Pattern of early-stage of global warming emerged in satellite measurements

The satellite-observed sea surface temperature (SST) provides an unprecedented opportunity to evaluate the ongoing global warming and has recently reached a milestone of 40-year temporal coverage. One of the major spatial features captured by satellites is strong subtropical (weak subpolar) ocean warming. In contrast, studies of past climate changes suggest that the greatest ocean warming should occur, however, at higher latitudes. Here, by comparing satellite observations with reconstructed mid-Pliocene SST and simulated SST evolution driven by abrupt increase in CO2, we find that the currently observed warming pattern is an expression of an early and temporary stage of planetary warming under the forcing of rapidly increasing greenhouse gas. The enhanced subtropical ocean warming, sharing similar spatial structure with the subtropical ocean gyres, is likely attributed to the background subtropical convergence of surface water. In a long-term perspective, the warming of the oceans at higher latitudes is expected to overtake the temporally strong subtropical ocean warming. This delayed but amplified subpolar ocean warming has the potential to reshape the ocean-atmosphere circulation and threaten the stability of marine-terminating ice sheets.