Climate change refers to variations over time in a number of factors that make up Earth's climate system.

The fundamental driver of this system is the sun, from which Earth receives continuous heat (and light). When this heat reaches the Earth’s atmosphere it can be reflected in the atmosphere or at the surface of the Earth and scattered back into space (step 2 below), or it can be absorbed by the atmosphere or surface of the Earth and enter the climate system (step 3) through what is known as the greenhouse effect (steps 4 and 5).