chicken_lipsforme wrote on Sep 26
th, 2011 at 1:38pm:
Humans are emitting carbon into the atmosphere, but carbon as a whole still only makes up 3% of the total, with human caused emissions being a fraction of that 3%.
If you had a fountain that pumped 3% of the total capacity of the reservoir into the air and back into the reservoir, then somebody stuck a hose in that was trickling in at a fraction of the rate of the actual fountain and caused the reservoir to overflow then it wouldn't matter that the hose was only trickling, it's still what caused the overflow.
It's the same with the carbon cycle, there is a relatively fixed amount of Co2 that cycles through the system over a short term, the problem is the excess CO2 - which was originally absorbed from the atmosphere during a very high CO2 phase by plants and microbes then stored safely underground as coal or oil - that we are reintroducing into the system that is throwing things out of a balance that has been maintained for about 5 million years.
We are adding more CO2 to the system than the system can naturally remove via the natural cycle, in fact the planet is managing to absorb about half of what we emit, but it is the other 50% of that fraction of 3% that is accumulating in the atmosphere and causing concentrations to increase by about 40% to date.