Today’s Wonder of the Day was inspired by Jeff from State College. Jeff Wonders, “Why is it colder on clear nights than on cloudy nights?” Thanks for WONDERing with us, Jeff!

How do you like to spend a chilly winter night? Do you gather your family for a favorite movie? Maybe you make some hot chocolate and settle in with a good book. If you’re like many people, you know there’s nothing better than getting cozy under a warm blanket on a cold night.

Did you know the Earth itself covers up with a blanket on some chilly nights? It’s true! But instead of warm fabrics like cotton or wool, the Earth’s blanket is made of clouds. 

You may have noticed the effect of clouds on temperature yourself. Clear nights tend to be quite a bit colder than cloudy ones. This is thanks to the amount of cloud cover, a measurement of the portion of the sky shielded by clouds.

At night, clouds can trap heat in the atmosphere. This helps to warm Earth’s surface, resulting in a higher temperature. Upper-level clouds have a stronger heat-trapping effect than lower-level clouds. Experts have found that they may raise the temperature as much as 13°F.

On clear nights, there are no clouds in the sky to trap heat. As a result, heat is able to escape Earth’s atmosphere. The temperature drops. That’s why clear nights can be quite a bit colder than cloudy nights. 

How about during the day? Clouds can have just the opposite effect on daytime weather. They can block heat from entering the atmosphere, driving temperatures down. That’s why many people will hope for a cloudy day during the dog days of summer—cloud cover can make the weather much more pleasant. Clouds that are lower in the atmosphere tend to block more heat than they trap.

As you can see, clouds have a big impact on the Earth’s climate. In fact, NASA estimates that without clouds, the planet would absorb about 20 percent more heat. However, the climate, in turn, also affects clouds. This relationship between clouds and climate is called cloud-climate feedback.

How could Earth’s changing climate affect cloud cover? Many scientists believe that the planet will have fewer clouds as its temperature rises. However, experts are still learning about cloud-climate feedback. One tool they use is a satellite called CloudStat. Since 1999, CloudStat has helped scientists study the relationship between Earth’s climate and clouds.

The next time you gaze up at a sky full of clouds, think about how they may have affected the day’s weather. From chilly nights to hot days, cloud cover plays a big part in determining temperature. Without them, our planet’s climate would be quite different!

Standards: NGSS.ESS2.D, CCRA.R.4, CCRA.L.3, CCRA.L.6, CCRA.R.10, CCRA.R.2, CCRA.W.2, CCRA.W.4, CCRA.L.1, CCRA.L.2, CCRA.SL.1, CCRA.R.1, CCRA.SL.1, CCRA.SL.2

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