Earth's temperature depends on the balance between energy entering and leaving the planet’s system. When incoming energy from the sun is absorbed by the Earth system, Earth warms. When the sun’s energy is reflected back into space, Earth avoids warming. When absorbed energy is released back into space, Earth cools. Many factors, both natural and human, can cause changes in Earth’s energy balance, including:
Variations in the sun's energy reaching EarthChanges in the reflectivity of Earth’s atmosphere and surfaceChanges in the greenhouse effect, which affects the amount of heat retained by Earth’s atmosphereThese factors have caused Earth’s climate to change many times.