Study: Sea Levels In Northeast Jumped By About 4 Inches In Two Years

Even the most dire predictions about global warming, and the accompanying rise in sea levels, estimate that the most severe and observable effects of rising ocean levels will not be seen for at least a few more decades.

But Long Island and New England appear to be well ahead of that curve.

A study recently published in the scientific journal Nature notes that the East Coast of the United States, from the New York Bight northward, saw a leap in sea levels of nearly 4 inches in just two years, in 2009 and 2010, while the standard observed average sea level rise worldwide has been only about 1 inch every 10 years. To the north, in Maine, the jump was closer to 5 inches over the same span.

The cause, the study notes, was not a more rapid localized version of global warming, but rather a dramatic change in the rate of the ocean current known as the Gulf Stream, which flows past the Northeast about 200 miles off the coast of Long Island.

The average speed at which the Gulf Stream is flowing northward off the Eastern Seaboard slowed by nearly 30 percent in the same period in which tide gauges along the coastline recorded the spike in sea levels. The slowdown was part of an overall flicker in the complex system of ocean currents that circulate water throughout the North Atlantic, the Caribbean and the Gulf of Mexico, known as the Atlantic Meridional Overturning Circulation.

The slowing of the Gulf Stream was also blamed for severe winters in Europe, which is kept warm despite its northern latitudes by the stream sending a plume of warm water toward its coastline. Some of the worst-case scenarios from climate change predictions have said that the loss of ice in the Arctic could starve the entire Atlantic current system of the freshwater that drives it, stifling the Gulf Stream and leaving Europe with a sub-Arctic climate more on par with that of northern Canada and Russia.

Short of that extreme, Stony Brook University Professor Henry Bokuniewicz, Ph.D., said that fluctuations in major ocean currents can dramatically affect the height along their fringes, depending on their rate of flow.

“As currents speed up or slow down, the sea water going across the currents actually tilts … so it’s higher on one side than on the other,” Dr. Bokuniewicz explained. “Coriolis force pushes the Gulf Stream to the right, so the pressure on the right side is greater than on the left. That pushes it up on one side and down on the other.

“So if the Gulf Stream slows down, and is pushing less hard on the right side, the sea level goes up along the coast,” he continued.

According to the study, conducted by scientists from the National Oceanic and Atmospheric Administration, or NOAA, and the University of Arizona, the slowing of the currents caused sea levels along the shores of the Northeast to swell quickly in 2009, 2010 and early 2011, causing flooding and beach erosion that would normally be seen only during strong storms.

“This event caused persistent and widespread coastal flooding, even without apparent weather processes,” the study’s authors wrote. “In terms of beach erosion, the impact … [was] almost as significant as some hurricane events.”

But local scientists say that the jump in sea levels locally does not mean that Long Island residents should be preparing to evacuate the coastline in the near future. The bump was mostly likely only a temporary phenomenon and will fold into the overall global average of an inch per decade over a longer time.

“These factors go through annual variations—some years it rises fast, some more slowly,” said Dr. Bokuniewicz, a professor at Stony Brook University’s School of Marine and Atmospheric Sciences. “The average of about 1 inch per decade would still be expected to be maintained in the long term.”

A number of other factors can also raise sea levels, such as the temperature of water, which gets less dense and expands as it warms. That effect is noticeable on tide gauges as the seasons change in any given year, Dr. Bokuniewicz said.

He also noted that, despite the increased levels of erosion and flooding noted in the study, the 4-inch increase overall is a relatively small one in terms of threats to people and their property.

“If you put it in the perspective of what we deal with every time a storm comes through, it’s pretty minor,” he said. “Even a small storm might raise the water level 2 feet. But this certainly doesn’t help the flooding or erosion problems.”