资源环境科技发展态势分析平台

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 (Koll & Cronin 2018). 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 RH, the LWCS feedback is independent of RH, and 2) the global histogram of free‐tropospheric column RH is largely invariant under warming.