What effect does respiration have on global C02 levels?

March 17, 2009 6:08 AM

What effect does respiration have on global C02 levels?

Since 1900 we've added 4 billion people to the planet, what effect does all those people breathing have on C02 levels (i.e is it significant?)

posted by zeoslap to science & nature (13 comments total)

The NYT to the rescue!

tl;dr? Nobody's sure yet, but it's leaning towards "negligible".
posted by turgid dahlia at 6:14 AM on March 17

"However, Joel S. Levine, an atmospheric scientist with the National Aeronautics and Space Administration, said the carbon dioxide produced by the respiration and decay of animal life is almost balanced by the uptake of carbon dioxide by vegetation in the process of photosynthesis."

So is it true that vegetation growth is keeping pace with population growth? I always thought that we we losing vegetation.
posted by zeoslap at 6:27 AM on March 17

Wikipedia has a little info on this (check the references down the bottom). My gut tells me that yes, population growth is vastly outstripping vegetation growth (because, frankly, forests are getting deforested a lot faster than people are getting depeopled) but then, as Carl Sagan said, "I prefer not to think with my gut."
posted by turgid dahlia at 6:34 AM on March 17

Human only or all animals?
posted by damn dirty ape at 6:45 AM on March 17

The increase in population has a negligible effect vis-a-vis exhaled CO₂*. There's a much larger increase due to the additional energy needed by a larger population in the form of wood-burning, coal/gas/oil-fueled furnaces and electricity plants, etc. Not to mention the higher standard of living that results in a higher amount of energy used per-person.

Today's humans require no more food energy and exhale no more CO₂ than previous ones, so a doubling in population only doubles an incredibly tiny figure. All animals require respiration, and humans are an incredibly small percentage of the figure "all animals." By comparison, ants are estimated to make up 15-20% of the terrestial animal biomass (that's by weight, not number!), and there are plenty of other insects and other invertibrates before you even get to mammals, much less humans.

In short, human activity has a significant effect on CO₂ levels, but human respiration has a negligible effect.

*It's CO₂, with an "oh", not C02 ("cee zero two")
posted by explosion at 6:49 AM on March 17

The New York Times article states that a typical human 'engaged in the activities of daily living' emits 166,440 liters, or 0.3 tons, of CO2 per year. Multiply this by 6.67 billion people, and you get 2 billion tons per year, which is significant in comparison to the total 27 billion tons emitted in 2004. The 0.3 tons per person doesn't include exercise or hard work, either.
posted by driveler at 7:15 AM on March 17

For certain definitions of "significant," I'd agree that our respiration is significant. However, 2 billion tons versus 27 billion tons emitted (plus that of clear-cutting and other activities not counted in your link) means that respiration is under 6% of our total CO₂ contribution.

I'm all for population control rather than continuing growth, but carbon dioxide emission doesn't really seem like a strong argument, considering the statistics.
posted by explosion at 7:32 AM on March 17

Related.
posted by Restless Day at 7:54 AM on March 17

What about methane emissions?
posted by ComfySofa at 8:43 AM on March 17

Late to the party, but I just want to comment on the vegetation/population growth thing. The only vegetation relevant to this discussion is, well, vegetables---agriculture, all the stuff we eat. The carbon we exhale doesn't magically manifest itself in our lungs from nothing. It's the same carbon that's in the food we eat (as carbohydrates, etc). And unless they've started sneaking coal and petroleum into our wheaties, that carbon all originally came from plants, which got the carbon from CO2 in the air.

Thus, respiration is a closed circle. There is no net gain of CO2 in the equation. If you want to factor in farming methods, etc, then sure, there's CO2 there, but that's a different question entirely.

They call food "fuel", right? Well our fuel just happens to be renewable. Funny how nature does that.
posted by gueneverey at 7:32 PM on March 17

There is no net gain of CO2 in the equation...

No, but there's a release of stored CO2. If you trash a forest, all those lovely trees, or carbon banks, are going to slowly release it back into the atmosphere. So while there's no net gain, there is still an increase. Forests aren't growing back as fast as they are being chopped down, and the stuff that's replacing them? Crops for (mostly) stock feed.
posted by turgid dahlia at 9:43 PM on March 17

Well yeah, of course there's a gain of CO2 if you chop down a forest to grow corn or tomatoes or anything else. But respiration does not necessitate that forests get chopped down. That does turn out to be the case in many parts of the world right now, but I think that's an issue several degrees removed from the question of "What effect does respiration have on CO2 levels?"
posted by gueneverey at 3:24 PM on March 18

That makes perfect sense gueneverey :)
posted by zeoslap at 7:32 AM on March 19