May 01 2007
Direct CO2 Emissions by Humans
As a fun exercise, I decided to see how much CO2 humans release due only to respiration on average and compare it to other sources. Numerical figures were found quickly by Internet search and may not represent current scientific understanding. Do not cite this without first verifying the accuracy of the sources. [The previous statement should not have to be said, but in reality it does.]
On average, a human will breath 16 times per minute [1]. Each breath will contain, on average, 0.037 grams of CO2 [2]. An average year is 525948.766 minutes. An average human will live to be 67 years old [3]. This means that the average CO2 exhaled by the average human in her lifetime will be 20861230 grams, or 23 tons. That’s a lot of mass, but this value is hard to compare to anything. The average CO2 exhaled by all humans in one year is 2230000000 tons, or 2.23 gigatons.
The current mass of CO2 in the atmosphere is 3000000000000 or 3 teratons [4]. The amount of CO2 added to the atmosphere by human respiration is obviously miniscule.
Volcanic activity alone injects around 200 teratons of CO2 into the atmosphere each year (Gerlach, 1995). I’m not sure of the largest source of atmospheric CO2, but this seems pretty large. Especially when compared to the worldwide CO2 emissions quoted below. Human respiration accounts for only 0.001115% of CO2 emissions (assuming volcanic activity were the only source of atmospheric CO2 - which it’s not).
[Added May 14, 2006] - The veracity of the volcanic CO2 emissions has been questioned in the first comment on this post.
Worldwide CO2 emission last year were about 28 billion tons (28 gigatons) [5]. Therefore, roughly 8% of anthropogenic atmospheric CO2 is due to human respiration.
So while human respiration accounts for only a small fraction of CO2 emissions compared to natural sources (volcanoes), when compared to anthropogenic sources, it explains a slightly-larger-than-small percentage. See Global Issues: Human Population for other consequences of over-population.
References
Gerlach, T.M., 1992, Present-day CO2 emissions from volcanoes: Eos, Transactions, American Geophysical Union, Vol. 72, No. 23, June 4, 1991, pp. 249, and 254 – 255
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6 Responses to “Direct CO2 Emissions by Humans”
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I think something is wrong with the units for the CO2 emitted by volcanic activity. I do not have access to the paper by Gerlach, but hoping that wikipedia quoted it correctly:
So it is teragrams, not teratons. 6 orders of magnitude.
Or I can shamelessly plug in my about CO2 from volcanoes, which cites a cite from Gerlach.
It appears you are right. I don’t have online access to EOS, and I don’t want to walk to the library to find the last-century draft (about 30 feet down the hall). And since I cited that wikipedia article, I guess I somewhat trust it.
That paragraph was mostly to lengthen this post. I’ll add a disclaimer to the original. The take-home message was Roughly 8% of anthropogenic atmospheric CO2 is due to human respiration.
I’ve heard this mentioned in the context of “if you think CO2 is a problem hold your breath” and “since you produce CO2 you are a hypocrite”.
Breathe Easy
The source of the CO2 is the plant and animal carbon you’ve consumed. It goes back into plants and animals. This is the short term carbon cycle. Unless you eat fossil fuels you can breathe easy.
The other day I realized that gasoline is heavy and that CO2 is heavier than aliphatic or aromatic CH. that gallon gas can is extrapolated to that 20 gal auto gas tank and the weight of the CO2 produced in using that weekly tank is more than most people can bear (literally).
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