Sea level is rising all over the world thanks to the heat-trapping effect of greenhouse-gas emissions, but according to a new study published in the Journal of Coastal Research, the northeastern U.S. and eastern Canada have seen the ocean rise at an accelerating rate in recent decades.
Based on readings at 23 tidal gauges stretching along the entire East Coast, John Boon of the Virginia Institute of Marine Science has determined that the rate of sea level rise began to accelerate in 1987 at points north of Norfolk, Va.
Considerable beach erosion at Surf City, New Jersey.
Credit: Jim Phillips
Boone concluded that if the acceleration continues at this rate — something that is not certain at this point — Boston will see 27 inches of sea-level rise by 2050, New York will see 20 inches and Norfolk will see 24 inches.
By contrast, Charleston, S.C., whose rate of sea level rise is closer to the worldwide average, will see less than 6 inches. (In all locations, the bulk of sea level rise will happen in the second half of the century, as warming temperatures continue to transfer more and more freshwater from the ice sheets in Greenland and Antarctica into the sea).
Scientists broadly agree that on a worldwide basis, sea level, already 8 inches higher than it was in 1900, is likely to go up by another 3 feet or so by the end of this century. That’s a global average. However, depending on local conditions, the change could be less in some areas, and greater, along with a greater threat to life and property, in others. The new study, which reinforces research published in Nature Climate Change last June, says that the northeastern U.S. falls into the “greater” category.
The increase was most evident at the eight stations with continuous records stretching back 75 years or more: Halifax, Nova Scotia; Portland, Maine; Boston; New York’s Battery; Sandy Hook and Atlantic City, N.J.; Baltimore, and Norfolk. Eight more stations in the same region, with records going back 43 years, also showed acceleration, although the speedup was less clear due to the shorter observation period.
Stations south of Norfolk, on the other hand, showed no acceleration. “Sea level is rising at these stations,” Boon said in a press release, “but there is no statistically significant acceleration in the rise rate during the period of record.”
The natural question, of course, is why this is happening? Boon offered no concrete answer, but suggested that it may have to do with a possible slowdown in the Gulf Stream as glacial meltwater dilutes the salty North Atlantic and weakens the circulation of warm water to toward the poles. That would make water pile up behind the slowdown, like traffic on a congested highway.
That’s not the only factor that affects local sea level. Another is the fact that some land is rising, still rebounding from the disappearance of the glaciers thousands of years ago, while other land is sinking. That’s one reason Norfolk’s projected sea level rise by 2050 is nearly as great as Boston’s: the Gulf Stream effect would be less in Virginia, but the land around Norfolk is sinking.
For people who are actually affected by rising seas and the increased coastal flooding they’re sure to bring, the overall exposure is what matters “My analysis focuses on relative sea level,” Boon said. “That value — the height of the sea surface in relation to the land, is what really matters to coastal communities.”
And if heat-trapping greenhouse gases continue to build in the atmosphere, that height is just going to keep going up.