By Deborah Zabarenko
WASHINGTON (Reuters) - Seas could rise higher along the California coastline this century than in other places in the world, increasing the risk of flooding and storm damage, dune erosion and wetland destruction, the U.S. National Research Council reported Friday.
Rising sea levels have long been seen as a consequence of climate change, because as the world warms, glaciers melt and contribute water to the Earth's oceans. At the same time, ocean waters tend to expand as they heat, pushing sea levels higher.
The report looked at how much seas could rise by 2100 along the U.S. West Coast, and found that the water off California's coast from the Mexican border to Cape Mendocino could rise between 16.5 inches and 66 inches by century's end, compared to what they were in 2000.
The high end of the range is higher than the projection for the global rise in sea levels, which runs from about 20 inches to 55 inches, scientists said in the report.
That global range is higher than predictions made in 2007 by the United Nations Intergovernmental Panel on Climate Change: between 7 inches and 23 inches, with an additional 6.7 inches if rapid changes in ice flow are part of the calculation.
But melting ice and expanding oceans are not the only forces at work, said Robert Dalrymple, a professor of civil engineering at Johns Hopkins University who headed the panel of scientists who contributed to the report.
"There are two components of regional sea level rise," Dalrymple told reporters in a telephone briefing. "What is the land doing in terms of moving up and down, and what is the sea level doing in terms of moving up?"
As global seas rise, some land may rise too, due to the movement of tectonic plates or the rebounding of land that used to be covered by ancient ice sheets. Without the heavy ice to weigh it down, some areas in northern Washington are rising, the report said.
"If the land is rising, then to the residents on that land, it looks like the sea level is falling," Dalrymple said.
Other factors include periodic ocean circulation patterns El Nino and La Nina, the scientists said.
Sea level rise as projected increases risk of damage from floods and storms, which ride into land on higher ocean water. It also endangers wetlands and could force dunes and bluffs to retreat as rising waters erode them, the report said.
While the projected sea level rise for northern California, Oregon and Washington state is lower than for the rest of California, the researchers cautioned that an earthquake of magnitude 8 or more could cause waters to rise by an additional 39 inches (1 meter).
This kind of strong earthquake, which could cause parts of the coast to quickly subside, is a possibility off the northern West Coast, the scientists said. Such quakes occur every few hundred to 1,000 years.
The study was commissioned by various state agencies of the three states, as well as the National Oceanic and Atmospheric Administration, the U.S. Army Corps of Engineers and the U.S. Geological Survey.
(Reporting By Deborah Zabarenko; editing by Todd Eastham)