[Liz]

Liz asked the Naked Scientists:

Hello, TNS!

Great show. I listen via podcast every week.

I wonder if the carbon dioxide emitted from human bodies times the 6 billion population count contributes significantly to climate change? In other words, does the population explosion figure into global warming directly through primary biological processes?

Best to you all,
Liz from North Carolina U.S.

What do you think?

[RD]

If the minute amounts of mineral oil in the human diet are ignored, then breathing is carbon neutral.

(Although if fossil fuel was used to cook the meal this would add CO₂ to the atmosphere).

[Chemistry4me]

Photosynthesis and respiration are reverse processes, but with increasing population and most likely decreasing vegetation, it is likely that more CO2 is being exhaled than can be absorbed by plants...

[elmejor]

Dont know for sure sure but certain media outlets, such as The New York Times, have begun referring to carbon dioxide — one of the basic constituents of the atmosphere and a substance we all constantly exhale — as a "pollutant."! very strange, if that is true then everything is a pollutant

[lancenti]

The mis-representation of carbon dioxide as a pollutant probably comes from the fact that videos and photos of smoke-belching exhaust from cars, coal factories and other places are all supposedly 'of' carbon dioxide.

Consequently, I agree with Chemistry4Me that with an increasing number of people and a decreasing number of trees, we're probably ending up with more CO2 in the atmosphere than the plants can cope with but since a holocaust to put down CO2 emissions from human beings can't be arranged, I don't think they factor it in unless some crazy organization starts calling for putting down people to save the environment.

[Bored chemist]

I wonder if those people who insist that CO2 isn't a polutant would change their minds if they were sat in a room full of the stuff.

[dentstudent]

I wonder if those people who insist that CO2 isn't a polutant would change their minds if they were sat in a room full of the stuff.

I agree, though it is a question of perspective, and one that is generally taken from an anthropogenic point of view. To plants, CO2 would not be deemed a pollutant.

[Karsten]

Wouldn't a higher CO2 content in the atmosphere not be good for plants? We are talking about small changes here. They may have a great effect on global temperatures, but would those increases be trouble for plants?

If we get to a point where we have so many humans on this planet that their exhaled CO2 becomes a problem for the balance of our climate, we have a lot of other things to worry about. Currently we are messing up the climate with fossil fuels. That has made enough changes to cause trouble and it took huge amounts of this stuff to get there. Without having numbers available, this should be more CO2 emissions by a large magnitude than the exhaled CO2 by humans (which is currently mostly balanced). If this exhaled CO2 becomes a problem for our climate because the photosynthesis producing plants are less abundant we have the problem that we will not have enough to eat. Plants are what we eat. If they go away, we go away. We may be able to use fossil fuels to power our life-style, but we cannot eat fossil fuels. Plants and plant eaters will stay balanced. I am confident (and worried) that the plant eaters will begin dying way before the plant eater's CO2 emissions becomes a problem for our climate. We need the plants much more urgently for food than for reducing our share of CO2.

Karsten