As California officials see it, global warming is happening so there's no time to waste in figuring out what to do.
California's interagency Climate Action Team on Wednesday issued the first of 40 reports outlining what the state's residents must do to adapt to the floods, erosion and other effects expected from rising sea levels.
Hundreds of thousands of people and billions of dollars of Golden State infrastructure and property would be at risk if ocean levels rose 55 inches by the end of the century, as computer models suggest, according to the report.
"Immediate action is needed," said Linda Adams, Secretary for Environmental Protection. "It will cost significantly less to combat climate change than it will to maintain a business-as-usual approach."
Few topics are likely to be more contentious than coastal development. But along the state's 2,000-mile shoreline, the impact would be acute, particularly in Orange and San Mateo counties where an estimated 110,000 people would be affected, according to the 99-page state-commissioned report by the Oakland-based Pacific Institute.
Detailed maps of the coastline, published on the institute's Web site, show residential neighborhoods in Los Angeles County could be inundated. Ocean waters could surge over airports in San Francisco and Oakland, through the ports of Los Angeles and Long Beach, and across large swaths of Huntington Beach and Newport Beach.
Roads, schools, hospitals, sewage plants and power plants may have to be relocated. More than 330 hazardous waste sites are at risk.
Dozens of world-class scientists and economists, many from the University of California and state research institutes, are examining potential effects of warming on snowpacks, wildfires, crops and electricity demand.
Detailed studies, now undergoing peer review, are to be released over the next month. Then the Climate Action Team is to send a comprehensive report to Gov. Arnold Schwarzenegger.
Sea levels along California have risen nearly 8 inches in the past century, although this varies with coastal dynamics. According to the Pacific Institute report, 260,000 Californians already live in flood zones but are assumed to be protected by existing structures, such as levees and sea walls.
A 1.4-meter sea level rise would increase the population at risk to 480,000. Currently, 1,900 miles of roads and highways are at risk of flooding, which would grow to 3,500 miles under the sea level rise projections.
The report estimated the cost of one adaptation strategy: protecting the coast with 1,100 miles of new or modified sea walls and levies. It would cost at least $14 billion to construct, and another $1.4 billion a year to maintain.
The report's estimate of 1 to 1.4 meters (55 inches) of sea level rise by the end of the century was calculated using two models from the United Nations' Intergovernmental Panel on Climate Change, a gathering of the world's top climate scientists. One model assumes countries will cut their emissions of the planet-heating greenhouse gases, and another assumes a business-as-usual emissions level.
Despite more than a decade of warnings from scientists, global emissions are continuing to rise, fueled by rapid population growth and economic development in nations such as China and India. Unless greenhouse gases are cut significantly, earth's temperature is expected to increase between 4 and 6 degrees Celsius by the end of the century, according to the U.N. panel.
As sea water warms due to rising air temperatures, it expands, causing the level to rise. But a second major factor, the melting of the Greenland and Antarctic ice sheets, was unaccounted for in the U.N. panel's models, designed in the mid-1990s, because of uncertainty over effects and timing.
Ice sheet melting has since accelerated. Dan Cayan, a researcher at the Scripps Institution of Oceanography and a lead scientist on the state's action plan, said the 55-inch estimate in the report is "probably conservative."
"As temperature climbs, melting is going to proceed at a greater pace," he said. "It is not necessarily going to proceed linearly, in the same proportion as it did in the past because melting begets more melting."