Recent permafrost retreat is very likely unprecedented in the Common Era

Permafrost, a defining feature of high-latitude landscapes, has been rapidly degrading in recent decades due to ongoing global warming. One of the clearest indicators of this degradation is the loss of permafrost area. While recent retreat is well documented, few studies have placed changes of permafrost extent in the context of pre-industrial natural variability. Here we show, using multiple simulations from the Paleoclimate Model Intercomparison Project Phase 3 (PMIP3) and 4 (PMIP4), reanalyses, and reconstruction products spanning the full or part of the Common Era that the recent permafrost retreat is very likely unprecedented in the last 2,000 years. Across datasets, we estimate a permafrost area decrease of 0.7 to 2.5 million km², with the largest losses occurring along the southern margins of discontinuous permafrost. These regions are found to hold between 43 and 138 PgC of soil organic carbon, now vulnerable to potential microbial decomposition. The resulting carbon emissions could have already amplified global warming by 0.2 ºC, with implications for the pan-Arctic environment and the stability of global climate. This work highlights the value of ESM simulations for assessing permafrost variability over the Common Era, especially when interpreted alongside proxy-based paleoclimate reconstructions.