Investigating the Dynamic Response of the Greenland Ice Sheet to Climate Forcing using a Geophysical, Remote-Sensing and Numerical Modelling Framework

Lead Research Organisation: University of Cambridge
Department Name: Scott Polar Research Institute

Abstract

An increasing number of scientific studies show that human activities, e.g. burning of fossil fuels, have increased the concentration of heat-trapping gasses in the atmosphere. It is estimated that global temperatures will increase by 2-5 degrees C during this century if we continue to add carbon dioxide and other 'greenhouse' gasses to the atmosphere. In the Arctic, warming is expected to be even faster and mean annual temperature may increase by 4-7 degrees C. The implications of global warming are of immense proportions because glaciers and ice sheets will melt faster and become increasingly prone to collapse. In Greenland, discharge from outlet glaciers is responsible for about half the annual loss of ice. The other lost half is due to runoff of surface meltwater. The combined effect of iceberg discharge and surface melt are currently greater than the total amount of snowfall falling onto the Greenland Ice Sheet. This ice sheet is therefore shrinking while releasing freshwater into the Atlantic Ocean. The imbalance amounted to -90 cubic km per year for 1996 and increased to -140 cubic km per year by 2000. In 2005, this imbalance may have increased to as much as -220 cubic km per year. The size of the Greenland Ice Sheet is thus diminishing at what appears to be a growing rate. Worldwide concern is associated with this trend because ice-sheet decay results in global sea-level rise and possibly even an obstruction of oceanic circulation, which in key places - such as the North Atlantic - is sensitive to freshwater released from melting ice masses. The Greenland Ice Sheet rests on bedrock above or close to sea level. Glaciologists have for years assumed that such position would be stable and that demise of the ice sheet would require thousands of years even under extreme global warming scenarios. This assumption may need revision. It was shown recently that surface meltwater could penetrate through over 1km of ice to the base of the Greenland Ice Sheet and cause ice-flow speed-up due to faster basal sliding. This mechanism is potentially dangerous because accelerated ice flow leads to thinning, which in turn leads to an increase in surface melt since a larger part of the ice sheet moves into lower and warmer elevations. The Greenland Ice Sheet may therefore be far more prone to decay than it was assumed in earlier projections of global warming. However, up until now the mechanisms by which this dynamic response between surface melt and ice flow have only been generally understood and the present generation of climate-ice sheet models which are used to forecast future sea-level change do not include them in any rigorous manner. This is particularly true in respect of: 1) the extent to which the surface, interior and basal water-plumbing and ice flow systems can moderate, amplify and transmit the dynamic response away into the interior of the ice sheet thereby drawing the inland ice reservoir down and, 2) the extent to which future changes in Greenland temperatures may increase both the area and length of time of which the ice sheet directly experiences these effects. This project directly addresses both of these shortcomings in current models and will implement a set of fieldwork, satellite remote-sensing and comprehensive Greenland Ice Sheet modelling simulations that will fully assess and implement those 'dynamical processes related to ice flow not included in current models... (which) could increase the vulnerability of the ice sheets to warming, increasing future sea-level rise.' (IPCC, WG1 - 2007).
 
