50-year satellite record: Polar ice sheets have lost 12.5 trillion tons since the 1970s

Greenland and Antarctica have shed 12.5 trillion US tons — 11.3 trillion metric tons — of ice since the late 1970s, raising global sea levels by roughly three centimetres, according to the most comprehensive satellite record of polar ice loss ever assembled. The findings, published in the journal Scientific Data, draw on 42 independent estimates from 27 satellite missions spanning more than four decades, and they reframe a widely held assumption about what is actually causing the ice to disappear.

The culprit is not primarily warm air melting ice from above. Eighty-four percent of the combined loss came from glaciers flowing faster and discharging ice directly into the ocean — a process driven by warming seawater eroding ice from below and around the edges. Surface melting accounted for just 16 percent of the total.

More than four-fifths of the ice lost was discharged into the ocean by faster-flowing glaciers, rather than melted at the surface — which tells us the long-term trend is being driven by the dynamic response of the ice sheets to a warming ocean.— Inès Otosaka, lead author and assistant professor, Northumbria University

The study was produced by the Ice Sheet Mass Balance Intercomparison Exercise (IMBIE), a large international collaboration backed by ESA and NASA. By reconciling measurements from instruments that observe ice in fundamentally different ways — altimeters tracking surface height, gravity sensors, radar and optical systems tracking glacier movement — the team built a single consistent record stretching back to 1972 for Greenland and 1979 for Antarctica.

The scale of the loss is easier to grasp with a comparison: 11.3 trillion metric tons is enough ice to stack roughly five feet deep across the entire continental United States, according to the Associated Press, as cited by Common Dreams. Or, as Otosaka put it, enough to fill a cube 23 kilometres — about 14 miles — on each side.

The two ice sheets did not lose ice at a steady rate. Both were close to balance through the 1970s and 1980s. In the 1980s, Greenland was shedding roughly 60 billion metric tons of ice annually; by the 2010s — a decade defined by repeated extreme summer melt events — that figure had climbed to 264 billion metric tons. From about 48 billion metric tons a year in the 1980s, Antarctica's losses grew to 202 billion metric tons in the 2010s. Every decade of the satellite record has brought greater ice discharge from West Antarctica, with the Pine Island and Thwaites glaciers playing a particularly significant role.

Greenland and Antarctica together now account for about one quarter of global sea-level rise. The 3.1 centimetres they have contributed since 1979 — Greenland responsible for 1.81 centimetres, Antarctica for 1.33 centimetres — may sound modest, but the consequences are not.

Just over three centimetres of sea-level rise may sound small, but that puts another six to nine million people at risk of coastal flooding and erosion. With the ice sheets set to lose much more ice in the decades ahead, global assessments like IMBIE are vital to protecting communities impacted by climate change.— Andrew Shepherd, IMBIE founder and professor, Northumbria University

Otosaka framed the per-centimetre stakes in sharper terms, telling Reuters — as reported by Common Dreams — that each additional centimetre of sea-level rise puts an estimated two to three million more people at risk of annual coastal flooding.

Between 2020 and 2023, the overall rate of loss slowed. Unusually heavy snowfall over East Antarctica offset some glacier losses on that continent, while a run of relatively mild summers in Greenland roughly halved surface melting there. Scientists are emphatic, however, that this represents short-term weather variation, not a reversal of the underlying trend. Net loss from the ice sheets is ongoing, and the long-term acceleration driven by ocean warming has not stopped.

There is a clear trend that the ice sheets are losing more mass and it has been increasing from decade to decade.— Inès Otosaka, ice scientist, Northumbria University

Researchers also warn that the effects of climate change on ice sheets can take decades to fully manifest, meaning losses could persist even if warming were brought under control. According to ESA, factoring in the risk of ice-sheet instability raises high-end projections of global sea-level rise by 2150 by a factor of 2.6.

The next phase of the research will attempt to break down ice loss by region, since different parts of the ice sheets are responding differently to climate pressures. Euronews reports that Greenland's Jakobshavn glacier is pulling back by as much as 50 metres a day. Understanding those regional differences is key to improving the sea-level projections that coastal planners and governments depend on.

These findings have implications for coastal planning, showing that we urgently need to develop plans for protecting coastal communities around the world from the impact of ice sheet melting.— Inès Otosaka, lead author

Why it matters — Hundreds of millions of people live in low-lying coastal areas whose flood risk is directly shaped by how fast these ice sheets lose mass — and this record shows that risk is being driven by ocean warming that is harder to reverse than surface air temperature.

Sources differ on Total sea-level rise contribution from Greenland and Antarctica since 1979: 3.14 cm (esa.int) vs ~3.1 cm / 31.4 mm (sciencetimes.com) vs 3.2 cm (euronews.com)

Reported by nature.com, people.com, esa.int, sciencealert.com, sciencetimes.com, gizmodo.com, commondreams.org, euronews.com, ground.news