San Francisco Chronicle
By David Periman
June 22, 2012
Global sea-level rise, induced by the warming climate, will hit California’s coastline harder than the other West Coast states over the coming decades and on through the end of the century, according to a new report from the National Research Council.
Oceans around the world are rising, but seas around California will rise even higher – by more than 3 feet before 2100, the report says. Tide gauges and satellites show that the rate of sea-level rise has increased steadily since 1900, and with each passing decade, storm surges and high waves will put low-lying regions like the Bay Area at heightened risk of dangerous flooding.
The forecasts come from the research arm of the National Academy of Sciences, which appointed the 12-member committee to investigate earlier estimates of sea-level rise and factor in all new available evidence. The result was a 260-page report issued Friday.
The report was commissioned primarily by California’s Department of Water Resources, along with state agencies from Oregon and Washington in order to aid their planning efforts.
The scientists estimated the rates of global sea-level rise, and compared their findings with other forecasts of the global future. The report did not recommend ways to deal with future issues.
“This is physical science, not political science,” said committee member Gary Griggs, an oceanographer and director of marine science at UC Santa Cruz.
The report estimates that California’s sea-level rise south of Cape Mendocino could range between a mere 1.5 inches to a full foot by 2030; the rise could range between 4.5 inches and 2 feet by 2050 and between 16 inches and 4.5 feet by the start of the next century.
“However,” the report’s scientists warned, “an earthquake of magnitude 8 or larger in this region could cause sea level to rise suddenly by an additional meter (3 feet) or more” beyond those estimates.
The estimates of future sea-level rise are so broad, the scientists said, because of all the uncertainties and knowledge gaps involved in this kind of forecasting.
The sea-level forecast for California below Cape Mendocino is substantially higher than projections for Mendocino north along the coasts of Oregon and Washington because of the great differences in the nature of the Earth’s crust between the two regions, the scientists noted.
From Cape Mendocino north, the coastal land mass lies along what is called the Cascadia Subduction Zone. There the entire sea floor beneath the Pacific is slowly diving beneath the coastal crust and pushing the land upward, which means that the sea is slowly receding. That’s not happening along the rest of California.
But if a major earthquake hits on the Cascadia Subduction Zone, as it did in 1700, records show, then the diving would stop, and sea level would rise more swiftly, the report said.
The new estimates of sea-level rise are substantially greater than the projections by the U.N. Intergovernmental Panel on Climate Change, known as the IPCC, in 2007. The effect of melting polar ice on sea level has been calculated since then far more precisely, Griggs said.
The Arctic effect
The council’s scientists calculated that the melting glaciers in the Arctic and the breakup of vast ice sheets in the Antarctic due to climate change are dumping water into the oceans at an ever-faster rate. The melting ice accounts for 65 percent of total sea-level rise, while the expansion of all the world’s oceans as they warm up accounts for the rest, said Robert A. Dalrymple, professor of civil engineering at Johns Hopkins University, who headed the committee.
During a telephone press briefing Thursday, Dalrymple noted that as sea level rises more and more rapidly, California’s coastline will become increasingly threatened by erosion, crumbling cliffs, and larger and larger waves hitting farther and farther inland.
“California wetlands are likely to keep pace with sea-level rise,” he said, “and sea-level rise will magnify the effects of every storm.”
The Bay Area will be particularly hard hit because its airports and many cities are barely above sea level now. With every few inches of sea-level rise, more and more of those urban areas will be flooded – and particularly so by storm surge waters, the report said.
Jeanine Jones, interstate resources manager for California’s Department of Water Resources, called the report “extremely helpful in planning for the future.”
The new sea-level estimates mean, she said, that “winds, waves and weather will need a lot more prediction and more monitoring than ever.”