What makes this so tricky to prepare for, however, is that sea levels won't rise evenly everywhere. There are huge variations. In some regions, like the Mississippi Delta, the land is sinking, due to sediment erosion or oil drilling. In other places, strong wind and ocean currents can warp the waters and affect local sea levels. Meanwhile, the shrinking ice sheets in Greenland and Antarctica have their own gravitational pull, creating further imbalances.
So what happens when you take all these factors into account? That's what a thorough new study (pdf), led by Mahé Perrette of the Potsdam Institute for Climate Impact research, tries to do. The authors predicted that the average global sea-level rise will be between 56 centimeters and 106 centimeters by 2100, assuming emissions keep rising unchecked. But they found lots of disparities.
Some regions will see sea-level rise that's between 10 to 20 percent higher than the global average — including India, Bangladesh, Japan, Argentina, Australia, and South Africa. Meanwhile, other areas will see slightly less sea-level rise than the global average, including the Pacific Northwest in the United States and Western Europe. Here's a neat interactive map from New Scientist that lets you explore the variations:
One of the biggest question marks, meanwhile, is what will happen to the Northeastern United States — particularly New York City. Will it get below-average sea-level rise or an extra-heavy surge? A lot depends on whether Greenland or Antarctica melts faster in the decades ahead. That's because of gravity.
As it turns out, the ice sheets on Greenland and Antarctica are so massive that they actually generate significant gravity and keep ocean levels in the surrounding areas artificially high. So if Greenland's ice sheet loses a lot of mass, that will reduce its pull and sea levels will rise more slowly in the northern Atlantic. But if Antarctica is the one losing lots of ice, then sea levels down south will recede and water will be redistributed to more northerly areas — including the Eastern United States.
Recently, climatologists have been arguing over which ice sheet will contribute more to sea-level rise in the decades ahead — a recent comprehensive survey in Nature suggested that Greenland would remain (relatively) stable and West Antarctica's ice sheet would do more of the melting. These debates aren't just of academic interest. They can have a big impact on coastal planning.
In any case, studies like these will prove helpful in allowing countries and cities to brace themselves for sea-level rise in the decades ahead. Virtually all coastal areas will need to start planning defenses. But it can make a big difference to know whether to prepare for a 1 meter rise or a 1.2 meter rise.
--Sea levels have been rising for the past 100 years. A look at how that rise may have made the storm surges from Hurricane Sandy worse.
--Can we stop the seas from rising? Yes, but less than you think.