Mon Prof Augmenté
Earth’s energy balance and the greenhouse effect
Age 18 · Science
Open to everyone until Tuesday, November 17
To keep it, print it while it is open.
Earth absorbs sunlight and gets rid of that energy by radiating infrared heat back toward space. Greenhouse gases in the atmosphere absorb part of this heat and send some back down, keeping the surface about 33 °C warmer than it would otherwise be.
In the picture
- Incoming sunlight: short-wave energy arriving from the Sun
- Reflected sunlight: about 30% bounces off clouds, ice and snow straight back to space
- Absorbed sunlight: land and ocean take in light energy and warm up
- Infrared radiation: the warm surface gives off long-wave heat upward
- Greenhouse gases: water vapour, CO₂ and methane absorb infrared and send part of it back down
Examples
- A car parked in the sun gets hot inside because light gets in easily but heat escapes slowly.
- A cloudy night stays warmer than a clear night because clouds send infrared heat back to the ground.
Key takeaways
- Without greenhouse gases, Earth’s average surface temperature would be about −18 °C instead of about +15 °C.
- When more energy comes in than goes out, Earth warms until the balance is restored; adding CO₂ shifts that balance toward warming.
Quiz: Earth’s energy balance and the greenhouse effect (Age 18)
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Without greenhouse gases, what would Earth’s average surface temperature be?
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What do greenhouse gases such as water vapour, CO₂ and methane do with the infrared heat rising from Earth’s surface?
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What happens when Earth takes in more energy than it radiates away to space?
The answers, each with its explanation, are in the app. This quiz is free there while the lesson is in the free week.
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