Polar Ice Sheets Melting Faster, Threatening East Coast [REPORT]
Superstorm Sandy A Taste Of Things To Come
A team of scientists just published a report in the journal Science that documents the role polar ice sheets play in the rise of global sea levels. Polar ice sheet melting in Antarctica and Greenland have contributed to a half-inch rise in sea levels over the past 20 years, they concluded.
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But don't bust out your "Global Warming Is A Hoax" hat just yet.
The study shows that recent melting is occurring at a pace roughly three times faster than anything recorded so far. That means that while polar ice sheet melting contributed to 10 percent of the sea rise in the 1990s, it accounts for 30 percent of sea-level rise today. There has been an overall increase in seal levels of a half-foot in the last century. It might not sound like a big deal, but for the superstorm-Sandy-ravaged East Coast, a few extra inches of water made the difference between coastal flooding and catastrophe.
In the 1990s, the polar ice sheets lost an average of 110 billion tons of ice a year. That rate increased to 379 billion tons a year between 2005 and 2010. Data from 2012 wasn't included in the study, a year in which Greenland experienced a record-breaking thaw.
The study involved 26 laboratories and was supported by the European Space Agency and the U.S. National Aeronautics and Space Administration. The data used for the study were based on measurements from 10 separate satellite missions. It was a comprehensive study that needed to be done due to a lack of understanding in the scientific community about how the polar ice sheets were behaving in the face of global warming, and what, exactly, their effect was on global sea levels. Until this study, scientists didn't have a clear answer as to whether or not the polar ice sheets were definitely melting.
Andy Shepherd, of the University of Leeds and a lead author on the study, told NPR that the results are, finally, conclusive.
"It wasn't clear because of the uncertainty of the data whether the ice sheet was growing or shrinking," Shepherd said. "And now we're able to say with confidence, over all that time period, that it was shrinking."
Shepherd went on to say that it's "good news" the polar ice sheets have only contributed to a half-inch rise over 20 years. But increased melting rates are unpredictable, and study co-author Ian Joughin believes people should be wary.
"[Increased melting rates} are a big cause for concern. What we really don't know is how much they are going to continue to go up. Unfortunately, there's a lot we still don't understand about the various processes that are controlling the fast ice flow, and how fast icebergs are discharged to the ocean" he told NPR.
There is enough ice in the polar ice sheets to raise sea levels by 200 feet.
Global warming doesn't just increase the sea level by melting polar ice sheets. Some estimates put almost half the sea-level increase of recent decades on warmer water itself. As the water warms, it expands and takes up more space.
The polar ice sheets in Greenland are melting at a faster rate than their southern counterparts in Antarctica, according to the study. This could be a possible explanation for the sea-level changes along the Eastern Coast of the U.S., which are experiencing sea levels rises that are three times higher than the global average.
"Cities in the hotspot, like Norfolk, New York and Boston already experience damaging floods during relatively low-intensity storms," Asbury Sallenger of the USGS said in a statement. "Ongoing accelerated sea-level rise in the hotspot will make coastal cities and surrounding areas increasingly vulnerable to flooding by adding to the height that storm surge and breaking waves reach on the coast."
Greenland's polar ice sheet is melting faster because of a double-down of warmth coming from increased ocean temperatures and warmer air. The average air temperature in Greenland is already warmer than Antarctica; so small increases mean much warmer temperatures for the northern polar ice sheets. Researchers don't yet know how much melting is caused by warm water and how much is caused by warm air, just that the two factors are combining for increased ice sheet melt.
But the situation in Greenland and the changes to sea level already observed are making some scientists nervous.
"If you extrapolate these results, Greenland is going to be a serious contributor to global sea-level rise" in coming years, Peter Wadhams, a professor of ocean physics at the University of Cambridge, England told the Wall Street Journal. "Its contribution, relative to other sources, is becoming greater and greater," he said.
Scientists once thought that global warming could raise the sea level by 10 feet by the end of the century. They've revised that estimate, and most experts believe the change will be closer to two or three feet. It doesn't sound like much, but Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research near Berlin told NPR a three-foot rise (one meter) is actually a very big deal.
"What today is a once-in-a-century storm surge event in New York City would happen every three years if you had a 1-meter rise in sea level," he said. "So a 1-meter sea level rise is huge."
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