The greenhouse effect — Geography, 11–13
How gases in the atmosphere keep Earth warm, and why extra greenhouse gases change the balance.
The idea
Sunlight warms Earth’s surface, which then sends energy back upward as invisible infrared radiation. Greenhouse gases, including carbon dioxide, methane and water vapour, absorb some of that radiation and send it in different directions, including back down. This natural blanket keeps Earth much warmer than it would otherwise be.
Why this matters
Scientists needed this explanation to solve a puzzle: why does Earth have a temperature suitable for liquid water instead of being frozen? The same idea explains why adding greenhouse gases can warm the planet. Burning fossil fuels, clearing forests and some farming practices increase these gases, strengthening the natural effect.
A worked example
Earth’s average surface temperature is about 15°C. Without the natural greenhouse effect, scientists estimate it would be about −18°C. The difference is 15 − (−18) = 33°C, showing why the effect is essential. Adding more greenhouse gases does not create the effect from nothing; it makes it harder for heat to escape.
The common trap
A reasonable mistake is to call the greenhouse effect itself bad. The word can sound like a glass greenhouse trapping all heat, so it is easy to confuse the natural effect with present-day global warming. The natural effect is necessary; the problem is the extra strengthening caused mainly by human activities.
Where it is used
This idea helps geographers explain changing temperatures, compare emissions from activities and plan responses such as insulation or lower-carbon transport. Climate models use it to test how the atmosphere may respond to different amounts of greenhouse gases. You meet it when judging claims about heating, energy or climate evidence.
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