Sea Level Rise and Coastal Regions

Marine terraces on the slowly uplifting coast of San Clemente Island, California.
Each terrace represents an interglacial high sea stand. The lowest (youngest)
terrace, where the road is seen, dates from the last interglacial period about
120,000 years ago, when sea level was 6 to 8 meters higher than present.
Photo provided by D.Muhs, USGS.

A large percentage of the world's population lives along a coastline at or near sea level. This means that even small increases in sea level can have significant societal and economic impacts through increased coastal erosion, susceptibility to storm surges, saltwater intrusion into groundwater, loss of coastal wetlands, and stresses on ecosystems and community infrastructure. There are two main causes of rising sea level: thermal expansion of warming ocean water and the melting of land-based ice (from the Greenland and Antarctic ice sheets and mountain glaciers). Sea level rise is often measured on a global scale, but there are significant regional differences. For example, current rates of sea level rise for the mid-Atlantic region from New York to North Carolina are considerably higher than the global average. Although some projections suggest that global sea level could rise between 18 and 59 centimeters (7 and 23 inches) by the end of the twenty-first century, there are large uncertainties associated with the dynamics of ice sheet melting that could result in these estimates being revised substantially. Geologic evidence associated with the Earth's glacial and interglacial history helps to frame our understanding of what is possible in the future based upon the extent to which sea level has risen in the past. Examination of records from previous interglacial periods shows that sea level has certainly been 6 meters (20 feet) higher and perhaps as much as 12 meters (40 feet) higher than present sea level. These past high sea stands provide an opportunity to understand how rapidly sea level can rise in response to a range of climate events and improve our ability to forecast future rates and patterns of sea-level rise.