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Related Article: History of climate change

Early in the twentieth century the prevailing notion was that people could alter climates locally, for example cutting down forests and ploughing fields, but not on a global scale.

A few pioneering thinkers suggested the increasing amount of pollution produced by Industrial revolution could cause global warming.

But it was not until the world started taking precise measurements of carbon dioxide from a mountain in Hawaii in the late 1950s that it was possible to confirm the link with a rise in temperatures.

Carbon dioxide and other gases such as methane make up a tiny part of the atmosphere but are key to keeping in the world’s heat, rather like the glass of a greenhouse.

As the gases increase more heat is trapped, like a blanket, causing the “greenhouse gas effect”.

Scientists have proved the theory by looking at 800,000 years of ice cores which show how much carbon was in the atmosphere and what the temperature was.

Computer models, that can account for changes in weather patterns and solar activity, have also been used to show the link between greenhouse gases and temperature rise. Thousands of scenarios have been run over a number of years in a ‘super computer’ to come up with the current predictions by the Met Office that global warming will continue unless carbon dioxide is brought under control.

The evidence became overwhelming two years ago after the Intergovernmental Panel on Climate Change issued a report by 152 scientists from 30 countries and reviewed by 600 experts that said global temperatures are increasing and it is very likely due to man made greenhouse gases.

Sceptics have pointed out that temperatures have gone down in recent years. This is due to weather patterns like El Nino that caused a very hot year in 1998 and a cooler year in 2008. However, according to the Met Office, the overall global trend has seen temperatures creep up by an average of 0.7 degrees since pre-industrial times and the gauge will keep on rising to 1.4C even if we stop polluting tomorrow. The UK has experienced 9 of the 10 warmest years on record since 1990. Natural variability will continue to bring warm and cool years but, because of climate change, the warm years will be warmer and more frequent.

Although the initial impact of global warming is a rise in average temperatures around the world it also causes changes in rainfall patterns, rising sea levels and a change in storm frequency.