In pursuing this goal, the two researchers utilized Peters' (1983) allometric relationships that depict metabolic and defecation rates as power functions of body weight, while for comparison they estimated the per capita rate of human respiration to be the product of average breathing frequency (10 breaths per minute), tidal volume (0.5 L) and mean CO2 concentration of expired air (3.5%), which yielded a mean individual carbon expiration rate of 251 g C per day, which was nearly identical to the estimated rate of 257 g C per day they derived from Peters' allometric relationships. Based upon these results, they concluded that human respiration releases 0.6 Gt C per year to the atmosphere, while similar considerations led them to conclude that domesticated animals release 1.5 Gt C per year to the air, to which an indirect release of 1.0 Gt C per year (derived from the decomposition of organic waste and garbage produced by humans and their domestic animals) needed to be added, which led them to their final total "personal" human carbon flux rate of 3.1 Gt C per year for all of humanity.

Working backwards in time, Prairie and Duarte calculated that the corresponding metabolic carbon flux rate for all of humanity in 1800 was 0.44 Gt C per year, indicative of a subsequent seven-fold increase; and they expect that the rate will rise still further to a value of 4.4 Gt C per year by 2050 at a minimum, noting that the true increase "may well exceed this estimate, since changes in diet and consumption habits are leading to a rapid increase in human body weight and food ingestion," and that "the number of domestic animals per capita and per capita waste production are also increasing, and are expected to continue to do so in the future."

Prairie and Duarte next point out that "the direct and indirect metabolic CO2 emissions by humans [are] not considered explicitly in the scenarios conducted by the IPCC, and [are] not incorporated, therefore, into current strategies to mitigate the climatic consequences of greenhouse gas emissions." But not to worry! The two insightful investigators are way ahead of us. They have already decided that our indirect metabolic CO2 emissions "may be reduced through the promotion of behavioral changes to reduce the per capita consumption of meat and organic waste production," and that our direct metabolic CO2 release may be reduced by adjusting human ingestion to certain "requirements."

What kind of requirements, you ask? How about "avoiding the excess food ingestion affecting much of the population in developed societies." That's right. They'd like to put us all on a diet, pertaining to both the quantity and quality of what we eat on a daily basis. And to prove they mean business in this regard, the two visionaries conclude their paper by matter-of-factly stating that "explicit consideration of this component may help improve current emission scenarios and mitigation strategies," which, of course, is the ultimate goal of all the "pillars of morality" that invoke fear of CO2-induced global warming in an attempt to mandate the minutiae of each citizen of the world's daily life.

Sherwood, Keith and Craig Idso

References
Peters, R.H. 1983. The Ecological Implications of Body Size. Cambridge University Press, New York, New York, USA.

Prairie, Y.T. and Duarte, C.M. 2007. Direct and indirect metabolic CO2 release by humanity. Biogeosciences 4: 215-217.