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Climate Sensitivity Estimated from Temperature Reconstructions of the Last Glacial Maximum

Schmittner, Andreas, Urban, Nathan M., Shakun, Jeremy D., Mahowald, Natalie M., Clark, Peter U., Bartlein, Patrick J., Mix, Alan C., Rosell-Melé, Antoni
Science 2011 v.334 no.6061 pp. 1385-1388
carbon, carbon dioxide, climate, climate change, climate models, emissions, simulation models, surface temperature, uncertainty
Assessing the impact of future anthropogenic carbon emissions is currently impeded by uncertainties in our knowledge of equilibrium climate sensitivity to atmospheric carbon dioxide doubling. Previous studies suggest 3 kelvin (K) as the best estimate, 2 to 4.5 K as the 66% probability range, and nonzero probabilities for much higher values, the latter implying a small chance of high-impact climate changes that would be difficult to avoid. Here, combining extensive sea and land surface temperature reconstructions from the Last Glacial Maximum with climate model simulations, we estimate a lower median (2.3 K) and reduced uncertainty (1.7 to 2.6 K as the 66% probability range, which can be widened using alternate assumptions or data subsets). Assuming that paleoclimatic constraints apply to the future, as predicted by our model, these results imply a lower probability of imminent extreme climatic change than previously thought.