Description In this project, researchers at the Scott Polar Research Institute in Cambridge worked innovatively and collaboratively with re-searchers at Aberystwyth University and Swansea University. The Aberystwyth and Swansea groups, led by Prof. Alun Hubbard and Dr. Bernd Kulessa, executed field campaigns uniquely designed to support a three-dimensional ice sheet model developed in Cambridge. By forcing the model with observational data, the team was able to realistically simulate the way in which the Greenland Ice Sheet speeds up when surface meltwater drains to the bed during summer months. More specifically, we were able to demonstrate that flow of the ice sheet is principally driven by the forcing from supraglacial lakes even though these lakes contain only a small fraction of the total amount of water produced on the ice sheet in summer. While the work by joint grant holders showed that the ground beneath the ice sheet is comprised of soft sediment, the implementation of such material in this grant showed that the ice sheet is more vulnerable than thought. This is not only because of the progressively increasing amount of meltwater produced on the surface of the ice sheet and stored in a growing number of lakes, it is also because the frequencies of extreme melt and rainfall events are increasing as well, causing high-discharge drainage events to occur regularly. This outcome was published in the journal Nature Communications in 2014. With an altmetric score of 144 one month after publication, the article was in top 5% of similarly aged articles published in the Nature journal. The research was globally reported in 16 different news media outlets. This article was followed up by an article published in the journal Science Advances. In that article we showed how the material properties of a soft basal sediment responded to the drainage of a nearby lake, supporting the assumptions of our previous investigation of ice sheet vulnerability. With an altmetric score of 141, that article was also in the top 5% of similarly aged articles published by AAAS in Science Advances. Another example of a core output with high impact is an article published in Nature Communications in 2018. In that third and most recent output, we showed that lakes on the Greenland ice sheet form networks that drain as a cascade when a chain reaction is triggered. The work also shows that lake drainage initiates and propagates fractures through which other lakes drain, and we present observational evidence for these fractures forming at locations that are much father inland than considered possible so far. With more than 30 news reports and an altmetric score of 400, this research output also reached a large global audience.
Exploitation Route There is a strong public interest in knowing more about the Greenland Ice Sheet. The new knowledge generated generated in this project has produced a much better understanding of the Greenland Ice Sheet and the way it influences sea level rise. The numerical model used in this project is the Community Ice Sheet Model (CISM). Modelling developments, which formed an essential part of this project, is available to other users of this freely available, community-based model. The algorithm developed to automatically map supraglacial lakes in satellite imagery has been past on and is now used by another research group, incl. the University of Sheffield.
Sectors Education,Environment

URL http://www.cam.ac.uk/research/news/chain-reaction-of-fast-draining-lakes-poses-new-risk-for-greenland-ice-sheet
 
Description The discoveries in this grant were published in top academic journals. The first of three major discoveries, published in the journal Nature Communications in 2014, was accompanied by a press release in which we explained why the Greenland Ice Sheet may be more vulnerable than previously thought due to weak nature of the geological materials in the ground beneath the ice. This project outcome was widely reported by news media, including International Business Times, which reaches 50 million people, The Pulitzer prize winning Christian Science Monitor inUSA, Yahoo News, Daily Mail, and various other news media in UK, USA, Germany, Austria, Denmark, Norway and Bangladesh, resulting in an altmetric score (144) that puts the article in the top 5% of similar aged articles in Nature Communications and in the top 1% of similar aged articles in general. Public outreach also included an interview on the Thom Hartmann program broadcast live on AM and FM radio stations in New York, Los Angeles, San Francisco, Atlanta, Detroit, Seattle, Portland, Phoenix, Santa Fe and Memphis, as well as online and on many local cable news stations in the USA. The high public impact from this study is now influencing policy- and other decision makers. In 2017, we published another key output in the journal Science Advances. That output integrated geophysical observations of the soft geological materials and were reported in 14 international news outlets, and tweeted 26 times. The third significant output, published in Nature Communications in 2018, showed that fast-draining melt lakes on the surface of drain in a chain reaction. In a press release entitled "Chain reaction of fast-draining lakes poses new risk for Greenland ice sheet" was shared 1516 times on Facebook, Twitter and Reddit. The research was reported in 30 global news outlets and the article has an altimetric score of 400.
Sector Environment,Government, Democracy and Justice
Impact Types Societal,Policy & public services

 
Description Attribution of glacier change in the 5th Assessment Report by the Intergovernmental Panel on Climate Change
Geographic Reach Multiple continents/international 
Policy Influence Type Citation in other policy documents
Impact Research on the rapid ice flow dynamics and the interaction of ice sheets and glaciers with the ocean was cited on page 354 and page 1168 of 'Climate Change 2013', the contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. A cited research article (Christoffersen et al., 2011) was amongst the first to demonstrate how subtropical water is brought into Greenland fjords, causing rapid retreat and acceleration of flow.
URL http://www.ipcc.ch/
 
