New York City flood risk rising due to climate change

http://www.usatoday.com/story/weather/2015/09/28/new-york-city-flooding-floods-flood-hurricane-sandy-climate-change/72987564/

The risk of major New York City flooding — such as what happened during Superstorm Sandy in 2012 — is likely to occur once every 25 years, rather than every 500 years, as a result of human-caused global warming, says a study released Monday.

The study, published in the Proceedings of the National Academy of Sciences, found that flood heights have risen about 4 feet since the year 850 to 2005, largely because of sea-level rise.

"Sea level is rising because of climate change," said Penn State meteorologist Michael Mann, one of the study's scientists. "But climate change also appears to be leading to larger and more intense tropical storms," he said.

During Sandy, many of New York City's subway and traffic tunnels flooded, and the storm surge breached the sea walls on the southern tip of Manhattan. The high storm surge was the result of a combination of factors, including rising sea level, high tide and the storm's force.

Monday's study was released a month before the third anniversary of Sandy, which slammed New York and New Jersey coasts on Oct. 30, 2012, killing dozens of people and causing $50 billion in damage.

"We wanted to look at the impact of climate change on sea level and storm characteristics to see how that has affected the storm surge on the Atlantic coast, specifically in New York City," said Andra Reed, a graduate student in meteorology at Penn State and the study's lead author. "Hurricane Sandy was the motivating factor."

Adam Sobel, a Columbia University atmospheric scientist who was not part of the study, told the Associated Press that the report, like many others, leaves little doubt that sea-level rise will be more rapid than it had been.

"This is just one more good study adding certainty to what we know already, which is that coastal cities around the world — including New York, but we're not the only one, nor the worst — are in trouble," Sobel said.

As for blizzards and nor'easters that aren't hurricanes, "we may see increasing flood heights associated with such storms for the New York City region, at least due to the rising sea levels discussed in our study," the study's Reed said.

She admits that nor'easters are very different storms than hurricanes, so a definite connection cannot be made.

Global warming causes sea-level rise in the following manner: As temperatures warm around the world, so do the seas. Heat-trapping greenhouse gases released by the burning of coal, oil and gas cause more ice glaciers and ice sheets to melt and water to expand. Warmer water takes up more space than cooler water. Scientists say global warming will be the primary cause of future sea-level rise.