Past, present and future Greenland Ice Sheet surface melt, 1500–2200 CE

The Greenland Ice Sheet is a major contributor to global sea-level rise, having lost ~4,900 Gt of ice since 1992 and already added ~13 mm to global mean sea-level. Even without further warming, it is committed to at least ~274 mm of additional sea-level rise, and complete melting would ultimately raise sea level by ~7 m. In this Review, we synthesise changes in Greenland Ice Sheet surface melt from 1500 to 2200 CE. Surface melt has increased rapidly by ~1% per year since the 1990s, driven by regional warming and changes in atmospheric circulation, particularly enhanced blocking. Several unprecedented extreme melt events lasting several days have occurred since 2007, with record cases such as in July 2012 affecting nearly the entire ice sheet surface. Absorbed shortwave radiation is the dominant driver of seasonal melt, but turbulent heat fluxes, cloud processes and albedo feedbacks strongly modulate melt variability across space and time. Climate models diverge in their representation of these processes, with projected melt and surface mass loss differing by up to a factor of two between three different state-of-the-art regional climate models even under identical forcing. Despite advances in regional climate and Greenland melt modelling, key uncertainties remain in quantifying extreme melt events and their drivers, meltwater retention, firn processes and the coupling between atmospheric forcing and surface energy balance, limiting confidence in projections. Addressing these gaps requires expanded observations, improved process representation in models and integrated use of emerging data-driven approaches to better constrain future melt and its contribution to sea-level rise.