The term “desert” is defined by a severe lack of precipitation, not exclusively by scorching, sandy landscapes. Any region receiving less than 250 millimeters (about 10 inches) of rain or its equivalent in snow per year is generally classified as a desert, regardless of temperature. This low moisture level is the universal criterion used by geographers to identify desert biomes across the world’s seven continents. These arid regions vary dramatically in distribution and characteristics, from intensely hot to permanently frozen, confirming the presence of deserts on six of the seven major landmasses.
Deserts of the Southern Continents
The southern continents host some of the world’s most recognized hot deserts. Africa hosts the largest of all, the Sahara, which dominates the northern third of the continent. This colossal arid region, characterized by extreme heat, is joined in the south by the Kalahari and Namib deserts. The Kalahari is technically a semi-arid savanna, receiving up to 500 millimeters of rain annually in some areas, but its deep, sandy soil causes rapid drainage, creating a “thirstland” environment.
The Namib Desert, stretching along the Atlantic coast, is a true desert and may be the world’s oldest, enduring arid conditions for over 55 million years. South America features the Atacama, a narrow coastal strip in Chile. The Atacama is the driest nonpolar desert on Earth, with some areas receiving less than 5 millimeters of rain per year. This extreme aridity results from a dual effect: the Andes Mountains create a rain shadow, and the cold Humboldt Current stabilizes the air, preventing moisture from forming rain clouds.
Australia, the smallest continent, is dominated by arid and semi-arid landscapes. The Great Victoria Desert is the largest in the country, consisting of sandhills and grassland plains. It receives a low and irregular annual rainfall of 200 to 250 millimeters. Australia’s second-largest desert, the Great Sandy Desert, is a vast expanse of salt marshes and sand hills across the western and northern parts of the continent.
Deserts of the Northern Continents
The northern continents of Asia and North America contain immense desert systems, displaying a wider range of temperatures than the hot deserts of the south. Asia’s most extensive arid region is the Arabian Desert, stretching across the Arabian Peninsula and considered an extension of the Sahara. This subtropical hot desert features vast sand seas, including the Empty Quarter, where summer temperatures can exceed 50 degrees Celsius.
The Gobi Desert in Asia is a notable example of a cold desert, situated on a high plateau and subject to extreme temperature swings. Winters are frigid, with temperatures plummeting below freezing, and its aridity is primarily caused by the rain shadow of the Himalayan mountains, which block moisture from the Indian Ocean. North America is home to four major deserts, including the Mojave, Sonoran, and Great Basin deserts. The Great Basin is classified as a cold desert, experiencing very cold winters and sagebrush vegetation, while the Sonoran Desert is warm with two distinct rainy seasons.
Antarctica and the Polar Deserts
Antarctica, despite being covered by a massive ice sheet, is fundamentally the world’s largest desert. This classification is based on the continent’s hyperarid climate, which results from extremely low precipitation. The frigid air over the continent holds very little water vapor, severely limiting the amount of moisture that can fall as snow.
The interior receives an average annual precipitation equivalent to less than 50 millimeters of water, placing it in the hyperarid category shared with the driest hot deserts. Temperatures remain so low that the small amount of snow that does fall rarely melts, accumulating over millennia to form the ice sheet. This persistent absence of moisture in the atmosphere, not the presence of ice, confirms Antarctica as a polar desert.
The Continent Lacking Major Deserts
Europe stands alone as the only continent generally considered to lack a major desert region that meets the standard geological definition. The continent’s climate is largely moderated by its proximity to the Atlantic Ocean and the influence of the Gulf Stream. This current brings warm, moisture-laden air inland.
Prevailing westerly wind patterns ensure that most of the landmass receives sufficient rainfall throughout the year to prevent widespread aridity. Significant mountain ranges, such as the Alps, also contribute to a temperate and habitable climate across the continent. While small, localized arid areas exist, they do not constitute a vast desert biome on the scale of those found on the other six continents.