Sunday, January 08, 2012

A real sea change

From: Scientific American Blog

By Mathew Stutz

International diplomats met two weeks ago at the UN Durban Climate Change Conference in South Africa to discuss a greenhouse gas reduction plan—displaying no urgency to reach any meaningful agreement. Meanwhile, researchers at the American Geophysical Union annual meeting in San Francisco are reporting what many scientists have suspected for a long time but have been thus far not been able to prove convincingly—that the world’s sea level is likely to rise by at least 3 feet in the next 100 years.

The vast Greenland ice sheet is melting at an increasingly rapid rate—much faster than most conservative estimates made by, among other authorities, the UN’s own Intergovernmental Panel on Climate Change (IPCC). In the last decade, scientific technologies have made fast advances toward more confident and precise measurements of the complex changes in the Greenland ice sheet.

Previous estimates by the IPCC were kept low because there was so much uncertainty in the measurements. Many suspected it was melting faster, but at best could only support such claims anecdotally. This scientific uncertainty has been cast erroneously by some as evidence that the risk of glacial melting was being exaggerated. It was always a distinct possibility that the ice sheets were melting more rapidly.

What’s more worrying is the range of possibilities is growing larger. Due to the nonlinear behavior of melting ice, a slight increase in the rate of melting now would result in an enormous difference in how much ice melts over the next 100 years. You can relate this powerful effect to how much a homeowner saves from a 1-2% drop in interest rates over the life of a 30-year mortgage.

Think of it this way—if sea level is forecast to rise 1 foot, it is really a mid-range estimate between 0.5 feet and 2 feet. If the mid-range estimate is now 2 feet or even 3 feet, the possible range suddenly expands from 1.5 to 6 feet. Our coastal inhabitants and managers must be able to comprehend the scope of what such a change would mean for us.

We can look to Louisiana to see a parallel. The Louisiana coast, made up of the expansive Mississippi Delta, has been ground zero for an ongoing coastal catastrophe for decades. Due to numerous man-made alterations, the delta is sinking, that is the sea level is rising, as much as 3 feet per century (leaving some portions of New Orleans 10 feet below sea level). As a result, one football field-sized area drowns on the Mississippi Delta every hour, 15 square miles every year.

At one time Louisiana had numerous strings of sandy barrier islands along the delta, some having served as popular resorts as far back as the mid- 1800’s. Those that remain today are shifting landward and shrinking in size faster than any other barrier islands in the lower US. Hurricanes have finished off most of the Chandelier Islands, Timbalier Island, and Isles Dernieres—and the remaining ones will eventually suffer the same fate.

The Chesapeake and the Albemarle-Pamlico estuaries are the next largest coastal wetland systems in the US. If the Mississippi Delta barrier islands and wetlands give us any insight about the future of the Outer Banks and the Albemarle-Pamlico system, they don’t stand a chance facing 3 feet of sea level rise.

The Outer Banks of North Carolina differ significantly from Louisiana’s barrier islands. Louisiana never had one continuous unbroken line of islands; the Outer Banks are wider and higher in many places. We may not see a total collapse of the entire Outer Banks but it is a virtual certainty that we will see the islands migrating toward the mainland. Patch-up jobs will not suffice. Within the sounds, the marsh and swamplands will disappear in a similar fashion to the Louisiana marshes.

There is no credible reason to believe that sea level will not continue to rise indefinitely. The year 2100 is not the end of time. Will 3 feet become 6 feet or 10 feet? There is enough ice in the Greenland ice cap to raise sea level by 20 feet, and Antarctica has 10 times more ice than Greenland. Whatever happens centuries from now, the immediate future has enough potential for catastrophic change that we can’t just bury our proverbial heads in the sand and hope that we can patch up our beaches or stick our fingers in the dike.

It is time to make bold and innovative changes to our future economic and environmental planning for our coast. In the past we worried about saving a few beach houses; we must see that the news we are receiving now threatens our entire coastal economy.

Cape Hatteras, North Carolina area as seen from Apollo 9

This imagery was acquired by the NOAA Remote Sensing Division to support NOAA national security and emergency response requirements. In addition, it will be used for ongoing research efforts for testing and developing standards for airborne digital imagery.  Individual images have been combined into a larger mosaic and tiled for distribution. The approximate ground sample distance (GSD) for each pixel is 50 cm (1.64 feet). Image file size is between 1 MB and 6 MB and covers 2.5 by 2.5 kilometers (1.55 miles.). NASA JSC Digital Image Collection

Mathew StutzAbout the Author: Mathew Stutz is an assistant professor of geoscience at Meredith College in Raleigh, NC. Stutz recently conducted a global survey with researchers at Duke University that found the Earth has 657 more barrier islands than previously known. His research also examines how climate change impacts the formation and evolution of these islands.

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