Isolating the Larsen-C Ice Shelf Mass Instability

Lead Research Organisation: University of Edinburgh
Department Name: Sch of Geosciences

Abstract

In 1988, the World Meteorological Organisation and the United Nations set up an international panel of expert scientists to collect information about climate change, in response to growing public concerns about issues such as global warming and the hole in Earth's ozone layer. Since then, the panel's major findings have shown that air temperatures and sea levels are rising faster than can be explained through natural changes, and that pollutants from 20th Century industrialisation are a likely factor. Earths' present-day climate changes are closely related to the ice frozen in its polar regions. As air temperatures rise, ice melts and drains into the oceans, causing sea level rise. The costs of this simple relationship could be enormous. There is enough ice frozen in Antarctica to raise global sea levels by 65 m if it were to rapidly melt, a change that would flood 13 of the worlds 20 largest cities including London. Some of the fastest climate changes on Earth have taken place at the Antarctic Peninsula, the warmest sector of Antarctica, due south of Chile and Argentina. Air temperatures measured there since early explorations in the 19th Century, show a warming of more than 5 degrees C during the past 100 years. Perhaps the most dramatic climate changes ever witnessed have occurred during the last decade, when, in 1995 and 2002, giant sections of the floating Larsen Ice Shelf - Larsen-A and /B, each about the size of Cornwall - disintegrated into thousands of icebergs, causing widespread alarm. These events, depicted as a solitary crevasse fracture in the opening scene of last years blockbuster The Day After Tomorrow, were truly catastrophic, and are probably the only natural disaster ever to be understated in a Hollywood movie. More importantly, the collapses have left scientists unsure as to what caused them and how they might affect our future climate. In the wake of each collapse, new embayments have been revealed where the floating Larsen Ice Shelf used to exist, and glaciers inland of these bays have accelerated, calving enough extra ice to raise global sea levels by 0.1 mm each year. Although this amount seems small, scientists are now concerned about the much larger ice field upstream of the remaining Larsen-C section, which contains enough ice to raise global sea levels by over 50 mm. That ice would be seriously at risk if the Larsen-C section were to collapse. We have designed a series of experiments, combining satellites and field exploration, to solve the mystery of Larsen Ice Shelf collapses. Our measurements will identify whether changes in the ocean or the atmosphere were to blame. We will use a sensitive radar system / similar to road speed cameras - to measure extremely slow changes in the ice shelf thickness of about 0.1 mm per hour. We will also drill through the top layers of the ice shelf and extract cores of ice, which, like tree rings, tell us how climate has changed over the past century. When combined with new satellite measurements of ice flow and thinning, our field measurements will allow us to detect whether the ocean beneath the floating Larsen Ice Shelf is warmer than expected, or whether summertime ice melting at the surface is greater than expected. Once the cause of the collapses has been identified, we will build a computer model of the ice shelf to investigate how it might fracture in the future. Our experiments will identify the cause of the catastrophic Larsen Ice Shelf collapses in 1995 and 2002. They will also determine whether the remaining Larsen-C section will become vulnerable in the coming years. And, most important of all, we will predict how fast global sea levels will rise if the Larsen-C collapses at some time in the future.

Publications

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Gourmelen N (2011) Ice velocity determined using conventional and multiple-aperture InSAR in Earth and Planetary Science Letters

Related Projects

Project Reference Relationship Related To Start End Award Value
NE/E014089/1 01/09/2008 31/07/2009 £303,054
NE/E014089/2 Transfer NE/E014089/1 01/08/2009 28/02/2013 £248,506
 
Description asal melt rates on Larsen-C Ice Shelf During the past decade, the Larsen Ice Shelf has progressively thinned and two large sections have collapsed, catastrophically, leading to increased ice discharge into the oceans and a consequent rise in global sea level. If similar events are to occur at the remaining Larsen-C section, the fate of a tenfold greater ice reservoir hangs in the balance. Although the origin of the underlying instability has yet to be determined, only three processes can realistically be to blame; enhanced basal or surface melting, or accelerated flow. To quantify rates of basal ice melting, a phase sensitive radar was deployed on the Larsen-C Ice Shelf. The radar is a high-precision instrument that directly measures changes in thickness of the ice shelf, in contrast to indirect methods that infer basal melting from surface observation while assuming steady state. We established three radar sites on Larsen-C where time-series of satellite altimeter data are also available. The sites were revisited twice over the course of one year to measure the annual mean and summertime rates of basal melting. The annual mean measurements proved difficult to interpret because of a lack of reproducibility in the radar layer structure within the ice shelf over long periods of time. Measurements made within one summer field season proved more reliable, yielding melt rates of between 4 and 8 m yr-1 near the grounding line, near zero over the ice shelf interior and around 2 m yr-1 near the ice front. Such a spatial pattern of melting is consistent with models of the ocean circulation beneath the ice shelf, while the magnitude near the grounding line suggests that waters with temperatures above the surface freezing point reach the inner cavity at least intermittently. Temporal variability in the melt rate is a strong candidate for driving the observed thinning to the ice shelf, at least over its southern half.
Exploitation Route Climate change policy, scientific research based on findings
Sectors Environment,Government, Democracy and Justice

 
Description Identification of the cause of the catastrophic Larsen Ice Shelf collapses in 1995 and 2002, used to determine whether the remaining Larsen-C section will become vulnerable in the coming years and how fast global sea levels will rise if the Larsen-C collapses at some time in the future.
First Year Of Impact 2008
Sector Environment,Government, Democracy and Justice
Impact Types Societal

 
Description STSE Mass Balance
Amount £316,000 (GBP)
Organisation European Space Agency 
Sector Public
Country France
Start 01/2012 
End 01/2014