The Impact of the Pattern of Surface Warming on Precipitation and Tropical Cyclone Activity in HighResMIP

In the eastern tropical and subtropical Pacific Ocean, observed sea surface temperatures (SSTs) have cooled by approximately 0.4 K per decade from 1979 to 2014. These observed SSTs are used as the boundary condition for the uncoupled, atmosphere-only CMIP6 HighResMIP simulations covering 1950-2014 (highresSST-present). The coupled atmosphere-ocean simulations covering 1950-2014 (hist-1950) do not show this observed cooling trend, instead showing near uniform warming across the tropics and subtropics. Differences in the pattern of surface warming may lead to different global and regional climate outcomes. We first consider the effect of the pattern of warming on precipitation. Global annual average precipitation is expected to increase globally with anthropogenic climate change, but trends in annual average precipitation are distributed unevenly across the surface of the Earth. Next, we consider the effect of the pattern of warming on tropical cyclone (TC) activity. TC activity is modulated by surface boundary conditions like sea surface temperature (SST). It is expected that changes in SST impact TC activity at both regional and global scales. However, the evolution of this impact in a warmer climate remains uncertain. TC tracks in each model run using the TRACKS and Tempest Extremes algorithms are obtained. We hypothesize that the observed cooling trends in the eastern tropical and subtropical Pacific Ocean will contribute to less TCs in the Eastern North Pacific Basin within the uncoupled, atmosphere-only simulations compared to the coupled atmosphere-ocean simulation. We also consider the trends in TC activity globally and compare the trends over the last 40 years of the historical period (1975-2014) and the full historical period (1950-2014).