- Car windows are designed to pass Visible radiation for safety
- 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:
- Visible Light?
- 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.
- When its not cloudy, it is transparent to visible light radiation.
- 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.
Wed Jan 14 23:06:17 PST 1998