The Rise in Sea Levels Could Be Almost Double Previous Estimates

Sea levels could rise an additional 39 inches by the end of the century — almost doubling previous estimates of the total potential increases in sea levels — due to the melting of Antarctic ice from climate change, according to a new study.

To put that into context, such an amount of extra ocean water would have put Hurricane Sandy's maximum flood height at the tip of Manhattan in 2012 at more than 17 feet, while parts of Hurricane Katrina's surge along in New Orleans in 2005 would have been taller than 23 feet.

The scenario is even more dire when combined with what we already know. The newly-identified increase from melting Antarctic ice would add to other climate change effects that the Intergovernmental Panel on Climate Change has predicted are on track to hiking sea levels by between 20 and 39 inches by 2100.

"This could spell disaster for many low-lying cities. For example, Boston could see more than 1.5 meters [about 5 feet] of sea-level rise in the next 100 years," said University of Massachusetts Climatologist Robert DeConto, a study co-author, in a statement. "But the good news is that an aggressive reduction in emissions will limit the risk of major Antarctic ice sheet retreat."

Published on Wednesday in the journal Nature, the study is yet another reminder that massive stretches of the world's coastlines, where most of humankind lives and works, will be inundated unless people erect costly defenses or curb carbon emissions substantially — though both are likely necessary.

"All the big airports from here to Boston are built on land near the water," said Larry Atkinson, an oceanographer at Old Dominion University in Norfolk, Virginia, a seaside city that's among the most vulnerable in the United States to higher sea levels. "It takes 50 years to move an airport. We should start thinking now."

The rising waters won't stop either. If greenhouse gas emissions continue unabated at current levels, the study predicts disappearing ice will add an additional 49 feet to sea levels by 2500.

The rapid increase in sea levels stems from warm ocean water melting the Antarctic ice sheets from the bottom up, the study said. The sheets then break off from their glaciers, hastening the melting process as they drift into warmer waters.

Anthony Carpi, an environmental scientist and dean of research at John Jay College in New York City, pointed out the Antarctic contains 90 percent of the world's fresh water — and the alarming results of the study show how previous sea level forecasts haven't adequately taken temperature trends in the South Pole into account.

"This is relatively unexpected," Carpi said. "We have models that predict sea level change in response to climate change, but most of them assume that ice sheets on both the continents of Antarctica and Greenland were relatively stable and wouldn't melt significantly. [The study] throws into the mix some pretty major melting of those sheets."

Both Atkinson and Carpi warn governments are moving too slowly to adequately deal with the issue.

New York State, for instance, has spent billions on recovering from Hurricane Sandy, and a number of ambitious plans have been floated to blunt future storms, including a seawall around Manhattan, and artificial reefs and oyster beds to protect Brooklyn.

Officials in the Norfolk area — home to the world's biggest naval base — are already thinking ahead, too. "There's a band of high land [in Norfolk]," said Atkinson. "If you are going to build a new hospital complex or high school, you are going to build it on that arc."

President Barack Obama agreed to carbon emission cuts at the United Nations Climate Change Conference in Paris last year with the goal of limiting global warming to less than 2 degrees Celsius compared to pre-industrial levels. He's also signed executive orders that compel federal agencies to take climate change into consideration when constructing new facilities.

But Atkinson says politicians in Washington have not given combating climate change or effects like a rising ocean sufficient emphasis. "The risk is so far out," he said. "It's just hard for people. People have anxiety buckets. They are already full. They don't want to throw this into them too."

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