The greenhouse effect occurs when certain gases in the Earth's atmosphere (the air around the Earth) entraps infrared radiation. This makes the planet become warmer, similar to the way it makes a greenhouse become warmer.
The greenhouse effect is caused by greenhouse gases; the most important greenhouse gases in Earth's atmosphere are water vapor, carbon dioxide, and methane. When there is more greenhouse gas in the air, the air holds more heat. This is why more greenhouse gases cause global warming.
The greenhouse effect is natural. It is important for life on Earth. Without the greenhouse effect, the Earth's average temperature would be around -18 or -19 degrees Celsius (0 or 1 degree Fahrenheit). Earth would be locked in an ice age. Because of the greenhouse effect, the Earth's actual average temperature is 14 degrees Celsius (57 degrees Fahrenheit).
The problem is that recently, the greenhouse effect has become stronger. This is because humans have been using large amounts of fossil fuels, which release carbon dioxide when they are burned.

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