In Greenland, 87% of the glacierized area terminates in the ocean, but mass lost at the ice–ocean interface, or frontal ablation, has not yet been fully quantified. Using measurements and models we calculate frontal ablation of Greenland's 213 outlet and 537 peripheral glaciers and find a total frontal ablation of 481.8 ± 24.0 for 2000–2010 and 510.2 ± 18.6 Gt a^-1 for 2010–2020. Ice discharge accounted for ~90% of frontal ablation during both periods, while mass loss due to terminus retreat comprised the remainder. Only 16 glaciers were responsible for the majority (>50%) of frontal ablation from 2010 to 2020. These estimates, along with the climatic-basal balance, allow for a more complete accounting of Greenland Ice Sheet and peripheral glacier mass balance. In total, Greenland accounted for ~90% of Northern Hemisphere frontal ablation for 2000–2010 and 2010–2020.

Ice losses from the Greenland and Antarctic ice sheets have accelerated since the 1990s, accounting for a significant increase in the global mean sea level. Here, we present a new 29-year record of ice sheet mass balance from 1992 to 2020 from the Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE). We compare and combine 50 independent estimates of ice sheet mass balance derived from satellite observations of temporal changes in ice sheet flow, in ice sheet volume, and in Earth's gravity field. Between 1992 and 2020, the ice sheets contributed 21.0±1.9 mm to global mean sea level, with the rate of mass loss rising from 105 Gt yr⁻¹ between 1992 and 1996 to 372 Gt yr⁻¹ between 2016 and 2020. In Greenland, the rate of mass loss is 169±9 Gt yr⁻¹ between 1992 and 2020, but there are large inter-annual variations in mass balance, with mass loss ranging from 86 Gt yr⁻¹ in 2017 to 444 Gt yr⁻¹ in 2019 due to large variability in surface mass balance. In Antarctica, ice losses continue to be dominated by mass loss from West Antarctica (82±9 Gt yr⁻¹) and, to a lesser extent, from the Antarctic Peninsula (13±5 Gt yr⁻¹). East Antarctica remains close to a state of balance, with a small gain of 3±15 Gt yr⁻¹, but is the most uncertain component of Antarctica's mass balance.

Ice discharge from Greenland's marine-terminating glaciers contributes to half of all mass loss from the ice sheet, with numerous mechanisms proposed to explain their retreat. Here, we examine K.I.V Steenstrups Nordre Brae ('Steenstrup') in Southeast Greenland, which, between 2018 and 2021, retreated ~7 km, thinned ~20%, doubled in discharge, and accelerated ~300%. This rate of change is unprecedented amongst Greenland's glaciers and now places Steenstrup in the top 10% of glaciers by contribution to ice-sheet-wide discharge. In contrast to expected behaviour from a shallow, grounded tidewater glacier, Steenstrup was insensitive to high surface temperatures that destabilised many regional glaciers in 2016, appearing instead to respond to a >2°C anomaly in deeper Atlantic water (AW) in 2018. By 2021, a rigid proglacial mélange had developed alongside notable seasonal variability. Steenstrup's behaviour highlights that even long-term stable glaciers with high sills are vulnerable to sudden and rapid retreat from warm AW intrusion.