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East Coast Faces Rising Seas From Slowing Gulf Stream

Experts on the sea level rise triggered by climate change have long known that it will proceed faster in some places than others. The mid-Atlantic coast of the U.S. is one of them, and the reason — in theory, anyway — is that global warming should slow the flow of the Gulf Stream as it moves north and then east toward northern Europe.

Now there’s a smoking gun that appears to validate the theory. A study in the February Journal of Geophysical Research: Oceans ties the measured acceleration of sea level rise in this area to a simultaneous slowdown in the flow of the Gulf Stream. “There have been several papers showing (sea level rise) acceleration,” said lead author Tal Ezer, of Old Dominion University’s Center for Coastal Physical Oceanography. “This new paper confirms the hypothesis for why it’s happening.” 

When higher seas are pushed ashore by a major event like Hurricane Sandy, the impact can be devastating.

Even without faster-than-average sea level rise, America’s East Coast would be at high risk. On average, scientists have projected that the oceans should rise by about 3 feet by 2100, inundating low-lying land, contaminating water supplies and undermining roads, airports, port facilities and power plants. Add the storm surges that come with hurricanes and other severe weather, and the danger gets even worse. A worldwide average of 8 inches of sea level rise since 1900 has already put millions of Americans at risk; 3 feet more will greatly multiply that risk; and the even higher levels that Americans could see will be a very bitter icing on top of that already unpleasant cake.

The slowing of the Gulf Steam is not the only reason the U.S. coast will see higher sea level than the world average in coming decades, Ezer said. In some places, the land itself is slowly sinking as it readjusts to the disappearance of continental ice sheets more than 10,000 years ago.

But that process can’t explain why sea level rise should actually be speeding up, as a report in the Journal of Coastal Research documented in October 2012. Another study, which appeared in Nature Climate Change in June 2012, showed the same thing, and suggested that a Gulf Stream slowdown could be a contributing factor. Ezer’s own paper in Geophysical Research Letters in September 2012, documented the phenomenon in Chesapeake Bay, and once again, suggested the Gulf Stream’s possible role.

Storm surge from Hurricane Sandy paralyzed the Hoboken, N.J., PATH system in last October's storm.

What makes this new study different is that it includes actual measurements of the Gulf Stream’s flow, from instruments mounted on underwater cables that stretch across the Florida Strait. It also uses satellite altimeter data to document changes in the height of the ocean from one side of the Gulf Stream to the other. Normally, the northeasterly flow of the stream literally pulls water away from the coast.

“It keeps coastal sea level a meter or a meter and a half lower than the rest of the ocean,” Ezer said. In recent years, however, the satellites show that the midpoint of the Gulf Stream doesn’t have as high an elevation as it used to, and that the edges aren’t quite as low — again, evidence that the stream itself is starting to slow down.

Theory says this is just what should be happening. Ordinarily, the Gulf Stream brings warm surface water from the tropics up along the U.S. coast, and then across to the eastern North Atlantic, where it cools and sinks to the bottom of the sea. The cold bottom water then flows south to the tropics, where it gradually warms, rises to the surface, and begins flowing north again. This constant flow, which meanders through all of the world’s oceans is sometimes called the global ocean conveyor belt, and the section that operates in the North Atlantic is called the Atlantic Meridional Overturning Circulation.

In a warming world, two things happen to throw a monkey wrench into the conveyor belt. First, melting ice, mostly from Greenland, dilutes the surface waters where the Gulf Stream reaches its northernmost extent. Since fresh water is less dense than salty water, the water has a more difficult time sinking to begin its journey southward. Second, the surface water is warmer than it used to be, and since warm water is less dense than cold water, this just adds to the problem.

Put the two together and you start to jam up the works, with the result that the whole conveyor belt slows down. And the water along the Atlantic coast of the U.S. begins to rise at an accelerating rate. While scientists expect sea level to rise by about 3 feet over the next 90 years or so, in places like New York City and Norfolk, Va., it could be significantly more. New York, where sea level is already a foot higher than it was in 1900, was just reminded of what happens when higher seas are pushed ashore by a major event like Superstorm Sandy.

Add several more feet of sea level to that destructive equation, and the potential destruction is difficult to imagine. 

Related Content
The Secret of Sea Level Rise: It Will Vary Greatly by Region
Sea Level Rising Faster Than Average In Northeastern U.S.
Arctic Storms: A Climate Danger Nobody’s Talking About
Climate Change, Sea Level Rise Spurring Beach Erosion
Three New Studies on Sea Level Rise Bring New Concerns
Sandy's Storm Surge Explained and Why It Matters

Comments

By Paul Richardson (York County/Virginia/23696)
on February 12th, 2013

Three words: wind, water, and solar. We have the technology and the resources to meet all of our energy demands, including transportation,  with wind water and solar.  Don’t believe me?  Just google Mark Z. Jacobson who is a civil and environmental engineer at Stanford.  He’s actually crunched the numbers and drafted a plan!  It’s the only way out of this mess, and it could be a huge boost to our economy to boot!

http://www.scientificamerican.com/article.cfm?id=a-path-to-sustainable-energy-by-2030

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By Dave (Basking Ridge, NJ 07920)
on February 13th, 2013

The gulf stream is huge – typically about 100 kilometers wide and about 1kilometer deep. You can’t expect to switch off / slow down something like that and not have the local sea level respond in a serious way.  I read an academic report somewhere that a slowing down of the gulf stream could lead to as much as an 8 inch additional SLR along the US eastern seaboard. Unfortunately I forget the specific reference but the mechanics of how something like that could– and apparently may now be starting to - happen is quite clear.

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By Chuck Greene (Ithaca, NY 14850)
on February 16th, 2013

Interesting article, but note that most of the current freshwater flux affecting the MOC and conveyor belt is not from Greenland’s melting ice sheet; it is from export from the Arctic Ocean. That Arctic Ocean freshwater is derived from precipitation and river runoff from Alaska, Canada, and Siberia; the inflow of lower salinity Pacific water into the Arctic Ocean through the Bering Strait; and, to a lesser extent, Arctic sea ice melting. Greenland’s ice sheet runoff is starting to achieve comparable levels to the runoff of large Siberian rivers, and it will only become more important with further melting.

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By William Hughes-Games (Waipara New Zealand 7447)
on February 17th, 2013

This presents an interesting possibility. If one took the sea level readings from stilling wells along the East coast and subtracted the effect of tides and of air pressure (a low passing by raises sea level, a high the reverse), one should be able to monitor the flow rate of the Gulf Stream and determine not only the change in its flow from year to year but also any seasonal changes. In so far as the Gulf Stream is powered by the freezing of ice in the Arctic and the resulting sinking brine, the Gulf Stream should pulsate over the year. At present, without as much ice cover, more ice is being produced each freezing period than in earlier years. If, for instance, the Gulf Stream pulsates with a delay of 6 months from the push to the move due to the inertia of that huge amount of flowing water, one would expect a strong Gulf Stream in the summer giving warm wet summers to the UK and a weak gulf stream in winter, giving cold nasty winters.

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By Chuck Schlicher (Portland, ME 04102)
on April 2nd, 2014

“In some places, the land itself is slowly sinking as it readjusts to the disappearance of continental ice sheets more than 10,000 years ago.”

I believe this statement is wrong.  In fact, the opposite is true… a phenomenon known as isostatic rebound.

http://en.wikipedia.org/wiki/Post-glacial_rebound

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