The largest desert on Earth is not in Africa. It has no sand, no dunes and no camels. It is Antarctica, and at around 14.2 million square kilometres it is considerably larger than the Sahara.
This is not a play on words but the definition. A desert is a region with very little precipitation, usually less than 250 millimetres a year. That says nothing about temperature. The interior of Antarctica receives less than 50 millimetres a year. It is not merely a desert but an extreme one.
Desert is a statement about water, not about warmth.
— TerraTally · Climate desk
Adopt that single correction and the world map reads differently. Three places show what becomes visible, and why the record lists do not agree with one another.
It depends on what is being measured
Dasht-e Lut, Iran. Satellites have recorded surface temperatures of more than 70 degrees Celsius in the Lut desert, among the highest values ever registered for a land surface. What matters is what was measured: the temperature of the ground, not of the air. Air temperature is recorded by convention in the shade and two metres above the ground. Dark, dry desert soil heats up in the sun far more than the air above it. Satellite records and weather station records are therefore two separate rankings, and they lead to different places.
Danakil, Ethiopia. Here the peak value is not the point; the permanent state is. At Dallol in the Danakil depression a mean annual temperature of about 34.6 degrees was measured over several years, the highest known value for an inhabited place. Inhabited means people work there all year round, not only in the bearable season. The depression also lies well below sea level and is volcanically active. It belongs to the same rift along which East Africa is currently separating from the rest of the continent.
Scale
14.2
million km² of Antarctica, the largest desert
>70
°C surface temperature in the Lut
34.6
°C annual mean at Dallol
Namib, south-western Africa. The Namib counts as one of the oldest deserts on Earth. It is dry for the same reason as the Atacama: the cold Benguela current runs along the coast, cools the air above it and prevents the cloud formation that would bring rain. What it brings instead is fog. The fog drifts inland from the sea regularly and carries an entire ecosystem. Some beetle species stand head down in the wind so that droplets collect on their bodies and run to their mouths. Where no rain falls, humidity becomes the water source.
Redefining the word has practical consequences. Deserts are not the exception; they cover a substantial part of the land surface, and they grow where rainfall fails or soils degrade. Equating desert with heat misses half the problem: dryness also arises in the cold, and it hits ecosystems that have just as little water available.
The three examples also reveal a pattern. Almost all extreme dry regions come down to a few mechanisms: the rain shadow behind a mountain range, a cold ocean current off the coast, subsiding air in the subtropical high pressure belts, or simply cold that allows almost no moisture in the air.
Antarctica is the last of these cases. Cold air can carry almost no water. That is why so little snow falls there, and why the coldest place on Earth is also its largest desert.