The temperature of the earth is directly related to the energy input from the Sun. Some of the Sun’s energy is reflected by clouds. Other is reflected by ice. The remainder is absorbed by the earth. If amount of solar energy absorbed by the earth is equal to the amount radiated back into space, the earth remains at a constant temperature. However, if the amount of solar energy is greater than the amount radiated, then the earth heats up. If the amount of solar energy is less than the amount radiated, then the earth cools down.