Ice cycles documented by combining satellite data with old aerial photos
By Summit Voice
SUMMIT COUNTY —Although many climate models suggest that warming over the Arctic will inexorably melt the region’s ice, Danish scientists say it may be too early to proclaim the end of the Greenland ice sheet.
Their study is based on a combination of satellite daya and old aerial photographs of the ice sheet in northwestern Greenland, one of two hotspots for ice sheet thinning and heavy glacial melt runoff. It suggests that the ice sheet has previously experienced rapid melting and thinning, and then stabilized, perhaps independently of external influences like regional air temperatures.
“That air temperatures have increased and melting has intensified is relatively well-understood. On the other hand, the UN’s climate panel, the IPCC, has for many years called for greater knowledge in relation to the other major effect on the Greenland Ice Sheet – the ‘thinning of the ice sheet’ which is the effect of the largest glaciers in Greenland flowing faster into the ocean than previously measured,” said professor Eske Willerslevs, of the Centre for GeoGenetics at the Natural History Museum of Denmark. “It turns out that the ice sheet, in relation to this point, behaves more dynamically and is able to more quickly stabilise itself in comparison to what many other models and computer calculations otherwise predict,” he said.
The study, published in Science, concludes that, based on existing data, it’s not possible to predict the demise of the ice sheet.
But there’s no disputing the current rate of melting, which is so great that some climate experts are warning of a tipping point, when the global climate becomes permanently transformed, potentially inundating low-lying cities and coastal zones around the world.
The Danish study suggests that the Greenland Ice Sheet is more robust than researchers have otherwise been able to predict using models and computer-based calculations.
“We’ve used a combination of old aerial photographs from the 80′s to construct a digital elevation map and recent satellite data,” Willerslevs said. “In this way we’ve been able to gain an overview of the thinning of the ice sheet over the last 30 years in northwestern Greenland. We are the first who have been able to show that the Greenland Ice Sheet was on as a dramatic diet at the end of the 80′s as it is today. On the positive side our results show that despite a significant thinning in peripheral regions from 1985-1992; the thinning slowed and then died out.”
Associate Professor Kurt H. Kjær, of the University of Copenhagen, had the idea to create new and comparable elevation models of the ice sheet along a 700 km long stretch of the northwestern Greenland coast using the old photos. This provided researchers with a relatively simple way of revealing more of the ice sheet’s secrets in comparison to other new methods.
“Our results show that the thinning of the ice sheet at the end of the 80′s and beginning of the 90′s eased over a 4-8 year period, after which a period of stability occurred until 2003. Our conclusion is therefore, that if we judged against longer periods of time, the current thinning of the ice sheet is likely to ease within an 8-year period,” Kjær said.
“These variations in the amount of thinning that we are able to document since the 80′s make it difficult to predict how much the world’s oceans will rise over a longer period of time — a century for instance — as a result of Greenland glacial melt-water runoff.
“However, it is certain that many of the present calculations and computer models of ice sheet conditions that built upon a short range of years since 2000 must be reassessed. It is too early to proclaim the ‘ice sheet’s future doom’ and subsequent contribution to serious water problems for the world.
“In this context it should be mentioned that the Greenland bedrock rises as the ice sheet in the peripheral regions and especially near the coast is in retreat and becoming thinner. This highlights the enormous forces that are at play in Greenland and of how difficult it is to predict what it means for Greenland as well as the rest of the world,” Kjær concluded.
Filed under: climate and weather, Environment, global warming Tagged: | climate, global warming, Greenland ice sheet, Intergovernmental Panel on Climate Change, sea level rise, University of Copenhagen