Varying Planetary Heat Sink Led to Global-Warming Slowdown and Acceleration

A vacillating global heat sink at ocean depths is associated with different climate regimes of surface warming under anthropogenic forcing: The latter part of the 20th century saw rapid global warming as more heat stayed near the surface. In the 21st century, surface warming slowed as more heat moved into deeper oceans. In-situ and reanalyzed data are used to trace the pathways of ocean heat-uptake. In addition to the shallow La Niņa-like patterns in the Pacific, which were the previous focus, we found that the slowdown is mainly caused by heat transported to deeper layers in the Atlantic and the Southern oceans, initiated by a recurrent salinity anomaly in the subpolar North Atlantic. Cooling periods associated with the latter deep heat-sequestration mechanism historically lasted 20-35 years.