Carbon dioxide behind Greenland ice
Thursday, 28 Aug 2008 09:03
Scientists arrived at their findings by using state-of-the-art computer climate and ice-sheet models
UK scientists have speculated that a fall in atmospheric carbon dioxide caused an ice-sheet to form on Greenland three million years ago.
Rather than study the effects of global warming on the ice-sheet, researchers from the universities of Bristol and Leeds set out to determine why it came into existence in the first place.
"Evidence shows that around three million years ago there was an increase in the amount of rock and debris deposited on the ocean floor around Greenland," said Bristol University's Dr Dan Lunt, who published the team's findings in the Nature science journal today.
"These rocks could not have got there until icebergs started to form and could transport them, indicating that large amounts of ice on Greenland only began to form about three million years ago.
"Prior to that, Greenland was largely ice-free and probably covered in grass and forest. Furthermore, atmospheric carbon dioxide levels were relatively high. So the question we wanted to answer was why did Greenland become covered in an ice-sheet?"
After studying possible reasons for the formation of the ice-sheet – including changes in ocean circulation and tectonic uplift, the increasing height of the Rocky Mountains and changes in the Earth's orbit – the scientists concluded the only possible reason was a fall in atmospheric carbon dioxide levels to pre-industrial times.
The British Antarctic Survey-funded study arrived at its findings by using state-of-the-art computer climate and ice-sheet models.
While the results suggested that climatic shifts associated with changes in ocean circulation and tectonic uplift did affect the amount of ice cover, and that the ice waxed and waned with changes in the Earth's orbit, none of these changes were large enough to contribute significantly to the long-term growth of the Greenland ice sheet.
Dr Alan Haywood from Leeds University said greater understanding of why ice formed on Greenland three million years ago would help to predict the response of the ice-sheet to future climate change.
Dr Haywood added: "So why did elevated atmospheric carbon dioxide concentrations fall to levels similar to the pre-industrial era?
"That is the million dollar question which researchers will no doubt be trying to answer during the next few years."