Mon Prof Augmenté
How Earth Keeps Warm
Age 18 · Science
Open to everyone until Monday, November 16
To keep it, print it while it is open.
About 30% of the sunlight reaching Earth is reflected straight back to space by clouds, ice and bright surfaces, and the rest is absorbed and warms the ground and oceans. The warm surface gives off infrared radiation, and greenhouse gases such as water vapour, CO2 and methane absorb part of it and send it back down, keeping Earth about 33 °C warmer than it would be without them.
In the picture
- Incoming sunlight: mostly visible light that passes through the air
- Reflected sunlight: about 30% bounces off clouds, ice and bright surfaces back to space
- Infrared from the surface: the warmed ground and oceans give off heat as invisible infrared radiation
- Greenhouse gas molecules: they absorb infrared and send part of it back down to the surface
Examples
- A car parked in the sun gets hot inside because sunlight comes in through the windows, but the heat cannot leave as easily.
- A cloudy night stays warmer than a clear night because the clouds and water vapour send infrared back to the ground.
Key takeaways
- Without the natural greenhouse effect, Earth’s average temperature would be about −18 °C instead of about +15 °C.
- Adding more CO2 and methane traps more infrared, which shifts the energy balance and warms the planet.
Quiz: How Earth Keeps Warm (Age 18)
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About how much of the sunlight reaching Earth is reflected straight back to space by clouds, ice and bright surfaces?
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Without the natural greenhouse effect, what would Earth’s average temperature be?
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Why does adding more CO2 and methane to the atmosphere warm the planet?
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