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Wednesday 24 December 2003
Climate change
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US scientists have reported that humans have had a significant influence on the earth's climate over the last ten thousand years. This report by Richard Black:
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Over timescales of thousands of year, the Earth goes through a natural cycle of warmer and colder periods, driven by changes in heat coming from the Sun. Professor William Ruddiman from the University of Virginia has now calculated that if the Earth had followed its natural cycle over the last ten thousand years, it ought to have got steadily colder. It hasn't because, he believes, human activities have been keeping the temperature steady.
"What should have happened with the natural climate is it should have cooled substantially. And instead humans just started adding greenhouse gases to the atmosphere at a rate which cancelled most, but not quite all, of that natural cooling; and so it's a combination of a natural cooling mostly cancelled by a human warming."
Our ancestors started adding the greenhouse gas carbon dioxide principally by cutting down trees for farming; whereas methane production started with wet farming of rice. Professor Ruddiman believes this ten-thousand year warming added almost a degree Celsius to the average temperature.
Listen to the words
timescales
periods of time set for development or completion of something
over timescales of
over time periods of
goes through a natural cycle
follows a pattern which has a regular rhythm
driven by
here, led by
steady
here, the same
cooled substantially
cooled by a large amount
greenhouse gases
gases which cause the earth's atmosphere to warm up. A greenhouse is a building made of glass used for growing plants.
ancestors
here, a general term meaning people who have lived on the planet before now
principally
mainly
wet farming
here, rice grown in water
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