The earth receives almost all of the energy from the sun which in turn heats up the earth. Energy is then radiated in the form of infrared radiation from the earth out to the atmosphere. The greenhouse gases present in the atmosphere will then trap and return a portion of the heat radiating from the earth.

The greenhouse gases are able to trap heat because they are able to absorb infrared radiation due to them having more than two component atoms and the presence of polar bonds in the molecules. After absorbing the infrared radiation, it will cause the molecule to vibrate and thus warm the air around the molecule of the greenhouse gas. This repeated process causes the air to be heated up and also traps the infrared energy and thus causes the temperature of the earth to increase.