Climate: Scientists say Arctic ice loss speeding up

Researchers try to pinpoint sea level rise projections

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Greenland’s glaciers are retreating inland rapidly. @bberwyn photo.

By Bob Berwyn

FRISCO — Sea level is set to rise at least three feet during the next few decades, NASA scientists and ice researchers said this week, updating their latest research and findings on how fast the world’s ice sheets and glaciers are melting.

The scientists said they’re still not sure exactly how fast the water will rise, but they’re getting closer to nailing down the timing, thanks to several ongoing research projects, including a five-year effort to measure ice loss around the edge of Greenland.

The goal, of course, is to help coastal communities prepare for the big changes ahead. Agriculture, transportation and other infrastructure like water treatment plants will all be affected by sea level rise.

In a teleconference hosted by NASA, a trio of scientists acknowledged that projecting sea level rise is tricky business. In some places, the long-term trend is masked by shorter, cyclical variations. That holds true for the U.S.

“Sea level along the west coast of the United States has actually fallen over the past 20 years because long-term natural cycles there are hiding the impact of global warming,” said Josh Willis, an oceanographer at NASA’s Jet Propulsion Laboratory in Pasadena, California. “However, there are signs this pattern is changing. We can expect accelerated rates of sea level rise along this coast over the next decade as the region recovers from its temporary sea level ‘deficit.'”

“The biggest thing in predicting is how fast polar ice sheets will melt … that’s still a big challenge,” said glaciologist Eric Rignot, with NASA’s Jet Propulsion Laboratory at the California Institute of Technology and with the University of California Irvine.

But the emerging signs of ice sheet meltdowns are concerning, and scientists know much more than they did even just a few years ago, when the Intergovernmental Panel on Climate Change released it’s last big report.

“Ice sheets are contributing more and sooner than previously observed,” Rignot said, adding that ice sheet melt will eventually dominate sea level rise, contributing anywhere from half a meter to several meters per century.

One Greenland glacier alone, the Jakobshavn Isbræ, could raise sea level by half a meter if it melts, Rignot said. Based on the latest scientific evidence, conservative estimates of sea level rise may not be reasonable, he added.

During the past few weeks, researchers watched in awe as a huge chunk of the Jakobshavn Glacier fell into the sea. Rignot made it clear that some of the recent observations of ice sheet decay and glacial retreat are unprecedented in the modern observation record.

“On a personal level, based the data I’ve collected over the past few years, I’m more concerned … Some of the ice retreat we’ve seen this summer … they are examples of what we are likely to see along the coast of Greenland …  we’ve never seen this on that scale before,” he said. “Personally I am in awe seeing how far and how fast glacier front is retreating inland.

“We are seeing an acceleration of ice loss right now,” he continued, emphasizing that the meltback being observed right now is not something that’s going to change with winter snowfall. The entire ice front is clearly retreating inland, he explained.

Based on the most recent observations, sea level rise of one foot per century is probable, three feet is possible and Rignot even raised the possibility of 30-feet of sea level rise if “ice goes into a rapid deterioration mode,” he said, adding that there’s really no reason to believe that ice sheets will react to global warming in a simple linear trend.

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