Joint Seminar: Structural dependence on observed historical SST lowers the strength of pattern effect

Integrating the effects of evolution of spatial pattern of surface temperature change on
multi-decadal timescale on the radiative feedbacks, termed as pattern-effect has provided
coherent estimates of equilibrium climate sensitivity (ECS). A difference between the
climate feedback assessed from an abrupt-4xCO2 simulation representative of a long-term
ECS and the climate feedback assessed from an Atmospheric General Circulation Model
(AGCM) simulation forced with observed historical sea-surface temperature (SST) and sea-
ice variations with pre-industrial forcing provides pattern-effect estimates. Apparently, this
method of computing the pattern-effect would rely on the observed SST boundary condition
dataset applied to the AGCMs since different SST reconstructions could have different
patterns of SST change over the historical period. In this study, we systematically explore
this by applying seven different observed SST datasets to MPI-ESM1.2-LR covering 1871-
2017 historical period. We find that the pattern-effect estimates range from 0.42 +/- 0.12 Wm-
K-1 to -0.1 +/- 0.12 Wm-2K-1 across the datasets with a mean estimate of 0.2 +/- 0.15 Wm-2K-1. The
pattern-effect could be primarily attributed to the differences in the cloud radiative
feedbacks. The major disparities in the pattern-effect among the datasets comes from the
early period while the estimates from 1970s/1980s until present are less dataset
dependent. We apply our new estimates of pattern effect to update the ECS reported in the
sixth assessment report of Intergovernmental Panel on Climate Change.




13:30–14:30 h


Bundesstr. 53, room 022/023
Seminar Room 022/023, Ground Floor, Bundesstrasse 53, 20146 Hamburg, Hamburg


Angshuman Modak, Stockholm University


Swantje Bastin

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