If you are taking a day trip to the Sahara desert in North Africa you want to bring lots of water and lots of sunscreen. But if you plan to stay the night, bring a cozy sleeping bag as well.
That’s because temperatures in the Sahara can drop as soon as the sun sets, from an average high of 100 degrees Fahrenheit (38 degrees Celsius) during the day to an average low of 25 degrees Fahrenheit (minus 4 degrees Celsius) during the night, according to NASA
So why is this dramatic temperature shift happening in arid deserts like the Sahara? And how do native animals and plants deal with such wild extremes?
Related: Could the Sahara ever be green again?
Heat and humidity
The reason arid deserts – arid regions about 35% of the land of the earth – getting so hot and then so cold is a combination of two key factors: sand and humidity.
Unlike a thermos, sand does not retain heat very well. When heat and light from the sun hit a sandy desert, grains of sand in the top layer of the desert absorb heat and release it back into the air, according to a 2008 report from NASA’s Jet Propulsion Laboratory in Pasadena, California. During the day, the radiation from the sun’s energy from sand causes the air to overheat and the temperature to rise. But at night, most of the heat in the sand quickly radiates into the air and there is no sunlight to heat it up again, making the sand and surrounding area colder than before.
However, this phenomenon alone does not explain such a drastic temperature drop. After all, when the sun sets on a tropical beach, you don’t have to put on a winter coat.
The main reason for the sharp temperature change is that the desert air is extremely dry. In arid deserts such as the Sahara and the Atacama Desert in Chile, the humidity – the amount of water vapor in the air – is practically zero, and unlike sand, water has an enormous capacity to store heat.
Water vapor in the air traps heat close to the ground like a giant invisible blanket and prevents it from disappearing into the atmosphere, according to World AtlasAir with a high humidity also needs more energy to heat up, which means that it also takes more time to dissipate that energy and cool the environment. Therefore, a lack of humidity in deserts causes these arid places to heat up quickly but also cool down quickly.
Adapt to extreme temperatures
Despite these rapid temperature changes, desert animals are well adapted to the extreme temperature changes in the desert.
“It’s usually a relatively minor problem for them,” said Dale DeNardo, an environmental physiologist at Arizona State University who specializes in desert animals. “The bigger challenge is getting enough food and water to survive.”
Reptiles, the most abundant and diverse animal group in the desert, are well adapted to extreme changes in temperature because they are cold-blooded or ectothermic, meaning they don’t have to invest energy in maintaining a constant body temperature. In other words, reptiles can use this energy elsewhere, such as hunting. Many reptiles also benefit from being small, which allows them to find shady spots during the day or warmer rocks at night. “There are many different places to be warmer or cooler, especially if you are little,” DeNardo told Live Science.
Related: How do lizards cool down?
Large warm-blooded or endothermic mammals, such as camels, are too big to hide from the sun and cannot lower their body temperature. Camels are more likely to survive by maintaining a constant body temperature in both hot and cold conditions. They do this by having a lot of insulation in the form of fat and thick fur, which keeps them from getting too much heat during the day and shedding too much at night, DeNardo said.
Desert birds, on the other hand, use evaporative cooling – where they use water to dissipate heat from their bodies, such as how humans sweat and dogs pant – through a range of different methods (some vultures urinate on their legs to cool off). But their ability to fly long distances between water sources or to catch food means they don’t have to worry as much about water conservation as other desert animals. “I call it cheating because they don’t really experience the limitations of a desert,” said DeNardo.
Plants, on the other hand, are more sensitive to extreme temperatures. “They face a much greater challenge because they cannot move,” said DeNardo. That’s why iconic desert plants, such as cacti, have evolved a range of defense mechanisms, such as spikes and toxins, to protect their precious water from predators. However, freezing temperatures at night can be deadly to plants because water freezes and expands in their tissues, causing irreversible damage. Therefore, plants only grow in areas where the air temperature does not drop below freezing for more than a few hours per night, also known as the freezeline.
Changing climate
Researchers are still figuring out how climate change can affect dry places and organisms, but “we will certainly see changes,” said DeNardo. “For most deserts, we predict an average temperature rise of 3 to 4 degrees Fahrenheit [1.7 to 2.2 C]
However, research indicates that “nights get warmer, but that’s not as bad as warmer days,” noted DeNardo.
Instead, the real problem is that climate change can affect the amount of annual rainfall desert animals rely on. “It will be less consistent, you will have relatively wet years and relatively dry years,” said DeNardo. “But even if most of them are wet enough, it only takes one very dry year to cause major problems.”
Originally published on Live Science.