There is no need to compare the glacier retreat with old photographs. In just a decade, anyone living near the Alpine mountains has witnessed it firsthand. Some glaciers have disappeared completely in many regions between 2,000 and 4,000 meters above sea level. It is the most striking visual evidence of global warming, and its consequences affect us all, whether we live near mountains or not. Glaciers are an undeniable measure of how we treat the atmosphere.

The latest World Meteorological Organization (WMO) report supports these observations with irrefutable data: in 2023, glaciers lost more than 600 gigatons of water, the greatest mass loss recorded in the past 50 years.

Understanding glaciers requires clarifying concepts that often confuse public opinion. Climatologists emphasize the need to distinguish between snow and glacial ice, as they are different states of water with distinct structures, formation processes, and climatic effects.

• Snow is frozen water in the atmosphere in crystal form. It is light, porous, and can compact over time.
• Conversely, glacier ice forms when accumulated snow compacts and recrystallizes, expelling trapped air. This process can take decades, centuries, or even millennia in the vast ice sheets of Greenland and Antarctica. Glacial ice is denser and darker, and moves like a river of ice under the force of gravity.

Distinguishing between the two is key to avoiding common media confusion between meteorology and climatology. Snowfall is a short-term meteorological event, while glaciers reflect long-term climate trends. Their current melting is a direct consequence of the progressive rise in temperature over the past 50 to 60 years.

The importance of glacial ice remains largely underestimated. Its loss has three major consequences that profoundly impact our planet:

UNESCO reports that between 2000 and 2020, glaciers lost approximately 1,163 gigatons (Gt) of ice, averaging 58 Gt per year. This amount is comparable to France and Spain’s total annual water consumption combined.

Nearly 2 billion people rely on seasonal glacier meltwater runoff that flows downstream, feeding rivers and aquifers. Rapid melting is decreasing this flow and making it increasingly unpredictable.

Scientific warnings about this phenomenon date back to the 1990s, and each new study has only confirmed and worsened these concerns. A paradigmatic case is the Himalayas: in 2009, NASA’s GRACE satellites detected that aquifers in the upper Ganges basin—spanning 907,000 km² and supporting nearly 8% of the world’s population—were declining at an alarming rate of 33 cm per year in groundwater levels. While agricultural overexploitation was a key factor, much of this loss was accelerating due to glacier retreat.

New studies in 2018 confirmed this trend and issued an even more severe warning: if global warming continues at its current pace, Himalayan glaciers could lose between 70% and 99% of their volume by 2100. In less than a century, the iconic image of immense snow-capped mountain ranges crowned by Everest could transform into a barren landscape of exposed rock.

When seasonal snow melts, its impact on sea levels is minimal, as it is usually replenished yearly. Glacial melting, however, is critical, as it releases water that has been stored for millennia, contributing irreversibly to rising sea levels.

The intensification of glacier melt significantly contributes to the global sea level rise, which is about 20 centimetres higher today than in 1900. Greenland’s glacier ice alone could raise sea levels by 30 centimetres by 2100.

As for mountain (alpine) glaciers, since 1961, they have lost more than 9,625 gigatons of ice, leading to a 27-millimeter rise in sea levels. Currently, mountain glaciers are losing around 335 gigatons of ice per year, contributing to an annual sea level rise of nearly 1 millimetre.

When a glacier retreats, it exposes its glacial bed—typically a surface covered with rocks and sediments transported over the years by ice, known as moraine. If the depression fills with water, it forms a proglacial lake. Moraine and proglacial lakes absorb solar energy differently than ice.

We have previously explained in more detail the concept of albedo and its importance in climate science. Albedo is a coefficient that indicates the percentage of solar radiation reflected by a surface compared to the amount it receives.

The highest albedo surfaces in nature are ice and snow, with values between 0.70 and 0.90, meaning they reflect most of the incoming solar radiation. Water has a much lower albedo, ranging from 0.03 to 0.10. Moraines also have a low albedo (10–30%), absorbing more heat and promoting local warming.

Heat absorption increases as glaciers retreat and expose more moraines and lakes, further accelerating melting and local warming.

The degradation of glaciers is a growing global concern. However, certain geographic regions attract particular scientific attention, with revealing studies highlighting their rapid changes:

• Greenland
  Although it is not technically a valley or mountain glacier, Greenland’s ice sheet is classified as an ice cap, a massive body covering an area greater than 50,000 km². It has a significant impact on sea levels and the global water cycle. Additionally, numerous outlet glaciers along its coastal margins transport ice into the ocean, behaving similarly to conventional glaciers by flowing and calving into icebergs.
• Chilean Patagonia

  Recent studies indicate that glaciers in this region are experiencing accelerated melting. Glaciologists—scientists specialized in the study of glaciers—project a 25% to 70% loss in glacier volume by the end of the century.

• European Alps
  The Alps have lost one-third of their ice volume in just the past 20 years. For instance, the Mer de Glace in the Mont Blanc massif has retreated by one kilometre and lost 160 meters of thickness, as widely documented in media reports. Even under the most optimistic scenarios, at least one-third of European glacier volume is expected to disappear by 2050.

The disappearance of ice is one of the clearest and most direct indicators of global warming. For this reason, glaciers are a powerful tool for raising awareness about the urgency of reducing greenhouse gas emissions. Understanding the role of glaciers as freshwater reserves and climate regulators is crucial for driving mitigation efforts and planning adaptation strategies in regions where water supply depends directly on glacier stability.

This year’s World Water Day theme, “Glacier Preservation”, is a call to action. Every effort counts in the fight to slow global warming and prevent surpassing the critical 1.5°C threshold.