Understand · 5 November 2026
Melting ice caps and glaciers: what is melting, how fast, and why
Mountain glaciers, the Greenland and Antarctic ice sheets, sea ice: all the planet's ice is retreating, but not in the same way or with the same consequences. The full picture, with the figures to back it up.
Melting ice, from melting glaciers to melting ice caps, refers to the retreat of the planet's ice under the effect of global warming: mountain glaciers, the Greenland and Antarctic ice sheets, and sea ice. According to an international study published in 2025 in the journal Nature, the world's glaciers lost about 5% of their volume between 2000 and 2023. The ice sheets lost more than 7,000 billion tonnes of ice in total between 1992 and 2020. This melting raises sea level, changes freshwater resources and accelerates warming itself.
People often talk about melting ice as if it were a single phenomenon. In reality, there are several kinds of ice, which do not melt at the same pace and do not have the same effects. Understanding these differences is the key to reading the figures and the headlines correctly.
What is happening
What are the different kinds of ice on the planet?
- Mountain glaciers: from the Alps to the Himalayas, from Alaska to the Andes, they form from snow that accumulates and compacts year after year. There are more than 200,000 of them worldwide.
- Ice sheets: the two immense domes of ice covering Greenland and Antarctica, several kilometres thick. Together, they hold most of the planet's fresh water.
- Ice shelves: the floating extensions of the ice sheets over the ocean, mainly in Antarctica. The large icebergs, like those in our catalogue, break off from them.
- Sea ice: frozen seawater, only a few metres thick. We have devoted a full article to it: Sea ice: why its melting speeds up global warming.
How does a glacier lose ice?
A glacier works like a bank account. Every winter, the snow that falls and turns into ice is a deposit. Every summer, the ice that melts, and for glaciers that reach the sea the icebergs that break off, are withdrawals. Glaciologists call this balance the mass balance.
When the climate is stable, deposits and withdrawals even out over several years. With warming, summers are longer and hotter, some precipitation falls as rain rather than snow, and the balance turns negative year after year. The glacier thins, then its front retreats.
Why is melting accelerating?
Several mechanisms reinforce one another:
- Albedo: fresh snow reflects most of the sunlight. When it disappears earlier in summer, it exposes darker ice, sometimes covered with dust, which absorbs more heat.
- Altitude: as it thins, the surface of a glacier or ice sheet drops to lower, and therefore warmer, altitudes. It is a vicious circle.
- The ocean: in Antarctica and Greenland, warmer seawater melts the floating tongues of ice from below. These ice shelves act like corks: when they thin, the ice upstream flows faster towards the sea.
Not all ice raises sea level
This is one of the most important ideas to remember:
- Sea ice and icebergs are already floating. Like an ice cube in a glass of water, their melting barely raises sea level.
- Glaciers and ice sheets rest on land. When they melt, or when their ice slides into the ocean, they add water to the sea, and its level rises.
A useful benchmark: according to the European Copernicus service, about 360 billion tonnes of melted land ice are needed to raise the global mean sea level by one millimetre.
What the data say
Melting glaciers in the mountains
The GlaMBIE study, published in February 2025 in Nature and bringing together measurements from dozens of teams, gives the most complete assessment to date:
- between 2000 and 2023, the world's glaciers lost about 6,500 billion tonnes of ice, or about 5% of their volume;
- this melting raised sea level by about 18 millimetres;
- the annual loss increased by about 36% between 2000–2011 and 2012–2023;
- Central Europe, which includes the Alps, lost the largest share of its ice: about 39% in just over twenty years.
In France, the Mer de Glace, the country's largest glacier, in the Mont Blanc massif, has retreated by about two kilometres since the mid-19th century. Visitors heading down to its ice cave today take long staircases, lined with signs showing the level of the ice over the decades.
