The frozen continent at the bottom of the planet holds a resource that most descriptions of Antarctica understate: an overwhelming share of Earth’s fresh water, locked away as ice. Beneath a surface famous for penguins and polar research lies a mass of ancient ice so vast that it dwarfs every lake, river, and aquifer combined. If that ice were counted as a reservoir, it would be by far the largest store of fresh water on the planet, and its behavior over the coming centuries will help determine how high the world’s oceans rise.
The scale is difficult to grasp from photographs alone, so the numbers that scientists use to describe the ice sheet do most of the explaining.
How much fresh water the ice sheet holds
The two remaining ice sheets on Earth, one covering most of Greenland and the other spanning Antarctica, together account for more than 99 percent of the planet’s fresh water ice. According to the National Snow and Ice Data Center’s ice sheet quick facts, those two sheets hold over 68 percent of all the fresh water on Earth. Antarctica accounts for the large majority of that total, because its ice sheet is many times the size of Greenland’s.
The Antarctic Ice Sheet, considered on its own, is commonly credited with holding roughly 70 percent of the world’s fresh water. That single figure captures the headline point: liquid fresh water in lakes, rivers, and living things is only a thin slice of the planet’s total, while the frozen store sitting on one continent contains most of it.
The physical size of the Antarctic ice sheet
The ice sheet covers almost 14 million square kilometers, roughly the combined area of the contiguous United States and Mexico. At its thickest, the ice reaches nearly 4.9 kilometers, about three miles, from surface to bedrock, and the sheet contains on the order of 30 million cubic kilometers of ice. Those dimensions make it the single largest mass of ice on Earth and the reason it can store so much water.
Glaciologists generally divide the sheet into three regions: the massive East Antarctic Ice Sheet, the smaller and lower-lying West Antarctic Ice Sheet, and the Antarctic Peninsula. That division matters because the regions behave differently. Much of the West Antarctic Ice Sheet sits on bedrock below sea level, which makes it more sensitive to warming ocean water than the thick, high, cold interior of East Antarctica.
How the ice forms and stays frozen
An ice sheet is built from snow that never fully melts. Over thousands of years, layer upon layer of snowfall compresses into dense ice, and the accumulated mass begins to spread outward under its own weight in broad domes. Near the coast, that ice drains toward the sea through fast-moving ice streams, outlet glaciers, and floating ice shelves, while snowfall in the interior replenishes the supply.
When the ice a sheet gains from snowfall roughly equals what it loses to melting, evaporation, and icebergs breaking off, it is described as being in balance. For most of the twentieth century the great ice sheets were nearly in balance, but that stability has shifted in the twenty-first century as warming has increased losses. The ice also shapes its surroundings: its high, cold plateaus alter storm tracks and generate powerful downslope winds, and its layers trap air bubbles that preserve a record of the atmosphere stretching back hundreds of thousands of years.
Why the frozen reservoir matters for sea level
Because the ice sheet stores water on land rather than in the ocean, its fate translates directly into sea level. The NSIDC estimates that if the entire Antarctic Ice Sheet melted, global sea level would rise by about 58 meters, roughly 190 feet, while the complete loss of Greenland’s smaller sheet would add about 7.4 meters. A total melt is not expected in any near-term scenario, but even partial losses from the most vulnerable sectors would be enough to reshape coastlines around the world.
That is why the ice sheets are among the most closely watched features on the planet. NASA tracks their changing mass as a key climate indicator, and its assessment of the ice sheets documents ongoing losses in both Greenland and Antarctica measured from satellites. Monitoring how much ice the sheets gain and lose each year gives scientists an early read on how quickly the world’s largest fresh-water store is being released into the sea.
A water tower for the planet
Framing Antarctica as a reservoir helps clarify its role in the global water system. Scientists sometimes describe the ice sheets as the planet’s water towers, holding fresh water in a frozen state and releasing it slowly through runoff that feeds ecosystems at the ice edge. The overwhelming majority of that water stays locked in place, which is precisely what keeps it out of the ocean and out of the accessible supply that supports life elsewhere.
That slow release is also why the ice is effectively unavailable as a practical water source, despite its enormous volume: it is remote, frozen solid, and concentrated far from the places where people live. The continent’s ice therefore sits at the center of two of the planet’s defining questions: where its fresh water is held, and how much of it might one day flow into the sea. For now, most of the world’s fresh water remains frozen on a single continent, a quiet reserve whose slow changes carry outsized consequences for the rest of the globe.
This article was produced with AI assistance and reviewed by Morning Overview editors.
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