When Terry Serigny was growing up in Leeville, Louisiana, in the 1950s, the Mississippi River Delta town was also known as Orange City for its many citrus groves. Today none of those groves remain. Leeville itself is vanishing, sinking into the Gulf of Mexico.

Old black-and-white photos hanging on the walls of Serigny’s bait shop show wetlands, small ridged islands with trees, and oil derricks where there is now only open water. “Everything that you see here has all been washed away,” he says, pointing to the photos. “There is nothing left to stop the saltwater from coming in.”

The Mississippi Delta is one of the fastest disappearing land masses on Earth. It has lost nearly 1,900 square miles since the 1930s, and is still losing a swath about the size of a football field every hour.

“This land loss crisis,” says the Louisiana Coastal Protection and Restoration Authority (CPRA), “is nothing short of a national emergency.” And yet, as a slowly unfolding catastrophe, it gets much less national attention than acute disasters like Hurricane Katrina in 2005 or the Deepwater Horizon oil spill in 2010.

This week, however, the CPRA announced a list of 39 long-term coastal restoration projects that it hopes to pay for, at least in part, with money the state receives from BP to compensate it for the 2010 oil spill.

The projects are all part of a 50-year, $50 billion master plan that the authority announced last year. That plan has an incredibly ambitious—some would say impossible—goal: to stop the land loss and even reverse it, in the face of a global rise in sea level, by the second half of this century.

Land loss threatens not only the people, culture, and economy of southern Louisiana, but also unique wetland ecosystems.

“Just as we’re losing species off the tops of mountains with global warming, we’re losing species off the tops of our natural levees, because the whole system is becoming wetter,” says Julie Whitbeck, a National Park Service ecologist who works at the Barataria Preserve, a 23,000-acre mix of forest and wetlands a 30-minute drive south of New Orleans. The preserve is losing land, especially along its western edge where it borders Lake Salvador.

On Friday and Saturday, crowds of scientists, schoolchildren, and other wildlife lovers will be descending on the preserve, which is part of Jean Lafitte National Historic Park, for a BioBlitz: a 24-hour effort to count and map some of the park’s many diverse species, from insects to alligators to bald cypress trees.

The BioBlitz is an annual event, sponsored at a different park each year by the Park Service and National Geographic. As much celebration as science, this year’s event will have an added edge because it’s taking place in a park and a region whose future is fundamentally uncertain.

Forces of Destruction

A disastrous confluence of forces is to blame for the gradual retreat of the Louisiana coast. Some forces, like floods from hurricanes or subsidence of muddy sediments, are natural. But the most serious problems are man-made.

One hundred years ago, the region’s two big rivers—the Mississippi and the Atchafalaya—dumped some 500 million tons of land-replenishing sediments onto the Delta every year. Today about half the rivers’ sediment load never reaches the Delta. Instead, it settles behind thousands of dams and levees or is channeled by those levees far out into the Gulf of Mexico.

Meanwhile, navigation canals built to facilitate oil exploration and shipping allow saltwater to intrude far inland, killing freshwater plants and trees. When the plants die, the soil crumbles, and land falls into the sea.

All of these challenges might be manageable were it not for another threat, one that will only worsen year after year: the rise of sea level caused by global warming. That rise is happening because seawater expands as it warms, and because glaciers and ice sheets are melting.

“For most of the last 7,000 years, sea level was rising at about one millimeter per year—that’s our best guess from the data,” says Harry Roberts, an oceanographer at Louisiana State University. “But since the 1990s satellite data suggest that the average global sea-level rise is now around three millimeters per year.”

Global sea-level rise is modulated from place to place by local effects—and the dominant local effect in Louisiana is geologic subsidence that is no longer being compensated by new sediment. “We’ve tripled the rate of sea-level rise and decreased the amount of sediment,” says Roberts. “We’ve got a major league problem here in Louisiana.”

Along the Louisiana coast, sinking land and rising sea combine to create a rate of relative sea-level rise that is far higher than the global average. Measurements by NOAA, the National Oceanic and Atmospheric Administration, show increases of almost .4 inch (10 millimeters) annually. That’s about three feet a century.

Turning the Tide?

