Abstract
AbstractThe climate's response to forcing depends on how efficiently heat is absorbed by the ocean. Much, if not most, of this ocean heat uptake results from the passive transport of warm surface waters into the ocean's interior. Here we examine how geographic patterns of surface warming influence the efficiency of this passive heat uptake process. We show that the average pattern of surface warming in CMIP5 damps passive ocean heat uptake efficiency by nearly 25%, as compared to homogeneous surface warming. This “pattern effect” occurs because strong ventilation and weak surface warming are robustly colocated, particularly in the Southern Ocean. However, variations in warming patterns across CMIP5 do not drive significant ensemble spread in passive ocean heat uptake efficiency. This spread is likely linked to intermodel differences in ocean circulation, which our idealized results suggest may be dominated by differences in Southern Ocean and subtropical ventilation processes.
Highlights
After a change in radiative forcing, surface warming is mitigated by the slow heating of the global ocean for centuries
We compare our spatially varying and spatially uniform experiments
Since these experiments share the same global-mean warming, differences between them will be due to the “pattern effect”—the influence that the geographic distribution of surface warming has on OHUp, and on κp
Summary
After a change in radiative forcing, surface warming is mitigated by the slow heating of the global ocean for centuries. Heat is not a passive tracer—its uptake, along with other processes such as wind changes, alters advection and mixing and redistributes existing background temperature gradients. This “redistributed” heat (Garuba & Klinger, 2016) can significantly influence the spatial distribution of ocean warming and, indirectly, OHU (e.g., Banks & Gregory, 2006), through changes in the North Atlantic (Bouttes et al, 2014; Garuba & Klinger, 2016; Rugenstein et al, 2013; Winton et al, 2013; Xie & Vallis, 2012). Bronselaer and Zanna (2020) find that the pattern of heat storage is increasingly determined by OHUp as the anomalous heat content in the ocean grows
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