The magnitude of land–ocean warming contrast depends on the pattern of SST warming

The land–ocean warming contrast—where global land mean warms more than the global ocean mean —is one of the most prominent features of global warming. In idealized CO₂-increase experiments, although there is inter-model spread, it is known that land warming is typically about 1.6 times larger than ocean warming. However, it remains unclear what determines the magnitude of this land–ocean warming contrast. For the 1980–2014 trend, observed land warming exceeds ocean warming by more than a factor of 2.3, and such a large observed land–ocean warming contrast cannot be reproduced by CMIP6 historical simulations. It is also well known that during this period there is a mismatch in the SST trend pattern between observations and historical simulations. In this study, we investigated how differences in sea surface temperature (SST) patterns affect the magnitude of land–ocean warming contrast. Using the climate model MPI-ESM, we conducted AGCM experiments forced by (i) a globally uniform SST warming (+2 K, +4 K, and +6 K), (ii) the same global-mean SST warming superimposed with the observed 1980–2014 SST trend pattern, and (iii) the same global-mean SST warming with the sign of the 1980–2014 SST trend pattern reversed. The results show that, despite having the same global-mean SST warming, land warming differs significantly among the SST patterns, and that the observed SST trend pattern tends to enhance the global-mean land warming. Under the observed SST pattern experiments, warming tends to be amplified across the entire Eurasian continent, which is a major contributor to the enhanced global-mean land warming. The strong warming over the mid-to-high-latitude Eurasian continent is explained primarily by pronounced Atlantic warming and warming in the northwestern Pacific, whereas the cooling tendency in the eastern equatorial Pacific affects the land-warming pattern over the North America through teleconnections. This study demonstrates that SST patterns exert a substantial influence on the factors controlling the magnitude of the land–ocean warming contrast, and suggests that the coupling between ocean and land temperature changes varies markedly depending on the future SST pattern change.