Recent global climate feedback controlled by Southern Ocean cooling

The magnitude of global warming is controlled by climate feedbacks associated with various aspects of the climate system, such as clouds. The global climate feedback is the net effect of these feedbacks, and its temporal evolution is thought to depend on the tropical Pacific sea surface temperature pattern. However, current coupled climate models fail to simulate the pattern observed in the Pacific between 1979 and 2013 and its associated anomalously negative feedback. Here we demonstrate a mechanism whereby the Southern Ocean controls the global climate feedback. Using climate model experiments in which Southern Ocean sea surface temperatures are restored to observations, we show that accounting for recent Southern Ocean cooling—which is absent in coupled climate models—halves the bias in the global climate feedback by removing the cloud component bias. This global impact is mediated by a teleconnection to the Southeast Pacific, where remote sea surface temperature anomalies cause a strong stratocumulus cloud feedback. We propose that this Southern Ocean-driven pattern effect is underestimated in most climate models, owing to an overly weak stratocumulus cloud feedback. Addressing this bias may shift climate sensitivities to higher values than currently simulated as the Southern Ocean undergoes accelerated warming in future projections.

Sarah M. Kang, Paulo Ceppi, Yue Yu, In-Sik Kang