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Last Updated: Dec 19th, 2007 - 13:17:15 |
The loss of ice from Greenland doubled between 1996 and 2005, as its glaciers flowed faster into the ocean in response to a generally warmer climate, according to a NASA/University of Kansas study.
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| This image shows the calving front, or break-off point into the ocean, of Helheim Glacier, located in southeast Greenland. The image, taken in May 2005, shows high calving activity associated with faster glacial flow. This glacier is now one of the fastest moving glaciers in the world. Image credit: NASA/Wallops |
The study will be published tomorrow in the journal Science. It concludes the changes to Greenland's glaciers in the past decade are widespread, large and sustained over time. They are progressively affecting the entire ice sheet and increasing its contribution to global sea level rise.
Researchers Eric Rignot of NASA's Jet Propulsion Laboratory, Pasadena, Calif., and Pannir Kanagaratnam of the University of Kansas Center for Remote Sensing of Ice Sheets, Lawrence, used data from Canadian and European satellites. They conducted a nearly comprehensive survey of Greenland glacial ice discharge rates at different times during the past 10 years.
"The Greenland ice sheet's contribution to sea level is an issue of considerable societal and scientific importance," Rignot said. "These findings call into question predictions of the future of Greenland in a warmer climate from computer models that do not include variations in glacier flow as a component of change. Actual changes will likely be much larger than predicted by these models."
The evolution of Greenland's ice sheet is being driven by several factors. These include accumulation of snow in its interior, which adds mass and lowers sea level; melting of ice along its edges, which decreases mass and raises sea level; and the flow of ice into the sea from outlet glaciers along its edges, which also decreases mass and raises sea level. This study focuses on the least well known component of change, which is glacial ice flow. Its results are combined with estimates of changes in snow accumulation and ice melt from an independent study to determine the total change in mass of the Greenland ice sheet.
Rignot said this study offers a comprehensive assessment of the role of enhanced glacier flow, whereas prior studies of this nature had significant coverage gaps. Estimates of mass loss from areas without coverage relied upon models that assumed no change in ice flow rates over time. The researchers theorized if glacier acceleration is an important factor in the evolution of the Greenland ice sheet, its contribution to sea level rise was being underestimated.
To test this theory, the scientists measured ice velocity with interferometric synthetic-aperture radar data collected by the European Space Agency's Earth Remote Sensing Satellites 1 and 2 in 1996; the Canadian Space Agency's Radarsat-1 in 2000 and 2005; and the European Space Agency's Envisat Advanced Synthetic Aperture Radar in 2005. They combined the ice velocity data with ice sheet thickness data from airborne measurements made between 1997 and 2005, covering almost Greenland's entire coast, to calculate the volumes of ice transported to the ocean by glaciers and how these volumes changed over time. The glaciers surveyed by those satellite and airborne instrument data drain a sector encompassing nearly 1.2 million square kilometers (463,000 square miles), or 75 percent of the Greenland ice sheet total area.
From 1996 to 2000, widespread glacial acceleration was found at latitudes below 66 degrees north. This acceleration extended to 70 degrees north by 2005. The researchers estimated the ice mass loss resulting from enhanced glacier flow increased from 63 cubic kilometers in 1996 to 162 cubic kilometers in 2005. Combined with the increase in ice melt and in snow accumulation over that same time period, they determined the total ice loss from the ice sheet increased from 96 cubic kilometers in 1996 to 220 cubic kilometers in 2005. To put this into perspective, a cubic kilometer is one trillion liters (approximately 264 billion gallons of water), about a quarter more than Los Angeles uses in one year.
Glacier acceleration has been the dominant mode of mass loss of the ice sheet in the last decade. From 1996 to 2000, the largest acceleration and mass loss came from southeast Greenland. From 2000 to 2005, the trend extended to include central east and west Greenland.
"In the future, as warming around Greenland progresses further north, we expect additional losses from northwest Greenland glaciers, which will then increase Greenland's contribution to sea level rise," Rignot said.
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Ireland’s Emissions of Greenhouse Gases on the Increase - Fri, 17 Feb 2006
Ireland’s annual emissions of Greenhouse Gases (GHG) in 2004 were up by 0.45 per cent on the 2003 emissions according to figures released today by the Environmental Protection Agency. This is a reversal of the downward trend in emissions over the previous two years.
Commenting on the latest figures, Dr. Mary Kelly Director General of the EPA expressed disappointment that the modest improvements in the two previous years had not been sustained. She said: “Today’s figures highlight the challenges facing Ireland in seeking to comply with its Kyoto commitments in a growing economy. Ireland needs to reduce greenhouse gas emissions in each sector of the economy if we are to meet our Kyoto target. Opportunities for reduction on a sector by sector basis must be identified and measures put in place to deliver on them”.
The emissions for the entire period from 1990 onwards have been revised based on new international guidelines, national research and improved data. The latest figures show that in 2004 Ireland’s GHG were 23.5% higher than in 1990. Ireland is committed under the Kyoto Protocol to limit emissions to 13% above the 1990 level in the period 2008-2012.
The breakdown of the figures show that agriculture is the single largest contributor to the overall emissions, at almost 29% of the total, followed by energy (power generation & oil refining) at just over 23% and transport at 17.5%.
The latest data indicates that emissions of greenhouse gases in Ireland during 2004 were 68.7 million tonnes of carbon dioxide (CO2) equivalent.
Dr Kelly said, “The Kyoto Protocol allows countries to comply with their commitments by a combination of measures including domestic reductions and the purchase of carbon credits. Ireland must, in the long term achieve as much as possible domestically.”
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