The world’s great ice sheets are losing trillions of tons of ice, but much of it isn’t disappearing the way you might imagine. Rather than simply melting under a warmer sun, enormous glaciers are picking up speed, carrying vast quantities of ice from Greenland and Antarctica into the ocean.

A sweeping new analysis of five decades of satellite observations suggests that this slow-motion exodus is responsible for more than four-fifths of the ice lost from Earth’s two great ice sheets. And as the planet warms, the consequences are already reaching coastlines thousands of miles away.

Different satellites measure different things. For instance, some track ice-surface height, others detect changes in Earth’s gravity (the less ice mass, the gentler gravity’s pull), and others measure how quickly glaciers move.

The new assessment brings those disparate pieces together. The international Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) team combined 42 independent satellite estimates from 27 missions, allowing researchers to track ice loss back to 1972 in Greenland and 1979 in Antarctica. 

The result is the longest satellite-based reconstruction of the ice loss from the two ice sheets ever assembled. However, what this reconstruction reveals is even more surprising. 

According to the study conducted by the IMBIE team, between 1979 and 2023, Greenland and Antarctica together lost 12 trillion tons (11,309 billion metric tons) of ice, with Greenland accounting for about 7 trillion tons and Antarctica about 5 trillion tons. The loss translated into 31.4 millimeters of global sea level rise, with Antarctica contributing 13.3 millimeters.

“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,” Andrew Shepherd, one of the researchers and founder of IMBIE, said. 

But this is not all. The researchers found something more revealing than the sum of ice loss at the poles.

Ice sheets can lose mass in several ways. Warmer air can melt snow and ice at the surface, while warmer ocean water can attack glaciers where they meet the sea and contribute to faster ice discharge.

The researchers separated these processes by combining satellite measurements with regional climate models. They found that 84 percent of the combined ice loss was linked to glacier dynamics, meaning glaciers accelerated and carried more solid ice into the ocean. 

Only 16 percent came from reduced surface mass balance, such as increased melting or reduced snowfall.

This result was not at all what the researchers expected.

“By reaching back to the 1970s, we can now see how the ice sheets have changed across half a century. 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, one of the researchers and an assistant professor at Northumbria University Newcastle, said.

The historical record shows how quickly that response has intensified. Greenland was close to balance in the 1970s, then quickly fell into net-loss territory, losing about 60 billion metric tons of ice per year in the 1980s and 264 billion metric tons per year in the 2010s. 

Antarctica’s losses increased from about 48 billion metric tons of ice per year in the 1980s to 202 billion metric tons per year in the 2010s.

The acceleration was especially pronounced from the 1990s onward, showing that the ice sheets did not respond instantly to a warming climate. Their behavior changed over decades as warming oceans and atmospheric conditions altered the balance between snowfall, melting and glacier flow.

The latest part of the record offers some relief, but not a reversal. From 2020 to 2023, ice loss slowed across the two ice sheets. It’s a bit like being happy that inflation is down, but that just means that prices for goods are increasing at a slower rate than before; they’re not getting any cheaper, though.

In East Antarctica, unusually heavy snowfall temporarily added enough mass to offset some glacier losses. Greenland also experienced several relatively mild summers, reducing surface melting. But the underlying glacier losses did not disappear.

The researchers therefore treat the slowdown as a short-term fluctuation rather than evidence that the long-term trend has changed.

Ice-sheet behavior is one of the biggest uncertainties in projections of future sea level. The study found that sea level rise by 2150 could be 2.6 times higher in the worst-case scenarios if ice sheets become unstable.

“These findings show the fundamental importance of using satellites to monitor the ice sheets and to evaluate the models used to predict the effects of climate change,” Diego Fernandez Prieto, head of the Science Section at the European Space Agency (ESA), said.

“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,” Professor Shepherd added.

The new record therefore does more than document how much ice has already disappeared. It gives scientists a baseline for tracking what happens next—and for understanding how changes in two remote ice sheets could reshape coastlines around the world.

The study is published in the journal Scientific Data.