Environmental Engineering Reference
In-Depth Information
Technical Note
.
: (cont.)
The main gases in our atmosphere are overwhelmingly
oxygen and nitrogen. These absorb very little at the
important wavelengths. The absorption spectra for oxygen
and ozone are shown in the
figure. Ozone is responsible for
the total absorption of ultraviolet radiation below wave-
lengths of
micron. The peak of the incoming radiation
falls at a wavelength where there is practically no absorption.
The absorption spectra of water vapor and carbon dioxide
are complex and cover much of the wavelength range of the
outgoing black-body radiation. They block a large part of
the spectrum. Note that where the absorption is already
.
%, adding more of the gas to the atmosphere cannot
change the peak absorption value. What does change is the
absorption in regions where it is not at
%. There, adding
more will block more. Part (b) of the
figure is the total
absorption of all the major greenhouse gases, and is very
complex. It does not include other minor greenhouse gases,
and the data that go into it are from the
s when the
carbon dioxide level was lower than it is today.
Calculating the response of the climate to a change in
greenhouse gases is by its nature complicated. The absorp-
tion spectra are complex and include what are called feed-
back effects (changing one thing changes something else)
that will be discussed later. The direction of change can be
calculated relatively simply, but for a precise answer, the
biggest computers are required to do it numerically.
for everything totals only about
GW at the daytime
peak in usage on a hot summer day.
It is simple to calculate roughly our planet
is surface
temperature if there were no greenhouse effect at all,
though it is complicated to calculate what happens in
the real world. With no greenhouse effect, none of the
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