|
Rising sea levels, caused at least partly by global climate change, are already contributing to beach erosion along the U.S. East Coast and seem likely to do so even more in the future, according to a recent study published in the journal Eos. About 70 per cent of the world's sandy beaches experience erosion, and although this is normally on a scale of no more than about one meter per year, it can be significant because most such beaches are only a few tens of meters wide. On the U.S. east coast, over 80% of beaches have experienced an underlying erosion trend over the last 150 years. There is, say the study's authors, "likely a global cause for the pervasive erosion phenomenon," but this cause is not immediately obvious. Storms are a major contributor to beach erosion, "but there is no apparent overall increase in storminess this century." In addition, human interference, often also a factor, "is neither worldwide in extent nor uniform regionally." However, the authors note, "what nearly all of the earth has experienced during the last century is an increase of relative sea level & Global mean temperature has increased about 0.5 C in the 20th century. This rise could be responsible for a significant portion (up to about 1/2) of the observed global sea level rise of nearly 20 cm during that period due to thermal expansion of the oceans and melting of small glaciers. An increasing concentration of greenhouse gases in the atmosphere is expected to raise global temperatures 1.5* to 4.5 *C in the 21st century and cause accelerated sea level rise. If it does, it will exacerbate already severe beach erosion problems along the highly developed U.S. East Coast, and oceanic beaches everywhere else." It is extremely difficult to determine accurately the extent to which sea-level rise impacts coastal beach erosion, because it is heavily masked by such other factors as shoreline changes from inlets and human engineering, as well as violent storms, which can erode in a matter of hours a greater portion of a beach than has been eroded over decades. However, by studying historical and contemporary data regarding shoreline levels and comparing with sea-level rise, the authors found strong support for an underlying correlation between rising sea levels and long-term beach erosion. In fact, on average, they found that the total extent of beach erosion is roughly 150 times that of the amount of sea-level rise. In conclusion, they note that the Intergovernmental Panel on Climate Change (IPCC) projects a further global sea-level rise of 20 cm by 2050; combined with ongoing regional post-glacial subsidence, sea levels along the coasts of New Jersey, Delaware and Maryland will rise about 40 cm during that period. "This projected rise," they conclude, "will result in as much as 60 meters of erosion on average, about two times the average beach width, causing enormous problems for the many "cities on the beach" in these highly urbanized coastal areas." .
|
