What Caused Greenland's Ice Sheet?
Posted on: Friday, 29 August 2008, 08:55 CDT
Only changes in carbon dioxide levels are able to explain the transition from the mostly ice-free Greenland of three million years ago, to the ice-covered Greenland of today
There have been many reports in the media about the effects of global warming on the Greenland ice-sheet, but there is still great uncertainty as to why there is an ice-sheet there at all.
Reporting yesterday (28 August) in the journal Nature, scientists at the University of Bristol and the University of Leeds show that only changes in atmospheric carbon dioxide are able to explain the transition from the mostly ice-free Greenland of three million years ago, to the ice-covered Greenland of today.
Understanding why the ice formed on Greenland three million years ago will help understand the possible response of the ice sheet to future climate change.
Dr Dan Lunt from the University of Bristol and funded by the British Antarctic Survey, explained: "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. 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?"
There are several competing theories, ranging from changes in ocean circulation, the increasing height of the Rocky Mountains, changes in the Earth's orbit, and natural changes in atmospheric greenhouse gas concentrations. Using state-of-the-art computer climate and ice-sheet models, Lunt and colleagues decided to test which, if any, of these theories was the most credible.
While the results suggest 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.
Instead, the new research suggests that the dominant cause of the Greenland glaciation was the fall from high atmospheric carbon dioxide levels to levels closer to that of pre-industrial times. Today concentrations are approaching the levels that existed while Greenland was mostly ice-free.
Dr Alan Haywood from the University of Leeds 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."
The paper: 'Late Pliocene Greenland glaciation controlled by a decline in atmospheric CO2 levels', by Daniel J. Lunt, Gavin L. Foster, Alan M. Haywood, and Emma J. Stone. Nature, 28 August 2008, doi:10.1038/nature07223.
This work was carried out in the framework of the British Antarctic Survey Greenhouse to ice-house: Evolution of the Antarctic Cryosphere and Palaeoenvironment programme. Dan J.Lunt is funded by British Antarctic Survey and Research Councils UK fellowships. Gavin L. Foster is funded by a NERC research fellowship. Emma J Stone is funded by a NERC studentship.
---
Image 1: This image of South Greenland was acquired on 16 February 2006 by Envisat's Medium Resolution Imaging Spectrometer (MERIS), working in Reduced Resolution mode. Credits: ESA
Image 2: Computer models show that while (tectonic) uplift of the Rocky Mountains may have contributed to increased ice cover on Greenland, this change was small in comparison with the ice sheet caused by a decrease in carbon dioxide. Credit: Dan Lunt, University of Bristol
---
On the Net:
Related Articles
- Last Time Carbon Dioxide Levels Were This High Was 15 Million Years Ago
- Carbon Dioxide Levels Rising Despite Economic Downturn
- Laser Test To Measure Atmospheric Carbon Dioxide
- Carbon Dioxide Levels Already in Danger Zone
- Decreased Soil Organic Matter Caused By Increased Atmospheric Carbon Dioxide
- Tenaska Proposes Nation's First New Conventional Coal-Fueled Power Plant to Capture Carbon Dioxide
- Hella Reduces Carbon Dioxide in Automotive Lighting, Electronics
- Carbon Dioxide in Atmosphere Increasing
- Recent Duke Study Links Global Warming, Increased Carbon Dioxide Levels With Poison Ivy Perils
- Study Yields Mixed Results on Potential for Pine Trees to Store Extra Carbon Dioxide
 |
 |
User Comments (1)
| 1. |
Posted by George becker on 08/31/2008, 18:42 I have read that the Panama isthmus closed about 3 million years ago which dramatically changed ocean currents and global weather patterns eg. drying out east Africa. My guess is that it also effected CO2 levels somehow. I think major climate changes follow major geology changes. |
RSS Feeds