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| Earth on Jun 19, 2011

Beautiful barrier islands seen from space, as sea level rises

If you love Earth’s oceans, check out this NASA survey – released in spring 2011 – offering new insights about barrier islands.

If you love Earth’s oceans and are curious about our world’s barrier islands – narrow strips of sand that parallel mainland coastlines – check out this article and interview by NASA.

It’s about a fascinating new survey of barrier islands – based on a global collection of satellite images from Landsat 7 as well as information from topographic and navigational charts – published in spring 2011.

NASA calls the survey “the most thorough assessment to date” of barrier islands, and none too soon. Sea level rose by an average of 1.7 millimeters (about 1/16 of an inch) per year during the 20th century. The average rise has increased to 3.27 millimeters (about 1/8 of an inch) per year since 1993. Scientists estimate that the rate of sea level rise will likely double or triple in the next 100 years due to climate change. Sea level rise in the 21st century will change the face of the world’s barrier islands, eroding and swamping some and creating new ones. These small islands, by the way, help protect coastal ecosystems during storms. Without barrier islands, many coastal wetlands could not exist.

Barrier island facing the Beaufort Sea, on the northern edge of Canada's Northwest Territories. Image Credit: NASA's Earth Observatory

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The satellite images used in the NASA survey were captured in 2000 and processed by a private company as part of an effort funded by NASA and the U.S. Geological Survey. Matthew Stutz of Meredith College, Raleigh, North Carolina, and Orrin Pilkey of Duke University, Durham, North Carolina led the survey.

Stutz, the study’s lead author, highlighted a series of key findings from the new survey during an interview with a NASA science writer. Here are some of the things they talked about:

Every barrier island is unique. Complex forces act on barrier island chains that underpin how islands form and how they’re likely to change over time.

Sea level rise can eliminate – or create – barrier islands. Extremely rapid sea level rise – especially when coupled with decreases in sediment supply – can inundate islands, causing them to break up and disappear.

There are far more barrier islands than previously thought. A survey conducted by the same researchers tallied 1,492 barrier islands in 2001, but Stutz and Pilkey counted more than 2,149 this time.

Previously unrecognized barrier islands along the northeast coast of Brazil, midway between the mouth of the Amazon River and the coastal city of São Luís. Image Credit: NASA's Earth Observatory

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Barrier islands cluster along tectonically calm coasts. In contrast, continental margins near actively colliding plates, which generate earthquakes and volcanoes, produce fewer barrier islands.

Northern hemisphere and southern hemisphere islands differ. The majority of northern hemisphere islands are in high-latitude Arctic or temperate climate zones, while most southern hemisphere islands are tropical.

Storms are key molders of barrier island shape. Storms tend to cause islands to retreat, carve new inlets that make them shorter and more numerous, and sometimes destroy them completely.

Arctic barrier islands are retreating the fastest. No surprise there, since temperatures are rising faster in the Arctic than elsewhere on Earth. Melting of sea ice and the permafrost that buffers arctic islands from waves have left them susceptible to constant pounding from storms.

As always, say these scientists, more research is needed. Stutz said:

It would be nice if we could say we can predict exactly how a given island or island chain will react to rising sea levels or some other environmental change, but we’re simply not there yet for most islands, especially for many tropical islands where research dollars are scarce. We’re still a long way from being able to accurately model how an individual island will change as a result of climate change or even simple development pressure.

Bottom line: A NASA survey of Earth’s barrier islands – released in spring 2011 – offers new insights about these narrow strips of land that line the world’s coastlines, protecting coastal ecosystems. Increasingly rapid sea level rise in the 21st century is expected to change the face of Earth’s barrier islands.

More barrier islands on Earth than previously thought

Harold Wanless on sea level rise in South Florida

William Chameides talks about America’s Climate Choices

Read more from NASA: What Will Climate Change and Sea Level Rise Mean for Barrier Islands?