Science Puzzle
Which Is the Biggest Desert on Earth?
The Sahara covers about 9 million square kilometres of North Africa, almost the size of the United States. The Gobi stretches across Mongolia and northern China and is bitterly cold in winter. Antarctica is buried under ice that's more than four kilometres thick in places.
Which of these is the biggest desert on Earth?
The Answer
Antarctica. At about 14 million square kilometres, it's the biggest desert on Earth, roughly one and a half times the size of the Sahara.
A desert isn't defined by heat or sand. It's defined by how little rain or snow falls. A common rule is less than 250 millimetres a year. The high middle of Antarctica gets less than 50 millimetres a year, almost all of it as snow, which makes it drier than much of the Sahara.
Cold air can hold very little water vapour, so there's hardly any moisture to fall as snow. The air over Antarctica is also mostly sinking, and sinking air warms up and dries out instead of forming clouds. Hot deserts like the Sahara sit under sinking air too.
So where did all that ice come from? Snow that falls on the high plateau almost never melts. A few centimetres a year, piled up over hundreds of thousands of years, has been squashed into ice up to four kilometres thick. The second biggest desert is the Arctic; the Sahara is the biggest hot one.
The principle: A desert is defined by how little rain or snow falls, not by heat or sand. Cold air holds very little water vapour, so the polar regions are among the driest places on Earth.