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Has the Historical Rise in the Air's CO2 Content Negatively Impacted Human Health?
Volume 5, Number 44: 30 October 2002

In a recent Opinion piece published in Trends in Ecology & Evolution, Loladze (2002) conducts what he calls a "thought experiment," wherein he concludes that the dilution effect of the extra plant biomass produced by the aerial fertilization effect of atmospheric CO2 enrichment tends to reduce the concentrations of a number of micronutrients found in plant tissues, many of which are important to human health and are currently present in common food plants in what are believed - by some - to be insufficient quantities.  Being one of that believing cadre, Loladze suggests that the increase in the atmosphere's CO2 concentration since preindustrial times may have caused an elemental imbalance in earth's plants, contributing to the problem of micronutrient malnutrition, which he says is harming the health and economy of over half of the world's population.

Loladze's thesis is based on the assumption that certain essential micronutrients should be present in plants at concentrations that are greater than, or at least equal to, their current concentrations.  By this thinking, any concentration reductions from those of the present are deemed to be bad.  This premise, however, is far too simplistic; for it is not the amount of those elements, but how they are used, that defines their utility or value to the plant and/or human body.

A case in point from the plant world is the commonly - but not universally - observed decrease in foliage nitrogen concentration that occurs in vegetation growing in air enriched with CO2.  Originally thought to be a negative response, this acclimation phenomenon has gradually come to be realized to be a positive reaction to atmospheric CO2 enrichment.  Not requiring as much nitrogen to maintain their photosynthetic machinery in top working condition when growing in air enriched with CO2, plants need not acquire as much nitrogen as they do in CO2-deficient air (such as that of the present) and, therefore, they need not expend the extra energy required to do so, growing bigger and better all the while.  And that is why it is openly acknowledged that atmospheric CO2 enrichment greatly enhances plant nitrogen use efficiency.

Another example of the importance of the "how elements are used" concept, which also applies to animals, is actually embodied in a complaint of Loladze.  He says that much of the experimental CO2 enrichment work in this area "has ignored chemical elements and has instead focused on complex compounds."  Does Loladze not realize that it is not the elements that do the life-sustaining work of plants and animals, but rather the complex compounds that are constructed from them and avidly sought by modern botanical explorers searching for previously-unrecognized plant substances possessed of health-promoting and medicinal qualities?  If he did appreciate this fact, he would probably not be so quick to report that many of those compounds "show little consistency in their response to high [CO2]," for that observation clearly contradicts his thesis of globally decreased food-derived health benefits associated with higher levels of atmospheric CO2.

The proof of the pudding, however, is clearly in the eating, as it is with all foods; and with respect to that eating, Loladze rightly notes that "plants are the basis of human nutrition, providing a staggering 84% of calorie intake worldwide."  Hence, as good nutrition is so important to good health, we ought rightly ask: How has human health varied over the course of the Industrial Revolution and up to the present day, during which time the air's CO2 content has risen by a full 35%, from approximately 275 to 375 ppm?

One good measure that can be employed to investigate this question is average life span, or its correlate, life expectancy, which has been growing ever larger with the passage of time within the industrial era.  This life-span extension is truly huge.  In fact, Oeppen and Vaupel (2002) have recently 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."  What is more, they note that "for 160 years, best-performance life expectancy has steadily increased by a quarter of a year per year," and they emphasize that this phenomenal trend "is so extraordinarily linear that it may be the most remarkable regularity of mass endeavor ever observed."

Oeppen and Vaupel also report there are no indications of the worldwide life-extension trend leveling off anytime soon.  Indeed, the most up-to-date data suggest that life expectancy extensions appear to be accelerating with time.  Tuljapurkar and Boe (2000), for example, report that in every one of the G7 countries - which would be expected to exhibit what Oeppen and Vaupel refer to as "best-performance life expectancy" - mortality over the period 1950-1994 "declined exponentially at a roughly constant rate."  As to the reason for this dramatic development, Horiuchi (2000) has noted 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."

More support for this suggestion comes from Manton and Gu (2001), who studied U.S. citizens over 65 years of age and found that disabilities in this age group decreased over the entire period of their study (1982-1999).  Even more importantly, perhaps, they found that disabilities decreased at a rate that grew ever larger with the passing of time.  For the periods 1982-1989, 1989-1994 and 1994-1999, for example, the percentage disability decline rates were 0.26, 0.38 and 0.56% per year, respectively.

Clearly, the increase in the air's CO2 content of the past two centuries, as devastatingly hurtful to humanity as Loladze makes it out to be, has had not the slightest impact on perhaps the most significant of all aspects of human health, i.e., longevity.  Hence, Loladze becomes but the latest fatality in a long line of Cassandras who have "envisioned various biological barriers and practical impediments" to better health and longer life, as Oeppen and Vaupel put it, but who consistently have been proven wrong by real-world data.  Furthermore, they rightly note that this "ignominious saga," of crying wolf when none is present, "is distorting public and private decision-making" in a number of important areas, not the least of which is the ongoing debate over the significance of anthropogenic CO2 emissions.

Let it finally be noted, therefore, that human life, in terms of both its length and quality, in all societies on earth, has been nothing but enhanced, and dramatically so, over the entire period of humanity's massive burning of fossil fuels ... which leads us to seriously consider the very real possibility that instead of reducing the quality of the food we eat - as suggested by Loladze - the historical and ongoing rise in the air's CO2 content has actually been improving it.

Sherwood, Keith and Craig Idso

Horiuchi, S.  2000.  Greater lifetime expectations.  Nature 405: 744-745.

Loladze, I.  2002.  Rising atmospheric CO2 and human nutrition: toward globally imbalanced plant stoichiometry?  Trends in Ecology & Evolution 17: 457-461.

Manton, K.G. and Gu, XL.  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.

Oeppen, J. and Vaupel, J.W.  2002.  Broken limits to life expectancy.  Science 296: 1029-1030.

Tuljapurkar, S., Li, N. and Boe, C.  2000.  A universal pattern of mortality decline in the G7 countries.  Nature 405: 789-792.