Global Warming Gases

Lorek

Random question that came up in conversation today and my friends and I were unable to deduct an answer.
Best I can come up with is that this situation is more complicated then it sounds and something is lost when saying it in layman's terms, but maybe someone here can explain this to me..

I'm told one of the major causes of global warming is the build up of various gases like carbon dioxide in the atmosphere, and this causes heat reflecting off the planets surface to basically "insulate" the planet. What I was wondering was why doesn't this cause also stop heat from the sun from passing through this layer of gas and getting to the planet in the first place? I would think this would even it out, or at least lessen the impact somewhat, but I can think of no way for heat to come in one way but not go out the other...

Deebaser

Greenhouse gases are almost transparent to solar radiation but strongly absorb and emit infrared radiation. Thus, greenhouse gases trap heat within the surface-troposphere system

(wikipedia)

Chanus

It's Wikipedia... but it's pretty comprehensive about the theories:

http://en.wikipedia.org/wiki/Global_warming

http://en.wikipedia.org/wiki/Greenhouse_gas

Steel Angel

Lorek wrote: »

I'm told one of the major causes of global warming is the build up of various gases like carbon dioxide in the atmosphere, and this causes heat reflecting off the planets surface to basically "insulate" the planet. What I was wondering was why doesn't this cause also stop heat from the sun from passing through this layer of gas and getting to the planet in the first place? I would think this would even it out, or at least lessen the impact somewhat, but I can think of no way for heat to come in one way but not go out the other...

From what I remember a chemist friend saying, some gasses do exactly that. But by definition, that would make them a non-greenhouse gas.

Dalboz

Deebaser wrote: »

Greenhouse gases are almost transparent to solar radiation but strongly absorb and emit infrared radiation. Thus, greenhouse gases trap heat within the surface-troposphere system

(wikipedia)

This is for the most part true. It has to do with the elecrtomagnetic spectrum. The sun doesn't give off energy in the entire EM spectrum evenly. Basically, high energy radiation can pass through, but low energy radiation cannot. When the high energy radiation (light, in this case) passes through the atmosphere and bounces off the surface of the earth, the energy levels lower, and you wind up with more infrared radiation, which cannot escape back through. That's why one of the other reasons for global warming/climate change is the reduction in energy absorbing surfaces (i.e., more paving and reflective rooftops). Ground covered by vegetation absorbs more energy, while paving reflects it. That's why developed areas in particular have gotten hotter faster.

This is a bit of an oversimplification, but it's the basic idea.