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Predicting global climate change
It is very difficult to accurately predict the likely changes associated with global
climate change for many reasons.
Some of the likely changes might occur naturally anyway so it is difficult to tell
whether an event is caused by human actions or not. This change may be the
frequency with which events such as floods, storms or droughts occur and this is
often detectable after many years when the trend is clear. Individual storms, or
even several, do not indicate a trend.
It is often difficult to identify trends as there may be limited historical date on
factors such as rainfall patterns, extent of sea ice or wind velocity. Some
historical data cannot be trusted. Temperature records from towns may show
warming that is actually caused by an increase in the heat-island effect as the
town grows rather than a global temperature rise. Historical data may come
from indirect sources such as pollen analysis of lake sediment cores or tree
growth rings. It can be difficult to interpret these to accurately estimate past
Many natural processes are interconnected so one change may have unexpected
Some changes such as sea level rise are very slow. The cause of the change may have
been happening for a long time before any change is noticed.
Different changes may occur in different locations or at different times. If one area
gets less rain than another may get more. If Britain warms up then there may
be less rainfall in Summer as the water vapour does not condense but in winter
it is cold enough for condensation, and higher evaporation rates over the ocean
means that more rainfall.
A positive feedback mechanism occurs where the environmental change causes
other changes that increase the rate or amount of the original change and therefore
increase its effect. These may increase temperatures directly or increase the
concentration of gases that will cause further temperature rise. Raised
temperatures may cause the following:
Warming may increase the rate of decomposition, causing more carbon dioxide to be
released and therefore more warming.
Warming reduces the area of snow and ice on the ground or floating on the sea. This
reduces the albedo so less sunlight is reflected, solar heating is increased and
temperatures rise further.
Warming of the sea may eventually cause methane to be released from methane
hydrate in marine sediments. This would cause further warming.
Warming may cause forests and areas with peat soil to become drier. Fires may
occur more frequently and last longer, adding extra carbon dioxide into the
A negative feedback mechanism occurs where the environmental change causes
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Higher temperatures may cause increased rates of photosynthesis, which would
stores more carbon in biomass. Levels of carbon dioxide in the atmosphere
would be lowered, which would cause cooling.
Warming would increase evaporation and cause the formation of more low-level
cloud. This would increase the albedo, reflect sunlight away and reduce solar
Overview of the Kyoto Protocol (1997)
MEDCs that sign up to the treaty were legally bound to reduce their emissions of
6 greenhouse gases (collectively) by average of 5.…read more
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Chlorine and Ozone depletion
Halogens, especially chlorine in the stratosphere, cause ozone depletion in a range
A single chlorine atom is a chlorine radical because it has an unpaired electron.
This makes it very reactive.
A chlorine radical can react with an ozone molecule, breaking it down to leave an
oxygen molecule and chlorine monoxide.
The chlorine monoxide can then react with a monatomic oxygen atom to make
chlorine dioxide.…read more
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Why is ozone depletion greatest in Polar Regions?
The chemical reactions involving chlorine and ozone require UV B but occur most
easily at very low temperature when ice crystals form that provide catalytic surfaces.
During the Polar winter the temperature drop and allow the ice crystals to form,
but there is no sunlight. When spring arrives, the crystals still exist and the
sunlight causes the ozone-depleting reactions to take place.…read more