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20 Sep 06 Greenland ice sheet melting faster: study National Geographic 20 Sep 06 Greenland's Ice Melt Grew by 250 Percent, Satellites Show John Roach for National Geographic News Yahoo News 20 Sep 06 Melting Greenland ice sheet spells more bad news on climate change By Patricia Reaney PARIS (AFP) - The Greenland icesheet, the second largest single store of frozen freshwater in the world, is melting faster than previous estimates, according to a study that adds to grim news about global warming. In 2001, the UN's top scientific forum on global warming projected that the thick slab of ice that covers most of Greenland would melt only slightly during the 21st century. But a study published on Thursday in the British weekly journal Nature calculates that the rate of Greenland ice loss increased by 250 percent between May 2004 and April 2006 compared with the two years between April 2002 and April 2004. Ice is now being lost at around 248 cubic kilometers (59.5 cu. miles) per year -- equivalent to a global sea level rise of about 0.5mm (0.02 inches) per year. Taking other accelerating factors into account, such as major losses at two big glaciers in recent years, Greenland is contributing almost 0.7mm a year, said Tavi Murray, an environmentalist at Britain's Swansea University. This is a significant rise compared to the 2001 estimates by the UN's Intergovernmental Panel on Climate Change (IPCC). If averaged out for the 110-year span, those estimates would give Greenland a contribution of around 0.5mm (0.02 inches) per year of the planetary rise in sea level. But the nature of global warming means that the rise would occur especially towards the end of the century -- not near its start, as the new paper implies. The new study says the central portion of the icesheet, at altitudes above 1,500m (4,875 feet), is thickening, thanks to increased snowfall. But the margins of the icesheet, which are at lower altitudes and are thinner, are eroding fast, especially in the southeast and northeast of Greenland, where glaciers are spewing ice into the sea faster than before. The research, which used computer models and satellite measurements made by NASA's two GRACE satellites, was carried out by Isabella Velicogna and John Wahr of the University of Colorado. The pair acknowledge that their work spans observations only four years, and climate science often needs to look at decades before drawing firm conclusions about longer trends. However, it concurs with a separate study on Greenland that was published in August by the US journal Science. It also comes less than a week after a paper, also published in Science, found that year-round sea ice in the Arctic shrank by one seventh between 2004 and 2005. Greenland is second to Antarctica as a single source of land ice. If the Greenland icesheet melted entirely, that would boost sea levels by seven metres (22.75 feet), although this apocalyptic scenario is discounted unless global warming becomes unstoppable. The IPCC estimated in 2001 that between 1990 and 2100, the mean global sea level would rise about 480 millimeters (19.2 inches) in a range from 90mm to 880mm (3.6 to 35.2 inches). At the bottom of this range, Greenland would not contribute anything to the increase; at the top of the range, it would contribute around 90mm (3.6 inches) over the 110 years. These ranges are based on how fast greenhouse gases, which trap solar heat, build in the atmosphere and help drive up Earth's surface temperature. PlanetArk 20 Sep 06 Greenland ice sheet melting faster: study By Patricia Reaney LONDON (Reuters) - Greenland's massive ice sheet is melting much quicker than scientists had estimated and the pace has accelerated lately, according to research published on Wednesday. An analysis of satellite observations shows the rate of ice loss rose 250 percent between the periods April 2002 to April 2004 and May 2004 to April 2006, most of it in southern Greenland. The ice sheet is now shrinking by about 248 cubic kilometers each year which is equivalent to a rise in sea level around the world of 0.5 millimeters. "There is an increase in mass loss and it is significant," said Isabella Velicogna, of the University of Colorado and NASA's Jet Propulsion Laboratory at the California Institute of Technology. "Los Angeles County uses about one cubic kilometer a year, so it is a lot of water," she added in an interview. The findings, based on data from the Gravity Recovery and Climate Experiment (GRACE) satellite, and published in Nature magazine, are consistent with earlier results showing increased melting due to rising temperatures blamed on global warming. But Velicogna and her colleague John Wahr go a step further because their analysis is very recent, up to April 2006, and shows the accelerated rate of loss is almost entirely in southern Greenland. "It was losing quite a bit of mass before 2004 but there is a very strong acceleration, which means things are changing," said Velicogna "It is more than we have been observing in the last century," she added. Scientists predict that global average temperatures will rise by between one and six degrees Celsius this century unless urgent action is taken now to cap and reduce carbon emissions. A rise of three degrees could cause a large rise in sea levels, loss of species and increase famine and disease. Greenland's ice sheet is so huge that if it melted entirely sea levels across the world would rise by about 7 meters (yards), Tavi Murray of the University of Wales in Swansea said in a commentary on the research. Murray believes the GRACE results could help scientists re-evaluate the rates of loss that can be expected from global warming. "Uncertainties remain, but the GRACE results provide one of the best estimates of overall mass balance of the ice sheet," he added. National Geographic 20 Sep 06 Greenland's Ice Melt Grew by 250 Percent, Satellites Show John Roach for National Geographic News Greenland's ice sheet is melting into the sea much faster today than it was just a few years ago, according to an analysis of satellite observations reported today in the journal Nature. The rate of ice-mass loss from the Danish-owned island increased by 250 percent during a period spanning May 2004 to April 2006 relative to the period from April 2002 to April 2004, the study concludes. The new finding confirms an independent analysis of the same satellite data reported in the August 10 issue of the journal Science. "Two hundred and fifty percent is huge," said Isabella Velicogna, an earth scientist at the NASA Jet Propulsion Laboratory in Pasadena, California, and study co-author. "We're talking two times and a half more mass loss. What that tells us is we want to keep our eyes open and check what's going on with these glaciers," she added. Ice is now being lost from the island at a rate of 59 cubic miles (248 cubic kilometers) a year, sufficient to push global sea levels up 0.02 inch (0.5 millimeter) a year, the team reports. If all the ice on Greenland were to melt into the North Atlantic Ocean, scientists estimate that global sea levels would rise by 23 feet (7 meters). Warming Link Both the Nature and Science studies use data from the Gravity Recovery and Climate Experiment (GRACE) satellites, which measure monthly changes in Earth's gravitational field. Liquid water is denser than ice and so has a stronger gravitational pull. The satellites can therefore measure changes in Greenland's mass over time to determine the rate at which ice is melting. The new study dates the start of accelerated melting to the spring of 2004 and finds the acceleration is confined to southern Greenland, Velicogna says. While the GRACE data alone do not say anything about the cause of Greenland's ice loss, the decrease does coincide with a warming climate and independent observations of increased glacier ice loss on the island. "This leads us to think this [mass loss] is probably associated with ice discharge," Velicogna said. Ice discharge—the dumping of glacial ice into the North Atlantic—is a process with built-in inertia, Velicogna says. Even if temperatures suddenly drop in Greenland, she says, the discharge would continue for several years. Velicogna adds that if the mass loss is indeed associated with warming global temperatures and temperatures continue to rise, the accelerated melting could spread to northern Greenland. "We don't know for sure, but it could happen and is something to be watched for," she said. links Greenland ice sheet still losing mass, says new University of Colorado study EurekaAlert 20 Sep 06 Related articles on Global warming |
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