IMBIE satellite record finds polar ice sheets lost 11.3 trillion tonnes since 1979

The longest satellite record of Earth's polar ice ever assembled has concluded that the Greenland and Antarctic ice sheets lost 11.3 trillion tonnes of ice between 1979 and 2023, a combined mass of 11,309 billion tonnes that pushed global mean sea level up by 31.4 millimetres. The assessment was published in the journal Scientific Data on September 16, 2026 by the Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) Team, a collaboration led by Northumbria University and supported by the European Space Agency and NASA.

The numbers rest on an unusually broad observational base. The IMBIE team combined 42 independent satellite surveys drawn from 27 satellite missions, reaching back to 1972 for Greenland and to 1979 for Antarctica with the help of the early Landsat archive. That span makes it the longest such record ever compiled, and it extends a monitoring series that previously began only in the 1990s. The team's earlier assessment, based largely on European satellite data, calculated about 21 millimetres of global mean sea level rise between 1992 and 2020. Incorporating NASA satellites allowed the researchers to look much further back in time.

Greenland accounted for the larger share of the total loss, while Antarctica contributed 13.3 millimetres to global mean sea level. The most consequential finding, however, concerns mechanism rather than magnitude: 84 per cent of the combined loss came from glaciers speeding up and discharging more ice into the ocean, with just 16 per cent attributable to melting at the surface. The polar ice sheets are now responsible for roughly a quarter of all global sea level rise.

The work was led by Dr. Ines Otosaka and Professor Andrew Shepherd at Northumbria University, together with Dr. Tyler Sutterley of the University of Washington Applied Physics Laboratory. Otosaka said that by reaching back to the 1970s the team can now see how the ice sheets have changed across half a century, and that more than four fifths of the ice lost was discharged into the ocean by faster flowing glaciers rather than melted at the surface.

Key Facts

Phys.org reported on September 16, 2026 that Greenland's rate of ice loss rose from around 60 billion tonnes a year in the 1980s to 264 billion tonnes a year in the 2010s. Antarctica followed a similar trajectory, climbing from roughly 48 billion tonnes a year in the 1980s to 202 billion tonnes a year in the 2010s. Greenland had been close to balance in the 1970s before that acceleration began, and the ice sheets as a whole were relatively stable through the 1970s and 1980s before melt kicked in during the 2010s.

All of Antarctica's net loss was caused by ocean melting rather than surface melt, according to the study. West Antarctica's ice discharge, led by the Pine Island and Thwaites glaciers, has risen in every decade covered by the record. Otosaka said the Jakobshavn glacier in Greenland is now retreating by up to 50 metres a day.

Eos reported on September 16, 2026 that IMBIE's previous assessment had calculated a rise of about 21 millimetres to global mean sea level between 1992 and 2020. The new work draws on data from 27 satellite missions spanning more than 50 years, and it charts ice sheet volumes in Antarctica back to 1979 and in Greenland back to 1972. Ines Otosaka, lead researcher and professor of geography and natural sciences at Northumbria University, said the result tells us the long term trend is being driven by the dynamic response of the ice sheets to a warming ocean.

The Associated Press reported on September 16, 2026 that the total equates to about 12.5 trillion US tons of ice, an amount the agency said would be enough to stack ice five feet deep across the continental United States. About five sixths of the melt did not come from hotter air but from warmer water eating away at the ice sheets from below and the sides as glaciers flowed into the ocean.

Most of the twentieth century saw sea level rise at about 1.4 millimetres per year. Between 2006 and 2015 the rate was more than twice as high, at 3.6 millimetres per year. The most recent years in the record, 2020 to 2023, brought a temporary slowdown in ice loss that the researchers attributed to record snowfall over East Antarctica and milder summers in Greenland.

Analysis

The headline figure of 11.3 trillion tonnes is arresting, but the mechanism behind it is what changes the scientific picture. For years much of the public conversation about polar ice has focused on surface melting, the meltwater lakes and darkening snow that follow warm summers. This record places the emphasis firmly elsewhere. Eos reported on September 16, 2026 that about 84 per cent of the calculated ice loss came from glaciers and ice sheets discharging directly into the ocean, leaving only 16 per cent to melting at the surface. Otosaka said this tells us the long term trend is being driven by the dynamic response of the ice sheets to a warming ocean.

What this really means is that the ice sheets are responding to ocean heat in a way that cooling the atmosphere alone cannot quickly undo. Warm water reaches the undersides and the fronts of marine terminating glaciers, thinning them and reducing the friction that holds them back, so they flow faster and calve more icebergs. That is a self reinforcing process rather than a simple thermometer reading, and it explains why the loss is concentrated in the fastest flowing outlets. Because the trigger is ocean heat rather than air temperature, the process can keep running even in decades when the atmosphere warms more slowly.

The regional pattern reinforces that reading. Greenland sat close to balance in the 1970s and then accelerated sharply. Antarctica's entire net loss is attributed to ocean melting. West Antarctica's discharge rises in every decade on record, led by Pine Island and Thwaites. The Associated Press reported on September 16, 2026 that independent ice scientist David Holland of New York University said the dominance of dynamic loss is exactly what you would expect in an ice sheet instability collapse scenario.

Shepherd's framing adds a timescale to the judgement. He said the changes are tracking decades behind global warming, which means we can expect them to continue for decades more even if we are able to stop heating the planet. The 2020 to 2023 slowdown should therefore be read as short term weather noise layered on a long term trend, not as a trend break. A good snowfall year in one basin does not switch off a mechanism that operates at the boundary between ice and ocean.

Why It Matters

Coastal risk is the immediate consequence. Shepherd said that just over three centimetres of sea level rise may sound small, but that it puts another six to nine million people at risk of coastal flooding and erosion. Otosaka's arithmetic is starker at the individual level: for every centimetre of sea level rise, another 2 to 3 million people get flooded at least once a year.

That matters because the ice sheets now account for around a quarter of all global sea level rise, on top of thermal expansion and the melting of mountain glaciers. The 31.4 millimetres contributed by Greenland and Antarctica alone is a permanent addition to the baseline that storm surges and high tides build upon, and it is already committed by the physics described in the study.

Rignot said the ice sheets are melting away fast, that we are melting the polar regions, and that sea level is rising worldwide and will exacerbate the vulnerability of coastal regions. The finding also shifts where adaptation planning needs to concentrate, because dynamic discharge into the ocean is not something that local emissions cuts can switch off in the short term.

Next Up

The IMBIE record now runs to 2023, and the next assessment will test whether the 2020 to 2023 slowdown persists or reverses. Researchers will also be watching whether the dynamic loss that dominates the record continues to track ocean temperatures decades behind atmospheric warming.

For now the study sets a new benchmark: 42 independent satellite surveys, 27 satellite missions, more than half a century of observations, and a single number, 11,309 billion tonnes, describing how much polar ice the planet has lost.