May 20th, 2013 by Joshua S Hill
Research has found that approximately 99% of our planet’s land-locked ice is held up in the Greenland and Antarctic ice sheets. The remainder, however, is out in the open, located primarily in the glaciers dotted throughout the appropriate latitudes across the planet.
And according to new research, those glaciers contributed approximately the same amount of water to sea level rise as the two ice sheets combined between 2003 and 2009.
All glacial regions lost ice mass over the period studied, but the biggest losses happened in Arctic Canada, Alaska, coastal Greenland, the southern Andes, and the Himalayas, losing an estimated 260 billion metric tonnes of ice annually during the study period, causing the oceans to rise approximately 0.7 millimetres per year.
The study, led by Clark University and involving the University of Colorado Boulder compared traditional mound measurements to satellite data collected from NASA’s Ice, Cloud and Land Elevation Satellite (ICESat) and the Gravity Recovery and Climate Experiment (GRACE).
“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.”
“Because the global glacier ice mass is relatively small in comparison with the huge ice sheets covering Greenland and Antarctica, people tend to not worry about it,” said CU-Boulder Professor Tad Pfeffer, a study co-author. “But it’s like a little bucket with a huge hole in the bottom: it may not last for very long, just a century or two, but while there’s ice in those glaciers, it’s a major contributor to sea level rise,” said Pfeffer, a glaciologist at CU-Boulder’s Institute of Arctic and Alpine Research.
ICESat, which ceased operations in 2009, measured glacier changes using laser altimetry, which bounces laser pulses off the ice surface to determine changes in the height of ice cover. The GRACE satellite system, still operational, detects variations in Earth’s gravity field resulting from changes in the planet’s mass distribution, including ice displacements.
GRACE does not have a fine enough resolution and ICESat does not have sufficient sampling density to study small glaciers, but mass change estimates by the two satellite systems for large glaciated regions agree well, the scientists concluded.
“Because the two satellite techniques, ICESat and GRACE, are subject to completely different types of errors, the fact that their results are in such good agreement gives us increased confidence in those results,” said CU-Boulder physics Professor John Wahr, a study co-author and fellow at the university’s Cooperative Institute for Research in Environmental Sciences.
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