Could Rising Seas Swallow California's Coast?

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Imagine San Francisco Airport under water, or Long Beach Harbor in Los Angeles, the second busiest port in America, washed away. Picture Orange County's Newport Beach completely submerged under the encroaching ocean.

That's the soggy future that could be in place for California at the end of this century if climate change continues unabated. According to the Pacific Institute, an environmental NGO that specializes in water, unchecked global warming may cause the world's seas to rise more than 4.6 ft. (1.4 m). The California government commissioned the institute's study, released on March 11, one of a number of forthcoming reports on how climate change will affect the coastal state and one of the most detailed analyses yet on the local impact of rising seas.

The Pacific Institute found that by 2100, an estimated 480,000 Californians will be at risk of increased flooding — almost double the number currently living in disaster-prone areas of the state — along with roads, schools, hospitals and other low-lying coastal infrastructure. Nearly $100 billion worth of coastal property could be at risk — and the cost to protect that land from flooding will likely be in the billions, even if we do control greenhouse-gas emissions. "This change is inevitable, and it's going to alter the character of California's coast," says Heather Cooley, a senior research associate at the Pacific Institute and a co-author of the study.

The report's warnings are so striking in part because it assumes a much higher sea-level rise than previous studies. The 1.4 m figure used in the Pacific Institute report — which comes from research by the Scripps Institute of Oceanography — is considerably higher than the estimates put forth in the U.N. Intergovernmental Panel on Climate Change's (IPCC) most recent assessment in 2007, which projected a sea-level rise of 18 to 59 cm by 2100. But the IPCC numbers were based on older data and took into account only the thermal expansion of the seas. (Water expands as it heats, so warmer seas rise.) The IPCC did not factor in the potentially far greater impact of melting ice caps in Greenland and Antarctica — Greenland alone has enough ice to raise sea levels by more than 20 ft. At the time of the IPCC report, the polar ice sheets were clearly melting, but it wasn't clear how fast they were going or how they would respond to rising temperatures in the future.

New research is clarifying the ice-cap question — and the results are sobering. Scientists at the Climate Change Congress in Copenhagen this week presented a study estimating that sea levels could rise globally by 1 m or more by the end of the century, with large regional differences around the world. At the lower end of the estimate, scientists say it's unlikely that seas will rise less than 50 cm even if we can get a grip on carbon emissions. The revised predictions are due to better data on melting in Greenland and Antarctica and from glaciers around the world, which are pouring water into the oceans and causing them to rise. Up to 600 million people in coastal areas around the world could be at increased risk for flooding. "Unless we take urgent and significant mitigation actions, the climate could cross a threshold during the 21st century committing the world to a sea-level rise of meters," says John Church, an oceanographer at the Centre for Australian Weather and Climate Research and one of the study's co-authors.

The Pacific Institute report takes that abstract number and shows what it will mean for the cities, streets, bridges, beaches and power plants in America's most populous — and vulnerable — state. Nearly half a million people will be at risk for what's called a 100-year flood event. That doesn't mean a flood that happens once a century, but rather a disaster that has a 1% chance of happening every year — which means it has a 26% chance of happening over the life of an average 30-year mortgage. The vulnerability is concentrated along the coastline of the Bay Area, where large parts of both San Francisco and Oakland could be threatened with extreme flooding by the end of the century. Even parts of the Pacific coastline that may be shielded from flooding could be at risk for increased erosion. Worse, as with Hurricane Katrina, it will be the poor and those without insurance who will likely bear the brunt of the flooding damage. "There's this notion that those living on the coast are all rich with insurance," says Cooley. "But in fact these populations are often poor, and they will be particularly vulnerable."

The best way to protect California's coast would be to sharply reduce carbon emissions now and hope to avert the worst of the warming. But even if we do cut carbon soon, we've locked in sea-level rise, and we need to begin protecting sensitive coastlines better than we did in New Orleans. The Pacific Institute study suggests that some 1,100 miles of improved coastal defenses — including dunes and seawalls — would be needed to protect against a 1.4 m sea rise. It won't be cheap — the cost will be at least $14 billion up front, according to the Pacific Institute, with an additional $1.4 billion a year in maintenance costs. But even that might not be enough. "Eventually you could see phased abandonment of certain areas that would experience flooding a lot," says Cooley. We're used to controlling the effects of nature, but if we fail to control climate change, we may have to surrender.

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