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Office of Science

Idea : E quilibrium climate sensitivity ( ECS, surface warming expected from CO 2 doubling) is a critical measure of global warming Several recent studies estimate ECS by establishing relations between ECS and currently observable quantities (e.g. Fig. 1)

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Office of Science

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  1. Idea: • Equilibrium climate sensitivity (ECS, surface warming expected from CO2 doubling) is a critical measure of global warming • Several recent studies estimate ECS by establishing relations between ECS and currently observable quantities (e.g. Fig. 1) • We search through >40,000 current-climate fields for predictors of ECS and test the statistical significance of the results • This requires a new technique for testing significance of the best correlations out of a huge dataset containing dependencies across fields and between models • Results: • Strong correlations are expected by chance • None of the current-climate predictors tested are significant at the 95% level. • Robust identification of observable predictors of ECS require a convincing physical mechanism • The best data-mined predictors of ECS are related to the Southern Ocean, suggesting this is a likely place to search for mechanisms connecting current climate to ECS Office of Science Statistical Significance of Climate Sensitivity Predictors Obtained by Data Mining (accepted by GRL 2/13/14)P. M. Caldwell, C. S. Bretherton, M. D. Zelinka, S. A. Klein, B. D. Santer, & B. M. Sanderson Fig 1: Relationship between ECS and the best-correlated current-climate predictor (summer-time specific humidity at 1000 mb averaged over 30-50S ). Each number represents a CMIP5 model. Publication: Caldwell, P.M., C.S. Bretherton, M.D. Zelinka, S.A. Klein, B.D. Santer, and B.A. Sanderson: Statistical Significance of Climate Sensitivity Predictors Obtained by Data Mining. Geophys. Res. Letters. Accepted. doi: 10.1002/2014GL059205 Fig 2: Number of fields correlated with ECS at >0.7 in absolute value as a function of the number of independent models assumed (blue line) and number expected by chance at 95% confidence level (red line).

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