Environmental Engineering Reference
In-Depth Information
stood in front of an old-fashioned hot stove, you can feel
the radiation coming from it though you cannot see it.
This radiation is what is partially blocked by greenhouse
gases and the temperature has to go up to let enough heat
out through that part of the radiation window that
remains open to balance what comes in from the Sun.
Carbon dioxide (CO
) is the gas most discussed. It is
the main human-caused (anthropogenic) contributor, but
it is not the only one (more about the others in
Chapter
).
What is a surprise to most people is that none of the
human-caused gases contributes as much to keeping our
planet warm as ordinary water vapor. (See
Technical
Note
if you are interested in more of the science of
the greenhouse effect.)
Although the Earth has a core of molten iron, in our
planetary greenhouse over
.
% of the energy reaching
the surface of our planet is sunlight. Rock is a very good
insulator and a relatively small amount of heat from the
interior reaches the surface. Glowing rivers of molten
rock do come from volcanoes, but they cover a tiny
fraction of the surface of our world and so contribute very
little to the surface heat. What comes in is sunlight; what
leaves is radiated heat called infrared radiation. We can
ignore all the rest.
The total power incoming from the Sun dwarfs every-
thing made by humans. The energy that comes in on the
sunlit side of the Earth in one hour equals the total of all
forms of energy used by humankind in one year. Sun
power totals about
.
million gigawatts (
GW equals
billion watts), equivalent
to the energy output of
million large electricity generating plants. All the
electrical power used in the United States by everyone
