Mechanisms for Decadal Variability of Ocean Heat Uptake Inferred From Adjoint Sensitivities

Abstract The occurrence of a period of slowdown in surface air temperature increase from 1998 to 2013 despite continued greenhouse gas emissions (the warming hiatus) has suggested that ocean heat uptake (OHU) is susceptible to decadal variability. Here, we identify mechanisms that lead to decadal changes in OHU to revisit the origin of the warming hiatus. Sensitivities of the vertical heat flux were calculated with the adjoint of the MITgcm ocean model to describe atmospheric forcing patterns that most effectively modulate OHU. By projecting historical atmospheric anomalies onto these sensitivity patterns, we quantified the contributions by different forcing, regions, and time‐periods. The impact of various climate modes on changes in OHU through multiple linear regression analysis revealed that the excessive OHU during the hiatus period is primarily governed by in‐phase uptake modulation by the El Niño Southern Oscillation and Atlantic Multidecadal Oscillation variability.