| Summary: | The position of the near-surface zero isotherm (ZIL) plays a key role in many physical and biological processes in the polar regions. Some of the processes that undergo important changes are the rain-snow phase transition, the thawing and freezing of the active layer of permafrost, glacier mass variations, and changes in biological activity. For that reason, the monthly mean ZIL position can be used as an indicator to monitor climate change in the Antarctic Peninsula and the changes that are expected to occur. We characterized the position of the ZIL using near-surface temperature in the ERA5 reanalysis after evaluating its performance in reproducing its arrival and regression against observations over the Antarctic Peninsula. Using this data set, we quantify a southward change in the ZIL of 23.9 km decade -1 from 1957 to 2020. This rate is faster than the global mean rate of temperature change which has been estimated at 4.2 km decade -1 . A congruence analysis attributes part of this southward shift, 10.8 km decade -1 , to the SAM. We also analyze the projections of the ZIL in the CMIP6 models during the 21st century. Although the position of the ZIL presents great variability between the different simulations, its trends are consistent and show a retreat of 23 ± 17 km decade -1 and 56 ± 26 km decade -1 under the SSP2-4.5 and SSP5-8.5 scenarios, respectively.
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