The Hockey Schtick appears to be excited about a new paper that finds that the lifetime of CO2 in atmosphere is only 5.4 years. This appears to actually be an abstract for a conference presentation, rather than an actual paper.
The abstract says
The isotope ratio C13/C12 of atmospheric CO2 has been measured over the last decades using mass spectrometry. From these data the fraction of fossil CO2 in atmospheric CO2 is straightforwardly calculated: 5.9%(1981) and 8.5%(2002). These results indicate that the amount of past fossil fuel and biogenic CO2 remaining in the atmosphere, though increasing with anthropogenic emissions, did not exceed in 2002 66 GtC, corresponding to a concentration of 31 ppm, that is 3 times less than the CO2 increase (88 ppm, 24 %) occurred in the last century.
So, the abstract appears to be correctly associating the change in C13/C12 ratio with anthropogenic emissions and uses this ratio to claim that the amount of atmospheric CO2 that is of anthropogenic origin is 31 ppm. The atmospheric CO2 concentration has increased by 88 ppm in the last century so, according to the abstract, only about a third of this is anthropogenic. Hmmm, strange! Not what most others seem to think. The general view is that all of this increase is essentially anthropogenic.
Let’s go a step further before trying to address what seems to be a slightly odd result. The abstract goes on to say
This low concentration (31 ppm) of anthropogenic CO2 in the atmosphere is consistent with a lifetime of t(1/2) = 5.4 years,
Now, I’m not an expert at this but I think they may have just explained why it appears that only 31ppm of the 88ppm increase this century appears to be anthropogenic. It is indeed correct that the C12/C13 ratio in fossil fuels is higher than in the atmosphere (plants “prefer” using C12 than C13) hence the change in the C12/C13 ratio is an indication that the rise in atmospheric CO2 is anthropogenic.
However, as the abstract itself indicates, an individual CO2 molecule does indeed only remain in the atmosphere for about 5 years before being used by a plant or absorbed in the ocean. The atmosphere doesn’t, however, simply lose a CO2 molecule; it is typically replaced by a CO2 molecule released from the biosphere or from the oceans. So, 5.4 years is not the time required for the excess atmospheric CO2 to be reduced by half, it is simply the typical lifetime of an individual CO2 molecule. Now, there is a higher C13/C12 ratio in the oceans than there is in fossil fuels, so we wouldn’t expect the C12/C13 ratio to remain precisely consistent with all of the increase being from fossil fuels (or, rather, a CO2 molecule using C12 absorbed by the oceans can be replaced by a CO2 molecule using C13).
So, we would only expect the change in C13/C12 from 1981 to 2002 (as observed by the authors of the abstract) to be entirely consistent with all of the CO2 increase being anthropogenic, if an anthropogenic CO2 molecule never left the atmosphere. But, as the abstract itself says, it typically only remains in the atmosphere for about 5 years. As I said, I’m not an expert at this, so maybe I’ve misunderstood something here, but it does seem that they’ve done a rather simplistic calculation that essentially ignores the carbon cycle, and also confuses the residence time of an individual CO2 molecule (about 5 years) with the time it would take for the increase in atmospheric CO2 to reduce by half (hundreds of years – see Skeptical Science for more).
When I first started reading this I thought that maybe the authors really were just trying to determine the typical residence time of individual CO2 molecules and that their abstract had been misinterpreted by the Hockey Schtick, but the abstract ends by saying
On these assumptions are based both the theory of Anthropogenic Global Warming and the climate models.
So, they do seem to be claiming that their results bring into question the fundamental tenets of anthropogenic global warming and climate change. When I read these types of things I often wonder what went through the authors’s minds when they did the work and wrote the abstract. Are they really experts in this field? Did they not consider that maybe they’ve made some fundamental mistake (as all good scientists should do)? Have they checked everything properly and spoken to others to see if maybe they have mis-understood something (as I clearly think they have)? Are they intentionally trying to mislead people? Of course, there’s always a possibility that I may have mis-understood something and maybe I have got some detail wrong. However, I doubt that what seems to be the conclusion of the study presented in this abstract (that most of the increase in atmospheric CO2 this century is not anthropogenic) is correct.