CU scientist: Sea levels to rise 6 feet, not 20, in next century

By Bill Scanlon, Rocky Mountain News (Contact)

Published September 4, 2008 at 4:28 p.m.
Updated September 4, 2008 at 4:28 p.m.

Text size

Photo by Tad Pfeffer © University of Colorado

While the disintegrating Columbia Glacier in Alaska is adding to ocean levels this century, the total global sea rise by 2100 may be lower than some are anticipating, according to a new University of Colorado at Boulder study.

More Local News

More stories »

Predictions that sea levels will rise 20 feet in the next century are wildly exaggerated, but a more realistic 4- to 6-foot rise still could put homes under water for hundreds of millions of people.

That's the conclusion of Colorado scientist Tad Pfeffer, whose work on the subject appears in Friday's edition of the magazine Science.

Pfeffer, a fellow of the University of Colorado's Institute of Arctic and Alpine Research, found that a 20-foot rise is well-nigh impossible, a finding that could dramatically change forecast scenarios.

He said global warming "is very real," but that for melting ice and glaciers to raise the sea level 20 feet would require a locomotion rate several times faster than has ever been seen before.

Pfeffer and his colleagues started with Greenland, asking the question: If Greenland's ice and glaciers were to raise global sea levels six feet in a century all by themselves — as has been postulated by some scientists — how fast would they have to melt?

They looked at the two main ways that ice can get to the oceans: by melting into rivers, and by glaciers riding the land and rivers and entering the sea as icebergs.

Their conclusion: Greenland's glaciers would have to start moving right away at a mind-boggling 49 kilometers (30.3 miles) per year for a century in order for enough of them to enter the ocean and raise the sea level six feet.

"The fastest we've ever seen a glacier move for more than about a day or so is 15 kilometers per year," he said.

That's the good news.

The bad news is that sea levels could very well rise from three to six feet in the next century.

And that means that the cities along every major river delta on the globe, including the Mississippi all the way upstream to southern Illinois, could be under water by 2100.

"It would be a terrible mistake if our analysis leads anyone to conclude we can forget about this problem," Pfeffer said.

"There are an awful lot of people who live within three feet of sea level, especially in the Third World — Bangladesh, China, Indonesia, the Pacific Islands," Pfeffer said.

"Mostly, it's people who don't have the resources" to embark on large engineering solutions, he said.

Even among richer nations, "It's not as simple as building a five-foot levee."

Most scientists agree that greenhouse gases such as gasoline, coal and other fossil fuels are entering the atmosphere and causing a build-up of carbon dioxide that is warming the planet more than can be explained by normal climate fluctuations.

That warming inevitably will melt some of the glaciers and ice caps in Greenland, Antarctica and other places, causing them to reach the oceans and raising sea levels, the scientists say.

But there is a big disagreement on how high the seas will rise, and that subject was a big unknown in last year's big report from the International Panel on Climate Change.

Pfeffer hopes his study shifts the debate from "20 feet will never happen" or "20 feet is impossible to deal with" to "five feet? We can do something about that."

A solid forecast of a 20-foot rise could lead policymakers to invest all the money in sea walls.

But four or five feet? "We could think a lot more carefully about solving more subtle but still expensive problems — salinization of estuaries, salt water working its way up rivers, land on the coast getting pressed down by increasing sea level rise, exacerbating the problem."

Martin Truffer, a geophysicist at the University of Alaska at Fairbanks, said Pfeffer's work "makes a lot of sense to me," because he elegantly points out the extreme unlikelihood that Greenland's glaciers can move as fast as some earlier predictions.

Truffer did note, however, that the factors slowing down the glaciers in Greenland aren't in play in Antarctica, where glaciers don't have similar restraints and can, in fact, plunge right into the sea.

Truffer also agrees with Pfeffer that even if sea levels rise at the current pace — with no future acceleration — "that's going to create problems for a lot of people. Once you start talking three or four feet, where the coasts are flat ... that's not something to be taken lightly by any means."

Pfeffer said the most accurate information on future sea level rise is crucial because "we need to know what kinds of problems we are going to have to solve.

"Let's get the numbers right. Let's not get locked into the idea that if we can't produce a Hollywood-style cataclysm, we don't have a story."

Subscribe to the Rocky Mountain News