Abstract
The ocean stores the bulk of excess 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-characterised, 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 from
$0.57\pm0.06$W/m$^2$K to
$0.7\pm0.02$W/m$^2$K over the past five decades.
This increase is attributed to steepening heat content gradients in the
ocean, and corresponds to $\sim$4 years’ delay until
temperature targets such as 1.5$^\circ$C or
2$^\circ$C are exceeded.