The diagram below shows variations in global temperature over the past 100 years. Note that the y-axis shows the difference in degrees Celsius from the 1900 mean (average) temperature.
You may be asked to describe what a line graph like this shows. Broadly, this graph shows that the overall trend is a rise in global surface temperature from 1900 to 2000.
In more detail it shows:
Remember that the gradient of this line graph shows how quickly or slowly the temperature is changing - the steeper the slope, the faster the change.
The temperature varied due to a combination of physical and human factors.
Physical causes of global warming and cooling include:
These physical causes of global temperature change have always existed and have been responsible for alternate heating and cooling cycles of the earth's temperature.
The human causes of global warming have been in the news a lot in recent years - you can probably think of a few examples. Human factors are the result of growing population and economic developments.
These different greenhouse gases [greenhouse gases: The main greenhouse gases in the atmosphere are carbon dioxide, methane and nitrous oxide. They are naturally occurring in atmosphere, but are believed to have increased through burning more oil, petrol, and coal, while forests have been removed.] - carbon dioxide, methane, nitrous oxide - have caused an enhanced greenhouse effect [greenhouse effect: The build up of greenhouse gases, such as Carbon Dioxide [CO2], in the atmosphere, is believed retain more heat in the atmosphere than would usually be the case. Naturally more of the radiation (heat) from the sun would be reflected back into space.] , trapping some outgoing infra-red radiation and keeping the earth warmer than it might otherwise be.
Collectively, these physical and human causes have produced the pattern seen in the graph above.
See how the technology of satellite radar has enabled vast weather systems to be detected, mapped, monitored and forecasted.
How can the movement of sea water affect climate? Watch this clip from Learning Zone Scotland for an in-depth explanation of El Niño and La Niña.
Evidence of global warming
Environmentalist James Lovelock on global warming
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