Environmental Engineering Reference
In-Depth Information
very much alike in composition, but very different in
surface temperatures because of the greenhouse effect.
Venus is too hot to support life, and Mars is too cold.
Yet all were formed about
billion years ago, and all are
made from the same stuff. The difference lies in their
greenhouse effects: too much for Venus, too little for
Mars, and just right for us.
The climate greenhouse effect is different in detail, but
not in principle, from that which allows tomatoes to be
grown in winter under a transparent roof. In the plant
greenhouse, the transparent double-paned roof lets in
sunlight and traps the heat that would otherwise escape.
In the atmospheric greenhouse, greenhouse gases trap
heat that would otherwise be radiated out into space. This
is not complicated in principle, though it is complicated to
calculate the surface temperature in the real world with
precision (something that will be discussed later). Human
activity that changes the greenhouse effect and traps more
heat drives the concern about global warming. Even
among the anti-green lobby there is no argument about
the reality of the greenhouse effect, only about how
human activity is changing it.
Our planet
.
is average temperature is determined by a
balance that is struck between the energy coming from
the Sun and the energy radiated back out into space.
What comes in depends on the temperature of the Sun,
and what goes out depends on the Earth
'
s surface tem-
perature and on what things in the atmosphere block parts
of the radiation. Think of it this way
'
what comes in from
the Sun is almost all in the form of ordinary visible light.
What goes out is mostly in the form of infrared radiation
which we can
-
'
t see but can certainly feel. If you have ever
