Cloud-Modified CESM1 Historical and RCP8.5 5-Member Ensemble

The relative importance of feedbacks and forcing in controlling surface warming patterns remains unknown and difficult to quantify. Here, we analyze three variants of the Community Earth System Model (CESM) with differing equilibrium climate sensitivities and cloud feedbacks, under identical historical and high-emission forcing scenarios. The standard CESM1 exhibits Arctic-amplified warming with the least warming in the Southern Hemisphere middle latitudes. Modifying CESM1 to reduce absorbed shortwave radiation biases results in stronger positive extratropical shortwave cloud feedbacks and slightly more late-21st Century warming at all latitudes. In contrast to CESM1, CESM2 exhibits almost 1°C more global warming and a shifted latitudinal warming profile, increasing warming in the low latitudes while reducing Arctic amplification. This pattern closely matches the pattern of enhanced low-latitude cloud feedbacks and reduced high-latitude surface albedo feedbacks. These results demonstrate the importance of radiative feedbacks in transient warming and the need to improve their representation in models.

This dataset consists of post-processed, single variable timeseries of CESM1 output in netCDF format.

The total dataset is approx. 23.66 TB. (We are willing not to include all of the ocean variables in order to reduce data volume, if necessary).

For these experiments, CESM1 was modified to reduce absorbed shortwave radiation biases, particularly over the middle and high latitudes of the Southern Hemisphere. As such, the modified CESM1 provides insight into the processes controlling shortwave cloud feedbacks, and the consequences of these feedbacks for climate sensitivity and transient warming.

The modified CESM1 was run under the same historical and high-emissions scenario forcing as the CESM1 Large Ensemble, facilitating easy comparisons to the CESM1 Large Ensemble dataset.

Five ensemble members of the modified CESM1 were run for 1850 or 1920-2005 with historical forcing, and continued for 2006-2100 under RCP8.5 forcing.