Greenland’s ice sheet is losing mass fast enough to raise global sea levels by roughly 0.69 millimeters each year, a rate that exceeds the combined contribution from all of Antarctica. Reconciled satellite records spanning 1992 to 2018 show that surface meltwater runoff, not glacier calving alone, has driven the bulk of Greenland’s losses. For coastal communities already dealing with more frequent high-tide flooding, the distinction between which ice sheet leads matters less than the compounding effect: every added fraction of a millimeter translates into measurably higher storm surges along low-lying shorelines worldwide.
Why Greenland now outpaces Antarctica in sea-level contribution
The gap between Greenland and Antarctica comes down to how each ice sheet loses mass. The IMBIE Team’s reconciled assessment, published in Nature, quantified Greenland’s mass balance from 1992 to 2018 and partitioned losses into two channels: surface mass balance, which captures melting and runoff at the ice sheet’s surface, and ice dynamics, which covers the speed-up and retreat of outlet glaciers. Surface meltwater runoff emerged as the dominant driver, accounting for the larger share of Greenland’s accelerating losses over the satellite era.
Antarctica tells a different story. A separate IMBIE assessment covering 1992 to 2017, published as a pan-Antarctic synthesis, attributed the continent’s losses unevenly across three regions: West Antarctica, East Antarctica, and the Antarctic Peninsula. West Antarctica’s fast-moving outlet glaciers and the collapse of ice shelves along the Antarctic Peninsula account for nearly all of the continent’s net loss. East Antarctica, by contrast, has remained near balance according to NASA’s overview of recent ice trends. Antarctic ice loss did accelerate after roughly 2012, but even that faster pace has not matched Greenland’s annual sea-level equivalent.
A peer-reviewed synthesis published in Surveys in Geophysics compared the two ice sheets’ contributions during the 2002 to 2017 satellite era and confirmed that both are net contributors to rising seas, yet Greenland’s rate leads. The practical consequence is straightforward: a single island covering about a quarter of Antarctica’s area is adding more water to the ocean each year than the entire southern continent. That imbalance underscores how sensitive Greenland is to modest warming of the atmosphere above the North Atlantic, where summer air temperatures and changing circulation patterns can sharply increase surface melt.
Another reason Greenland’s signal stands out is timing. While Antarctica’s most rapid acceleration is concentrated in the last decade of the record, Greenland’s losses ramped up earlier and stayed high for longer. Years with intense surface melt, such as those associated with persistent high-pressure systems over the ice sheet, leave a clear imprint in the mass-balance time series. The cumulative effect is that Greenland has contributed more to sea-level rise over the satellite era, even though Antarctica holds far more ice in total.
Satellite gravimetry, altimetry, and the 360-gigatonne benchmark
The confidence behind these numbers rests on a specific observational toolkit. NASA has described how satellite gravimetry and altimetry together track changes in ice-sheet mass over time. Gravimetry missions, including the GRACE and GRACE-FO satellites, measure shifts in Earth’s gravity field caused by gains or losses of ice. When large volumes of ice melt or flow into the ocean, the local gravity field weakens slightly, and those changes can be detected as the satellites orbit.
Altimetry missions, by contrast, measure changes in ice-sheet surface height. Laser and radar pulses bounce off the ice and return to the satellite, allowing scientists to build a precise record of elevation over time. Where surface height drops persistently, and where corrections for snowfall, compaction, and bedrock motion are applied, those changes can be translated into mass loss. When gravimetry and altimetry show consistent trends over the same regions and time periods, the resulting mass-balance estimates carry high confidence.
Converting ice loss into sea-level rise relies on a widely used ratio: 360 gigatonnes of ice lost equals one millimeter of global mean sea-level rise. This benchmark reflects the volume of water added to the oceans when a given mass of grounded ice melts. In reconciled datasets, such as those produced for the IMBIE assessments, annual mass changes are reported directly in gigatonnes and then expressed as sea-level equivalents using this conversion. That approach allows independent researchers to verify how a given year of extreme melt translates into the tenths of a millimeter added to global oceans.
The European Space Agency’s review of the IMBIE2 Greenland results emphasized that Greenland’s ice loss was “much faster than expected,” highlighting that surface processes are now the primary engine of change. While warm ocean water still undercuts marine-terminating glaciers and promotes calving, the dominant signal in the reconciled record is surface meltwater runoff. This shift matters because surface melt can respond rapidly to year-to-year atmospheric variability, potentially driving large swings in Greenland’s annual contribution to sea-level rise.
Gaps in the record and what to watch through 2025
The strongest reconciled data currently available ends at 2018 for Greenland and 2017 for Antarctica. No publicly released IMBIE update extends the combined gravimetry–altimetry reconciliation into the early 2020s. GRACE-FO, launched in 2018, and ICESat-2, also operational since 2018, are collecting the raw observations needed for such an update, but the formal reconciliation process that made the original IMBIE assessments authoritative has not yet produced a new peer-reviewed benchmark covering recent years.
That lag matters because Greenland experienced exceptional melt seasons after 2018, and Antarctica’s Thwaites Glacier system has drawn intense monitoring. Whether Greenland’s surface-mass-balance losses have continued to dominate its total contribution, and whether Antarctica’s post-2012 acceleration has closed the gap, are open questions that only a new reconciled dataset can answer definitively. Until then, projections of near-term sea-level rise must lean on the last fully vetted period while acknowledging that the ice sheets may already be behaving differently.
Regional splits within Antarctica add another layer of uncertainty. The available NASA and IMBIE summaries confirm the broad pattern of West Antarctic losses, Antarctic Peninsula shelf collapse, and East Antarctic near-balance, but detailed dynamical-versus-surface-balance breakdowns for each region during the most recent satellite years remain sparse in the peer-reviewed reconciliation literature. Localized processes, such as changes in ocean circulation beneath ice shelves or shifts in snowfall over the high interior, could either amplify or partially offset the continent’s net contribution, yet their combined effect since 2017 is not yet captured in a unified record.
Through 2025, several indicators will be especially important to watch. For Greenland, the frequency of summers with widespread surface melt, the extent of meltwater ponding at high elevations, and the response of outlet glaciers to ocean temperature changes will shape whether its annual sea-level contribution stays near recent highs. For Antarctica, trends along vulnerable marine-based sectors of West Antarctica, including Thwaites and neighboring glaciers, will determine whether the continent’s acceleration continues or plateaus.
For coastal planners, the precise ranking of Greenland versus Antarctica is less critical than the combined trajectory of both ice sheets. Even if future reconciled datasets show that Antarctica has narrowed the gap, the existing records already lock in a future where millimeter-scale annual increases accumulate into centimeters of additional sea-level rise over a few decades. In that context, Greenland’s current lead is a warning signal: an ice sheet once thought to change slowly is now responding quickly enough to be a central driver of coastal risk within a single human lifetime.
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*This article was researched with the help of AI, with human editors creating the final content.
