Strengthening of ocean heat uptake efficiency associated with the recent climate hiatus

TLDR

The rate of increase of global‑mean surface air temperature has slowed in the last decade. The study examined whether state‑of‑the‑art general circulation models can reproduce the recent climate hiatus using multimodel ensembles of historical simulations. The authors used multimodel ensembles of historical climate simulations from state‑of‑the‑art GCMs to assess the hiatus. GCM ensemble means do not reproduce the slowed surface‑air‑temperature trend, indicating an internal ocean heat‑uptake origin, while models exhibit weakening heat‑uptake efficiency versus strengthening in observations, explaining the overestimation of the trend and suggesting a future recovery from the hiatus.

Abstract

Abstract The rate of increase of global‐mean surface air temperature (SAT g ) has apparently slowed during the last decade. We investigated the extent to which state‐of‐the‐art general circulation models (GCMs) can capture this hiatus period by using multimodel ensembles of historical climate simulations. While the SAT g linear trend for the last decade is not captured by their ensemble means regardless of differences in model generation and external forcing, it is barely represented by an 11‐member ensemble of a GCM, suggesting an internal origin of the hiatus associated with active heat uptake by the oceans. Besides, we found opposite changes in ocean heat uptake efficiency ( κ ), weakening in models and strengthening in nature, which explain why the models tend to overestimate the SAT g trend. The weakening of κ commonly found in GCMs seems to be an inevitable response of the climate system to global warming, suggesting the recovery from hiatus in coming decades.