Ocean Heat Content responses to changing Anthropogenic Aerosol Forcing
Strength: regional and multi-decadal variability
Abstract
The causes of decadal variations in global warming are poorly
understood, however it is widely understood that variations in ocean
heat content are linked with variations in surface warming. To
investigate the forced response of ocean heat content (OHC) to
anthropogenic aerosols (AA), an ensemble of historical simulations were
carried out using a range of anthropogenic aerosol forcing magnitudes in
a CMIP6-era global circulation model. We find that the centennial scale
linear trends in historical ocean heat content are significantly
sensitive to AA forcing magnitude (-40.5$\pm$0.7
x10$^{22}$ (J century$^{-1}$)/(W m$^{-2}$),
R$^2$=0.99), but interannual to multi-decadal variability in global
ocean heat content appear largely independent of AA forcing magnitude.
Comparison with observations find consistencies in different depth
ranges and at different time scales with all but the strongest aerosol
forcing magnitude, at least partly due to limited observational
accuracy. We find broad negative sensitivity of ocean heat content to
increased aerosol forcing magnitude across much of the tropics and
sub-tropics. The polar regions and upper Pacific show the strongest heat
content trends, and also show the strongest dependence on aerosol
forcing magnitude. However, the ocean heat content response to
increasing aerosol forcing magnitude in these regions is either
dominated by internal variability, or strongly state dependent, showing
different behaviour in different time periods. Our results suggest the
response to aerosols in these regions is a complex combination of
influences from ocean transport, atmospheric forcings, and sea ice
responses.