Romain Roehrig

CNRM, Université de Toulouse, Météo-France, CNRS, CNRM, Université de Toulouse, Météo-France, CNRS, CNRM, Université de Toulouse, Météo-France, CNRS
Author ProfileAbstract
We investigate the dependence of radiative feedback on the pattern of
sea-surface temperature (SST) change in fourteen Atmospheric General
Circulation Models (AGCMs) forced with observed variations in SST and
sea-ice over the historical record from 1871 to near-present. We find
that over 1871-1980, the Earth warmed with feedbacks largely consistent
and strongly correlated with long-term climate sensitivity feedbacks
(diagnosed from corresponding atmosphere-ocean GCM abrupt-4xCO2
simulations). Post 1980 however, the Earth warmed with unusual trends in
tropical Pacific SSTs (enhanced warming in the west, cooling in the
east) that drove climate feedback to be uncorrelated with – and
indicating much lower climate sensitivity than – that expected for
long-term CO2 increase. We show that these conclusions are not strongly
dependent on the AMIP II SST dataset used to force the AGCMs, though the
magnitude of feedback post 1980 is generally smaller in eight AGCMs
forced with alternative HadISST1 SST boundary conditions. We quantify a
‘pattern effect’ (defined as the difference between historical and
long-term CO2 feedback) equal to 0.44 +- 0.47 [5-95%] W/m2/K for
the time-period 1871-2010, which increases by 0.05 +- 0.04 W W/m2/K if
calculated over 1871-2014. Assessed changes in the Earth’s historical
energy budget are in agreement with the AGCM feedback estimates.
Furthermore satellite observations of changes in top-of-atmosphere
radiative fluxes since 1985 suggest that the pattern effect was
particularly strong over recent decades, though this may be waning post
2014 due to a warming of the eastern Pacific.