Can the state stem the loss of its land? The master plan released last year by the CPRA sets a goal of gradually reversing land loss and achieving a net gain in land by 2061, something that last occurred in the 1930s.

To reach that goal the state will try to restore sediment to the delta using two different strategies. One would punch holes in the levees to divert muddy water from the Mississippi and Atchafalaya rivers into marshes, allowing the rivers to lay down sediments there much as they once did during their seasonal floods.

The second strategy would rebuild marshes with sediment dredged from riverbeds and the Gulf of Mexico, and then pumped through a statewide network of pipes into areas of open water that are still shallow enough to be reclaimed.

Both approaches have already been used to some extent, with mixed success. A recent NOAA report found no evidence that earlier river diversions had slowed the rate of wetland loss in the state—but the CPRA points out that those diversions were not designed to capture water that was laden with sediment.

Local fishermen have long complained that the sudden huge influx of freshwater into brackish marshes drives out valuable salinity-loving species such as speckled trout and oysters. The CPRA counters that the marshes in question weren’t always brackish; they got that way because of the very encroachment by the sea that the CPRA is trying to push back.

Kerry St. Pé, director of the Barataria-Terrebonne National Estuary Program, says sediment diversions from the river won’t work because the Mississippi no longer carries enough sediment; it’s captured behind dams far upstream. “To rely on the river to recreate the delta is not going to happen,” St. Pé says. He favors piping dredged sediment to the most vulnerable parts of the delta.

“We have sediment being dredged all the time for navigation on the Mississippi River,” St. Pé says. “Right now they take it offshore and dump it! We need the sediment; we need elevation. And the only way to get that is to harvest sediment and to pump it to repair what’s there now and to restore what we’ve lost.

“We know what these features were, and we can try to re-create as much of that as we can. Where there were marshlands, restore marshlands; where there were ridges and barrier islands, restore ridges and barrier islands.” St. Pé says sediment pumping restored Bayou Dupont, a 450-acre marsh that had been open water.

The CPRA master plan does include $20 billion for marsh creation projects like that. But the agency and the scientists who devised the plan maintain that Louisiana will lose its battle against the sea without projects that divert sediment from the Big Muddy River. By channeling as much as 250,000 cubic feet per second through gaps in the levees, the diversions would get much more mud for the buck than dredges and pipelines.

Implacable Sea

To achieve its goal of stopping the loss and achieving a net gain in land within 50 years, Louisiana needs not just $50 billion and a lot of mud. It also needs a relatively optimistic scenario of future sea-level rise to come true.

“I think it’s extremely unlikely that we’ll go back to a situation of net land gain,” says Torbjörn Törnqvist, a geologist and climatologist at Tulane University who, like St. Pé, worked on the master plan. “Climate change is working against us.

“Within restricted areas you could have a net gain, but for the Louisiana coast as a whole I think that’s virtually impossible to achieve,” he says. “Which means we’re going to have to make very tough choices. There will be significant areas that will have to be abandoned. Politically that’s tough, but it’s inevitable.”

It’s all but certain that sea level will continue to rise for generations to come; if we don’t control the heat-trapping gases that cause global warming, disaster awaits all the world’s coastal cities.

“We’re setting ourselves up for melting large parts of Greenland and West Antarctica,” says Törnqvist. “It may take a number of centuries for this to play out, but when those things start to happen, it’s going to be game over here in New Orleans. But don’t forget, it’s going to be game over in New York City as well, and every other coastal city in the world.”

At Jean Lafitte, park officials recognize that their park might not be around in 2100. “In the meantime, how do we best manage?” Whitbeck asks. “What do we want the landscape to be while we’re subsiding?”

St. Pé, however, whose family has lived on the delta for more than 200 years, bristles at the very notion of retreating. An entire culture is at stake, he says; the bayou culture, with its food and music, is the source of everything that draws people to New Orleans and the rest of the delta.

“We can’t leave; we have no choice,” says St. Pé. “It’s much more than moving people out of here. It’s all the infrastructure, all the industries, all the refineries. You’d have to move all of that, and that’s not going to happen.

“It’s easy for someone in some other place to talk about having a mass exodus from the area. But that’s not going to happen. I say as soon as they move everyone off the San Andreas fault, and everyone in the Midwest out of tornado alley, then we can talk about moving us out of here too.”