A new study that included contributions by University of Colorado researchers shows that glacial melt from sources not including the Greenland and Antarctic ice sheets contributes as much to sea level rise as does the ice loss from those two land masses.
The study, published Thursday in the journal Science, showed that all glacial regions lost mass from 2003 to 2009, and that the biggest losses occurred in Arctic Canada, coastal Greenland, the Himalayas, the southern Andes and Alaska.
But because 99 percent of the Earth's land ice is contained in the massive Antarctic and Greenland ice sheets, public attention is not as fixed on melting that continues elsewhere.
The new study reports that glaciers outside the Antarctic and Greenland ice sheets lost an average of about 260 billion metric tons of ice annually during the study period. That contributed to an oceans rise of 0.03 inches, or about 0.7 millimeters per year.
"For the first time, we've been able to very precisely constrain how much these glaciers as a whole are contributing to sea rise," said geography assistant professor Alex Gardner of Clark University in Worcester, Mass., lead study author. "These smaller ice bodies are currently losing about as much mass as the ice sheets."
Professor Tad Pfeffer, a glaciologist at CU's Institute of Arctic and Alpine Research, was a co-author of the study. He said that because the collective global glacier ice mass is relatively small in comparison with the huge ice sheets covering Greenland and Antarctica, people tend not to focus as much on it.
However, Pfeffer said, "If you look at the data, the actual measurements, they are contributing just as much, or slightly more, as the ice sheets today. It's like a hole in the bottom of the bucket. The fact that there's not as much ice in the bucket doesn't matter, because the hole is just as big, and so it's going to run out just as fast."
The study compared traditional ground measurements to satellite data from NASA's Ice, Cloud and Land Elevation Satellite (ICESat) -- built by Boulder's Ball Aerospace & Technologies -- and the Gravity Recovery and Climate Experiment to estimate ice loss for glaciers across the planet.
CU physics professor John Wahr, also a co-author on the study, emphasized the value of the study drawing its data, and conclusions, from multiple measurement techniques, as opposed to, for example, simply taking ground ice-loss measurements of a sample glacier area, then making broader extrapolations from those measurements.
"This is the first study where people have actually used several different (measurement) techniques," Wahr said. "An individual method is subject to its own set of errors, but when you get agreement between two techniques, you can be reasonably confident you have the right answer."
The independent ice-loss measurement methods applied in the study "agree pretty much spot-on," Wahr said.
NASA's ICESat satellite was successfully operated from the CU campus by a team made up primarily of undergraduates from its launch in 2003 to its demise in 2009, when the science payload failed. The students participated in the decommissioning of a functioning satellite in 2010, bringing the craft into Earth re-entry to burn up. ICESat's successor, ICESat-2, is scheduled for launch in 2016 by NASA.
The study involved a total of 16 researchers from 10 countries. In addition to Clark University and CU, major research contributions came from the University of Michigan, the Scripps Institution of Oceanography in San Diego, Trent University in Ontario, Canada, and the University of Alaska Fairbanks.
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