Dec 28 2007
World Population, Carbon Dioxide, and Eugenics
One thing that often gets overlooked in the climate policy discussions is the role of the global human population. I just visit the usual blogs; I don’t read the newspaper, try not to watch TV news, and in all ways try to avoid the mainstream media. They are absolutely horrible at reporting science news, and that’s almost exclusively what I’m interested in. Am I passing judgement on those that care that Paris Hilton got new sunglasses? Maybe, but that’s a discussion for a different time.
Right now, I’ll be talking about population. In the past year that I’ve been blogging, I’ve done posts on a variety of subjects. Perhaps my favorite was about the role of human respiration in contributing to global CO2 concentrations. This post is a follow-on to that post, so go read that one first. 
Interestingly, there was a recent (2006) paper in Biogeosciences Discussions by Prairie and Duarte titled Direct and indirect metabolic CO2 release by humanity that I was unaware of at the time of the last posting on this topic. (I believe that the paper should be free, but don’t know for sure.)
Abstract: The direct CO2 released by respiration of humans and domesticated animals, as well as the CO2 derived from the decomposition of their resulting wastes was calculated in order to ascertain the direct and indirect metabolic contribution of humanity to CO2 release. Human respiration was estimated to release 0.6 Gt C year?1 and that of their associated domestic animals was estimated to release 1.5 Gt C year?1, to which an indirect release of 1.0 Gt C year?1, derived from decomposition of the organic waste and garbage produced by humans and their domestic animals, must be added. These combined direct and indirect metabolic sources, estimated at 3.1 Gt C year?1, has increased 7 fold since pre-industrial times and is forecasted to continue to rise over the 21st century.
They estimate that human respiration contributes 0.6 gigatons of carbon per year, which is remarkable close to my back of the envelope calculation of about 2 gigatons per year. One of the conclusions that I drew from my previous post was that human respiriation is not a non-significant source of carbon dioxide in the atmosphere. Even further, all anthropogenic sources of CO2 are a result of population growth - almost by definition. Below is a graph of estimated world population from 1950 to 2050 under a few different scenarios - of which I don’t know the difference. The data was obtained from the United Nations Population Division of the Department of Economic and Social Affairs.
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(Sorry for the crappy plot, my normal plotting software is on the fritz.)
And here is a figure obtained from the paper cited above of the direct and indirect metabolic release of CO2 per year.
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Why hasn’t population control been discussed in relation to climate change policy? I believe it is because it is construed by some as a form of eugenics. But is it?
Eugenics: The study of hereditary improvement of the human race by controlled selective breeding.
So the answer is obviously “no”. The reasoning behind controlling the population is not selective breeding, but because we do not need more people. In a modern society it is not necessary to have twelve kids. I can understand that people want to have kids. It’s an evolutionary instinct to want to reproduce. (I am not an evolutionary biologist. I am not an expert in anything closely related to evolution - so no hate mail from the fundies please.) Three of the four scenarios provided by the UN population division eventually level off. For this to happen, the birth rate must equal the death rate. Since people are living longer with the advances in medical science, the solution needs to be to reduce the birth rate.
References:
Population Division of the Department of Economic and Social Affairs of the United Nations Secretariat, World Population Prospects: The 2006 Revision and World Urbanization Prospects: The 2005 Revision, http://esa.un.org/unpp, Friday, December 28, 2007; 2:52:13 PM.
Prairie, Y. T. and Duarte, C. M.: Direct and indirect metabolic CO2 release by humanity, Biogeosciences Discuss., 3, 1781-1789, 2006.
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2 Responses to “World Population, Carbon Dioxide, and Eugenics”
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Hello,
Apart from a trivial remark (your back of the envelope calculation of 2.23 GT CO2/yr corresponds to 0.61 GT C which is … exactly the figure cited by the study) and a less trivial one (6 fold overestimate of annual CO2 from volcanoes, altering the reasoning: the real figure to be compared with is the total emission to atmosphere, around 200 GT C/yr), I think we should not compare directly emissions from human respiration and industrial emissions.
Even though they are emissions of the same molecule, they do not participate in the same process. The 7 GT C of industrial emissions are direct net additions to the atmosphere, then to be recycled on a short timescale through exchanges with biosphere and oceans. They can only be compared with volcanic emissions (200 Tg CO2 = 0.06 GT C) when carbon comes directly from the lithosphere and is exchanged with it in a much higher timescale (10^5 years).
On the other hand, emissions from human respiration (and associated emissions from domestic animals,…) participate directly to the biosphere, and as such, the whole cycle should be taken into consideration in order to assess the net impact. That means, estimating the imbalance created in the biospheric carbon cycle by the metabolic needs of human population, not only the gross CO2 emissions. More CO2 emitted by humans and domestic animals can be balanced by more CO2 absorbed by cultivated plants in order to nourish them, or less CO2 released directly by the same plants since they are eaten instead of rotting. But the cultivated plants can take the place of ancient rainforests which absorbed more CO2, etc… I personally don’t know if a net impact assessment is feasible, I mean, if it is possible to distinguish such impact to the general figure of “land use change” estimated to a net release of 1 to 2 GT C/yr.
However, the results given by this UN study are interesting: the 3.1 GT C/yr figure is a small but not negligible fraction of the gross CO2 emissions from the terrestrial biosphere (120 GT C/yr).
Happy new year and best wishes.
Yves
Errata and precisions in the previous comment, plus further remarks:
- the overestimate of volcanic CO2 made in the post referred to (200 teratons C/yr vs 200 teragrams C/yr) was not “6 fold” but 6 orders of magnitude, therefore “10^6 fold”
- in the 2nd ยง (7 GT C from fossils vs 0.06 GT C from volcanoes) I obviously mean per year
- having read the article from Prairie and Duarte they tend to make the mistake I mentioned: compare gross CO2 metabolic emissions with CO2 fossil fuel emissions and (net) carbon balance from land use change (”The calculated direct and indirect metabolic CO2 release by humans represents about half of the CO2 released from fossil fuel combustion, and nearly twice that released from changes in land use”). That confirms my impression that this study, though very interesting, is only halfway to a complete evaluation of the impact of those metabolic processes, and as such could sow confusion in the public debate. However I think this topic has to be addressed for such purpose and I thank you for having posted about it. Keep up the good work.
Yves