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An SUV plows through the brackish water on 7th Ave. in Normandy Beach, NJ, during a 2010 storm. (Aristide Economopoulos | The Star-Ledger)

In much of the measurable world, a four-inch change — about the length of the screen on an old iPhone — doesn't amount to much.



But in oceanography, it's huge, and a new study published this week shows that sea levels along the east coast jumped up to four inches and stayed that way for two years in 2009-2010.



To ocean-watchers, the rise in sea levels, particularly from Newfoundland to New York, constituted an "extreme sea level rise event," according to Paul Goddard, a geosciences doctoral candidate at the University of Arizona and lead author of the paper published in the journal Nature Communications.



Statistical analysis suggests how extreme the sea level rise was: a 1-in-850 year event, the study said. It is "unprecedented during the past century," he said.



The rise in the sea level began to taper off south of New York City, but Goddard said measurements of a gauge near Cape May still showed a three-inch rise during that time, which is still considered high. Tide gauge stations off Sandy Hook and Atlantic City did not provide data that could be used in the study, he said.



The researchers found a prolonged sea level rise as far south as Cape Hatteras, N.C.

Coastal sea levels still haven't returned to 2009 levels, Goddard said.



Such a sea level rise is equivalent to jamming 30 years of normal sea level rises into that two-year period, said Jon Miller, a Stevens Institute of Technology/New Jersey Sea Grant coastal specialist.



The one bit of good news is that the forces driving the change are not permanent, said Miller, who was not on the research team. "It goes up, but it does come down," he said.



It's not just the sea level rise that is noteworthy, Goddard added.



"The thing that stands out is the time extent of this event," as well as the amount of coastline affected, he said. "This event is not associated with any particular storm or hurricane, which would cause hourly or daily extreme sea levels."



The two-year rise caused "persistent and widespread" flooding, without the assistance of storms, and also caused beach erosion "almost as significant as some hurricane events," the study said.



Miller said the erosion then was not on the level of Hurricane Sandy erosion, saying beach erosion then was "more akin to extreme seasonal change."



Miller did recall people complaining about more frequent nuisance flooding during that period.



The causes behind this water level rise involve ocean circulation and the atmosphere, the study says. Specifically, the study said a circulation pattern known as the Atlantic Meridional Overturning Circulation showed a marked decline in strength at that time.



This particular circulation pattern brings warm tropical water north, where it cools, gets denser and sinks before it heads back south, according to the National Oceanic and Atmospheric Administration.



A co-author of Goddard's, Jainjuin Yin, assistant professor of geosciences at the university, studied ocean changes that suggested a weakening of the circulation pattern could lead to higher sea levels in North America.



While this was happening, a second phenomenon was occurring. A climate pattern called the North American Oscillation took shape such that winds would push water onto the northeast coast, the study said.



The findings in the report do nothing to diminish the impact global warming is having on coastal communities, Goddard said. If anything, the study says extreme sea level events may be linked to "human-induced climate change" and may worsen the impact of major storms.



Adding melting Artic and Antarctic ice will likely add to a future of higher sea levels along the North American coast, especially the northeast, the study said.



"For the 21st century, modeling results suggest that the increase in the greenhouse gas concentrations is likely to cause more extreme sea level rise events ... along this densely populated coast," it says. "Once coastal storms compound high sea levels, more damages will result."



Scientists from NOAA's Geophysical Fluid Dynamics Laboratory in Princeton also contributed to the study. NOAA funded the research.



Tim Darragh may be reached at tdarragh@njadvancemedia.com. Follow him on Twitter @timdarragh. Find NJ.com on Facebook.