Rising sea levels threaten to overtake large portions of the Everglades, damaging sensitive ecosystems and potentially frustrating expensive efforts to restore the massive marsh, according to scientists observing the project.

Projections indicate that sea level rises associated with melting ice sheets and expanding, warming water could cause saltwater to move "well into the Everglades," degrading animal and plant species as it makes its way toward the center of southern Florida, said Hal Wanless, a scientist with the Department of Geological Sciences at the University of Miami.

"What we simply see is when saltwater moves into the freshwater marshes, the marshes die," Wanless told reporters Tuesday, indicating that scores of species, from fish to birds, could be displaced.

He said the focus of the park's $10.9 billion restoration project -- said to be the largest rehabilitation program in the world -- should be on measures strengthening the area's defenses against impending sea water, such as rebuilding mangrove forests.

"It's going to take a major commitment," he said.

The Intergovernmental Panel on Climate Change projects that sea levels could rise by as much as 1.9 feet by the end of this century. But the group notes that its computer models don't account for the full effect of melting ice sheets and can't confidently foretell the maximum potential rise in the oceans.

A 'wicked messy problem'

The "upper values of the ranges are not to be considered upper bounds for sea level rise," the IPCC warns.

Wanless says the rise could reach between 3 feet and 5 feet, or more if there's rapid melting along the ice sheets.

"A 6-foot rise would certainly mean a loss of the Everglades," he said.

The 30-year restoration project is the most ambitious effort to restore natural water flow in the world, according to park officials. It encompasses the entire 2.4-million-acre marsh and is focused less on climate change and more on immediate threats such as phosphorus seeping into its fragile ecosystems and the 21 billion gallons of water diverted annually to farmers' fields.

Yet the threat of climate change has taken on a new emphasis among scientists observing the project.

Jayantha Obeysekera, director of the Hydrologic & Environmental Systems Modeling Department at the South Florida Water Management District, called climate change a "wicked messy problem" that could frustrate assumptions built into the project.

Rising sea water could disrupt plans surrounding flood control, water supply and ecosystem restoration, he said, adding that global projections are ill-suited to address local problems caused by rising sea levels.

"We really need the local, regional climate modeling in terms of what it means for us," Obeysekera said.

For now, scientists say the restoration work should continue. But it could all be washed away if the United States and other industrial nations don't act aggressively to counter climate change.

"If we are going to spend this money, we need to get a hold of global warming," Wanless said. "If we do that, we can save the Everglades."

The risk of losing an area under expensive restoration

But even Wanless' most optimistic projections were ominous. Under the best scenario, involving a robust global effort to minimize the human impact of climate change, he indicated that sea levels would likely rise 3 feet by the end of this century.

That would mean large swaths of low-lying areas in the Everglades would be lost.

"That's going to seriously impact the lower Everglades," he said. "But that's what happens."

The ongoing restoration of higher sections of the park could still be saved, he said.

"I don't think it's time to throw in the towel."