The Largest Deserts in the World (Antarctica Counts)

The technical definition of a desert is a region that receives less than about 250 mm of precipitation a year. Temperature does not enter into it at all, so the polar regions qualify, and they are the largest deserts in the world by a wide margin.

The largest deserts by area

1. Antarctic Desert — about 14 million km². The largest desert on Earth. The interior receives almost no snowfall; some valleys have not seen precipitation in millions of years.
2. Arctic Desert — about 13.9 million km². Spread across northern Canada, Greenland, Alaska, Russia and Scandinavia, plus the frozen Arctic Ocean.
3. Sahara — about 9.2 million km². The largest hot desert, roughly the size of the contiguous United States, spanning 11 countries across North Africa.
4. Arabian Desert — about 2.3 million km². Covers most of the Arabian Peninsula, including the vast sand sea of the Rub' al Khali (the "Empty Quarter").
5. Gobi — about 1.3 million km². Mongolia and northern China; a cold desert, with freezing winters, in the rain shadow of the Himalaya.
6. Kalahari — about 900,000 km². Southern Africa; technically a semi-desert, since parts receive enough rain to support grass and scrub.
7. Patagonian Desert — about 670,000 km². The largest desert in the Americas, in southern Argentina, in the rain shadow of the Andes.
8. Great Victoria Desert — about 350,000 km². The largest of Australia's several deserts.
9. Syrian Desert, Chihuahuan Desert, Great Basin Desert, Thar Desert — each in the range of 200,000–500,000 km².

The driest place on Earth

Parts of the Atacama Desert in northern Chile are the driest places on the planet that are not in Antarctica. Some weather stations there have never recorded any rain, and the average is close to 1 mm per year. The Atacama is kept arid by a double rain shadow (the Andes to the east, the Chilean Coast Range to the west) and by the cold Humboldt Current offshore, which suppresses evaporation and cloud formation. Its soil is so Mars-like that NASA tests instruments there.

Is the Sahara growing?

Yes, on balance. The Sahara has expanded by roughly 10% over the last century, mostly by pushing south into the Sahel during the dry season. The change is driven partly by natural climate cycles and partly by human-caused warming and land use. The boundary is not fixed — it advances and retreats — but the long-term trend is expansion.