Permafrost Cloud Feedback May Amplify Climate Change

Abstract Rising temperatures entail important changes in the soil hydrologic processes of the northern permafrost zone. Using the ICON‐Earth System Model, we show that a large‐scale thaw of essentially impervious frozen soil layers may cause a positive feedback by which permafrost degradation amplifies the causative warming. The thawing of the ground increases its hydraulic connectivity and raises drainage rates which facilitates a drying of the landscapes. This limits evapotranspiration and the formation of low‐altitude clouds during the snow‐free season. A decrease in summertime cloudiness, in turn, increases the shortwave radiation reaching the surface, hence, temperatures and advances the permafrost degradation. Our simulations further suggest that the consequences of a permafrost cloud feedback may not be limited to the regional scale. For a near‐complete loss of the high‐latitude permafrost, they show significant temperature impacts on all continents and northern‐hemisphere ocean basins that raise the global mean temperature by 0.25 K