It does snow in Antarctica, creating the vast white landscape people imagine. However, the nature of this snowfall is surprising. Despite being covered by an ice sheet that holds 90% of the world’s freshwater, the continent receives exceptionally low precipitation. The volume of new snow is so minimal that the entire landmass qualifies as the world’s largest desert.
The Paradox of the Polar Desert
Antarctica is classified as a desert based strictly on its annual precipitation volume, not its temperature. A desert is defined as a region receiving less than 250 millimeters (10 inches) of precipitation per year, measured as a liquid water equivalent. The continent meets this condition because its extremely cold atmosphere holds very little moisture. The average annual precipitation across the continent is only around 150 millimeters (6 inches) of water equivalent. This lack of moisture is pronounced in the interior, where the high polar plateau receives less than 50 millimeters (2 inches) per year, making central Antarctica drier than the Sahara Desert. Coastal areas and the Antarctic Peninsula receive slightly more precipitation, sometimes exceeding 200 millimeters annually. The snow that falls rarely melts due to the frigid temperatures, and over millennia, this minimal annual snowfall has compressed into the immense ice sheet covering the continent.
How Snow Forms in Extreme Cold
The physical mechanisms of precipitation in ultra-low temperatures result in ice forms distinctly different from typical snowflakes. Standard, fluffy snow is rare because the air lacks the water vapor content necessary for large crystals to grow. Instead, “diamond dust” accounts for a significant portion of the interior’s precipitation. Diamond dust consists of extremely tiny ice crystals that precipitate directly from a clear or nearly clear sky. This is sometimes called “clear-sky precipitation” because it falls without a visible cloud layer overhead. The crystals form when the temperature is well below freezing, often below -25°C in the interior. The process involves the direct deposition of water vapor onto an ice nucleus, forming small, well-defined six-sided crystals, such as hexagonal plates or columns. These small crystals catch the sunlight as they descend, creating a glittering, diamond-like effect near the surface. At the Plateau Station in East Antarctica, diamond dust has been recorded on over 300 days a year, making up more than 70% of the area’s total precipitation.
The Role of Wind and Snow Movement
While new snowfall is scarce, the Antarctic landscape often appears to be in the middle of a massive blizzard. This is due to the dynamic movement and redistribution of snow that has already fallen, driven by powerful downslope winds. These gravity-driven air currents, known as katabatic winds, are a defining feature of the continent’s weather. Katabatic winds originate on the high, cold plateau, where air is cooled and becomes dense. Gravity pulls this heavy, cold air mass down the slopes of the ice sheet toward the coast, often reaching hurricane force speeds. These winds regularly gust over 150 miles per hour in coastal funneling zones. When these powerful winds sweep across the surface, they lift and carry the existing fine, granular snow into the air, creating what looks like a whiteout blizzard. This action shifts snow from the high interior toward the coast, forming large drifts and obscuring the measurement of new snowfall. The entrained snow particles can increase the density of the airflow, which accelerates the wind, creating a self-sustaining cycle of snow redistribution across the continent.