There is a coastward migration of the world's population, which is occurring at the same time as rising sea level and shoreline recession; this is the definition of a collision course. Rates of beach erosion along the U.S. east coast average slightly less than a meter per year, putting expensive beachfront development at risk to storm impact. Global sea levels have risen about 20 cm in the last century; relative rates of rise have more than doubled this amount in some areas due to land subsidence. Future sea levels are projected to rise significantly faster than occurred in the 20th century, resulting in acceleration of the present rate of shore recession.
There is much debate about future rates of sea level rise, and even some disagreement about the historical rate based on analysis of tide gauge records [IPCC, 2001; Douglas etal, 2001]. An array of satellites are providing the requisite measurements to determine global sea level changes in concert with tide gauges and terrestrial references. At the same time, new technologies such as airborne and spaceborne laser mapping are beginning to provide the data sets necessary for three-dimensional monitoring of shoreline changes.