An engaging item in today’s Physorg Newsletter reported on a recent study, published in Nature Geoscience, that examined the Earth’s carbon chemistry during a period known as the Paleocene-Eocene thermal maximum, or PETM. During this torrid interval, which took place about 55 million years ago, the Earth’s average temperature shot up by 7° C. over a span of about 10,000 years. Atmospheric carbon dioxide spiked as well, but — and here’s the rub — only by 70 percent.
We read:
Doubling of atmospheric carbon dioxide is an oft-talked-about threshold, and today’s climate models include accepted values for the climate’s sensitivity to doubling. Using these accepted values and the PETM carbon data, the researchers found that the models could only explain about half of the warming that Earth experienced 55 million years ago.
The conclusion, [Rice University oceanographer Gerald] Dickens said, is that something other than carbon dioxide caused much of the heating during the PETM. “Some feedback loop or other processes that aren’t accounted for in these models — the same ones used by the IPCC for current best estimates of 21st Century warming — caused a substantial portion of the warming that occurred during the PETM.”
It seems to me there are two possibilities here. Either, as Mr. Dickens seems to suggest, fluctuations in the Earth’s temperature are due to things other than carbon-dioxide levels, or — which he does not suggest — warming is even more sensitive to CO2 than is currently believed. Perhaps the second possibility seems unlikely because temperature increases since the beginning of the Industrial Age — during which time atmospheric concentrations of CO2 have already risen by about a third — have been comparatively modest, perhaps a single degree Centigrade.
At the very least, it is obvious that there is more to the story of Earth’s fluctuating temperature than human activity; after all, 15,000 years ago, my Brooklyn neighborhood lay under several thousand feet of ice. I doubt that ancestral Haida Indians smoking salmon were responsible for its disappearance.
Meanwhile, at the recent G-8 meetings, the developed nations were talking in terms not only of reducing carbon emissions, but also of simply not allowing the temperature to rise beyond a certain threshold — currently set, according to this item in the Times, at 2° C. I’m not sure what this hubristic gesture is interpreted to mean in practical political or economic terms, but the implication is that anything and everything will be sacrificed, if necessary, by the prosperous nations of the world, in what may well be, in light of this latest study, an utterly futile gesture. At the same time, however, the “developing nations” (who apparently deserve, for some reason, a chance to “catch up”) will exempt themselves, and will be free to belch forth as much CO2 as it takes to get their hands on our collars. Noblesse oblige.
You can read the Physorg story here, or, if you are a Nature Geoscience subscriber (or have $18 burning a hole in your pocket), you can download the source document here.