Plants in a glass house in the hills stay warm in the cold. Using this idea, explain why the Earth's average temperature is rising, which gases and human activities are to blame, and what harm the warming does.

1. 1 · Define. The greenhouse effect is the trapping of the Earth's heat by certain gases in the atmosphere, like the glass of a greenhouse.
2. 2 · How it works. Sunlight warms the Earth; the warm surface gives out heat as infrared rays; greenhouse gases stop this heat escaping.
3. 3 · Gases and sources.
   • CO₂ from burning coal, petrol and wood, and from deforestation.
   • Methane (CH₄) from plant-eating animals such as cattle.
   • Nitrous oxide (N₂O) from nitrogen fertilisers and industry.
4. 4 · Global warming. More of these gases trap more heat, so the Earth's average temperature keeps rising.
5. 5 · Effects.
   • Glaciers and snow caps melt; sea level rises; low islands such as the Maldives may go under water.
   • Weather becomes unpredictable.
   • Crops ripen early with smaller grains and lower yields; some fish eggs fail to hatch.
6. 6 · Draw it. [Diagram: sun's rays entering the atmosphere; heat from the Earth sent back down by a layer of greenhouse gases; labels CO₂, CH₄, N₂O]
7. 7 · Real life. Planting trees and saving fuel cut the CO₂ we add.
8. 8 · Close in one line. So the greenhouse effect, made stronger by human activity, causes global warming.

Scoring tip: Name at least two greenhouse gases with their formulas, and give three effects.