Page last updated at 12:48 GMT, Friday, 14 November 2008

Climate change 'to halt ice age'

Current ice coverage in north America
Polar ice would spread further south in the next ice age

A new model of the Earth's climate suggests that human-made carbon dioxide emissions may prevent the onset of the next ice age.

Based on geological history, the Earth would be expected to enter a new ice age in 10,000 to 100,000 years.

Researchers say even small changes in carbon dioxide levels right now could prevent this from happening.

They tell the journal Nature this may not be good news as the planet could change in ways that are unprecedented.

Man made change

The scientists say that over the past 400,000 years, sea temperature and ice coverage have been more variable than before.

This variation is a sign of the climate changing from one state to another, and signals the coming of an ice age.

Professor Thomas Crowley who developed the new model at Edinburgh University, UK, says this natural event might be postponed or even prevented by human-induced changes - especially the CO2 emissions from industrial processes.

"In the last 100,000 years, global CO2 levels increased by around 1.5 parts per million - but now we put out this much every year. The natural process is 100,000 times slower than the way humankind is changing CO2 levels," he says.

Averting catastrophe

The researchers looked at variations in oxygen levels in the shells of tiny sea creatures found in samples taken from the world's ocean beds. When combined with data on past sea levels, these give an estimate of global temperatures and sea-ice cover for the past three million years.

Professor Crowley warns against seeing increases in carbon dioxide levels as a good thing and adds that we might end up with a planet completely different from anything we've ever known.

"It doesn't mean we've averted catastrophe. A rise of just three to five degrees will give us temperatures unheard of for 50 million years - but at that time the world was a different place, with no ice caps.

"This time round, we are raising the temperature at such a rate that we may create a different world, a non-glacial atmosphere with polar ice sheets."

Rapid increases in global temperatures may not initiate immediate rapid polar ice melting, say the scientists; and there is no past geological evidence to indicate how a polar ice cap might behave if sitting on a warmer world.

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