Simulating the permafrost thermal regime in the Northwestern Antarctic Peninsula from 1950 to 2100

Abstract. Permafrost underlies most of the Antarctic ice-free areas, being crucial for terrestrial ecosystems, influencing pedogenesis, hydrology, geomorphic dynamics, and the carbon biogeochemical cycle. However, uncertainty in the evolution of permafrost temperature is particularly relevant in the Antarctic Peninsula, a climatic hotspot of the continent where an increase in mean annual air temperature of 3.4 ± 1.2 °C has been recorded, together with a rise in both the frequency and intensity of warm-weather episodes. The impact on permafrost is difficult to foresee, due to a scarce monitoring network implemented following the International Polar Year in 2007–2008, with limited temporal coverage that constrains trends evaluation. In this study, we simulate past and future permafrost temperature evolution in the Northwestern Antarctic Peninsula using the CryoGrid Community Model at five permafrost observatories from the University of Lisbon’s network (PERMANTAR). Simulations forced with ERA5 reanalysis reconstruct ground temperature evolution since 1950, revealing a warming trend at all depths, with mean annual ground surface temperature, temperature at the top of permafrost, and mean annual ground temperature warming at rates between 0.19 and 0.29 °C dec⁻¹. Four distinct periods are identified since 1950: early sustained warming (1950–1975), highly variable warming and cooling (1975–2000), a short cooling period with increased snowfall (2000–2015), and intense warming after 2015 that accelerates permafrost temperature increases at 20 m depth, resulting in mean annual ground temperatures above -2 °C. Future projections using the ACCESS‑CM2 model under SSP1‑2.6, SSP2‑4.5, and SSP5‑8.5 reveal progressive permafrost degradation and a widespread transition to positive mean annual ground temperatures at 20 m depth during the 21st century, with timing and magnitude strongly influenced by elevation, snow cover duration, and local changes in ocean–atmosphere interactions. In the SSP1-2.6, warming rates ranging from 0.21 ± 0.01 to 0.23 ± 0.01  °C dec⁻¹ are predicted for the sites, resulting in extensive permafrost degradation at low altitude. Under SSP2‑4.5, all sites are projected to develop positive mean annual ground temperatures at 20 m between 2049 and 2087, with warming rates ranging from 0.31 ± 0.01 to 0.43 ± 0.01 °C dec⁻¹, implying increased permafrost degradation and increased susceptibility of coastal terrestrial ecosystems in the Northwestern Antarctic Peninsula to climate-driven change. Under the SSP5-8.5, with warming rates between 0.46 ± 0.01 and 0.62 ± 0.01 °C dec⁻¹, the degradation of permafrost is predicted to occur more rapidly, with positive mean annual ground temperature values at 20 m reached between 2045 and 2071. The projected warming and associated permafrost loss will change surface and subsurface hydrology, biochemical fluxes and geomorphological processes, impacting the sensitive terrestrial ecosystems.