Sea level rise is one of the most widespread impacts expected to result from global warming. Scientific understanding of sea level change has progressed significantly in the past few years, especially for past and current sea level rise. For instance, it is now clear that sea level rise accelerated during the 20th century. Projecting future sea level rise, however, is now less certain because of recent, unexpected changes in large polar ice sheets that were assumed to be stable. This fact sheet briefly describes the current state of the science on sea level rise.