Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: [Phys-l] Albedo and GW.

-----Original Message-----
From: [mailto:phys-l-] On Behalf Of Larry Woolf
Sent: Monday, September 04, 2006 2:59 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] Albedo and GW.

Dry air is nearly transparent, in the IR as well as visible. You can
verify this for yourself by walking around in the high desert at night:
exposed to the sky feels cold, even if the air is not particularly cold.


Air has windows of transmission in the IR; some regions are quite opaque:

It is true that the wavelength range where room temperature bodies emit
most of the IR (7.5-13 microns), air is quite transparent.

This is a very important point. As Larry points out, CO2 in dry air absorbs
very differently than H2O in moist air. It has narrow bands in which IR is
totally blocked and adjacent bands which are almost totally transparent. In
the desert at nighttime or in the shade, your skin therefore feels very cool
because of the many transparent regions of the CO2 IR absorption spectrum.

Doubling the amount of CO2 therefore has little effect on the IR transmitted
to space or reradiated back to earth. Changing the H2O content of air
results in significant changes in the IR budget. That is why many are
skeptical that the observed small climate changes over the last half century
are human induced. If models simply parametize, instead of carefully
reproducing the CO2 absorption spectrum, they will exaggerate the effects of
increasing the CO2 content of the atmosphere.

Bob at PC