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Linearity of outgoing longwave radiation: From an atmospheric column to global climate models
  • Yi Zhang,
  • Nadir Jeevanjee,
  • Stephan Fueglistaler
Yi Zhang
Princeton University

Corresponding Author:[email protected]

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Nadir Jeevanjee
Geophysical Fluid Dynamics Laboratory
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Stephan Fueglistaler
Princeton University
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The linearity of the global-mean outgoing longwave radiation (OLR) with surface temperature has important implications for climate sensitivity. Global climate models robustly produce a 1.9 W/m2/K of global-mean longwave clear-sky (LWCS) feedback. This number is consistent with idealized single-column atmospheric models. However, there is considerable spatial variation in the LWCS feedback including negative values over tropical oceans known as the “super-greenhouse effect” which is compensated by larger values in the subtropics/extratropics. Therefore it is unclear how the idealized model results are relevant for the global-mean LWCS feedback in comprehensive climate models. Here we show with a simple analytical theory and model output that the compensation of this spatial variability to produce a robust global-mean feedback can be explained by two facts: 1) when conditioned upon free-tropospheric column relative humidity (RH), the LWCS feedback is independent of RH, and 2) the global histogram of column RH is largely invariant under warming.
16 Sep 2020Published in Geophysical Research Letters volume 47 issue 17. 10.1029/2020GL089235