Sea levels have risen about 8 inches since the beginning of the 20th century. The ocean is projected to rise by as much as 3 feet or more by the end of this century.
Earth’s climate history shows there have been times when ice sheets rapidly changed and created and multiple meters of sea level rise in a century. As Earth’s ice sheets continue to change, a key question facing scientists now is: Could human-caused global warming be pushing us toward one of those times.
More than 160 million people live along coasts in the U.S., about half the nation’s population. Eleven of the world’s 15 largest cities lie along shores, including New York City, Tokyo and Mumbai, India. Sea level rise means the ocean will gradually inundate low-lying areas, and storms like hurricanes, bolstered by even higher seas, will extend their reach inland. All of society bears the burden for storm damage, and those costs are expected to rise. Annual losses from flooding in the world’s biggest coastal cities could rise from about $6 billion a year today to $1 trillion a year by 2050.
Read more details here: http://climate.nasa.gov/climate_resources/125/