Isolating the Larsen-C Ice Shelf Mass Instability

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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.