Life
on Earth depends on greenhouse gasses.
Without any greenhouse gasses in our atmosphere the Earth would be extremely cold. The Earth is not the only planet in the
solar system with significant amounts of
greenhouse gasses in its atmosphere.
Venus has so high a
concentration of greenhouse
gasses that the planet is extremely hot. Venus is even hotter than it
would
otherwise be, although it is close enough to the Sun to be pretty
warm
anyway.
Mars
has Carbon Dioxide, Methane,
and Water Vapor
in its rather thin atmosphere.
Mars is producing Methane. We
do not know if it is being produced by micro-organisms or by volcanic
activity.
Titan
has several greenhouse gasses in its atmosphere.
These particularly include Methane.
This Moon is much warmer than it would be without any greenhouse
gasses.
On Earth, the most important of the
greenhouse gasses is water vapor.
This
contributes, probably, over half of the total effect of greenhouse
gasses. Carbon Dioxide is responsible for
about one fifth of the
greenhouse gasses effect, and Methane probably
about half as much as
the Carbon Dioxide.
There are several other greenhouse gasses,
including Ozone, and some
largely man made ones like the
Hydrofluorocarbons.
The
amount of Water
Vapor
in the atmosphere
depends largely on its
temperature. Warm air can hold
more than cold
air, so a temperature rise from other things will be
increased by the
increasing amount of Water Vapor.
Carbon
Dioxide has increased from about 280 parts per million (ppm) to about
390 ppm since the industrial
revolution started.
Methane
has increased from about 700 parts per billion (ppb) to about 1700
ppb.
There
are many other greenhouse gasses that have increased from zero or very
low levels to measurable amounts.
One of the many things we do not know is what
temperature
is necessary to provoke a runaway greenhouse effect as
described in
the Methane
Gun.
Steve Challis
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