Can thawing permafrost alter the general circulation of the atmosphere?

Thawing Arctic permafrost has been assigned increasing importance as a key element in the global climate system over the past decades. One quarter of land surface of the northern hemisphere are permafrost regions, containing about 50% of the global below-ground carbon pool. Permafrost degradation and the associated climate feedback pose a potential tipping element that might be reached even within 1.5 °C global warming. Besides the potential release of additional carbon, permafrost degradation also holds the potential to significantly alter the surface characteristics of affected landscapes, resulting in further feedback processes that are poorly understood so far.

In the presented study, we investigate the impact of permafrost degradation onto the structure of the atmospheric boundary layer (ABL) as a first feedback link to the global circulation. High-resolution Large Eddy Simulations (LES) are used to quantify the role of surface heterogeneity as a particular driver for boundary layer characteristics. Our virtual experiments simulate the structural changes of the ABL linked to long-term enhanced permafrost thaw, including e.g. the formation of new ponds and lakes, or increased spatial heterogeneity in vegetation structure with the establishment of different grass and shrubs species. Such changes may result in shifted fingerprints of heat and momentum fluxes into the atmosphere. Through this connection, ongoing climate change may lead to permanently altered influences of thawed permafrost on temperature and moisture profiles within the Arctic atmosphere, including changes in the boundary layer height. A particular focus of our study will be placed on the potential loss of water being drained away from the ecosystem after permafrost degradation, where the dried out soil not only changes the carbon cycle processes but also exhibits new surface characteristics. We quantify how the ABL reacts to those changes in idealized LES experiments, and investigate how atmospheric changes may further affect permafrost degradation.