A warming world
Everyone's fascinated by the weather and people have been keeping track of air temperature for hundreds of years. There are local records for central England which go back to the mid-1600s.
Scientists can confidently estimate global average temperatures since 1850 based on historical observations. These show an unmistakable warming trend. The years from 1995 to 2006 included 11 of the 12 hottest years on record.
Warming can also be detected through its effects - such as the melting of glaciers and ice sheets.
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