Sea Level Rise
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What It Is
Rising temperatures are causing global sea levels to rise through two primary mechanisms. Water expands as it warms and this thermal expansion causes water levels to rise. Hotter temperatures are also melting land ice, like glaciers and polar ice caps, which adds more water to the ocean. Satellite and tide gauge measurements (from Australia’s Commonwealth Scientific and Industrial Research Organisation and NOAA) have shown an absolute sea level increase of 1.7 mm per year from 1880 to 2011 across the world’s oceans, a rate that increased from 2.7 to 3.2 mm per year from 1993 to 2011.
Why It's Important
The rate of sea level rise may increase even faster in the future with the melting of the West Antarctic Ice Sheet. The ice sheet has entered an “unstoppable” state of retreat and melting could add about 4 feet to sea level rise for a guaranteed total of 10 feet, though that will take centuries. In the U.S. alone, nearly 30,000 square miles of land – home to 12.3 million people today – lies less than 10 feet under the high-tide line, including more than half the area of 40 large U.S. cities like New York City, Boston and New Orleans. Roughly one third of the U.S. population lives on low-lying land that is vulnerable to consequences of varying severity, from permanent inundation to saltwater intrusion into freshwater sources. Unless adaptation measures are taken, sea level rise could cost the globe $1 trillion annually by 2050.
