Glaciers and Ice Sheets
Glaciers are formed from snow that has compacted to form ice, which then deforms and flows downhill. An ice sheet is an expanse of ice originating on land that covers an area of more than 50 000 km2. There are two principal ice sheets, one in Greenland and one in Antarctica. Loss of ice from glaciers and ice sheets contributes to global mean sea-level rise. Changes in land ice also have implications for freshwater resources, ecosystems, and communities.
Earth’s glaciers lost more than 400 gigatons in 2025, equivalent to approximately 1 mm of sea-level rise
Explanation
Global cumulative glacier mass change is the total change in glacier mass worldwide over a given period (since 1975 here). Global estimates combine field observations of glacier mass balance with satellite measurements to assess mass changes across glacier regions. Cumulative mass change is expressed in gigatonnes (Gt). These estimates cover glaciers worldwide, excluding the Greenland and Antarctic ice sheets.
Methodology
The WGMS uses a geostatistical method developed by Zemp et al. (2020) and Dussaillant et al. (2024). The method accounts for the limited sampling of glaciers. The annual anomalies of glacier mass balance as measured in situ are interpolated and calibrated using observations of glacier height and area made by satellites. Time series for individual glaciers are aggregated to regional and global scales.
Eight of the ten most negative annual glacier mass balances since 1950 have occurred since 2016
Explanation
Glacier mass balance – the amount of mass gained or lost by a glacier – is commonly expressed as the annual thickness change averaged over the glacier area in metres water equivalent. The mass balances of individual glaciers are affected by changes in temperature, precipitation, humidity and cloudiness. Melt rates are also strongly affected by the glacier albedo, the fraction of sunlight that is reflected by the glacier surface.
Methodology
Global glacier observations are based on standardized in situ measurements of glacier mass balance and length changes reported by national and regional monitoring programmes worldwide.
Reference glaciers are glaciers which have more than thirty years of ongoing glaciological measurements. They are representative of nineteen mountain regions. The reference glaciers used in calculations are only a small fraction of the world’s glaciers and are unevenly distributed geographically. Nevertheless, more globally complete observed trends from satellite data consistently show widespread and accelerating glacier mass loss.
Glacier mass balance measures the change in thickness of the glacier, and while this is related to the amount of mass gained or lost by the glacier, it is not possible to directly estimate the mass loss from the glacier mass balance without also knowing the area of the glacier.
Systematic glacier observations extend back to the mid-twentieth century, with some individual glacier records beginning earlier. The length and continuity of records vary by region and glacier.
-5,162.3 Gt
in 2026-07-01 (NASA GRACE)
Explanation
The Greenland ice sheet is a large body of land ice. The mass of the ice sheet can be monitored using a variety of satellite observations. The mass can be measured directly or indirectly.
Methodology
The mass of the Greenland ice sheet has been measured in a number of different ways. The mass can be measured directly by the GRACE satellites that detect small variations in the Earth's gravitational field. The IMBIE dataset combines information from three methods all of which involved satellite information: gravimetric measurements (GRACE), measurements of the surface height, and the "input-output" method (e.g. Mankoff et al.) which tracks the gain and loss of ice separately using a combination of satellite data, reanalysis data, and ice sheet models.
-2,516.1 Gt
in 2026-07-01 (NASA GRACE)
Explanation
The Antarctic ice sheet is a large body of land ice: The mass of the ice sheet can be monitored using a variety of satellite observations. The mass can be measured directly or indirectly.
Methodology
The mass of the Antarctic ice sheet has been measured in a number of different ways. The mass can be measured directly by the GRACE satellites that detect small variations in the Earth's gravitational field. The IMBIE dataset combines information from three methods all of which involved satellite information: gravimetric measurements (GRACE), measurements of the surface height, and the "input-output" method which tracks the gain and loss of ice separately using a combination of satellite data, reanalysis output, and ice sheet models.