Some Sidetrips - The Greenhouse Effect I

• Car windows are designed to pass Visible radiation for safety reasons.

• It turns out that most glasses do NOT pass IR radiation.

• So, visible light from the 5200K Sun passes through the windows and is absorbed by the black leather interior of the car. The leather heats up to around 350K and radiates:
  1. X-rays?

  2. Visible Light?

  3. IR radiation?

• Since the glass is opaque to IR radiation, the energy in the original visible radiation gets trapped in the car and it gets hot in there!

The Greenhouse Effect II

• The Earth's atmosphere is alot like a glass window.

  1. When its not cloudy, it is transparent to visible light radiation.

  2. Some of the molecules in the atmosphere Absorb IR radiation - specifically CO .

• Just like the case of the car's interior, much of the visible light radiation from the Sun is absorbed by various things at the surface of the Earth. These things heat up and reradiate E-M radiation appropriate to their temperature. The temperature of the Earth is around 250K and its radiation spectrum peaks at around 11 m. Some of this radiation is trapped by the CO in the atmosphere and there is a net heating. As the CO content of the atmosphere goes up because of fossil fuel burning and deforestation, the amount of incoming radiation doesn't change, but the amount of trapped outgoing IR radiation increases. This is the cause of global warming. Is it happening? You bet.