CO2 output

So someone told me that humans only account for five percent of the “greenhouse gas” production of the planet earth. In other words, the other parts of nature put out 95 percent of the greenhouse gasses.

Is this true?



You need to be careful when asking a question of this sort. Carbon dioxide is only one of many different greenhouse gases like methane, nitrous oxide, and flurocarbons. Since CO2 has been in the news lately, I’ll address that specifically. I seem to remember there being a thread on this topic within the past couple of days, but I’m too lazy to search for it right now. Sorry for the duplication.

I’ve seen lots of numbers every which way, but the ones that most closely resemble the question you posed involve the carbon cycle. Do a google search, you’ll get lots of hits.

Sources of CO2 emission in Gigatons during the period 1992-1997:
Respiration = 50 (about 4 GtC for humans, alone)
Decomposition = 50
Chaning Land Use = 1.5
Surface Ocean = 90.8
Fossil Fuels and Production = 6.2

Total it all up:
Natural: 188.3 GtC
Human: 10.2 GtC

Therefore, the argument goes, humans account for ~5% of CO2 emissions.

This isn’t the whole truth, though. Just as there are sources of CO2 emissions, there are sinks - new plant growth, ocean absorbtion, et al. The net change in the atmosphere is small, but increasing. Without fossil fuel emissions, the carbon cycle is relatively stable over time. The potential environmental problem is that small alterations to this cycle can lead to a cascade effect. Forests have been cleared to produce documents describing all aspects of this issue, so I needn’t go any further.
Here’s the graphic where I got the numbers for this answer:

Other fun stuff:
The average person exhales 2.2 pounds of CO2 per day.
When burned, one gallon of gasoline produces about 20 pounds of CO2.