Glaciers around the world are rapidly retreating…
Southeast Louisiana’s coastline continues to subside…
And Antarctic ice is breaking into the ocean at an accelerating rate.
The result, many scientists fear, is that Louisiana may be inundated by the sea much sooner than anyone realizes.

Shrinking ice caps and glaciers in Antarctica and elsewhere could hasten a rise in sea level over the next century and complicate the restoration of Louisiana’s coastal wetlands, scientists say.

A series of recently published studies of the western Antarctica ice sheet conclude that those changes are adding .24 millimeters a year to the average height of the world’s oceans. Though that doesn’t seem like much-it’s equivalent to about 9/100ths of an inch a year-scientists warn that they expect the rate of both melting ice and the movement of ice off the Antarctic landmass into the ocean to increase.

Similar studies have concluded that the Arctic Ocean ice sheet has decreased by 9 percent in the past 30 years and could decline another 10 percent by 2100. When increases in the annual melting of the Greenland ice sheet are included, the Arctic melt could add another 6 inches to the sea level.

Scientists in China recently announced that melting glaciers have reduced the height of Mount Everest in Nepal by 5 feet, and US researchers say that of the nearly 700 named Alaskan glaciers, fewer than a dozen currently are advancing. The vast majority of glaciers in Alaska, like those in the western United States and elsewhere around the world, are melting rapidly, adding fresh water to the world’s oceans.

By 2100 several glaciologists say, the combination of melting ice and ice flowing into the ocean could increase the worldwide sea level by between 2 and 3 feet, compared to 1998 estimates of a rise of about 1.6 feet during this century.

That could be the difference between dry land with healthy wetlands and drowned wetlands, marshes and coastal communities, say several scientists working on the state’s coastal restoration program.

In part, that’s because Louisiana’s coast also must contend with subsidence-the land sinking under its own weight-and erosion. If the shrinking-ice scenario proves true, that means the coast could be facing the equivalent of a 4-foot to 6-foot rise in sea level over the next 100 years.

The new ice and glacier studies add to the debate over measurements of climate change among scientists worldwide.

“A lot of climatologists tend to downplay what’s going on, but glaciologists are most emphatic because they’ve seen it everywhere in the world’s ice sheets,” said Ted Scambos, a glaciologist with the National Snow and Ice Data Center at the University of Colorado at Boulder. “Not just in Antarctica, but in the Arctic and elsewhere, things are shrinking and retreating.

“I’d be surprised if we didn’t see at least 2 feet by 2100,” Scambos said. “It’s hard to see how it wouldn’t get to that level, since in the past 10 years we’ve seen an increase in the rate that already would result in half of that.”

Virginia Burkett, a researcher with the US Geological Survey in Lafayette, said scientists with the Intergovernmental Panel on Climate Change have not yet adopted the larger sea-level estimates proposed by glaciologists.

The panel is the international organization made up of thousands of scientists from a variety of specialties and dozens of countries that have been warning about the effects of global warming that they believe is being caused by increases in manmade pollutants, such as carbon dioxide. Burkett is one of several scientists contributing information about the effects of climate change on the world’s coasts, including Louisiana, for the panel’s next climate-change report.

But she, like other scientists, is concerned about what’s been happening to the western Antarctica ice sheet.

As recently as 1998, the international panel concluded that the shelf was stable-snowfall was creating new ice at a rate equal to melting or the calving of icebergs. Indeed, there is still no evidence of a speedup of melting in eastern Antarctica, scientists say.

But in 2002, the Larsen B ice shelf-bigger than the state of Rhode Island-broke away from the coast of the Antarctic Peninsula, followed soon after by the calving of even larger icebergs-as big as Massachusetts and Connecticut-from the Ross Ice Shelf in western Antarctica.

Since then, scientists have been watching an unexpected speed-up in the movement of onshore ice into the ocean vacated by those new icebergs.

“It’s sort of like having a crowded parking lot in front of a freeway,” said Scambos, who has been measuring the time and speed of ice movement using satellites. “When the parking lot is emptied out, the cars on the freeway move faster.”

And that’s what scientists have measured in Antarctica: ice moving into the water at rates four to six times faster than 10 years ago.

The ice that was already in the water as part of the ocean shelf did not affect sea level rise, since its mass and weight already were accounted for. But the new ice is adding more mass and weight, pushing the sea level higher.

Concern over the western shelf is nothing new, said Chris Rapley, director of the British Antarctic Survey. In the late 1960s, scientists said it might be unstable because the ice sat on terrain that was below current sea level and was being squeezed by surrounding ice shelves.

If the bottom of the ice slab melted, the whole thing could float, making it much easier to slide off land and into the sea. If the entire shelf were to slip into the water, it would raise sea level worldwide by 16 feet, more than enough to swamp the city of New Orleans even without local subsidence.

But Rapley said that even with the present increase in melting, such an occurrence, if it happens at all, is several hundred years away.

Glaciologists also aren’t sure of the reasons behind the Antarctic melt. Though it could be the result of human-induced rises of world temperatures increasing ocean heat and melting ice from both the bottom and top of the shelf, the local temperature changes could be the result of some unknown decades-long weather or ocean circulation pattern.

In Louisiana, the results could require engineers and scientists to tinker with the Louisiana Coastal Area Ecosystem Restoration plan now being considered by Congress.

That plan includes proposals for diverting fresh water and sediment from the Mississippi River to offset subsidence and promote plant growth. But the size of the diversions and their locations were determined using assumptions relying on the older estimates of future sea level.

“We can’t ignore it in our risk assessments,” said Robert Twilley, a Louisiana State University biologist who led a team that used sophisticated computer modeling that included the older sea level estimates to design individual projects.

“There’s always the issue of the thresholds by which wetlands may not sustain themselves,” Twilley said. “When we see that number, where are we? We know wetlands have experienced rates of inundation as high as 31 inches over 100 years, but those were mangroves in the Pacific.

“Can we get our coast to withstand up to 31 inches in 100 years?” he said. “That’s a critical assumption for our entire program, and if these new reports don’t put that out on our radar screen, then we’re making a fatal mistake in our planning process.”

Denise Reed, a plant biologist at the University of New Orleans, said the concern is complicated by the fact that different parts of the coast will react differently to higher water levels. Salt marshes, for instance, may be able to withstand water rises of as much as 3 feet per century, if enough sediment and nutrients can be provided to them.

But the already rapidly eroding barrier islands that protect the interior marshes would be topped quickly, increasing the threat of erosion from hurricanes and winter storms.

Further inland, flotant-floating freshwater marsh-could be killed if salt water is pushed into it too quickly.

And there’s no guarantee that the sea level rise would occur evenly during the next 100 years, she said. It could come as a series of pulses, which would make it even more difficult for freshwater, brackish or saltwater marsh systems to survive.

And people living and working in the wetlands and on bayou ridges or coastal beaches also would be affected, she said.

“The obvious effects will be on coastal communities and infrastructure,” she said. “There will be a need for major adaptations, higher levees and other improvements.”

Jon Porthouse, coastal restoration project manager for the state Department of Natural Resources, however, said the restoration plan can be adjusted to take the higher sea level into account.

“If we’re off in our estimates of sea level rise by 100 percent, a foot and a half, that just means the magnitude of our effort will have to be that much greater,” he said. “It doesn’t mean it’s impossible, that we’re not going to achieve restoration. It just means we’ll have to go back and look at our assumptions and determine what kind of restoration will be available to us.”