Sea levels are rising, and rising faster every year.
According to the latest report of the Intergovernmental Panel on Climate Change, sea levels rose an average of 1.7 millimeters a year during the 20th century. Some areas have had larger rises than others, and measurements vary from year to year at different locations.
Measuring sea level is difficult. Scientists use tidal gauges and satellite altimeter data to measure these changes, and there are some questions about the precision of these tools. Variations in land level complicate matters further; it is often difficult to distinguish rising seas from falling land. And as water warms, it expands.
Still, there is no question about the basic facts. Since 1993, the average rate of increase has nearly doubled, to 3.2 millimeters a year. The retreat of glaciers and the melting of the Greenland ice sheet have contributed to these accelerating increases. Extreme sea levels during storm surges like that of Hurricane Sandy in 2012 have increased since 1970, mainly the result of rising seas.
By 2081, yearly increases are likely to be as high as 16 millimeters a year, or about six-tenths of an inch. By the end of this century, seas will have risen by as much as three feet, and levels will almost certainly continue to rise for many centuries.
The National Oceanic and Atmospheric Administration has a web tool that shows the effect of changing sea levels across the country. A three-foot rise in sea level in Malibu, Calif., for example, would put many houses near Malibu Beach under water. In New York, most of Harlem River Drive and Franklin D. Roosevelt Drive south of 168th Street would be inundated, and Ellis Island would be about half its present size. In Florida, Tampa and Miami would lose large areas of land, and much of the Keys would disappear.