Roughly 45 billion cubic meters of irrigation
water were used for biofuel production in the [sic] 2007, or some 6 times more water than people drink globally” (ICSU, 2009). The authors also point out that “severe water pollution
can result from runoff from agricultural fields and from waste produced during the production of biofuels,” and that “the increase in corn [production] to support ethanol goals in the
United States is predicted to increase nitrogen inputs to the Mississippi River by 37%.” In light of this evidence, there can be little doubt that biofuels are a much less efficient
use of scarce water resources than are fossil fuels. This means increased reliance on fossil fuels would make it more difficult to increase food production per unit of water in the future,
one of Tilman et al.’s three strategies to solve the food vs. nature conflict. References Elcock, D. 2009. Baseline and projected water demand data for energy and competing water use
sectors. U.S. Department of Energy, ANL/EUS/TM/08-8 for US DOE/NETL. Tilman, D., Cassman, K.G., Matson, P.A., Naylor, R. and Polasky, S. 2002. Agricultural sustainability and intensive
production practices. Nature 418: 671-677. ICSU. 2009. Biofuels: environmental consequences and interactions with changing land use. Proceedings of the Scientific Committee on Problems
of the Environment (SCOPE) International Biofuels Project Rapid Assessment, International Council for Science (ICSU). 22-25 September 2008, Gummersbach, Germany. R.W. Howarth and S.
Bringezu, eds. Wu, M., Mintz, M., Wang, M. and Arora, S. 2009. Consumptive water use in the production of ethanol and petroleum gasoline. U.S. Department of Energy, Office of Scientific
and Technical Information, Center for Transportation Research, Energy Systems Division, Argonne National Laboratory. 9.5.6. Conclusion The production and use of biofuels has increased
dramatically in recent years, due largely to government mandates and taxpayer subsidies. But the alleged environmental benefits of these “renewable fuels” disappear upon close inspection.
As Doornbosch and Steenblick (2007) say in their OECD report, “when such impacts as soil acidification,
Climate Change Reconsidered 708 fertilizer use, biodiversity loss and toxicity of agricultural pesticides are taken into account, the overall environmental impacts of ethanol and biodiesel
can very easily exceed those of petrol and mineral diesel. The conclusion must be that the potential of the current technologies of choice— ethanol and biodiesel—to deliver a major contribution
to the energy demands of the transport sector without compromising food prices and the environment is very limited.” The decision by the IPCC and many environmental groups to embrace
ethanol pits energy production against food production, making even worse the conflict between the two that this section has addressed. There can be little doubt that ethanol mandates
and subsidies have made both food and energy more, not less, expensive, and therefore less available to a growing population. The extensive damage to natural ecosystems already caused
by this poor policy decision, and the much greater destruction yet to come, are a high price to pay for refusing to understand and utilize the true science of climate change. Additional
information on this topic, including reviews of newer publications as they become available, can be found at http://www.co2science.org/subject/b/biofuels.php References Doornbosch, R.
and Steenblick, R. 2007. Biofuels: is the cure worse than the disease? Organization for Economic Cooperation and Development. Paris.