Greenland’s ice sheet gains snow and loses ice every year, but the two sides of that ledger no longer balance. Satellite gravity measurements indicate an average loss of about 264 gigatons per year between 2002 and 2025. That transfer of land ice to the ocean raised global mean sea level by approximately 0.8 millimeter per year over the same period.
Treating 264 gigatons as a fixed annual allowance would be misleading. Some years bring heavy snowfall and relatively cool summers; others combine prolonged surface melting with rapid iceberg discharge. Greenland lost far less mass in the 2023–2024 season than in several exceptional melt years, yet a quieter year did not reverse the persistent multidecade decline.
Two Routes Off the Ice Sheet
The first route is surface mass loss. Snow accumulates mainly in the high interior, while summer warmth melts snow and bare ice at lower elevations. Meltwater may refreeze within the snowpack, collect in lakes, drain through fractures, or run from the ice sheet into the ocean. Sublimation and wind-blown snow also affect the surface balance, although runoff accounts for much of the summer loss.
Darkening amplifies melting. Fresh snow reflects most incoming sunlight, but older granular snow, exposed ice, dust, soot, and biological material absorb more energy. Once seasonal snow disappears, darker glacier ice remains exposed for longer, allowing additional melt even without a further increase in air temperature.
The second route is dynamic discharge through outlet glaciers. These fast-moving corridors carry inland ice toward fjords, where it breaks off as icebergs or melts at the submerged glacier front. Warmer ocean water can undercut a terminus, while the loss of rigid sea ice and floating ice tongues may reduce resistance. A retreating front can then allow the glacier to accelerate and draw ice from farther inland.
Surface and dynamic losses interact. Thinning can steepen or flatten local ice slopes, changing flow. Meltwater reaching the bed may briefly lubricate glacier motion, although an efficient drainage network can later reduce water pressure and slow it. The response differs among Greenland’s many outlets, so one mechanism cannot explain every region or season.
How Mass Is Weighed From Space
No instrument can place the ice sheet on a scale. Instead, several measurement systems observe different parts of the budget. Satellite gravimetry detects small changes in Earth’s gravity caused by shifting mass. Laser and radar altimeters measure surface elevation, which can be converted to mass after accounting for snow density, bedrock motion, and the compression of older snow.
A third approach calculates the input-output balance. Snowfall and surface runoff are estimated across the ice sheet, then compared with ice flowing through gates near the coast. Agreement among these independent methods strengthens the conclusion that Greenland is losing mass, but their annual values need not match exactly. They cover different periods, resolutions, and physical quantities.
Bedrock complicates the calculation because Greenland rises as ice weight is removed, while the solid Earth also retains a response to much older ice changes. Atmospheric pressure and ocean mass influence gravity observations as well. Corrections for these effects are part of the estimate, which is why reported totals include uncertainty ranges rather than perfect precision.
Loss Is Concentrated Around the Margins
The high central plateau can gain snow during a year when the ice sheet as a whole shrinks. The strongest thinning occurs mainly around lower-elevation margins and major outlet glaciers. Western, southeastern, and northwestern drainage sectors have all undergone periods of rapid change, but the leading contributors shift as fjord temperatures, sea ice, snowfall, and glacier geometry vary.
Coastal retreat also removes floating or already buoyant ice that does not immediately raise sea level. That loss still matters. It adds fresh water to the ocean and can expose a glacier front to greater calving or reduce the resistance that had slowed grounded ice upstream. Mass-balance studies designed specifically for sea-level accounting distinguish this peripheral floating loss from grounded ice entering the sea.
A Long-Term Signal Beneath Annual Noise
Weather can temporarily narrow the annual deficit. Persistent cloud cover may limit solar heating, and a snowy winter can brighten the following summer surface. Conversely, blocking high-pressure systems can produce clear skies, warm air, and widespread melt. These variations create sharp peaks and pauses in the record without erasing the longer response to atmospheric and ocean warming.
If Greenland’s entire ice sheet melted, global mean sea level would rise by more than seven meters, but complete loss would require far longer than this century. The immediate concern is the fraction released over coming decades and centuries. Its pace depends on future warming and on how outlet glaciers respond to poorly mapped beds and fjords.
Greenland’s mass-loss rate is therefore best understood as a changing balance, not a countdown to disappearance. Snowfall still adds enormous amounts of ice each year. Surface runoff and glacier discharge now remove more, leaving a measurable deficit whose cumulative effect reaches coastlines worldwide.