Global permafrost evolution 1960–2100: A new high-resolution model assessing past change and projecting scenario-based futures.

Permafrost is experiencing rapid and widespread degradation in response to atmospheric warming, with profound implications for landscape stability, infrastructure planning, hazard assessment, and carbon-climate feedback. While probabilistic approaches to global permafrost modelling exist (Gruber, 2012), no framework currently spans the 1960–2020 period, a critical window encompassing the acceleration of anthropogenic climate change and the most pronounced observed warming in permafrost regions. Here, we present GRAPE-60 (Global ReAnalysis-driven Permafrost Extent estimate over a 60-year period), a high-resolution equilibrium-based permafrost model that integrates modern reanalysis datasets (ERA5 and JRA-55) with digital elevation models (ASTER and SRTM) to quantify global permafrost evolution from 1960 to 2020 and extend this framework to project future change under differing climate scenarios. Through systematic evaluation of multiple model configurations against borehole observations, we identify ERA5-ASTERDEM as the optimal combination, achieving an area under the receiver operating characteristic curve of 0.96 for historical periods. Independent comparison of the downscaled air temperatures product against ESA CCI satellite-derived land surface temperature (1996–2020) yielded a mean bias of +0.79°C (σ = 1.64°C), demonstrating agreement within the uncertainty bounds of the reference dataset. Our historical results reveal a net global permafrost loss of 2.49 × 10⁶ km² (8.9% of the exposed land area) between 1960 and 2020, with marked spatial patterns: continuous permafrost zones contracted by 21% while isolated patches expanded by 12%, indicating widespread degradation and fragmentation. To project future permafrost trajectories, we utilise GRAPE-60 as a spin-up and bias-correct temperature forcings from selected CMIP6 Earth System Models under SSP1-2.6, 2-4.5, 3-7.0, and 5-8.5 scenarios. Preliminary results reveal scenario-dependent pathways ranging from near-stabilisation under aggressive mitigation to substantial additional losses under high-emission futures. This work provides the first high-resolution, multi-decadal reconstruction of global permafrost evolution 1960-2020 and establishes a methodological framework for tracking and projecting future changes in this critical and rapidly transforming component of the cryosphere.