Eli5: How is it possible that deserts are super hot at day time and below freezing point at night time?
In: Earth Science
Lack of humidity. When the air is really dry, it can’t hold onto the heat. Also, the sky is more likely to be clear, which lets the heat radiate out into space.
Water is an excellent heat sink – it absorbs tons of heat during the day and then releases it at night, cooling the days and warming the nights in most of the world.
But what if you have no water? No lakes, oceans, puddles, or even plants with water in them?
Then you’re relying on the much lower heat capacity of sand, barely 1/5th that of water. This leads to wild temperature swings as the sun boils the surface during the day and all the heat escapes into cloudless nights.
There is nothing to keep the temperature.
You can try it with your fridge.
Unplug and open an empty fridge and it will be warm inside very fast.
Unplug and open a full fridge and you will have much more time to close it again before it gets warm inside.
Biomass, water (air humidity) and soil all stabilize the temperature of an ecosystem. Desert hasn’t much of it. Because of that the heat can easily radiate out into the nightsky, and next day the sun will have everything heated up in minutes.
Clouds are very good at both trapping heat in and reflecting it away, deserts rarely have any clouds so they experience maximum heating in the day followed by maximum cooling at night.
Humidity behaves similarly as well I believe, but I’m not as sure.
There isn’t much to hold the heat in a desert. Sand and rock are awful at retaining heat and cool quite quickly. Water holds its temperature actually quite well in comparison, and the larger the body of water, the better it retains heat.
This is similar to how clear winter nights are frequently so cold and cloudy nights are not. Water vapor is an excellent greenhouse gas (absorbs infrared light, which is the light range emitted by materials at the temperature of the earth surface), so if there is no water vapor (air is really dry), there is no “blanket” to keep in the heat. It all radiates out to space. Well, deserts are dry as dry can be. No blanket to keep the heat down in the lower atmosphere.
The role of water vapor in climate change is a bit of a challenge because it is a powerful greenhouse gas but difficult to predict how climate change will affect water vapor distribution, and that will have a very strong impact on warming, or lack of warming, at any particular region.
You don’t actually see it go from hot to freezing in a day unless it is high altitude.
You get about 30 degree F temperature swing. It gets relatively colder at night but its much less pronounced than in the mountains
An area being a desert has nothing to due with temperature, it’s based on annual precipitation (less then 10 inches per year IIRC). Antarctic is a desert.
There isn’t much to trap the heat during the day so it dissipates. Same reason Las Vegas doesn’t really cool down at night, it has too much black top (streets) which trap the heat and release it more slowly (aka also at night).
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