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
escala de tiempo
Over timescales of
goes through a natural cycle
sigue un ciclo natural
en este caso, a un mismo nivel
gases de efecto invernadero
en este caso, arroz cultivado en agua