State-of-the-art coupled global climate models (GCMs) fail to simulate key features of observed seasonal precipitation trends since 1980, including drying of the southwestern US, the southeastern US, East Africa, and subtropical South America, as well as wetting of the Maritime Continent and the Amazon. They also fail to simulate the sea-level pressure (SLP) trends since 1980 associated with a poleward shift of the North Pacific storm track in the mid-latitudes and a strengthened Pacific Walker Circulation. We show that state-of-the-art atmosphere-only climate model ensembles driven by observed sea-surface temperatures (SSTs) simulate historical precipitation and SLP trends that are more similar to those observed in the regions noted above, suggesting that the observed pattern of SST changes has shaped regional precipitation and SLP trends. Analysis of the coupled and atmosphere-only model ensembles reveals that multidecadal SST patterns similar to those of the interannual El-Ni˜ no Southern Oscillation are responsible for some of the regional trends simulated. The tropical Pacific zonal SST gradient is found to have substantially contributed to observed drying over the southwestern and southeastern US, signifying a key role for tropical Pacific warming patterns in future precipitation trends in these regions.
Pillai et al. (Wed,) studied this question.