The rates of sea level rise along the U.S. Atlantic Coast are increasing 3 to 4 times faster than they are globally, according to a new report by the U.S. Geological Survey.
“Since about 1990, sea-level rise in the 600-mile stretch of coastal zone from Cape Hatteras, N.C. to north of Boston, Mass. — coined a ‘hotspot’ by scientists — has increased 2 — 3.7 millimeters per year; the global increase over the same period was 0.6 — 1.0 millimeter per year.”
The data and analysis in the report indicates that as temperatures continue to rise, the rates of sea level rise along the U.S. Atlantic Coast will continue to increase.
The report also makes a connection between the ‘hotspot’ located along the U.S. Atlantic Coast and the slowing of the Atlantic Ocean circulation. Computer models show that this observed change in circulation is possibly tied to changes in water temperature, salinity, and density, in the sub-polar North Atlantic.
“Many people mistakenly think that the rate of sea level rise is the same everywhere as glaciers and ice caps melt, increasing the volume of ocean water, but other effects can be as large or larger than the so-called ‘eustatic’ rise,” said USGS Director Marcia McNutt. “As demonstrated in this study, regional oceanographic contributions must be taken into account in planning for what happens to coastal property.”
Though there are projections of a sea level rise of roughly two to three feet, or more, by 2100; the rise isn’t consistent around the globe, the levels vary regionally. “Differences in land movements, strength of ocean currents, water temperatures, and salinity can cause regional and local highs and lows in sea level.”
“Cities in the hotspot, like Norfolk, New York, and Boston already experience damaging floods during relatively low intensity storms,” said Dr. Asbury (Abby) Sallenger, USGS oceanographer and project lead. “Ongoing accelerated sea level rise in the hotspot will make coastal cities and surrounding areas increasingly vulnerable to flooding by adding to the height that storm surge and breaking waves reach on the coast.”
“During the 21st century, the increases in sea level rise rate that have already occurred in the hotspot will yield increases in sea level of 8 to 11.4 inches by 2100. This regional sea level increase would be in addition to components of global sea level rise.”
“To determine accelerations of sea level, USGS scientists analyzed tide gauge data throughout much of North America in a way that removed long-term (linear) trends associated with vertical land movements. This allowed them to focus on recent changes in rates of sea-level rise caused, for example, by changes in ocean circulation.”
Sea levels globally are projected in some cases to rise a foot by 2050, and double the risk of coastal floods in many areas. However, the projections actually range as high as 19 inches by 2050, a foot being on the conservative side. With the regional sea rise along the Atlantic Coast factored in, many of the largest cities in the U.S. face the possibility of massive, expensive floods occurring regularly.