An Overview of the Causes and Effects of Sea Level Rise

The average person's view that sea level is constant is not shared by everyone, and for good reason. Petroleum companies and their geologists find oil on dry land once covered by prehistoric seas, and paleontologists find marine fossils on desert plains. Nevertheless, within the period of time relevant to most decisions, the assumption that sea level is stable has been appropriate. Only in a few cases have local changes in relative sea level due to land subsidence and emergence been large enough to have important impacts. Recently, however, the view that current sea level changes are unimportant has been called into question. Coastal geologists are now suggesting that the thirty centimeter (one foot) rise in sea level that has taken place along much of the U.S. coast in the last century could be responsible for the serious erosion problems confronting many coastal communities.' Furthermore, according to the National Academy of Sciences, the expected doubling of atmospheric carbon dioxide and other greenhouse gases could raise the earth's average surface temperature 1.5-4.50C (3-80F) in the next century. Glaciologists have suggested that the sea could rise five to seven meters (approximately twenty feet) over the next several centuries from the resulting disintegration of the West Antarctic ice sheet. A more immediate concern is that the projected global warming could raise the sea as much as one meter in the next century by heating ocean water, which would then expand, and by causing mountain glaciers and parts of ice sheets in West Antarctica, East Antarctica, and Greenland to melt or slide into the oceans. Thus, the sea could reach heights unprecedented in the history of civilization. Until this effort, no one had attempted to forecast sea level rise in specific years or determine its importance to today's activities.* A rise in sea level of even one meter during the next century could influence the outcomes of many decisions now being made. In the United States, thousands of square miles of land could be lost, particularly in low-lying areas such as the Mississippi Delta, where the land is also subsiding at approximately one meter per century. Storm damage, already estimated at over three billion dollars per year nationwide, could also increase, particularly along the well-developed and low-lying Atlantic coast. Finally, a rising sea will increase the salinity of marshes, estuaries, and aquifers, disrupting marine life and possibly threatening some drinking water supplies. Fortunately, the most adverse effects can be avoided if timely actions are taken in anticipation of sea level rise. Although action may be taken to limit the eventual global warming from rising atmospheric CO2, the warming expected in the next sixty years and the resulting rise in sea level are not likely to be prevented. Most CO2 emissions are released by burning fossil fuels. Because these fuels are abundant and relatively inexpensive to produce, a voluntary shift to alternative energy sources is very unlikely. Regulatory action that would effectively limit CO2 concentrations is also unlikely. Such actions by any one nation, even the