National Geographic Magazine
As the planet warms, the sea rises. Coastlines flood. What will we protect? What will we abandon? How will we face the danger of rising seas?
By Tim Folger
In May the concentration of carbon dioxide in the atmosphere reached 400 parts per million, the highest since three million years ago. Sea levels then may have been as much as 65 feet above today’s; the Northern Hemisphere was largely ice free year-round. It would take centuries for the oceans to reach such catastrophic heights again, and much depends on whether we manage to limit future greenhouse gas emissions. In the short term scientists are still uncertain about how fast and how high seas will rise. Estimates have repeatedly been too conservative.
Global warming affects sea level in two ways. About a third of its current rise comes from thermal expansion—from the fact that water grows in volume as it warms. The rest comes from the melting of ice on land. So far it’s been mostly mountain glaciers, but the big concern for the future is the giant ice sheets in Greenland and Antarctica. Six years ago the Intergovernmental Panel on Climate Change (IPCC) issued a report predicting a maximum of 23 inches of sea-level rise by the end of this century. But that report intentionally omitted the possibility that the ice sheets might flow more rapidly into the sea, on the grounds that the physics of that process was poorly understood.
As the IPCC prepares to issue a new report this fall, in which the sea-level forecast is expected to be slightly higher, gaps in ice-sheet science remain. But climate scientists now estimate that Greenland and Antarctica combined have lost on average about 50 cubic miles of ice each year since 1992—roughly 200 billion metric tons of ice annually. Many think sea level will be at least three feet higher than today by 2100. Even that figure might be too low.
In a state exposed to hurricanes as well as rising seas, people like John Van Leer, an oceanographer at the University of Miami, worry that one day they will no longer be able to insure—or sell—their houses. “If buyers can’t insure it, they can’t get a mortgage on it. And if they can’t get a mortgage, you can only sell to cash buyers,” Van Leer says. “What I’m looking for is a climate-change denier with a lot of money.”
Unless we change course dramatically in the coming years, our carbon emissions will create a world utterly different in its very geography from the one in which our species evolved. “With business as usual, the concentration of carbon dioxide in the atmosphere will reach around a thousand parts per million by the end of the century,” says Gavin Foster, a geochemist at the University of Southampton in England. Such concentrations, he says, haven’t been seen on Earth since the early Eocene epoch, 50 million years ago, when the planet was completely ice free. According to the U.S. Geological Survey, sea level on an iceless Earth would be as much as 216 feet higher than it is today. It might take thousands of years and more than a thousand parts per million to create such a world—but if we burn all the fossil fuels, we will get there.
No matter how much we reduce our greenhouse gas emissions, Foster says, we’re already locked in to at least several feet of sea-level rise, and perhaps several dozens of feet, as the planet slowly adjusts to the amount of carbon that’s in the atmosphere already. A recent Dutch study predicted that the Netherlands could engineer solutions at a manageable cost to a rise of as much as five meters, or 16 feet. Poorer countries will struggle to adapt to much less. At different times in different places, engineering solutions will no longer suffice. Then the retreat from the coast will begin. In some places there will be no higher ground to retreat to.
By the next century, if not sooner, large numbers of people will have to abandon coastal areas in Florida and other parts of the world. Some researchers fear a flood tide of climate-change refugees. “From the Bahamas to Bangladesh and a major amount of Florida, we’ll all have to move, and we may have to move at the same time,” says Wanless. “We’re going to see civil unrest, war. You just wonder how—or if—civilization will function. How thin are the threads that hold it all together? We can’t comprehend this. We think Miami has always been here and will always be here. How do you get people to realize that Miami—or London—will not always be there?”