The surface warming produced by enhanced greenhouse gas
concentrations leads to a vertical profile of atmospheric temperature that
actually reduces the temperature at the base of the stratosphere. So when
we use the term "global warming" we are referring to the earth's surface.
We might even then say that a cooling of the lower stratosphere might be
evidence of "global warming".
It is important to recognize that the energy the earth receives
from the sun is fixed, and the energy the earth re-radiates to outer space
is fixed. Global warming is a result of the redistribution of energy
within the earth/atmosphere/ocean system and not a result of gaining more
from the sun or losing less to outer space. In subsequent units we will
quantify the contributions to warming from the anthropogenic increases in
various greenhouse gases and other human factors influencing the energy
balance.
The greenhouse gases are not limited to some narrow layer as
suggested in the accompanying sketch but they are distributed quite
uniformly throughout the troposphere. Ozone, which is produced by solar
radiation in the stratosphere and by processes at the earth's surface, is
less uniform and has a peak concentration in the stratosphere.
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