Description Times Atlas Greenland ice error: lesson in how scientists should mobilise
Geographic Reach Multiple continents/international 
Policy Influence Type Implementation circular/rapid advice/letter to e.g. Ministry of Health
Impact Following a gross error of the mapped extent of ice in Greenland in the 13th edition of The Times Comprehensive Atlas of the World in 2011, the publisher, HarperCollins, incorrectly claimed in a press release that climate change had resulted in a 15% decrease in ice extent since the last atlas was published 12 years earlier. Because the error was picked up in news headlines around the world, I took the initiative to write an open letter with colleagues at the Scott Polar Research Institute and posted it as a press release on the University of Cambridge News site . The letter, which strongly refuted the claim and pointed out how the land ice in Greenland had been incorrectly mapped, was circulated to the press with help from the rapid response team of the Science Media Centre. The swift manner in which the false claim by Harper Collins was corrected helped prevent a public backlash similar to the one that followed the mistake in the estimated disappearance of Himalayan glaciers reported in the Fourth Assessment report by the Intergovernmental Panel on Climate Change in 2007. The atlas story was featured on the BBC, The Guardian, Telegraph, Daily Mail, The Independent, New York Times, Mirror, Reuters, Science AAAS, Nature, New Scientist and several other major news outlets. In 'Times Atlas ice error was lesson in how scientists should mobilise' - an invited piece for The Guardian - I explain why scientists need to mobilise and swiftly confront mistakes and errors in the reporting of climate change. The piece received 11,000+ page views in 2 days.
URL http://www.theguardian.com/environment/2011/sep/21/times-atlas-error-scientists-mobilise
 
Description Coupling hydrology and ice flow in the Community Ice Sheet Model 
Organisation University of California, San Diego (UCSD)
Country United States 
Sector Academic/University 
PI Contribution In this collaboration, the Cambridge group integrated hydrological processes in the Community Ice Sheet Model, which they use to simulate the flow of glaciers and ice sheets in Antarctica and Greenland.
Collaborator Contribution The collaborators at the Scripps Institution of Oceanography provided a validated hydrological model.
Impact The collaboration with Prof. Helen Fricker and her research group at the Scripps Institution of Oceanography has so far produced three significant peer-reviewed journal articles: Bougamont, M., P. Christoffersen, A. L. Hubbard, A. A. Fitzpatrick, S. H. Doyle, and S. P. Carter, Sensitive response of the Greenland Ice Sheet to surface melt drainage over a soft bed, Nature Communications, 5, 5052-5052, doi:10.1038/ncomms6052, 2014. HIGH IMPACT RESEARCH OUTPUT WITH ALTMETRIC SCORE OF 144 ONE MONTH AFTER PUBLICATION. OUTPUT REPORTED IN 17 NEWS OUTLETS. Christoffersen, P., *M. Bougamont, S. P. Carter, H. A. Fricker, and S. Tulaczyk, Significant groundwater contribution to Antarctic ice streams hydrologic budget, Geophysical Research Letters, 41(6), 2003-2010, doi:10.1002/2014gl059250, 2014. SELECTED AS RESEARCH HIGHLIGHT BY AGU EDITORS AND FEATURED AS RESEARCH SPOTLIGHT IN EOS NEWSLETTER. Beem, L. H., S. M. Tulaczyk, M. A. King, *M. Bougamont, H. A. Fricker, and P. Christoffersen, Variable deceleration of Whillans Ice Stream, West Antarctica, Journal of Geophysical Research-Earth Surface, 119(2), 212-224, doi:10.1002/2013jf002958, 2014. SELECTED AS RESEARCH HIGHLIGHT BY AGU EDITORS AND FEATURED AS RESEARCH SPOTLIGHT IN EOS NEWSLETTER.
Start Year 2011
 
