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четверг, 31 марта 2016 г.

Scientists nearly double sea level rise projections for 2100, because of Antarctica




This story has been updated.
Sea levels could rise nearly twice as much as previously predicted by the end of this century if carbon dioxide emissions continue unabated, an outcome that could devastate coastal communities around the globe, according to new research published Wednesday. 
The main reason? Antarctica.
Scientists behind a new study published in the journal Nature used sophisticated computer models to decipher a longstanding riddle about how the massive, mostly uninhabited continent surrendered so much ice during previous warm periods on Earth. They found that similar conditions in the future could lead to monumental and irreversible increases in sea levels. If high levels of greenhouse gas emissions continue, they concluded, oceans could rise by close to two meters in total (more than six feet) by the end of the century. The melting of ice on Antarctica alone could cause seas to rise more than 15 meters (49 feet) by 2500.
The startling findings paint a far grimmer picture than current consensus predictions, which have suggested that seas could rise by just under a meter at most by the year 2100. Those estimates relied on the notion that expanding ocean waters and the melting of relatively small glaciers would fuel the majority of sea level rise, rather than the massive ice sheets of Greenland and Antarctica.
The projection “nearly doubles” prior estimates of sea level rise, which had relied on a “minimal contribution from Antarctica,” said Rob DeConto of University of Massachusetts, Amherst, who authored the study with  David Pollard of Penn State University.
The research already has created a buzz in the community of scientists studying Antarctica, and experts largely praised the new model as thorough and impressive, while noting its remaining uncertainties.
“People should not look at this as a futuristic scenario of things that may or may not happen. They should look at it as the tragic story we are following right now,” said Eric Rignot, an expert on Antarctica’s ice sheet and an earth sciences professor at the University of California, Irvine, who was not involved in Wednesday’s study. “We are not there yet … [But] with the current rate of emissions, we are heading that way.”
 
Places as far flung as South Florida, Bangladesh, Shanghai, Hampton Roads in Virginia and parts of Washington, D.C., could be engulfed by rising waters, Strauss said. Even by 2100, Miami Beach and the Florida Keys could begin to vanish. New Orleans essentially could become an island guarded by levies. Floods that pushed as far inland as the surge from Hurricane Sandy could ravage parts of the East Coast with far greater frequency.
The researchers behind Wednesday’s study make clear that their model has limitations and that human behavior can alter the possible outcomes. For instance, the worst-case scenario — of seas rising nearly 4 feet due to Antarctic ice loss alone by 2100 — assumes that very high emissions continue for carbon dioxide and other greenhouse gases.
In Paris late last year, world leaders forged an historic agreement to begin scaling back such emissions in coming years. They embraced the goal of holding global warming “well below” 2 degrees Celsius above pre-industrial levels, but at the same time, it has been widely noted that current country-level commitments to cut emissions fall far short of this target.
But even under a more moderate emissions scenario, Wednesday’s study found that the Antarctic contribution to sea level rise still could reach about two feet by 2100, and much more by 2500. Only if countries sharply reduce emissions does the model show that it’s possible to preserve Antarctica in roughly its current state.
“This research highlights the importance of doing even much better than the Paris agreement if we’re going to save our coastal cities,” Strauss said.
 
Полная версия: https://www.washingtonpost.com/news/energy-environment/wp/2016/03/30/antarctic-loss-could-double-expected-sea-level-rise-by-2100-scientists-say/?wpisrc=al_alert-hse
Play Video1:13If carbon emissions continue unabated, expanding oceans and massive ice melt would threaten global coastal communities, according to new projections. (Daron Taylor/The Washington PosShould the new research prove correct, it could trigger a “tectonic shift” in expectations for the speed and severity of the sea level problem, said Ben Strauss, director of the program on sea level rise at Climate Central, an independent organization of scientists based in New Jersey. He said that while the study’s findings represent potentially grave problems for many coastal areas in the decades ahead, the century beginning in 2100 could see truly catastrophic shifts, unless societies make sharp cuts in greenhouse gas emissio