RAPID: Warming Holes--Can Climate Models Represent the Variability and Sources of Regional Temperature Trends in the Continental United States?

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This is one of 16 Rapid Response (RAPID) projects funded as the result of a Dear Colleague Letter (NSF 11-006) encouraging diagnostic analyses of climate model simulations prepared for the Intergovernmental Panel on Climate Change Fifth Assessment Report (IPCC AR5). Research conducted in these projects is expected to lead to more detailed model intercomparisons, better understanding of robust model behaviors, and better understanding and quantification of uncertainty in future climate simulations.This project addresses the region of zero or negative summertiime temperature trends which occurs over the midwestern US and is commonly referred to as a "warming hole". Work performed under the grant seeks to determine whether the warming hole occurs as the result of the natural variability associated with low-frequency modes, or whether it is caused by some anthropogenic climate forcing (aerosols, for example). The project has three main tasks: 1) evaluating the extent to which the 20th century climate simulations prepared for the AR5 are capable of reproducing the warming hole; 2) assessing whether warming holes, defined as regions of reduced warming over multiple decades, are captured in the internal variability of the models, and, if so, whether they occur in preferred locations, such as the U.S. Midwest; 3) determining whether the model simulations capture the observed local relationships between regional U.S. temperatures and clouds and precipitation and the global teleconnections to sea-surface temperatures.The broader impact of the project lies in its support of the IPCC AR5, which is intended to provide information on climate change and its consequences to decision makers worldwide. The ability of climate models to represent the warming hole is important for assessing the reliability of future midwest temperature projections from the models.