Sea Level Rise Won't Be a "Hollywood Cataclysm"

Mason Inman
for National Geographic News
September 4, 2008
Sea levels will rise a bit higher—but not catastrophically high—in the coming century, according to a new study.

The oceans will likely rise between 2.5 and 6.5 feet (0.8 and 2 meters) by 2100, researchers say.

This is not as high as the predictions from some scientists, who have warned that sea levels may rise as much as 16 feet (5 meters) by 2100.

Just because the amount of sea-level rise predicted in the new study is "not a Hollywood cataclysm, it doesn't mean it's not important," said study leader Tad Pfeffer of the University of Colorado in Boulder.>>

"A Real Outlier"

As greenhouse gases heat up the planet, the polar regions and high elevations are warming the fastest.

(Learn how the greenhouse effect works.)

That has caused glaciers, ice caps, and the vast ice sheets in Greenland and Antarctica to melt and break apart. (See photos of Greenland's ice sheets crumbling.)

In the new study, Pfeffer and colleagues examined estimates of 16 feet (5 meters) or more of sea level rise, which they thought seemed unrealistic.

Focusing on outlets, where ice can flow easily across bedrock, the team looked at how much faster Greenland's glaciers would have to move toward the sea to create such a huge sea level rise.

A 16-foot (5-meter) rise would require glaciers to flow at "unrealistically high velocities," Pfeffer said.

"We can't say it's impossible, but [that estimate] is a real outlier," he added.

Instead, it seems more plausible that seas would rise 6.5 feet (2 meters) of sea level rise by 2100, the study found.

That would inundate much of Bangladesh, displacing millions of people, and would also endanger many low-lying coastal cities such as New Orleans and New York City, scientists have warned.

The new research will be published tomorrow in the journal Science.

Conservative Estimates

The United Nations' Intergovernmental Panel on Climate Change (IPCC) 2007 report—the latest scientific consensus on climate change—predicted sea levels would rise between 7 and 23 inches (18 and 59 centimeters) by 2100.

But that was a conservative estimate, most scientists agree.

The report "specificially excluded dynamic effects—that's ice calving into the ocean—instead of meltwater flowing in," Pfeffer said. As a result, "everyone admits that the [IPCC] forecast is low."

The new study adds those possible dynamic contributions that the IPCC left out, said geophysicist Anders Carlson of the University of Wisconsin in Madison.

"The research does point out that we will probably have more sea level rise than predicted in the report," Carlson added.

This fits with a recent study led by Carlson, which examined signs left behind by the ancient Laurentide ice sheet that covered much of North America during the last ice age.

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