Permafrost cloud feedback

Rising temperatures in the northern permafrost zone are profoundly altering key surface and subsurface processes, triggering important climate feedbacks. The most prominent of these is the accelerated decomposition of formerly frozen soil organic matter, leading to the release of carbon into the atmosphere. In addition, changes in surface and soil hydrology may influence regional and global climate through cloud radiative effects. The thawing of previously impervious soil layers increase hydrologic connectivity, thereby enhancing drainage and increasing landscape drying. This process limits evapotranspiration during the spring and summer months, reducing the formation of low-altitude clouds throughout the snow-free season. The decrease in summertime cloud cover, in turn, allows for greater shortwave absorption at the surface, amplifying temperatures and further accelerating permafrost degradation.

In this study, we investigate recent trends in cloud cover and soil moisture to identify potential signals of a permafrost-cloud feedback in observational and reanalysis datasets. While substantial disagreement exists between data sources regarding the signal strength and spatial patterns, we observe a consistent increase in the correlation between summertime cloud cover and soil moisture over recent decades, coupled with widespread drying in formerly permafrost-affected regions—supporting the hypothesis of a permafrost-cloud feedback. Additionally, we use multiple Earth-system model simulations to quantify the temperature contribution of this feedback under a high-warming scenario. Our results show a robust global temperature increase across all model setups, driven by reduced water availability due to permafrost degradation.