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 on 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.
The University of Bristol was founded in 1876 as University College, Bristol. It was the first higher education institution in England to admit women on an equal basis with men. The University is internationally distinguished, a world leader in research, a member of the Russell Group and of the Worldwide Universities Network. It has around 12,500 undergraduate and 3,500 postgraduate students and organises its academic affairs in six faculties with some 45 departments and 15 research centres.
In the 2001 Research Assessment Exercise, 15 of the University's units of assessment achieved the top grade of 5* and a further 21 were awarded grade 5. Thus 36 (78 per cent) of the 46 units of assessment were judged as world class or of international standing. Seventy-six per cent of the academic staff work in departments ranked at these levels. For further information, please see our website: www.bristol.ac.uk
British Antarctic Survey (BAS) is a world leader in research into global environmental issues. With an annual budget of around £45 million, five Antarctic Research Stations, two Royal Research Ships and five aircraft BAS undertakes an interdisciplinary research programme and plays an active and influential role in Antarctic affairs. BAS has joint research projects with over 40 UK universities and has more than 120 national and international collaborations. It is a component of the Natural Environment Research Council. More information about the work of the Survey can be found at: www.antarctica.ac.uk
The University of Leeds is one of the largest higher education institutions in the UK with more than 30,000 students from 130 countries. With a turnover of £450m, Leeds is one of the top ten research universities in the UK, and a member of the Russell Group of research-intensive universities. It was placed 80th in the 2007 Times Higher Educational Supplement's world universities league table and the University's vision is to secure a place among the world's top 50 by 2015. www.leeds.ac.uk
Issued by: Public Relations Office, Communications and Marketing Services, University of Bristol. Contact: Cherry Lewis, Research Communications Manager. Tel: 0117 928 8086, mob: 07729 421885, email: Cherry.firstname.lastname@example.org
Cherry Lewis | EurekAlert!
Global study of world's beaches shows threat to protected areas
19.07.2018 | NASA/Goddard Space Flight Center
NSF-supported researchers to present new results on hurricanes and other extreme events
19.07.2018 | National Science Foundation
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
20.07.2018 | Power and Electrical Engineering
20.07.2018 | Information Technology
20.07.2018 | Materials Sciences