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  • Knutti, R., G.A. Meehl, M.R. Allen and D. A. Stainforth, 2006: Constraining climate sensitivity from the seasonal cycle in surface temperature. Journal of Climate, 19, 4224-4233.

The estimated range of climate sensitivity has remained unchanged for decades and recently even increased, resulting in large uncertainties in long-term projections of future climate under increased greenhouse gas concentrations. Here we use the multi-thousand member ensemble of climate model simulations from the climateprediction.net project and a neural network to establish a relation between climate sensitivity and the amplitude of the seasonal cycle in regional temperature. Most models with high sensitivities are found to overestimate the seasonal cycle compared to observations. A probability density function for climate sensitivity is then calculated from the present day seasonal cycle in reanalysis and instrumental datasets. Subject to a number of assumptions on the models and datasets used, we find that climate sensitivity is very unlikely (5% probability) to be either below 1.5 to 2 K or above about 5 to 6.5 K, with the best agreement found for sensitivities between 3 and 3.5 K. This range is narrower than most probabilistic estimates derived from the observed 20th century warming. The current generation of general circulation models are within that range but do not sample the highest values.



Last Updated: 2007-02-26

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