WASHINGTON Some of Greenland's glaciers are moving about 30 percent faster than they did 10 years ago, contributing to rising global sea levels, but that still may not be enough to reach the most extreme projections for 2100, scientists reported on Thursday.
Researchers have been monitoring the big ice sheets of Greenland and Antarctica for decades as one indication of the impact of human-spurred climate change.
Made of compacted snow, these glaciers can move toward the sea, and when they get there, they dump water into the oceans around them. The faster they move, the more water they add, and the higher the oceans get.
Not all glaciers move at the same pace, according to Twila Moon and her co-authors at the University of Washington and Ohio State University, whose research is published in the current issue of the journal Science.
Inland glaciers with no outlet to the sea poke along at top speeds of 30 to 325 feet a year, the researchers found, while those that end at the ocean can travel 7 miles a year.
The glaciers that flow to the sea around Greenland are the ones to watch, Moon said in a telephone interview, because that is where four-fifths of the loss of ice in Greenland occurs.
Satellite surveys of more than 200 glaciers showed that these comparatively fast-movers in the east, southeast and northwest areas of Greenland increased their speed by an average of 30 percent from 2000 to 2011.
The researchers found that the glaciers heading for the water were not accelerating as much as had been speculated in earlier projections of the worst that could happen. Based on those projections, there was a previous forecast of sea level rise of about 6 feet by century's end.
NOT WORST CASE, BUT STILL RISKY
That would be enough to inundate parts of the U.S. Gulf coast, Alaska, Italy, France, England, Scotland, Denmark, Brazil, India, Sri Lanka, Bangladesh, China, Japan, the Korean peninsula, Southeast Asia and Australia, according to maps of sea level rise at the Center for Remote Sensing of Ice Sheets ( here ).
The latest research indicates this is unlikely by 2100.
"Two meters is really kind of a worst case," Moon said. "Now we have the luxury of a little bit more time and being able to actually look at the observations from the last 10 years. At this point it doesn't look like there's any evidence for the worst-case scenario."
A low projection of 8 inches is within reach, the researchers found, and even a small rise in sea level can add to the risks of storm surges and floods. As Moon put it, "If you raise the floor of a basketball court, you're going to have a lot more slam-dunks."
Because multiple factors contribute to sea level rise, it is difficult to determine the exact impact of Greenland's melting glaciers. Global seas have been rising by a bit more than 1 inch (about 30 millimeters) a year.
Just knowing how much ice is going into the ocean around Greenland does not give the complete picture, according to a related article in Science. Projections of regional sea level rise are complicated, but they are needed, said co-author Joshua Willis of NASA's Jet Propulsion Laboratory.
"What people really need to know is, how is sea level going to change in my backyard?" Willis said in a telephone interview. To figure that out, he said, scientists must not only figure out the glacier melt situation on a global scale but also add factors like wind, geology, water temperature and even gravity that can have powerful impacts in specific areas.
In southern Louisiana, for example, the land is sinking as the seas are rising, creating a potential double-whammy there. In Greenland, by contrast, the land may actually rise as the weight of heavy ice slides off, like a couch cushion rebounding after a person gets up after a long sit.
(Editing by Mohammad Zargham)