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Evaluate the nature and scale of climate change in the past 20,000
years up to the present day. (40 marks)
Climate change refers to the change in global temperatures and precipitation over
time due to natural variability or to human activity. It can be caused for a number of reasons
and has a wide variety of effects on the environment. 2 million years ago the last ice age
took place and since then there have been a series of glacial retreats and advances. The earth
has been through 2 different types of phases ice ages which are known as `glacial periods'
and periods where ice has retreated, known as `interglacial periods'.
The earth, 15,000 years ago experienced a warmer period where the ice sheets began
to retreat. Initially the temperatures were cool and there was low precipitation, in particular
over the poles. However, temperatures began to rise which causes the ice sheets to melt.
5,000 years later, (i.e. 10,000 years ago) the whole planet went through a cooling
phase where ice re-advanced causing periglacial conditions in the north of Britain.
Temperatures were around 7*c in summer and in winter around 0*c. Some parts of Scotland
was experiencing temperatures of -9*c. The cooling phase is known as the Younger Dryas
and it is believed that the transition between warming to cooling happened over a period of
a decade or so, but the onset may have been faster. Since then, the earth has not
experienced a period like this, to the size, extent or rapidity of the climate change.
Following the cooling phases the world underwent a period known as "Climatic
Optimum" where global temperatures were on average 1-3*c warmer than present. Britain
experienced temperatures of 2-3*c warmer than today. Hence, 8000 years ago the summers
in Britain were wet and the winters were cool and dry. This climatic optimum has never
happened and therefore is the warmest world temperatures ever.
6,000 years ago (4000BC) the planet underwent another phase of cooling as
temperatures dropped significantly and precipitation which was constant to begin with,
began to rise this period was known as neo-glacial.
In 450AD the planet experienced a mini climate optimum with worldwide
temperatures increasing which lead to the cultivation of grapevines in the south of England.
(Warm weather is needed for grapevines, hence why France and Spain produce a lot of wine).
The warm continental climate was however caused many storms and precipitation levels
were higher than normal.
More recently between 1430 and 1850AD a period named as the "Little Ice Age"
took places which affected parts of the world, in particular a large proportion of Europe. This
was the coldest period experienced since around 1250AD. It caused wine production to
come a halt immediately, forests to alter by replacing beech to oak and pine to withstand
the cold, fishing migrated southwards to escape the cold and the health of the UK got much
worse too. Furthermore the cold temperatures caused the River Thames to freeze over and
fairs were held on ice. Peter Bruegel painted a few images of the ice age illustrating the type
of weather which was experienced in Europe.
It is now believed that records began about 20,000 years ago and so from then on
the extent and scale of a warming or cooling period can be measured.
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Changes in sea level is one example as the presence of rias and fjords suggests rising
(eustatic) sea levels, flooding glacial and river valleys due to a warming of the climate.
Isostatic uplifts like the raised beaches in Scotland also show changes in the climate.
Glacial deposits show records of ice advancing during colder periods, e.g the varved
(layers of sediment) lake deposits of Lake Pickering in North Yorkshire. Glacial deposits are
composed of different amounts and shapes of till.…read more
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during the cooler autumn. The width of the ring depends on the conditions of each year. A
wide band indicates a warm and wet year, a narrower one is cooler and drier conditions.
Recent investigations on these two type of analysis have caused a changed in view. With sea
floor spreading the isotope variations are an indication of changes in volume of ice rather
than water temperatures but ice volume does reflect climatic conditions.…read more