Thursday, Dec. 14, 2006 | In Encinitas and Solana Beach, the U.S. Army Corps of Engineers is currently developing a $30 million sand restoration project to buffet golden stretches of shrinking beach.

But the corps admits it hasn’t considered one question about the 50-year-long project: Whether rising seas fueled by global warming could swallow that restoration, making it a moot point in coming decades.

Across the San Diego region, other government officials are on the cusp of wrestling with the implications of sea-level rise. As they evaluate expensive projects such as beach and wetlands restorations, they say that rising seas are an increasing concern. And many scientists say they should be worried.

In the last century, San Diego, San Francisco and Seattle have seen a 7-inch increase in average sea levels measured by tidal gauges. Sea levels have been increasing since the end of the last ice age, but accelerated again in the 1990s. It is not known how much of a role global warming played.

While scientists have reached consensus that human-fueled greenhouse gas emissions are making the world warmer – the least-dire prediction says the earth will be 1 degree Celsius hotter in 2050 – they have not reached consensus about the implications for the world’s oceans.

They generally agree that a warmer world means sea levels will rise, though they do not agree on how much. Estimates based on complex global climate models are broad. Some say the seas will rise at the historical rate. Others say the rate of rise could triple.

The United Nations’ Intergovernmental Panel on Climate Change projected in 2001 that global sea levels would rise between 4 inches and 2.5 feet by 2100.

“If sea-level rise approaches the higher end of these estimates, this will be a challenge to our local coastal and estuarine setting,” said Dan Cayan, a Scripps research meteorologist, in an e-mail. “It will be hard to keep up with these rises, which are considerably more than we have adapted to.”

Some scientists offer even more dire predictions. A University of Arizona study released in March predicted the possibility of a 20-foot rise in sea levels by 2100, fueled by melt from the Greenland and Antarctic ice sheets.

Researchers have reliable information on San Diego’s beach erosion over past millennia, but not over recent years. In the last 6,000 years, the cliffs of North County have receded about 600 meters, said Reinhard Flick, an oceanographer for the California Department of Boating and Waterways and a Scripps research associate. But more recent changes in beach width are harder to detect, Flick said, with Del Mar having the only detailed measurements. And those only date to the late 1970s.

In that time, Del Mar’s beaches have shrunk, fueled by three factors, Flick said: sea-level rise, storm-fueled erosion and a lack of sand replenishment.

“There’s a lot more going on,” Flick said. “The other effects seem to be larger than sea-level rise alone would cause. That’s not to say that there’s no effect.”

Continuing rises in ocean levels could have profound implications in San Diego, where millions have been invested in sand-replenishment projects and where thousands live along the coast.

“Very frankly, I don’t think anything can be done about it, except to build seawalls,” said Tim Barnett, a Scripps marine physicist. “But then what happens to your beaches?”

Barnett said each foot of future rise would penetrate inland by about 100 feet. While that is a more profound problem in low-lying places like south Florida and coastal Louisiana, it would also have significant impacts in coastal San Diego.

“I think we’re looking at a beach system that we have in San Diego that’s seriously endangered in the future,” Barnett said. “Places like Mission Beach are potentially in real deep trouble.”

Sea-level rise as a global-warming byproduct is caused by two primary factors: More water in the world’s oceans from melting polar ice caps and glaciers as well as the expansion of that water. As water warms, it takes up more space.

Local officials say they’re on the cusp of considering the rising seas’ potential impacts on San Diego beaches and coastal wetlands, which are constrained by inland development. At beaches, seawalls and housing development prevent natural sand replenishment. At wetlands, rising seas would push the habitat further inland – to areas that are already developed. The areas where those wetlands currently exist would be submerged.

The U.S. Army Corps of Engineers’ project in Encinitas and Solana Beach proposes to replenish two storm-bashed stretches of beach every five years. The Corps says winter storms have stripped beaches bare, allowing strong swells to nip away at the bases of seaside bluffs. The engineers have not, however, weighed the potential effects of sea-level rise, a spokesman said.

“I don’t believe that at this point we’ve factored sea-rise level into any of the projects,” corps spokesman Greg Fuderer said. “It’s something we’re aware of – but as far as modifying a project because of it, I don’t believe we have.”

Environmentalists say long-term projections of sea-level rise should be considered as the engineers consider the long-term restoration project.

“Not just for the sake of the environment,” said Stefanie Sekich, vice chairwoman of Surfrider Foundation’s San Diego chapter, “but for the sake of the taxpayer.”

If the ocean rises 2.5 feet in the next century, “we know that sand replenishment is going to become a lot more expensive,” she said. “And in certain places (like Solana Beach and Encinitas) it just might not be viable.”

Elsewhere in the region, ocean rise is on officials’ minds, The San Diego Association of Governments spent $17.5 million in 2001 to replenish 2.1 million cubic yards of sand on the region’s beaches. And it was just a pilot project. Sandag estimates the region’s beaches have a sand deficit between 25 million and 30 million cubic yards of sand – or between 5 billion and 6 billion gallons, enough to give every living person a gallon of sand.

“We have an immediate need to do something on the beach today,” said Rob Rundle, the principal regional planner at SANDAG, which replenished 12 area beaches in 2001. “But is what you’re doing going to solve the problem in the long-term? When you add in sea-level rise, maybe not.”

At the Tijuana Estuary, officials are studying the feasibility of a 220-acre wetlands restoration that could cost $100 million. Clay Phillips, the estuary’s manager, said the potential effects of sea-level rise are a concern.

“It is something we’ve discussed and rung our hands about a little bit,” Phillips said. “We’re thinking about it on a system-wide basis. It certainly is on the radar throughout the National Estuarine Research Reserve System.”

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