Sea level rise in the US may be worse than expected

Yahoo News 6 Feb 09;

WASHINGTON – Long-term sea level increases that could have a devastating effect on southern Florida and highly populated coastal areas may be even larger than once thought, a report suggests.

Some studies have suggested that melting of ice in Antarctica and other areas could raise sea levels by 16 feet to 17 feet over the long run, a potential threat to coastal areas such as Washington, D.C., New York City and California.

But a report in Friday's edition of the journal Science warns that factors not previously considered could one day boost that increase to up to 21 feet in some areas.

The study did not list a time frame for such a dramatic change. But co-author Peter Clark, a geoscientist at Oregon State University, stressed that they "aren't suggesting that a collapse of the West Antarctic Ice Sheet is imminent."

The most recent International Panel on Climate Change report estimated sea level rise of up to 3 feet by the end of this century.

"People have been trying prepare for sea level rise for some time, it's not a new issue," Clark said, noting that the U.S. Fish and Wildlife Service and U.S. Geological Survey are holding a meeting in San Francisco on the effects of coastal change.

Earlier research has focused on melting ice adding water to the oceans and on thermal expansion of sea water in a warmer climate over long periods of time.

In the new report geophysicist Jerry X. Mitrovica and physics graduate student Natalya Gomez of the University of Toronto, Canada, and Clark, say other factors need to be considered.

_When an ice sheet melts, its gravitational pull on the ocean is reduced and water moves away from it. That means sea levels could fall near Antarctica and rise more than expected in the northern hemisphere.

_Antarctic bedrock that currently sits under the weight of the ice sheet will rebound from the weight, pushing some water out into the ocean.

_The melting of the West Antarctic ice sheet will cause the Earth's rotation axis to shift, potentially moving water northward.

"The net effect of all of these processes is that if the West Antarctic ice sheet collapses, the rise in sea levels around many coastal regions will be as much as 25 per cent more than expected," Mitrovica said in a statement.

Antarctic Meltdown Would Flood Washington, D.C.
Andrea Thompson, livescience.com 5 Feb 09;

Washington, D.C., and other coastal U.S. cities could find themselves under several more feet of water than previously predicted if warming temperatures destroy the West Antarctic Ice Sheet, a new study based on a model predicts.

The West Antarctic Ice Sheet (WAIS) towers about 6,000 feet (1,800 meters) above sea level over a large section of Antarctica. It holds about 500,000 cubic miles (2.2 million cubic kilometers) of ice, about the same amount of ice contained in the Greenland Ice Sheet.

This vast swath of ice is the anchor for numerous glaciers that drain into the polar sea and is bounded by the Ross and Ronne Ice Shelves. Whether or when this ice sheet might melt is still very uncertain, but even a partial melt would have a bigger impact on some coastal areas than others.

The new research found that sea level rise would not be uniform around the globe, owing to odd gravitational effects and predicted shifts in the planet's rotation.

Collapse concern

Throughout hundreds of millions of years in Earth's past, polar ice caps have grown and receded in cycles lasting thousands or even hundreds of thousands of years. When caps melted, seas rose.

What's different today is that melting of ice at both poles is occurring faster than what has naturally occurred in the past.

Some scientists are worried that our current path of warming could cause the collapse of all or part of the WAIS over the coming decades or centuries. These worries have been further fueled by a recent study in the journal Nature that indicates that more of the WAIS is warming that was previously thought.

"The West Antarctic is fringed by ice shelves which act to stabilize the ice sheet - these shelves are sensitive to global warming, and if they break up, the ice sheet will have a lot less impediment to collapse," said co-author of the new study Jerry Mitrovica, of the University of Toronto and the Canadian Institute for Advanced Research.

In its most recent report, released in 2007, the Intergovernmental Panel on Climate Change (IPCC) estimates that a full collapse of the ice sheet would raise sea levels by 16 feet (5 meters) globally.

Mitrovica and his colleagues say that this is an oversimplification, and that sea level rise will be higher than expected, and greater in some places than in others.

