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Curious Kids: why is air colder the higher up you go?

By Zoran Ristovski, Professor, Queensland University of Technology

The air up high is just really bad at 'holding' onto the radiation coming from the Sun, and the warmth passes straight through it on its journey toward the ground. Kevin Spencer/flicr, CC BY-NC

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Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to curiouskidsus@theconversation.com.


Why is air colder the higher up you go? Shouldn’t it be hotter as you’re getting closer to the Sun? – Flynn, age 6, Sydney.


Thank you Flynn, that’s a great question. A lot of people have probably wondered this.

As you may know, hot air rises. So why is it so cold at the top of a mountain?

Well, it helps if you imagine the ground here on Earth as a big heater. It keeps us warm, and if you move away from the heater you feel cold.

So what “heats up” the heater? The light and warmth from the Sun. Scientists call this light and warmth “radiation”.

Light and warmth travel from the Sun

The light and warmth from the Sun travel through space towards Earth, and pass through our atmosphere. (The “atmosphere” is what we call the swirling air that surrounds our planet.)

But the atmosphere isn’t very good at holding onto the warmth from the Sun. The heat just slips straight through it. (For the adults reading: that’s because air at higher altitudes thins out as the gas particles expand and lose energy.)

Eventually, the heat from the Sun hits the ground and the ground soaks it up. This especially happens in forests and oceans, which are very good at absorbing heat. Other places, like snow fields, are more likely to reflect the radiation – meaning it bounces back toward the Sun instead of being soaked up by the ground.


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The ocean and forests are especially good at soaking up and holding onto heat from the Sun.
Pixabay/Stocksnap, CC BY

Up, up, up

The higher up you go, the further you are away from the “heater” that is keeping us all warm – the ground that has absorbed the warmth from the Sun. At the top of mountains it can get so cold people could die within minutes without special protection. That’s because the air up there is just really bad at “holding onto” the radiation coming from the Sun, and the warmth passes straight through it on its journey toward the ground.

And all the way up in space, there is a lot more radiation from the Sun, and astronauts wear special suits to protect themselves from it. But there’s also no air in space, which means there’s really nothing much at all to “hold onto” the warmth of the Sun and make the temperature around you feel warm.

So if you were unlucky enough to be caught in space without a suit, you would freeze to death before the Sun’s radiation would get you.




Read more:
Curious Kids: how is global warming heating up the Earth?


The Conversation

Zoran Ristovski has received a number of grants from the Australian Research Council (ARC) as well as other funding bodies.

Branka Miljevic receives funding from the Australian Research Council, the Australian Department of Education Endeavour Leadership program, the Australian Academy of Science and various internal QUT grants.


Originally published in The Conversation.