The Greenland ice sheet and the Antarctic ice sheet
The international IMBIE programme, supported by NASA and the European Space Agency, combines measurements from several families of satellites. Its latest assessment, published in 2023, shows that:
- between 1992 and 2020, the two ice sheets raised sea level by about 21 millimetres;
- their ice loss rose from about 105 billion tonnes per year in the early 1990s to about 372 billion tonnes per year between 2016 and 2020;
- Greenland is responsible for about two-thirds of this contribution;
- in Antarctica, the loss comes mainly from West Antarctica and the Antarctic Peninsula, while East Antarctica remains close to balance.
Sea level rise
According to the IPCC's Sixth Assessment Report (2021), global mean sea level rose by about 20 centimetres between 1901 and 2018. Above all, the rise is accelerating: about 1.3 millimetres per year between 1901 and 1971, then about 3.7 millimetres per year between 2006 and 2018. The IPCC finds that sea level rose faster in the 20th century than in any other century in the last three thousand years.
Melting land ice is not the only cause: seawater also expands as it warms (this is called thermal expansion). But the share due to ice is growing as melting accelerates.
Immense reserves
The ice sheets hold far more ice than everything that has melted so far. If all the ice in Greenland melted, sea level would rise by about 7 metres; for Antarctica, it would be nearly 58 metres. Nobody expects total melting within a few centuries, but these figures show that even a small fraction of these reserves is enough to redraw coastlines.
Why it matters
For coastlines
A few extra centimetres are enough to worsen flooding during storms and coastal erosion. The IPCC estimates that extreme sea-level events that used to occur about once a century will happen every year in many places by 2100. A large share of the world's population lives near the coast, and many major cities are built by the sea.
For fresh water
Mountain glaciers are natural water towers: they store water in winter and release it in summer, when rivers need it most. At first, melting increases river flow. But as glaciers shrink, this contribution eventually declines. Regions that depend on this water for farming, drinking water or hydropower, from Central Asia to the Andes, are particularly exposed. This is one of the reasons the United Nations declared 2025 the International Year of Glaciers' Preservation.
For mountains
The retreat of glaciers also destabilises the slopes they used to support, and thawing frozen ground at high altitude increases rockfalls. Mountain huts, climbing routes and ski lifts have to adapt.
For the climate itself
Less snow and ice means fewer white surfaces to reflect sunlight: melting feeds warming. And fresh water pouring into the North Atlantic from Greenland could, according to scientists, help weaken the major ocean currents, a very active field of research.
Can we still limit melting?
Yes. Some future melting is already unavoidable, because ice responds with a delay to the warming that has already occurred. But the amount of ice lost by the end of the century depends directly on how much warming we reach. Projections show that every tenth of a degree avoided preserves a significant share of the remaining glaciers. Limiting warming to 1.5 °C rather than 2 °C or more makes a considerable difference for glaciers, ice sheets and sea level.
What everyone can do
Melting ice depends on the total amount of greenhouse gases emitted by humanity. Every tonne avoided counts. Our detailed guides help you act where it matters most:
- Calculate your carbon footprint to identify your main levers;
- Take the train instead of flying;
- Heat your home to 19 °C;
- Eat less red meat;
- Make your electronic devices last.
Frequently asked questions
What causes melting ice caps and glaciers?
Global warming, driven by greenhouse gases from human activities. Longer, hotter summers, less snow and a warmer ocean make glaciers and ice sheets lose more ice each year than they gain.
What are the effects of melting glaciers?
Sea level rise, which worsens coastal flooding and erosion; in the long run, less fresh water for regions that depend on glaciers; unstable mountain slopes; and faster warming, because the ice that disappears no longer reflects sunlight.
Does melting sea ice raise sea level?
Barely, because sea ice already floats, like an ice cube in a glass. It is glaciers and ice sheets, resting on land, that raise sea level as they melt.
Can we still stop glaciers from melting?
Some melting is already unavoidable, but how much ice is lost by 2100 depends directly on how fast greenhouse gas emissions are cut. Every tenth of a degree avoided preserves a large share of the remaining glaciers.