The Arctic, despite its vast expanses of ice and snow, is scientifically classified as a desert. This often puzzles many, as the common image of a desert is one of scorching heat and barren sand. This perception leads to a misconception that abundant ice implies high precipitation. However, the scientific classification of deserts hinges on a different criterion than temperature or visible moisture. This article explores the scientific principles explaining why the Arctic is indeed a desert.
Defining a Desert Environment
A desert is primarily defined by its lack of precipitation, not by its temperature. Scientists classify a region as a desert if it receives very low amounts of annual precipitation, typically less than 250 millimeters (about 10 inches) per year. Deserts can be hot, like the Sahara, or cold, like the polar regions.
The crucial factor is the balance between precipitation and potential evapotranspiration, often quantified by an aridity index. This index considers the water supplied by precipitation relative to the atmosphere’s capacity to draw moisture away through evaporation and plant transpiration. If a region loses more water than it gains from precipitation, it is considered arid. This allows the Arctic, with its freezing temperatures and permanent ice cover, to fit the desert definition.
Atmospheric Conditions Limiting Arctic Precipitation
The Arctic’s desert classification stems from meteorological phenomena that limit atmospheric moisture. Extremely cold air, a constant feature of the polar environment, holds very little water vapor compared to warmer air. At lower temperatures, water molecules have less energy, making it harder for them to evaporate. Any moisture present condenses and falls as very light snow or ice crystals.
A persistent high-pressure system, known as the polar high, dominates the central Arctic. This system features sinking air, or subsidence. As this air descends, it warms slightly and becomes drier, preventing cloud formation and precipitation. This descending dry air creates stable weather conditions.
The Arctic’s geographic characteristics also contribute to its aridity. Much of the Arctic Ocean is covered by sea ice for most of the year, limiting the evaporation of moisture into the atmosphere from the ocean surface. Prevailing winds carry cold, dry air from the interiors of continents. While some moisture is transported into the Arctic from lower latitudes, particularly from the North Atlantic, cold temperatures rapidly cause it to precipitate out before reaching the coldest parts of the region.
The Paradox of Arctic Ice and Snow
The presence of vast ice sheets and extensive snow cover in the Arctic appears contradictory to its classification as a desert. This apparent paradox is resolved by understanding the long-term accumulation of frozen precipitation rather than high annual snowfall. The existing ice and snow are not the result of heavy, frequent precipitation events. Instead, they are a consequence of thousands of years of accumulation.
Because Arctic temperatures remain below freezing for most of the year, the small amounts of snow that do fall rarely melt. This allows even light annual snowfall to persist and gradually build up over centuries. Over time, these layers of snow compact under their own weight, transforming into dense ice sheets and glaciers. Therefore, the immense volume of ice is a testament to the region’s consistently cold temperatures and the preservation of past precipitation, rather than an indicator of current high precipitation rates.