The warming of the Earth’s atmosphere caused by increasing levels of gases, such as water vapour and carbon dioxide. These gases absorb radiation emitted naturally from the ground, so slowing down the loss of energy from Earth. The greenhouse effect has always existed; without it, Earth would be too cold for plants, animals and people to survive. But because of the increase in greenhouse gas emissions in recent years, the greenhouse effect is a lot stronger, so leading to global warming. See also global warming, greenhouse gases and radiation.

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Source: Environmental Protection Agency