Influence of Observed Multi-Decadal Southern Ocean SST Variability on the Tropics since 1949

Observations show multi-decadal variability in Southern Ocean (SO) sea surface temperature (SST) since the late 1940s. These observed trends are not well captured by coupled climate models, thus the impact of the SO SST variability might be missing in historical simulations and needs to be assessed. Recent studies have explored how observed SO SST cooling from 1979 to 2013 can drive tropical SST cooling and Antarctic sea ice expansion. Here, we examine the earlier SO warming period from 1949 to 1978 by nudging SO SST anomalies to observations in an ensemble of coupled climate model simulations under historical radiative forcing. Compared to the freely evolving control ensemble, the inclusion of observed SO SST evolution produces a more realistic positive SST trend in the tropical eastern Pacific and Atlantic during the SO warming period. Furthermore, approximately half of the observed difference in tropical eastern Pacific SST trends between the warming and cooling periods is driven by SO SST variability. The SO-driven response tends to offset the radiatively-forced response in tropical SST and Antarctic sea ice trends.