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Miércoles, 31 de diciembre de 2003 - 02:55 GMT
Cambio climático
Glaciares

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:

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.

Richard Black, BBC

timescales
escala de tiempo

Over timescales of
por períodos

goes through a natural cycle
sigue un ciclo natural

driven by
impulsado por

steady
en este caso, a un mismo nivel

cooled substantially
enfriado sustancialmente

greenhouse gases
gases de efecto invernadero

ancestors
ancestros

principally
principalmente

wet farming
en este caso, arroz cultivado en agua



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