|
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.
The
atmosphere is an incredibly thin layer, extending to no more
than 500 kilometres above the surface.
 |
| Relative to
the Earth, the atmosphere is as thin as the skin of an
apple |
Its
protective layer is, relatively speaking, no thicker than
the skin on an apple.
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.
Water
vapour
Virtually
all the weather occurs in the lowest 15 kilometres, the troposphere.
The
principal components of the atmosphere are nitrogen (78%),
oxygen (21%), argon (1%).
Important gases present in smaller concentrations include
carbon dioxide (0.01 to 0.1%) and ozone (0 to 0.01%).
Water vapour is also present although its concentrations vary
greatly from 0 to 7%.
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 eight 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.
Global
warming
Some
of this heat is absorbed, some is reflected back to space
by clouds or the Earth’s surface itself.
Changing concentrations of carbon dioxide and other greenhouse
gases can close the atmospheric ‘window’ which allows the
excess heat to escape.
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.
Like
an apple, if you bruise the skin, you will soon damage what
lies beneath.
|
