Acid Rain
Fossil fuels such as coal, oil and natural gas were formed from living organisms.
When they are burned, they release sulphur and nitrogen into the air, which
combine with oxygen to form sulphur dioxide and nitrogen oxides.
Sulphur dioxide can damage the breathing system of humans, and is also poisonous
to many plants.
Sulphur dioxide and nitrogen oxides dissolve in rain, making it acidic (with a pH as
low as 4).
Acid rain damages plants because it affects the soil in which they are growing,
washing out ions that the plants need to grow. It can wash aluminium ions from the
soil into lakes, where it affects the gills of fish and therefore poisons them.
The acid rain also makes the rivers and lakes acidic, so plants and animals that
usually live there cannot survive.
Acid rain often affects areas a long way from where the sulphur dioxide is
originally released, as it is carried high in the air for long distances. Coal burning
power stations in Britain have produced acid rain that has affected trees in
Norway.
Acid rain can be reduced if the number of coal burning power stations can be
reduced. These gases are also produced by the burning of petrol in car engines,
but can be removed by catalytic converters fitted to the exhaust system.
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Greenhouse effect
The earth’s atmosphere contains several different gases that trap heat energy,
keeping the earth warm.
Carbon dioxide allows radiation from the sun to warm the earth, but when the
ground re-emits this radiation, some of it is trapped in the atmosphere. This is
called the greenhouse effect because the carbon dioxide behaves like the glass in
a greenhouse.
There are concerns that this effect is increasing, as the amount of carbon dioxide
and other greenhouse gases (such as methane and CFCs) have increased.
Carbon dioxide is released into the atmosphere by the burning of fossil fuels by
industry and in vehicle engines.
Large scale deforestation (cutting down of trees) in areas such as the rainforests
also increases the release of carbon dioxide into the atmosphere. This is because:
 Trees are burnt, releasing carbon dioxide.
 Trees are broken down by microbes, which release carbon dioxide in
respiration.
 Trees remove carbon dioxide from the atmosphere by photosynthesis,
keeping it “locked-up” as wood – if the trees are cut down this doesn’t
happen.
Methane is released into the atmosphere by bacteria which live in rice fields, and
by cattle.
The possible effect of these extra greenhouse gases is to increase the
temperature of the Earth – this is called global warming.
If this did happen, it could cause changes in the climate – for example some areas
could become deserts or there could be an increase in storms. It may also cause a
rise in sea level if the ice caps at the North and South poles melt.
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