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Should we Trust Emergent Constraints?

Presentation Date
Tuesday, December 11, 2018 at 5:45pm
Walter E Washington Convention Center 146B



Emergent constraints (ECs) have the potential to remove the cloud of uncertainty surrounding anthropogenic warming, but only if they impose real constraints on the climate system. As a result, verifying the credibility of proposed ECs is critically important. An essential ingredient in this verification is the presence of a clear physical explanation for a given EC's predictive power. These explanations are hard to test, but a new methodology for decomposing correlation between an EC and equilibrium climate sensitivity into terms related to physical processes and geographical regions makes this task easier. Of the 19 previously-published constraints evaluated in this study, only 4 are found to be consistent with their proposed explanation and robust to changes in ensemble. Six ECs were discredited by this evaluation and 6 more lacked a testable physical explanation. Two ECs were found to be repeats of other constraints in the ensemble. This low acceptance rate suggests that more care is needed in evaluating potential constraints. A framework for combining the predictions of the 4 seemingly-credible ECs is introduced. This framework implies stronger climate sensitivity than predicted by the CMIP5 models as a whole.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. All authors are supported by DOE’s Regional and Global Climate Modeling Program under the project “Identifying Robust Cloud Feedbacks in Observations and Models”. IM Release LLNL-ABS-754906

Funding Program Area(s)