What arrives and what leaves
Show on a big screenA tin roof is hot by afternoon. By night it is cool.
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The rule
The ground absorbs sunlight and sends out heat. Greenhouse gases hold part of that heat back.
Absorb means take in. Reflect means send back.
- Sunlight comes down through the air.
- The ground reflects some of it.
- The ground absorbs much of the rest and sends out heat.
- Greenhouse gases hold some of that heat back.
The idea
Sunlight does not all reach the ground. Clouds and air reflect some. They absorb some. The ground reflects some, and absorbs the rest.
The warm ground sends out heat as infrared rays. You cannot see them. This is how the surface loses heat.
At night no sunlight comes in. Warm surfaces still send out heat. So they cool.
Greenhouse gases include carbon dioxide, methane and water vapour. They absorb this outgoing heat and hold part of it back. So the heat leaves Earth more slowly. That keeps Earth warm enough for life.
| Part | What it does |
|---|---|
| Ground | Absorbs sunlight, then sends out heat |
| Greenhouse gases | Hold part of that heat back |
| Extra carbon dioxide | Holds back more heat, so Earth warms. This is global warming |
Try the lab to finish this lesson.