What is global warming and evidence to support the theory

Notes on global warming and methods used to measure and support the theory.

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Al Hill 13.6
Global Warming
Is the increase in the worlds average temperature which has occurred in the 20th century, and according to
the IPCC (International Panel on Climate Change) there has been an increase of 0.74 +/ 0.18 degrees
during the 20th century which many believe is due to human activities. This is known as anthropogenic
climate change. However we must consider that since the earth's creation the average temperatures have
varied and there has been natural climate change with one example being carbon dioxide in sea water
dissolving and forming carbonate rocks.
The beginning of the human influence on the climate was at the beginning of the 19th century during the
industrial revolution, whereby countries developed through the growth of factories as well as the internal
combustion engine which affected the balance of the carbon cycle within the atmosphere. The industrial
revolution lead to an increase in the number of greenhouse being released such as methane and carbon
dioxide which are believed to have caused the `greenhouse effect'.
These green house gases reduce heat loss from the earth's surface as they prevent infra red radiation,
which has reflected off the surface, from leaving the atmosphere. Whilst some of this radiation does
penetrate through the green house gases as well as the ozone layer, more and more are becoming trapped
which is leading to a rise in the earth's temperature. On the other hand some scientists argue that the rise in
temperatures can be simply explained by the natural changes as mentioned earlier, and that we are just in a
hot period and it likely that temperatures will naturally cool as we return into an ice age.
The role of methane has had 72 times the effect on global warming than that of carbon dioxide over the
past 20 years, however much less has been produced. It sources are from the decay of some kinds of
bacteria, particularly in wet conditions and from the digestion of ruminant herbivores. An example of this is
in the production of rice, as the waterlogged paddies provide an ideal location for the bacteria to grow and
as the world's population is increasing the amount of rice being demanded is rising with it. In addition the
amount of meat has also increased which has lead to more methane being produced by cows which travel
up into the upper atmosphere where it will eventually form carbon dioxide and water.
Evidence for global warming
Dendrochronology is the dating of past events by using tree ring growth. Over time
tree's increase in width via cell division and when there is plenty of moisture and tree's
are growing quickly, then these new cells are large. However as conditions worsen the
new cells produced are smaller, and it is the contrast between the large and small cells
which give the appearance of rings. It could be suggested that if the rings are similar
then the climate experienced little changes, however there are many factors which affect
tree growth such temperature, light and many other examples. Therefore scientists need
to refine their methods as well as improving the reliability before dendrohronology can be
an accurate method of measuring climate change.
Peat bogs are made up of partly decomposing plant material which is acidic, cool and anaerobic which
prevent which prevents bacteria from decomposing organic materials. This therefore means that from
pollen grains to plant tissues are preserved, which allows scientists to see what was found in the area
thousands of years ago, and gives a reflection of what the climate was like. E.g. pollen from a horse
chestnut tree represents warmer conditions whereas pollen from birch tree's shows cooler conditions.

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Al Hill 13.6
Risks of global warming
Flooding has been one of the many threats linked to global warming, and with 100 million people living on
areas of land less than 1m above sea level, the effects of rising sea level could be catastrophic. The rising
temperatures have lead to ice, particularly in the Antarctic Peninsula, to melt which has lead to an increased
volume of water in the oceans.…read more

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