World Population and Global Warming

L. David Roper


It is well established that carbon dioxide and the Earth’s average temperature form a mutual positive feedback system. (


This short paper is an attempt to quantify the amount of carbon dioxide emitted by humans breathing and to compare it to the emissions due to other human activities.

Carbon Dioxide Emissions by Breathing of Humans


Each day the average person breathes in about 15,000 liters, or approximately 35 pounds, of air. ( Since air is 21% oxygen (molecular weight 16) and 78% nitrogen (molecular weight 14) by volume, oxygen is 23.5% by weight and nitrogen is 76.5% by weight in air. So the amount of oxygen breathed in per day by the average person is about 35*0.235 = 8.2 lbs.


Humans breath out about 16% oxygen by volume, so about 5% of the air by volume is converted to CO2, which is about (5/21)x8.2 = about 2 lbs of CO2 every day.


The molecular weight of O2 is 32 and the molecular weight of CO2 is 12+32=44. Therefore, humans emit 44x2x/32 lbs = about 2.8 lbs of CO2 breathed out every day or about 1005 lbs = about 0.5 tons per person per year.


In 2005 the Earth population was about 6.66x109. So the emitted CO2 per year by their breathing was about 3.3x109 tons. Most of that population is due to the using of fossil carbon compounds to farm (fuel and fertilizer). The fraction of fossil carbon compounds used to burn for energy in agricultural infrastructure can already be accounted for in the atmospheric CO2 by calculation from fossil fuel extraction.

In 2002 CO2 emissions due to human activities were about 25x109 tonnes = 27.6x109 tons ( Breathing comprises about 3.3x109 tons of that amount, or about 12% of it. It may be not all of the human breathing is accounted for in "emissions due to human activities"; some of the fossil fuel used to make food available may not be counted.

Globally, annual average emissions of carbon dioxide per capita due to human activities (other than breathing) have been fairly stable since 1990. For 2002, this figure was up to 3.93 tonnes from 3.85 tonnes in 2001 ( Per capita CO2 emissions for 2002 = 3.93 tonnes/person = 4.33 tons/person. Breathing adds about 12% more (0.5 tons per person per year)

This calculation just adds to the realization that the global-warming problem is, in essence, a population-explosion problem. Global warming may be one of nature’s ways to decrease human population.

For the long term the best way to reduce global warming is to reduce human population in a benign way by educating women and providing world-wide free contraception information and devices. If humans do not consciously do that, nature will do it due to the effects of global warming, the decline of petroleum extraction and the eventual entry into the next 115,000-year Major Ice Age. (See .)

The fossil-carbon compounds burned in agriculture are already accounted for in fossil-fuel burning calculations, assuming a certain % of the fossil-carbon being burned, the rest going into making useful compounds. Fossil-carbon compounds used for fuel and fertilizer and for food processing and transportation equipment, allow some carbon to be taken out of the soil, depleting the soil, which is difficult, if not impossible, to calculate. That is, some of the fossil carbon used to make agriculturally useful compounds should be counted as putting CO2 into the atmosphere.

It is obvious that the population explosion occurred because of the availability of fossil carbon fuels. Without coal, petroleum and natural gas the population would be much smaller. It probably is a good approximation to assume that the current population is largely due to the existence of fossil carbon.

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