Basics

Spend a day at the ocean, and you’ll notice that the sea rises and falls with the ebb and flow of the tides. Spend a summer and you’ll realize that those changes balance out over time. The average level of the sea appears to stay constant.

But if you return to the same stretch of seashore for many years, you’ll see that sea level isn’t constant. Over the past century or so, oceans all over the world have been sneaking imperceptibly but steadily higher — about eight inches higher, on average, since around 1900. And the rate of sea level rise appears to be accelerating. The reason, scientists almost universally agree, is global warming; and global warming is triggered by the increase of heat-trapping greenhouse gases pumped into the atmosphere, especially carbon dioxide (CO2) from the burning of fossil fuels.

Scientists also agree that sea level will continue to rise and that by the end of this century it will stand somewhere between two to seven feet higher than it is today. What that means for a particular area depends largely on local factors.

Next Section: Causes