The Atmosphere and Climate Modeling - Introduction to Carbon Capture and Sequestration - page 52

Figure 2.2.2 also illustrates that the energy balance in the atmos-
phere is quite complex, as different mechanisms contribute to the tem-
perature of the surface of the earth. That these effects are often
counterintuitive can be illustrated with the following example. Suppose
we were to eliminate all clouds in the atmosphere; would this increase or
decrease the temperature of the earth? Clouds have two effects: they
refl ect the radiation from the sun, and they contribute to the greenhouse
effect. The latter effect is something we have experienced; nights are less
cool if the night sky is cloudy. Despite these local effects, the net balance
is that the cooling effect of clouds is larger than their heating effect.
Section 3
The atmosphere
Let's consider the atmosphere in more detail. Figure 2.3.1 gives an illus-
tration of the different layers of the atmosphere. From the pressure and
density curves we see that a substantive gas layer around the earth
extends into the stratosphere. It is this gas layer that is responsible for
the greenhouse effect.
Absorption of radiation by the atmosphere
An interesting question is hidden in the results of the last section. We
have seen that because of the greenhouse effect the radiation from the
earth gets refl ected back to the earth, but the radiation from the sun does
not get refl ected back in the same proportion. How is this possible? How
does the atmosphere differentiate between the radiation from the sun
and that from the earth?
To answer this question we need to know the difference between the
radiation from the sun and the radiation emitted by the earth. The sun has
a higher temperature and therefore emits radiation at a shorter wave-
length compared to radiation emitted by the earth (according to the
blackbody radiation law). The radiation from the sun is in the ultra-violet