Surface and sub-surface drivers of autumn temperature increase over Eurasian permafrost

While most Arctic amplification research is focused on sea ice reduction and its feedbacks onto the climate system, the impacts of permafrost degradation in high latitudes and subsequent land–atmosphere interactions potentially resulting in terrestrial-based amplification are still unclear. Previous work has shown that thermodynamics plays a large part in surface air temperature increases over continuous and discontinuous permafrost at the end of the lengthening warm season. Here, a novel information flow methodology is applied to determine the specific land surface drivers of autumn surface air temperatures over different frozen ground regions in Eurasia. The influences of a changing surface energy balance are particularly apparent in the continuous and discontinuous permafrost regions. There, autumn surface air temperatures transition from being driven by summer and autumn sensible heat flux in the late twentieth century to a combination of latent and ground heat flux as the twenty-first century progresses. Changing seasonal snow patterns aid this transition, whereby continued thermodynamically influenced warming initially occurs through early-year insulation and subsurface hydrothermal heat transport. Later in the twenty-first century, a likely switch to late-season soil heat gain due to direct atmospheric exposure occurs as less snow remains in autumn. This role of evolving surface-atmosphere energy exchange reinforces the importance of the terrestrial contribution to Arctic amplification, as the high latitudes become a hot spot for increasing land–atmosphere interactions.