Water covers more than 70 percent of Earth’s surface, yet only a tiny fraction of it is available for human use. Most of Earth’s water is salty ocean water, and of the small portion that is fresh, the overwhelming majority is frozen. Glaciers and ice sheets act as the planet’s largest freshwater reservoir, quietly storing water over thousands to millions of years.
To put this into perspective, about 97 percent of Earth’s water is found in the oceans. That leaves roughly 3 percent as freshwater. Of that freshwater, an estimated 68–69 percent is locked up in glaciers and ice sheets, making frozen ice the single largest store of freshwater on the planet. The remainder is split mainly between groundwater, surface water (lakes and rivers), soil moisture, and atmospheric water vapor.
The vast majority of glacial freshwater is stored in two places: Antarctica and Greenland. Antarctica alone contains about 90 percent of the world’s ice and roughly 70 percent of its freshwater. If the Antarctic Ice Sheet were to melt entirely—a scenario that would take centuries to millennia—it would raise global sea levels by nearly 60 meters. Greenland’s ice sheet, while much smaller, still contains enough water to raise sea level by about 7 meters if fully melted.
Beyond these massive ice sheets, the rest of Earth’s glaciers—mountain glaciers and ice caps—account for a relatively small share of total freshwater, less than 1 percent. However, despite their smaller volume, these glaciers play an outsized role in human and ecological systems. In regions such as the Himalayas, Andes, Alps, and Rockies, seasonal meltwater from glaciers supports hundreds of millions of people by feeding rivers, sustaining agriculture, and maintaining ecosystems during dry periods.
What makes glacial water unique is its timescale. Unlike rivers or lakes, which cycle water over months or years, glaciers store water over extremely long periods. Snowfall accumulates, compresses into ice, and may remain frozen for thousands of years before melting. In this sense, glaciers act as a long-term savings account for freshwater—one that is now being rapidly drawn down due to global warming.
As global temperatures rise, glaciers are losing mass at accelerating rates. This does not mean Earth is losing water overall, but rather that freshwater is being redistributed from land-based ice into the oceans. When glaciers melt, they contribute directly to sea-level rise, altering coastlines and increasing flood risk for low-lying communities. At the same time, the loss of glacial storage threatens long-term water security in glacier-dependent regions.
It is also important to note that only a very small fraction of Earth’s freshwater—less than 1 percent—exists as easily accessible surface water in lakes and rivers. This highlights a striking imbalance: humans depend almost entirely on a sliver of the planet’s freshwater, while most of it remains frozen or underground.
Understanding that nearly two-thirds of Earth’s freshwater is locked in glaciers helps explain why the cryosphere is so central to climate science. Changes in glaciers are not just visual indicators of warming; they represent a fundamental shift in how Earth stores and moves its freshwater.
In a warming world, glaciers are transitioning from stable reservoirs to diminishing ones. How fast that transition happens will shape sea levels, water availability, and climate feedbacks for generations to come—making Earth’s frozen water one of the most consequential components of the global system.