| 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 at a rate which cancelled most, but not 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.
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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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