A sea level rise of 200 feet would put almost all of Florida, much of Louisiana and Texas, the entire East Coast of the United States, large parts of Britain, much of the European Plain, and huge parts of coastal Asia under water. The cities lost would include Miami, New Orleans, Houston, Washington, New York, Amsterdam, Stockholm, London, Paris, Berlin, Venice, Buenos Aires, Beijing, Shanghai, Sydney, Rome and Tokyo.
Nobody alive today, nor even their grandchildren, would live to see such a calamity unfold, given the time the melting would take. Yet the new study gives a sense of the risks that future generations face if emissions of greenhouse gases are not brought under control.
“This is humanity as a geologic force,” said Ken Caldeira, a researcher at the Carnegie Institution for Science in Stanford, Calif., and another author of the paper. “We’re not a subtle influence on the climate system – we are really hitting it with a hammer.”
Climate scientists have long assumed that countries would recognize the dangers of continuing to dig up and burn the world’s fossil fuels. Yet they have been saying that for 30 years, and political efforts in that time to limit the burning have been ineffectual.
The long-running political gridlock has prompted scientists to start thinking about worst-case scenarios. And recently, major advances have been made in the computerized analysis of the huge ice sheets covering Antarctica and Greenland.
The researchers involved in Friday’s paper decided to use one of these ice-sheet models to attempt the most detailed analysis yet of the potential consequences of burning all fossil fuels. As the first of its kind, the paper is likely to undergo intense scientific scrutiny.
A United Nations panel has said that the rise of the sea would not likely exceed three feet in that period, and would probably be less. While some island nations may be wiped out by a rise of that magnitude, experts believe most major cities could be protected from it, though at a likely cost in the trillions of dollars.
The ice sheets respond slowly enough to changes in the climate that it simply takes longer than a century for large-scale melting to begin. But from that point, the paper found, about half the Antarctic ice sheet would melt or fall into the sea in the first thousand years.
“I didn’t expect it would go so fast,” Dr. Caldeira said. “To melt all of Antarctica, I thought it would take something like 10,000 years.”
The more basic finding that the whole ice sheet could eventually melt is less surprising, at least to scientists who specialize in studying the history of the earth. “As a paleoclimate person, I don’t feel like this is necessarily a shock to me,” said Robert E. Kopp, a professor of earth system history at Rutgers University, who studies sea level but was not involved in the new research.
Paleoclimatologists have established that Antarctica was once a lush, green continent, icing over only in the past 35 million years, amid a general cooling of the world’s climate. Moreover, rates of sea level rise like those outlined in the paper have occurred in the past.
Human civilization is built on the premise that the level of the sea is stable, as indeed it has been for several thousand years. But the deeper history of the earth reveals enormous shifts, on the order of a hundred feet or more within a few thousand years.
Sea levels far higher than those of today have been documented at more than a thousand sites around the world. Along the East Coast, seashells from just 3 million years ago can be dug up by the shovel-full a hundred miles inland from the current shore.
Studying this evidence, scientists concluded long ago that the great ice sheets are sensitive to small changes in the earth’s average temperature, caused by wobbles in its orbit around the sun. They believe that human emissions are about to produce a large change.
Though the climate is still in the earliest stages of this shift, the ice sheets in both Greenland and the low-lying, western part of Antarctica are already showing serious signs of instability.
The higher, colder ice sheet in eastern Antarctica, by far the largest chunk of land ice on the planet, had long been assumed to be more stable. But for several years, evidence has been accumulating that at least large parts of that ice sheet are vulnerable, too.
The new study confirms previous findings that how much of the world’s ice will melt is closely linked to how much total fossil fuel humans burn. These studies suggest that a rapid shift away from those fuels over coming decades would preserve much of the ice, or at least slow the melting drastically.
The exact timing is open to question, he said, but “the idea that most of it would melt, I believe, is a robust result.”
Scientists focus on melting ice in part because the consequences are relatively easy to visualize. But if anything like the scenario in the paper were to play out in the real world, the problems would go far beyond a rise of the sea and a retreat from the coasts.
In a rough calculation, the scientists found that burning all fossil fuels might raise the average temperature of the planet by something like 20 degrees Fahrenheit. Past research suggests that an increase that enormous would likely render vast stretches of the earth too hot and humid for human habitation, cause food production to collapse, and drive much of the plant and animal life of the planet to extinction.
In interviews, scientists said that such long-term risks raise profound moral questions for people of today.
“What right do we have to do things that, even if they don’t affect us, are going to be someone else’s problem a thousand years from now?” asked Ian Joughin, an ice sheet expert at the University of Washington who was not involved in the new research. “Is it fair to do that so we can go on burning fuel as fast as we can?”