The oceans cannot absorb infinite amounts of CO2

While North Carolina and most of the South of the US reels under drought like conditions and the local newspaper is filled with all kinds of stories about water shortages, this one sentence, steeped in science-speak has caught the attention of climate scientists and general climate change worriers.

The third process is indicated by increasing evidence (P =0.89) for a long-term (50-year) increase in the airborne fraction (AF) of CO2 emissions, implying a decline in the efficiency of CO2 sinks on land and oceans in absorbing anthropogenic emissions.

Huh? What they’re saying is that while increasing CO2 emissions are rightfully blamed for the bulk of global warming, a not insignificant (18% to be precise) percentage can be linked to the fact that the oceans just are not absorbing CO2 at the rate that they used to. The reasons are yet unclear, but the trend can definitely be seen.


The noise in the data is clear indication that there are many natural factors that greatly influence this uptake. But recent observational studies (not a free paper, look up reference 2, so I won’t link to it) in the North Atlantic are backing up this trend.

The reasons could be as simple as decreasing solubility with increasing temperature, or with increasing ocean acidity, who knows. But it points in the general direction of our climate models being in danger of underestimating climate change effects.

What does this mean for climate research? Well, there was a really interesting paper out in Science today (Reference 3, not free!) talking about the uncertainties in climate change estimates. The best guess (95% confidence interval) is between 2 and 4.5 degrees Celsius rise in temperature with doubling of CO2 levels in the atmosphere. But the probability graph around this estimate is not symmetrical, it has a long tail towards the right (>4.5 degrees). The paper discusses why this uncertainty is not related to model limitations, but is an inherent feature of the way climate change processes work, through non-linear feedbacks and multiplying processes.

What these observations tell us is that uncertainty in climate estimates is not a bug, it’s a feature and will never go away. Also, all the uncertainty is on the wrong side, meaning we’re always in danger of underestimating climate change. There goes one more excuse for not tackling climate change with all the urgency it deserves.

We will never predict how bad it will be, we only know it will be pretty bad, possibly worse.

1) Contributions to accelerating atmospheric CO2 growth from economic activity, carbon intensity, and efficiency of natural sinks — Canadell et al., 10.1073/pnas.0702737104 — Proceedings of the National Academy of Sciences

2) Schuster, U., and A. J. Watson (2007), A variable and decreasing sink for atmospheric CO2 in the North Atlantic, J. Geophys. Res., doi:10.1029/2006JC003941, in press.

3) Gerard H. Roe and Marcia B. Baker (26 October 2007) Why Is Climate Sensitivity So Unpredictable?Science 318 (5850), 629. [DOI: 10.1126/science.1144735]