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The
Earth is surrounded by a layer of air that we call the atmosphere.
Without the atmosphere there would be no life on Earth and, worse,
no weather!
Amongst
its many functions the atmosphere protects us from ultraviolet radiation
from the Sun; it recycles water and it moderates the electrical
and magnetic forces that act upon the Earth.
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| The
atmosphere extends no further than 500km above the earth's surface |
And
yet, the atmosphere is an incredibly thin layer, extending to no
more than 500 kilometres above the surface.
Its
protective layer is, relatively speaking, no thicker than the skin
on an apple. Yet without that layer it would, like the apple, soon
go ‘bad’.
There
are four parts to the atmosphere; the troposphere, stratosphere,
mesosphere and the ionosphere. Virtually all the weather occurs
in the lowest 15 kilometres, the troposphere.
The
principal components of the atmosphere are nitrogen (78 per cent),
oxygen (21 per cent), argon (1 per cent). Important gases present
in smaller concentrations include carbon dioxide (0.01 to 0.1 per
cent) and ozone (0 to 0.01 per cent). Water vapour is also present
although its concentrations vary greatly from 0 to 7 per cent. But
of course, it is the water vapour that provides us with our weather.
The
weight of all those gases is considerable. In fact the air exerts
a pressure which is usually sufficient to support a column of mercury
30 inches tall. So the pressure on top of, say, the Clifton Suspension
Bridge is about 8 millibars lower than it is on the Portway beneath.
The
composition of gases within the atmosphere is finely balanced. The
atmosphere is largely transparent to incoming heat radiation from
the sun. Some of this heat is absorbed, some is reflected back to
space by clouds or the Earth’s surface itself. But changing
concentrations of carbon dioxide and other greenhouse gases can
close the atmospheric ‘window’ which allows the excess
heat to escape.
The air exerts a pressure which is usually sufficient to support
a column of mercury 30 inches tall. So the pressure on top of,
say, the Clifton Suspension Bridge is about 8 millibars lower
than it is on the Portway beneath. |
| Richard
Angwin |
The
result is global warming and unless this issue is addressed by governments
in a serious and concerted way then major changes in the world’s
weather patterns are only a generation away.
Some
of the most potent and long-lived greenhouse gases, such as CFCs
and HCFCs are the result of industrial processes.
These
same gases are also having a destructive effect on the ozone layer.
Ozone molecules are made up of three oxygen atoms. As CFCs break
down in the upper part of the atmosphere they release chlorine.
It
is the chlorine which acts to break up the ozone molecules. The
resulting ozone depletion has been monitored for many years and
increasing levels of ultra-violet radiation can have serious implications
for human health.
We
take our atmosphere for granted. We pollute it with noxious chemicals
and yet we still expect it to perform with the utmost efficiency.
But like an apple, if you bruise the skin, you will soon damage
what lies beneath.
by
Richard Angwin
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