In particular, the IPCC estimate ignores three important effects of such a massive ice melt:

* Gravity: Like planets and other cosmic bodies exert a gravitational pull on each other, huge ice sheets exert a gravitational pull on the nearby ocean, drawing water towards it. If an ice sheet melted, that pull would be gone, and water would move away. In the case of the WAIS, the net effect would be a fall in sea level within about 1,200 miles (2,000 km) of the ice sheet and a higher-than-expected rise in sea levels in the Northern Hemisphere, further away.

* Rebound: The WAIS is called a marine-based ice sheet because the weight of all that ice has depressed the bedrock underneath to the point that most of it sits below sea level. If all, or even some, of that ice melts, the bedrock will rebound, pushing some of the water on top of it out into the ocean, further contributing to sea level rise.

* Earth's rotation: A collapse of the WAIS would also shift the South Pole location of the Earth's rotation axis (an imaginary line running through the Earth from pole to pole -about 1,600 feet (500 meters) from its present location. This would shift water from the southern Atlantic and Pacific oceans northward toward North America and the southern Indian Ocean.

Mitrovica and his fellow researchers took these effects into account and came up with a new projection of what would happen across the world if the WAIS melted out. Their findings are detailed in the Feb. 6 issue of the journal Science.

"The net effect of all of these processes is that if the West Antarctic Ice Sheet collapses, the rise in sea levels around many coastal regions will be as much as 25 per cent more than expected, for a total of between 6 and 7 meters [20 to 23 feet] if the whole ice sheet melts," Mitrovica said. "That's a lot of additional water, particularly around such highly populated areas as Washington, D.C., New York City, and the California coastline."

Submerging threat

Six meters of sea level rise would eventually inundate the nation's capital, because even though it doesn't have an extensive coastline, it was originally a low-lying, swampy area connected to the Chesapeake Bay.

It would also put virtually all of south Florida and southern Louisiana underwater. The West Coast of North America, Europe and coastal areas around the Indian Ocean would all be inundated more than previously expected.

Antarctic Ice Sheet Collapse May Swamp U.S. Coasts
Will Dunham, PlanetArk 6 Feb 09;

WASHINGTON - North America's coastlines would be hit especially hard by rising sea levels if the huge West Antarctic Ice Sheet collapses and melts in a warming world as some experts fear, scientists said on Thursday.

The loss of that ice sheet alone would inundate some coastal areas, swamping New York, Washington D.C., south Florida, Los Angeles, San Francisco and Seattle, with sea levels in some places higher by 21 feet or more than today, the researchers wrote in the journal Science.

Factors including changes in the Earth's rotation from the loss of the huge ice sheet would make sea level changes highly variable around the globe, they said. The southern Indian Ocean region also would be heavily affected, they added.

"You pay the price in North America," University of Toronto geophysicist Jerry Mitrovica said in a telephone interview.

"The peak sea level rise occurs on the coasts of the United States -- the New York area and down the coast, the eastern seaboard of the United States," Mitrovica added. "On the West coast, it's even just a little bit bigger."

The West Antarctic Ice Sheet covers about 350,000 square miles (900,000 square km), the size of U.S. states Texas and Oklahoma combined. Its volume equals about 100 times the amount of water in all of North America's Great Lakes, said Natalya Gomez of the University of Toronto, another researcher.

Mitrovica said this is not imminent, but rather: "It's a time scale of hundreds of years."

The United Nations Intergovernmental Panel on Climate Change estimates a loss of the ice sheet would raise sea levels around the world on average by about 16.5 feet.

But Mitrovica said the additional ocean volume would not be like adding water to a bath tub and watching the level rise equally, due to other complicated factors.

The researchers said the melting of the ice sheet would cause the Earth's rotation axis to shift about a third of a mile from its current position. This would move water from the southern Atlantic and Pacific oceans northward toward North America and into the southern Indian Ocean.

The loss of the ice sheet also would erase its previous gravitational pull on the surrounding ocean, pushing water away from Antarctica, they said. And the bedrock underneath could rise without the weight of the ice sheet holding it down, pushing some water out into the ocean.

The study did not consider possible melting of other ice sheets in Greenland or Antarctica that could raise sea levels.

(Editing by Maggie Fox and Cynthia Osterman)