AMO-phase dependent linkage between atmospheric blocking and accelerated Greenland ice sheet melting

Understanding the relative contributions of anthropogenic forcing and internal variability to the summer melt of the Greenland Ice Sheet (GrIS) is essential for accurately projecting future sea-level rise. Here, we show that internal variability, particularly that associated with the Atlantic Multidecadal Oscillation (AMO), accounts for about 58% of the post-1994 increase in summer GrIS melt, while anthropogenic global warming contributes the remaining 42%. We find that during the positive phase of AMO, persistent atmospheric blocking over Greenland intensifies in both frequency and spatial extent, especially over the northern and western sectors. These blocking events, which strongly modulate surface energy fluxes, play a key role in triggering extreme melt episodes. Using ERA5 reanalysis and MARv3.12 simulations, we demonstrate that these enhanced atmospheric perturbations have become an important driver of intensified summer melting. Furthermore, we reveal that a weakened meridional potential vorticity gradient (PVy) underpins the observed amplification of blocking, providing a dynamical bridge between large-scale circulation anomalies and accelerated surface melting. Our findings highlight the pivotal role of mid-to-high-latitude atmospheric dynamics in shaping GrIS vulnerability under internal climate variability.