The XX Factor

CO2 and the Oceans: The Denialists Lose

Indeed, Emily Y., it would be a great boon if it turned out that the case for climate change is weak and life on our planet could hum along as usual, CO 2 emissions and all. But the case isn’t weak and we can’t. You pointed to a new study by Wolfgang Knorr at the University of Bristol about how the oceans have absorbed CO 2 since 1850. I asked Yale geologist Jeffrey Park about Knorr’s findings because he also has a new paper on the topic . He wrote back:

Knorr is NOT saying that global warming isn’t happening, or that CO 2 levels are not increasing. Instead, he is evaluating a very specific hypothesis about the progression of Earth’s carbon cycle as atmospheric-CO 2 levels and global temperature both increase. There are a number of reasons, based on physics, chemistry and biology, to expect an eventual decrease in Earth’s ability to absorb human CO 2 emissions. Currently roughly half of what we emit gets absorbed by the oceans and the land biosphere and rock weathering. We don’t understand each of these processes well enough to predict the exact division between CO 2 -absorption processes, but it’s a good bet that the ocean is the principal sink for CO 2 . We also don’t know enough about the processes to predict exactly when the absorption of CO 2 will slow down, so scientists are devising experiments to estimate the rate, past and present. This is the context of Knorr’s study.

Knorr takes estimates of human CO 2 emissions since the mid-19th century and plots them on the same graph as concurrent estimates of atmospheric CO 2 . Knorr’s result still implies that CO 2 levels will continue to increase, and that the greenhouse effect will continue to increase. What he doesn’t see is evidence for exhaustion of Earth’s ability to sequester a constant fraction of the CO 2 we emit. If his conclusion is correct, then it offers some consolation that this particular climate process is not getting worse, but the consolation is small. Warming will continue.

Knorr’s focus on the long term (since 1850) is useful, but there have been other estimates that have focussed on only the last 50-60 years, and three papers were published by independent research groups in the same month that reached conclusions different from Knorr.

Park says that when you look at Knorr’s data, “it becomes clear that his estimation method won’t do a very good job at estimating changes in trend since 1960.” Here’s yet more explanation . So, sorry, however much we might wish that climate change is less likely, this one study doesn’t show it.

Knorr himself doesn’t say otherwise. His quote on the University of Bristol Web site : “Like all studies of this kind, there are uncertainties in the data, so rather than relying on Nature to provide a free service, soaking up our waste carbon, we need to ascertain why the proportion being absorbed has not changed.” Not exactly a free pass for the CO 2 emitters.

As for global temperatures, despite the cold and snow, 2010 may be on track to be the hottest year ever. Here’s the Economist on the complexity . And while it doesn’t look like we’ve had a single year as hot as 1998, the past decade was the warmest on record (hotter than the ‘90s, which were hotter than the ‘80s).