Lisa Gardiner / Windows to the Universe
Energy from the Sun that makes its way to the Earth’s surface can have trouble finding its way back out to space. This is because of a natural process called the greenhouse effect. Without the greenhouse effect, Earth’s temperature would be below freezing. However, Earth’s greenhouse effect is getting stronger as we add more greenhouse gases to the atmosphere. And that is warming the climate of our planet.
Heat is radiated into the atmosphere from the Earth’s surface, which is warmed by sunlight. As the heat makes its way back to space, much of it is absorbed by greenhouse gases in the atmosphere. Greenhouse gases are more complex than most other gas molecules in the atmosphere, with a structure that can absorb heat. They radiate the heat back to the Earth’s surface, to another greenhouse gas molecule, or out to space.
Sometimes during this Century, the amount of the greenhouse gascarbon dioxide in the atmosphere is expected to double. Other greenhouse gases like methane and nitrous oxide are increasing as well. The quantity of greenhouse gases is increasing as fossil fuels are burned, releasing the gases and other air pollutants into the atmosphere. Greenhouse gases also make their way to the atmosphere from other sources. Farm animals, for example, release methane gas as they digest food. As cement is made from limestone, it releases carbon dioxide.
With more greenhouse gases in the air, heat passing through on its way out of the atmosphere is more likely to be stopped. The added greenhouse gases absorb the heat. They then radiate this heat. Some of the heat will head away from the Earth, some of it will be absorbed by another greenhouse gas molecule, and some of it will wind up back at the planet’s surface again. With more greenhouse gases, heat will stick around, warming the planet.
source : windows to the universe