Thursday, December 22, 2011
If you thought that global carbon emissions were increasing linearly over time (roughly true) and that a constant fraction of them were retained in the atmosphere each year (also roughly true) then you would expect that the atmospheric concentration of CO2 would increase quadratically. A quadratic fit to the annual Mauna Loa data is above and you can see that this simple brain-dead model explains 99.91% of the variation in the data from 1958 to 2010. Not often you see an R2 of 99.91%. If you were willing to assume that the coupled system of planet/civilization were to continue to behave in the same way for a few more years, then we'll hit 400ppm in 2015.
If you are willing to extrapolate a few decades (admittedly a sketchier assumption) it looks like we'll be in the mid 430s by 2030:
For context, the pre-industrial concentration was about 280ppm, and I've made that the bottom of these graphs.