Failure of an atmospheric model to capture the U.S. 'warming hole'

Earlier analyses revealed that most CMIP5 global climate models do not reproduce the warm season "warming hole" (absence of recent warming) in the central United States. From these results, it could be inferred that the warming hole results from intrinsic internal variability of the climate system. Prior work suggested that the source of this variability lies in the oceans, notably the equatorial Pacific. Here we analyze results from a large ensemble of simulations of the period 1959-2007 using version 5 of the NCAR Community Atmosphere Model (CAM5) driven by observed sea surface temperatures. While the interannual variability of temperatures in the warming-hole agrees well with observations, no ensemble member reproduces the warming hole. Further analysis of trends in diurnal temperature range point to the absence of an increase in short-wave reflectivity as the the cause for the missed warming hole. These results suggest that the atmosphere component of a leading climate model may be missing an important dynamical link between sea-surface temperature and cloudiness over the continental U.S., implying a need for caution in using this and similar models to project future changes in regional climate.