Antarctica qualifies as a desert because it receives an average of roughly 2 inches (about 50 millimeters) of precipitation per year across the entire continent. That’s far below the 250-millimeter (10-inch) threshold scientists use to classify a region as a desert. Despite holding about 70% of Earth’s fresh water locked in its ice sheet, Antarctica gets less new precipitation annually than almost anywhere else on the planet.
What Makes a Place a Desert
A desert isn’t defined by heat or sand. It’s defined by how little precipitation falls. Any region receiving less than 250 millimeters (10 inches) of precipitation per year qualifies. By that measure, the Sahara and Antarctica belong to the same category, even though their temperatures differ by over 100°C at the extremes.
Scientists further distinguish between types. Hot deserts like the Sahara form because trade winds heat up as they move toward the equator, drying out the air and clearing cloud cover so the sun bakes the ground. Polar deserts like Antarctica form through an entirely different process, but the result is the same: almost no moisture reaches the surface. The U.S. Geological Survey defines polar deserts specifically as areas with less than 250 millimeters of annual precipitation and average temperatures that stay below 10°C even in the warmest month. Antarctica meets both criteria easily.
Why Antarctica Gets So Little Precipitation
The fundamental reason is temperature. Air’s ability to hold water vapor depends directly on how warm it is. As air temperature drops, the molecules in it slow down, and the maximum amount of water vapor the air can carry plummets. Antarctica’s interior regularly hits minus 50°C in winter and rarely climbs above minus 20°C even in summer. At those temperatures, the atmosphere is nearly incapable of holding moisture. The air over the interior plateau is essentially freeze-dried.
This is the same principle behind why winter air feels so dry indoors. Cold outdoor air holds very little moisture to begin with, and when it’s heated inside your home, the relative humidity drops even further. Scale that effect to an entire continent surrounded by ocean, and you get a place where the atmosphere simply can’t deliver meaningful precipitation to most of the landmass.
The Role of Katabatic Winds
Even the snow that does fall over Antarctica often doesn’t stay where it lands. Gravity-driven winds called katabatic winds form when dense, cold air pools on the high interior plateau and then rushes downhill toward the coast, accelerating as the terrain steepens. These winds blow persistently year-round and carry extremely dry air from the interior out toward the margins of the continent.
Research published in the Proceedings of the National Academy of Sciences found that this dry air causes roughly 35% of snowfall along East Antarctica’s coastal margins to sublimate, meaning the snow turns directly from ice crystals back into vapor before it ever accumulates on the ground. As the katabatic air descends and warms through compression, it becomes even drier, intensifying this effect. So the continent’s own wind patterns actively strip away a significant portion of whatever precipitation the atmosphere manages to produce.
Coasts vs. Interior
Antarctica’s desert status applies to the continent as a whole, but precipitation varies dramatically by location. The vast interior plateau, home to the South Pole, is the driest zone. Some interior stations record the equivalent of less than 20 millimeters of water per year, making those areas drier than the heart of the Sahara.
The coasts are a different story. Intense storms with hurricane-force winds can dump heavy precipitation around the steep margins of the continent, with some areas of the Antarctic Peninsula and northern West Antarctica receiving the equivalent of up to 10 feet of water annually as snowfall. These coastal zones technically exceed the desert threshold, but they represent a small fraction of the continent’s total area. The interior overwhelmingly dominates the average.
The Largest Desert on Earth
At 14.2 million square kilometers (5.5 million square miles), Antarctica is the largest desert on Earth by a wide margin. The Sahara, often thought of as the world’s biggest desert, covers about 9.2 million square kilometers. Antarctica is more than 50% larger. The Arctic polar desert ranks second, with the Sahara coming in third.
This ranking surprises most people because Antarctica doesn’t look like a desert. Its surface is covered in ice thousands of meters thick, built up over millions of years. But that ice accumulated incredibly slowly, precisely because so little new snow falls each year. The ice sheet persists not because Antarctica receives a lot of precipitation but because temperatures are so cold that almost nothing ever melts. Snow that fell thousands of years ago is still there, compressed into glacial ice, simply because there’s no mechanism to remove it except the slow flow of glaciers toward the sea.
Climate Change and Antarctic Precipitation
Antarctica’s extreme dryness may be shifting. Analysis of weather data from 1979 to 2023 has identified several large drainage basins across both West and East Antarctica where total and extreme precipitation are increasing significantly. Greenhouse gas emissions appear to be the primary driver of these trends. Warmer global temperatures mean the atmosphere can carry more moisture, and some of that additional moisture is reaching Antarctica’s margins during storms.
This creates a counterintuitive situation. More snowfall on the ice sheet could theoretically add mass and partially offset ice loss from melting and glacier calving at the edges. But much of Antarctica’s precipitation arrives during extreme events rather than steady snowfall, and those same warming conditions accelerate ice loss in other ways. The continent remains firmly a desert for now, though the boundary between its dry interior and wetter coasts continues to evolve.