Ocean Heat Uptake Efficiency Increase Since 1970

The ocean stores the bulk of anthropogenic heat in the Earth system. The ocean heat uptake efficiency (OHUE)–the flux of heat into the ocean per degree of global warming–is therefore a key factor in how much warming will occur in the coming decades. In climate models, OHUE is well‐characterized, tending to decrease on centennial timescales; in contrast, OHUE is not well‐constrained from Earth observations. Here OHUE and its rate of change are diagnosed from global temperature and ocean heat content records. OHUE increased over the past five decades by 0.19 ± 0.04 W/m2K, and was on average 0.58 ± 0.08 W/m2K during this period. This increase is attributed to steepening anthropogenic heat gradients in the ocean, and corresponds to several years' difference in when temperature targets such as 1.5 or 2°C are exceeded.