Title Subglacial hydrology implemented the Community Ice Sheet Model v 2.0 (CISM2) 
Description A new scheme for 'subglacial hydrology' was implemented into the Community Ice Sheet Model (CISM). This model development has allowed routing of water in the CISM. 
Type Of Technology Software 
Year Produced 2014 
Open Source License? Yes  
Impact This model development has provided key new insights to the subglacial hydrology of ice sheets. Peer-reviewed articles based on outputs from the model include 1) the first quantitative assessment of the hydrologic budget of Antarctic ice streams, and 2) a novel new assessment of the Greenland Ice Sheet's sensitivity to climate change. Bougamont, M., P. Christoffersen, A. L. Hubbard, A. A. Fitzpatrick, S. H. Doyle, and S. P. Carter, Sensitive response of the Greenland Ice Sheet to surface melt drainage over a soft bed, Nature Communications, 5, 5052-5052, doi:10.1038/ncomms6052, 2014. HIGH IMPACT RESEARCH OUTPUT WITH ALTMETRIC SCORE OF 144 ONE MONTH AFTER PUBLICATION. OUTCOME REPORTED IN 17 NEWS OUTLETS. Christoffersen, P., *M. Bougamont, S. P. Carter, H. A. Fricker, and S. Tulaczyk, Significant groundwater contribution to Antarctic ice streams hydrologic budget, Geophysical Research Letters, 41(6), 2003-2010, doi:10.1002/2014gl059250, 2014. SELECTED AS RESEARCH HIGHLIGHT BY AGU EDITORS AND FEATURED AS RESEARCH SPOTLIGHT IN EOS NEWSLETTER. 
URL http://oceans11.lanl.gov/cism/
 
Description Chain reaction of fast-draining lakes poses new risk for Greenland ice sheet 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact This press release, issued by the University of Cambridge, described research published in Nature Communications. The press release featured text and imagery used in many articles published in the global news media.
Year(s) Of Engagement Activity 2018
URL http://www.cam.ac.uk/research/news/chain-reaction-of-fast-draining-lakes-poses-new-risk-for-greenlan...
 
Description Press release ("A more vulnerable Greenland Ice Sheet") 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact The vulnerability of the Greenland Ice Sheet remains uncertain and the speed at which the ice sheet will lose mass in the future due to flow as well as melting is an outstanding scientific question. Addressing this question is a core activity of my research group. Recently, I led a project in which we forced a three-dimensional model of the ice sheet's flow with measured volumes of surface meltwater and a layer of porous sediment as observed along the bed. The model showed that the ice sheet may be more vulnerable than thought so far because increased volumes of meltwater draining to the bed lubricates the flow of ice by weakening the underlying soft ground. The faster flow accelerates the transport of ice from interior to coast, a dynamic response so far not seen ice sheet models based on simpler parameterisations of the basal environment. The outcomes from this study were published in the journal Nature Communications on 29 September 2014, together with a press release in which we explain why the Greenland Ice Sheet may be more vulnerable than previously thought. This result was widely reported by news media, including Inter-national Business Times, which reaches 50 million people, The Pulitzer prize winning Christian Science Monitor, Yahoo News, Daily Mail, and various other news media in UK, USA, Germany, Austria, Denmark, Norway and Bangladesh. Outreach also included a live interview on the Thom Hartmann program broadcast live on AM and FM radio stations in New York, Los Angeles, San Francisco, Atlanta, Detroit, Seattle, Portland, Phoenix, Santa Fe and Memphis, as well as online and many local cable news stations.


The article in Nature Communications obtained an altmetric score of 144 one month after publication due to high media interest and journalistic reporting. This puts the article in the top 5% of similar aged articles in Nature Communications and in the top 1% of similar aged articles in general.
Year(s) Of Engagement Activity 2014
URL http://www.cam.ac.uk/research/news/greenland-ice-sheet-more-vulnerable-to-climate-change-than-previo...
 
Description Science talks for primary school groups 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact These 'science talks' are offered to primary school groups visiting the Scott Polar Research Institute and the Polar Museum. The talks are based largely on my own research and are aimed to spark the childrens' imagination and their interest in the 'natural environment' and 'science' in general.

According to feedback from teachers, the visits significantly change the children's understanding of science and polar environments.
Year(s) Of Engagement Activity 2006,2007,2008,2009,2010
URL https://www.spri.cam.ac.uk/museum/groupvisits/