It always helps to have some background scientific knowledge on climate change – it makes it easier to sort credibility and call people’s bluffs. I thought I’d give a brief explanation of the Earth’s energy balance, something that confused me for a long time.
All substances can absorb a certain amount of radiation – they must then emit or radiate it back out, usually in the form of long-wave radiation (heat). Some molecules, however, possess certain chemical properties which allow them to absorb (and therefore emit) an extremely large amount of radiation relative to their size. These molecules are called greenhouse gases. I recently asked a chem major exactly which properties determined this amount of absorption. They replied, “You don’t know enough quantum chemistry yet.”
When solar radiation, in the form of short-wave radiation (light), approaches our atmosphere, about 30% is reflected right off. The remaining 70% reaches the atmosphere and the Earth’s surface.
The surface of the Earth absorbs some of the radiation. It can’t hold onto this energy indefinitely (it wants to have room to absorb the next rays of light), so it emits it back out. Even though it received the radiation in the form of light, it emits it in the form of heat. It is this emission that determines the temperature of the Earth.
Greenhouse gases allow short-wave light to pass straight through the atmosphere, but they do absorb some of the long-wave heat that the Earth just emitted. The more greenhouse gases present, the more radiation the atmosphere, as a whole, can absorb. When atmospheric particles (greenhouse gases, in this case) emit this radiation back out, it goes uniformly in all directions. Some goes up and escapes out to space. But some goes down and hits the Earth’s surface again.
Therefore, the Earth has to absorb and emit some of the radiation twice. This increases the temperature of the Earth.