Global warming and the greenhouse effect

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					Global warming and the greenhouse effect

There has been much publicity about Global warming and the greenhouse effect and it is
really important to understand what these words mean and what effect they may have on the
future of the planet.

We live as it were on a knife-edge as fart as the temperature of the planet is concerned. If
the Earth was closer to the Sun the temperature at the Earth‟s surface would rise and if it
was further away the temperature would fall.

Being too cold is as bad as being too hot. The Earth‟s atmosphere plays a vital part in
keeping the planet at a temperature where life as we know it can exist. Take the atmosphere
away and we would have temperatures like those on the Moon which has no atmosphere to
„protect‟ it. During the lunar night the equatorial temperature on the Moon‟s surface falls to -
184 oC while at mid-day it can rise to as much as 101 oC! Imagine these temperatures on the
Earth and you can see why the atmosphere is so important. It is changes in our atmosphere
that are of so much concern at present.

Venus is a planet much the same size as our Earth but only about two thirds of the distance
from the Sun. Because of this you would expect the surface temperature of Venus to be
higher than that on Earth. However Venus is covered with a thick atmosphere and it may
surprise you to find that the average temperature at the surface of the planet is a staggering
467 oC! Over 96% of this atmosphere is carbon dioxide with about 3% of nitrogen and minute
traces of water vapour, oxygen, carbon monoxide, helium, and sulphur dioxide.

Venus is an example of an extreme example of global warming and the greenhouse effect.

So what is the greenhouse effect and how can it contribute to global warming and should
we worry if it does?

During the day the radiation from the Sun falls on the surface of the Earth – the energy at
ground level is roughly 800 J per second on every square metre of the Earth‟s surface. This
radiation is spread over the wide range of wavelengths but because the Sun is a very hot
body (the surface of the Sun has a temperature of about 6000 oC) a lot of this radiation is of
fairly short wavelength. The Earth warms up so that the ground reaches say 20 oC at the
latitude of London. The ground the radiates some of this energy back into space but because
the surface of the Earth is so much colder than the surface of the Sun this radiation has a
much longer wavelength – much of it in the infra red region of the spectrum. It is this balance
between incoming radiation from the Sun and outgoing radiation from the Earth that keeps
the surface temperature of the planet stable and allows life to continue. Too much radiation
escaping from the Earth and we would freeze, too little and we would „fry‟! The atmosphere
absorbs some of this outgoing radiation and so helps to keep the planet „warm‟.

This is where the greenhouse effect comes in. The glass of a greenhouse acts just like the
Earth‟s atmosphere – allowing short wavelength radiation in from the Sun but preventing
some of the longer wavelength radiation from the ground from leaving – so the inside of the
greenhouse warms up.

Not all gases absorb infrared. The most important absorbers are the so-called "Greenhouse
gases" such as carbon dioxide, water vapour, methane, sulphur dioxide, nitrous oxide and
the chlorofluorocarbons (CFCs). At present some 100 000 million tons of carbon dioxide
every year are produced from biological processes. However people are now adding a
further 5000 million tons due to emissions from factories, cars and aircraft. This massive
extra amount of pollution is absorbing more of the outgoing radiation and so that planet is
warming up – global warming. In Britain we emit just over three tons of greenhouse gases

per person per year as compared with nearly seven tons per person per year by the people
of the USA.

The destruction of the rain forests removes a most important absorber of carbon dioxide -

The results of global warming may be a radical change in the climate of our planet and steps
must be taken to prevent this. The raising of the mean sea level due to the melting of the
south polar ice cap is just one effect, and this would result not only in the flooding of many
major cities that are sited at “sea level” but also the disappearance of low lying islands.

The following two photographs show the change in the Upsala glacier in Patagonia. The first
was taken in 1928 and the second in 2004.

                                        Archivo Museo Salesiano (top), Daniel Beltra, Greenpeace (bottom).

Storms and unseasonable temperatures have also been predicted.

A most useful source of information is:

If you want to see the effect of global warming vist the following site:

What can we do?
(a) Use nuclear power stations or renewable energy sources as an alternative to coal burning
power stations.
(b) Attempt to reduce the carbon dioxide emissions from all forms of transport.
(c) Try to preserve the forests of the planet especially the equatorial rain forests
(d) Attempt to recycle as much waste as possible by supporting recycling programmes

It remains to be seen just how accurate these prophecies are!

Concentrations of carbon dioxide in the atmosphere are naturally regulated by a number of
processes known as the “carbon cycle”. This is shown in the following diagram. You can see
that the balance of carbon in our atmosphere has been upset by the 6.3 billion tonnes
released due to the burning of fossil fuels.

                                    Atmosphere 730



                           Plant respiration
                           Residue decay                                         90            88

                                                                               Oceans 38 000

                                                  Soil and
   Fossil fuel burning                           vegetation
                                                   2000             Figures given are in billions of metric tons


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