Robert Rohde, who is lead scientist for Berkeley Earth, has created a really nice illustration of the carbon cycle. It shows how the CO2 cycles between the different carbon reservoirs, and how our emissions have perturbed the carbon cycle so that atmospheric CO2 concentrations have risen from around 280ppm in the mid-1800s to over 410 ppm today.
If we were to cease emitting CO2 into the atmosphere, then CO2 would continue to be taken up by the natural sinks, and the atmospheric concentration would actually drop. However, as I discuss in this post, there is a limit to how much can be taken up by the natural sinks. As a consequence, between 20% and 30% of our emissions will remain in the atmosphere for thousands of years.
As Robert Rohde pointed out on Twitter, the process that ultimately draws down atmospheric CO2 is sedimentation, which is very slow. It will probably take more than 100000 years for atmospheric CO2 to return to pre-industrial levels. We’ve essentially perturbed the carbon cycle so that atmospheric CO2 concentrations will remain elevated for a very long time.
Credit: Robert Rohde