CLIMATE CHANGE - the greenhouse effect.

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EVIDENCE FOR CLIMATE CHANGE
Temperature records over long periods. Since the 1850s temperatures have been measured using
thermometers giving a reliable and short term record of global temperature change.
Studying Peat bogs Peat is an accumulation of partially decayed organic matter,
mainly the remains of dead plants. In the anaerobic and often acidic conditions of a peat bog, the decay rate is slowed or stopped altogether.
Pollen grains are particularly well preserved in peat (due to tough outer layer) which is useful for reconstructing past climates because:
Each species of plant has a distinctive type of pollen, allowing us to identify the plant species from which it came.
Peat forms in layers: the deeper the layer the older the peat. Carbon-14 dating allows the age of a particular peat layer to be
established.
Each species of plant has a particular set of ecological conditions in which it flourishes best. If we find pollen from a species favouring
warmer conditions, we can infer that the peat was laid down when the climate was warmer.
Dendrochronolgy (tree ring analysis) Every year, trees produce a new layer of xylem vessels by the division
of cells underneath the bark. The diameter of the xylem vessels varies accordingly to the seasons when they are produced. Scientists can take
core samples from trees and then date each ring by counting them back from when the core was taken. By looking at the thickness of the
rings they can see what the climate was like each year.
The Greenhouse Effect:
1. The Sun radiates energy, largely as visible light, and the Earth absorbs some of this energy.
2. The Earth warms up and in turn radiates energy back into space as infrared radiation.
3. Some of this energy that is radiated is absorbed by gases in the atmosphere, warming it.
The gases in the atmosphere that are stopping the infrared are the greenhouse gases.
However, anthropogenic sources of greenhouse gases e.g. from burning fossil fuels, farming and deforestation are enhancing the green
house effect causing a rise in average global temperature.
METHANE: produced by anaerobic decay of organic matter in waterlogged conditions, for example in bogs and rice fields. Decay of
domestic waste in landfill and animal waste are other sources of methane. Produced in digestive system of animals e.g. cows which are
released when they belch or fart. Incomplete combustion of fossil fuels also releases methane.

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There is massive stores of methane e.g. in permafrost ­ as temperatures increase these stores will thaw and release large amounts of
methane into the atmosphere.
A molecule of methane absorbs more infrared than CO2 however it doesn't stay in the atmosphere very long.
CO2: concentrations increase as more fossil fuels are burnt. The destruction of natural sinks of CO2 also increases concentrations e.g.
deforestation as the trees store carbon as organic compounds.…read more

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