Faster glaciers drove 84% of polar ice loss

The Greenland and Antarctic ice sheets together lost 11.309 trillion tonnes of mass between 1979 and 2023. The estimate, with an uncertainty of 565 billion tonnes, corresponds to 31.4 ± 1.6 millimeters of global mean sea-level rise. This result brings together nearly half a century of observations; it is neither a description of a single extreme summer nor a forecast of future loss.

The international IMBIE collaboration compared and reconciled 42 independent estimates built from 27 satellite missions. The methods observe different properties: altimeters measure changes in ice height, optical and radar sensors track speed and volume, and gravimetry missions detect changes in Earth's gravity field caused by mass loss. Regional climate models helped separate surface processes from glacier motion.

That separation changes the intuitive picture. In the reconciled record, 84% of the combined loss came from dynamic imbalance: glaciers carried more ice from the interior into the ocean. The remaining 16% was associated with surface mass balance, which includes snowfall gains and losses through melting, runoff, sublimation and wind erosion. “Ice loss” therefore does not mean only water melting in sunlight.

Antarctica lost 4.780 trillion tonnes between 1979 and 2023, equivalent to 13.3 ± 1.4 millimeters of sea-level rise; the study attributed its net loss to ice dynamics. Greenland lost 6.215 trillion tonnes between 1972 and 2023. There, 67% of the loss came from increased ice discharge and 33% from reduced surface mass balance.

Rates increased markedly after the 1990s. Greenland's average annual loss rose from 60 ± 19 billion tonnes in the 1980s to 264 ± 18 billion tonnes in the 2010s. From 2020 to 2023 it fell to 199 ± 29 billion tonnes as milder summers reduced surface melting. Heavy snowfall in East Antarctica also offset some recent losses. The authors treat this interval as short-term variability, not a reversal of the trend.

The record cannot by itself predict sea-level rise at each coast: ocean circulation, gravity, land motion and future emissions alter regional effects. Its contribution is a long, comparable series for testing models. By showing that accelerated delivery of ice to the ocean dominates the balance, it focuses attention on the component that is hardest to represent in sea-level projections.