Sometimes getting out of the sun is the best way for an animal to avoid overheating. Reptiles control their body heat via the environment, so if an area is too hot or sunny, they'll simply move to a shadier area to cool off. Conversely, if they want to warm up to boost their metabolism, they'll seek the sun. Because they don't use any type of internal regulation, reptiles spend less energy dealing with their temperature, meaning they need far less food than other animals. But their dependence on the outside world also leaves them extremely susceptible to environmental changes—even a cloud passing in front of the sun can affect small reptiles.
Sensitivity to the environment means that climate change poses a big problem for reptiles—some scientists estimate that 20 percent of lizard species could go extinct by 2080 if warming trends continue. Even if somehow we could completely halt global warming tomorrow, six percent of lizard species are still doomed to extinction thanks to the greenhouse gases currently present in our atmosphere. Mexico's blue spiny lizard, for example, has been forced to spend more time hiding from the sun rather than hunting or reproducing, something that's driving it to extinction.