Editor’s Comments: Understanding Sea-Level Rise

The US Geological Survey released a disturbing report in June. Since 1990, according to tide gauge data collected throughout North America by USGS scientists, sea-level rise along parts of the East Coast is occurring much faster than predicted. The full report is available online at http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1597.html.

When we think of sea-level rise, most of us tend to think of the world’s oceans as one giant bathtub, so to speak, with the continents scattered throughout; it seems intuitive that if the amount of water in the bathtub increases, the water level should go up pretty much the same amount all over the world.

That’s only partly true, it turns out. The water level is increasing as ice caps and glaciers melt. But, as the report details, and as USGS Director Marcia McNutt has explained in interviews, the rate of rise varies tremendously in different parts of the globe.

Several things contribute to the differences, including regional temperatures and salinity of the water. Changes in density and salinity in the north Atlantic, for example, may be altering the circulation patterns throughout the entire Atlantic Ocean, resulting in regional variations in water level.

If you’re already in a low-lying area-the Seychelles islands, for example-you probably already have a good sense that the water level is rising, and you’re aware of the problems that’s going to cause. But if you’re in an area that’s somewhat higher or farther inland, you might not have the same sense of urgency.

Ironically enough, because of all these variables, sea level rise in the Republic of Seychelles has actually been less than in many other-more unexpected-parts of the Indian Ocean, such as the eastern coast of Africa.

On the East Coast of the United States, a roughly 600-mile stretch from North Carolina to Massachusetts is experiencing a higher-than-expected increase, ranging from 2 to 3.7 millimeters per year, compared to a millimeter or less on average worldwide. Scientists expect this rate of increase to remain fairly steady.

The practical question becomes how to prepare for the increase, a topic we covered back in 1999 in “The Rising Tide:  Global Warming Accelerated Coastal Erosion,” http://www.erosioncontrol.com/EC/Articles/4856.aspx, and again as recently as our last issue with the “Shoreline Strategies” article on the front cover, http://www.erosioncontrol.com/EC/articles/17159.aspx. A series of articles coming up in Erosion Control will continue to explore the options-from structural solutions to policy changes in coastal areas-and will include interviews with people in some of the areas that expect to be hit hard by the changes, such as Olympia, Washington, where much of the downtown area is built on fill from an inlet and lies only about a foot above the current tidal elevation.

The author of the first couple of articles is David C. Richardson, an environmental journalist and longtime writer for Forester publications, who has just been awarded a fellowship to the Woods Hole Oceanographic Institution in Massachusetts. Look for his first article in the September/October 2012 issue, and add your questions and comments to the online versions of the articles at http://www.erosioncontrol.com.