The Sun's radiation warms the Earth's surface, and the warm surface then radiates heat back towards space. Some gases in the atmosphere absorb part of this heat. These gases include carbon dioxide, methane and water vapour, and they are called greenhouse gases.
After a greenhouse gas absorbs heat radiated from the Earth, it releases the energy again in all directions. Some of this energy goes back down towards the Earth's surface, which keeps the Earth warm. This is known as the greenhouse effect.
The greenhouse effect is natural and useful. Without greenhouse gases the Earth would be much colder, and it would be too cold for most life as we know it.
