First 418 words of the document:
Evidence for global warming
Since the 1850's temperature has been measured around the world using thermometers. This is very
reliable, but only a short term record of global temperature change.
Using tree rings to work out how old a tree is. Most trees produce one ring within their trunks every
year, and the thickness of the ring depends on the climate when the ring was formed, when it's
warmer the rings are thicker. Scientists can then date each ring and see what the climate was like for
each year. It cannot give very accurate results at all, just an estimate of the climate.
Pollen in peat bogs.
Pollen can be preserved in peat bogs, and they accumulate in layers, so the age of the pollen
increases with depth. Scientists can take cores and extract pollen grains to identify the species the
pollen came from, and this can give an estimate of climates, as only mature trees would produce
pollen, so the climate then would have to have been favourable for those trees.
Ice cores from the Antarctic is quite accurate. Air is trapped in the ice, and the proportions of
isotopes in the ice reflect the air temperature at the time that the layer was laid down. This data can
go back as far as 3000000 years.
Greenhouse gases, like carbon dioxide and methane contribute to the greenhouse effect. The
greenhouse effect is when radiation from the sun is reflected back from the earth as infrared
radiation, which is absorbed by the greenhouse gases in the atmosphere. This maintains the
temperature at a higher level.
However, with an increasing level of greenhouse gases, global temperatures are rising. Humans are
enhancing the greenhouse effect by burning fossil fuels, which produces carbon dioxide, and
destroying carbon sinks, like trees. Methane levels are also rising because of greater fossil fuel
extraction, and more decaying waste, as well as greater amounts of cattle for food, which give of
methane as a waste gas.
Some argue that the evidence does not prove that humans are the cause of global warming, because
the data is not that reliable before daily weather records, or they think the evidence was subject to
bias. Also, though there may be a correlation, this does not prove causation.
Other pages in this set
Here's a taster:
Rising temperature. This will affect the metabolism of all organisms, as enzymes denature
once past 40 decrees Celsius. It will also affect the distribution, as conditions in their habitat
may change, and they may not be able to survive the change, so will have to move out of
Changing rainfall patterns, some areas may get more rain, some may get less, this will affect
the lifecyles of some plants and distribution of species, e.…read more