PrintSea Level Rise
Warming causes ocean water to expand and melts mountain glaciers. (Despite a few outliers or oddities, the great majority of mountain glaciers are melting.) The big ice sheets of Greenland and Antarctica are also losing mass. With continuing warming, we expect more sea-level rise. The recent rise has been about 3 millimeters per year, or just over an inch per decade, and sea level has risen almost a foot (just under 1/3 m) over the last century or so. We expect sea-level rise to continue and probably accelerate moderately, with at least a slight chance of a large acceleration if the big ice sheets change rapidly. A foot of sea-level rise might not seem like a lot when the biggest hurricanes can have storm surges of 10 or rarely even 20 feet (3 to 6 m). But, the last foot may be the one that goes over the levee or into the subway tunnels, so even a relatively small change in sea level can have large consequences for cities and other human-built structures.
Video: Sea Level Rise (1:17)
DR. RICHARD ALLEY: This figure comes from the US government from NOAA, National Oceanographic and Atmospheric Administration. And all it does is show regions that will go underwater-- shown by the reddish color, such as here-- for various levels of sea level rise. And this is one meter of sea level rise over here on the left.
And you see certain places that are starting to get a little bit damp. This is two meters of sea level rise, and you see big areas where a whole lot of people live are in trouble, then. And this is four meters of sea level rise. And this one over here is eight meters of sea level rise. And you see really big areas getting wet.
The worst case scenario that we can dream of is actually a good bit bigger than eight meters. Clearly, people could build walls to hold back the sea. The Netherlands has done it. It's been done around New Orleans with dikes, although though sometimes fail. But it gets expensive if you're trying to wall off that much of the coast. So one suspects that if we head towards the worst case somewhere well out in the future, that it could become very expensive or we lose a lot of land.