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How hot does it get in the desert? – Henry, age 5, South Bend, Indiana
When you think of a desert, you probably imagine giant waves of sand dunes beneath a blazing Sun. You’d be picturing a hot desert, like the Sahara in Africa.
Some of the most scorching temperatures recorded on Earth have been in deserts. The hottest air temperature on the Earth’s surface was 134 degrees Fahrenheit (56.7 degrees Celsius) in Death Valley, California. The highest ground temperature was 177.4 F (80.8 C) in the Lute Desert in Iran.
For comparison, a very hot bath is around 110 F (43 C). So these temperatures are way beyond anything safe for your skin.
What makes some deserts so broiling hot, and why do they exist in the first place? It has to do with how Earth’s atmosphere moves around our planet and interacts with what’s on the ground.
What is a desert?
Climate scientists like me define a desert not by temperature but by how much precipitation it gets – any form of water falling from the sky, whether rain, snow or hail. If an area receives less than 10 inches (250 millimeters) of precipitation a year, it is officially a desert.
There’s nothing in this definition about being hot. In fact, there are cold deserts, too. The biggest desert on Earth is Antarctica, where the average winter temperature can be as low as -75 F (-60 C) in the interior highlands.
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Antarctica counts as a desert because it rarely snows there. It’s covered by a large ice sheet that’s the result of tiny amounts of snow accumulating over tens of millions of years.
Where are they, and why?
The equator is an imaginary line wrapped around the middle of the Earth, separating it into two halves: the Northern and Southern hemispheres. Lines of latitude are imaginary rings parallel to the equator that further divide up the hemispheres. Latitude is measured in degrees, starting at 0 degrees at the equator up to 90 degrees at each pole.
If you look at a globe, you’ll notice an interesting pattern. Most of the world’s hot deserts – including the Sahara, the Arabian Desert and Australia’s Great Victoria Desert – are lined up within two horizontal belts around the Earth that lie at roughly 30 degrees north and 30 degrees south of the Equator.
These locations are not a coincidence. They’re related to how the atmosphere moves around Earth.
Globally, the equator gets the most direct sunlight, so the air near ground level there becomes warm and rises. At the poles, the air is very cold and sinks. This continuous rising and sinking motion creates a giant loop of moving air for each hemisphere, almost like a slow‑moving conveyor belt in the atmosphere.
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Because the Earth spins, the giant moving air loop gets twisted and broken into three smaller loops for each hemisphere. As a result of this atmospheric motion, air generally rises at the equator and latitudes around 60 degrees and sinks at the poles and latitudes around 30 degrees.
When air rises, it expands and cools. As its temperature goes down, water vapor condenses to form precipitation. When air sinks, it compresses and warms up, causing water to evaporate and creating dry conditions.
That’s why deserts are found around 30 degrees and near the poles. Those are the places where atmospheric motion causes the air to sink – resulting in dry desert conditions.
Why does it get so hot?
The deserts near the 30 degrees latitude line can get incredibly hot for three reasons.
The first reason can be found in the clouds. In most parts of the world, moisture in the air forms clouds. On a cloudy day, you might notice that clouds block the Sun’s light, helping create cooler temperatures. Because desert air is extremely dry, it lacks this protective shield. With no clouds to provide shade, all of the Sun’s incoming solar energy reaches the Earth’s surface, heating the ground at full intensity.
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Another reason behind these deserts’ high temperatures is what you find below your feet. At the beach, you might notice that the sand feels much warmer than the ocean on a hot day. That’s because of the difference in their specific heat, a term scientists use to describe how much energy something needs to change its temperature.
Water has a very high specific heat and therefore takes a lot of energy – and hence a long time – to warm up. Conversely, rocks and sand have low specific heats; they absorb the energy from the Sun and warm up very fast. For the same reason, they can’t hold onto that warmth when the Sun goes down. Once night falls, all that heat escapes right back into space. This is why a desert can go from roasting at noon to freezing at midnight.
A final reason those hot deserts stay hot has to do with the way water removes heat when it evaporates. In nondesert places, plants release water into the air, cooling the surrounding area. Scientists call this phenomenon evaporative cooling. It’s the reason you can feel cold when you get out of a pool even on a warm day.
In deserts, the ground is dry and there are very few plants, so almost no evaporative cooling happens. Without this natural cooling system, the Sun’s heat stays trapped at ground level, making the daytime desert feel scorching.
How global warming is changing the desert
Because our planet is warming up due to human activities such as burning fossil fuels – coal, oil and natural gas – and cutting down forests, deserts are experiencing some major shifts.
In many parts of the world, global warming makes deserts hotter, drier and dustier. It also makes them spread outward into places that used to have more plants. When regular land turns into a dry desert, it’s called desertification.
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Climate change doesn’t affect every place the same way, though. In some desert regions, shifting wind patterns are actually bringing more rain than usual, leading to a partial greening of the desert. This has been observed in the Thar Desert in India and Pakistan, the southern fringe of the Sahara Desert and some deserts in northern and northwestern China. Such major shifts in desert conditions change the ecosystem, making it harder for native animals and plants, which are adapted to the desert environment, to survive.
Deserts are some of the most extreme, beautiful and finely balanced places on Earth. Understanding how the atmosphere and the land work together reveals how even the hottest places on our planet are connected to the rest of the world.
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