The contribution of changing surface thermodynamics on twentieth and twenty-first century air temperatures over Eurasian permafrost

Abstract

The high latitudes are a hotspot for past and future climate change as forced climate signals have begun to emerge from internal variability in recent decades. New tools, such as initial condition large ensembles, provide a simulated range of possible climate realities that allow for separating the externally forced and internally variable components of the climate system. In addition, interactions between environmental variables and atmospheric circulation patterns can be detected in an unforced climate scenario and removed to isolate thermodynamic influences on the climate system. In the Arctic, this separation between dynamic and thermodynamic influences can be used to examine the impact of permafrost degradation on surface air temperatures (SAT). While impacts from permafrost degradation and subsequent carbon release have been thoroughly studied, geophysical influences have not received as much attention. This study employs the Community Earth System Model’s Large Ensemble to simulate and analyze these geophysical impacts over three time periods: 1976–2005, 2021–2050, and 2071–2100. As soil is thawing earlier and freezing later, we focus on spring and autumn to determine permafrost’s thermodynamic influence on SAT across Eurasia. We find that large internal variability, primarily due to atmospheric dynamics, affects spring SATs through 2100 while variability in autumn SATs will decrease over time due to increasing thermodynamic surface factors. These thermodynamic surface influences are most prominent in areas of continuous and discontinuous permafrost and lesser in non-permafrost regions, likely the result of a changing seasonal surface energy budget resulting from degradation and loss of permafrost.