Greenhouse Gases?

How do the greenhouse gases trap radiation?

• I'm not denying that greenhouse gases don't trap radiation but no one says anywhere HOW they do. Also what are the "greenhouse gases"? Is that just another way of saying CFCs?

• Answer:

  Great question. The major greenhouse gasses in Earth's atmosphere are water vapor (natural), and carbon dioxide and methane (natural but increasing due to human activity). There are a few others, in trace amounts, including CFCs, but these do not play a major role in the greenhouse effect. All matter - solids, liquids, and gasses - absorb and emit radiation at all wavelengths, however not equally at all wavelengths -- more at some and less at others, depending on temperature and chemical composition. The Sun's peak emissions, for example, are in the visible wavelengths, whereas the earth's peak emissions are in the infra red. Greenhouse gasses really don't "trap" radiation, per se. Instead, they are largely transparent in visible wavelengths, but absorb strongly in the infra red. Thus, greenhouse gasses, while largely transparent to incoming solar radiation, absorb a portion of the infra red radiation emitted by Earth's surface that would otherwise be radiated out into space. Retaining this additional energy in the Earth system shifts Earth's energy balance towards higher temperatures.