The West Coast of North America has caught a break that has left sea level in the eastern North Pacific Ocean steady during the last few decades, but there is evidence that a change in wind patterns may be occurring that could cause coastal sea-level rise to accelerate beginning this decade.

That is the conclusion of researchers at Scripps Institution of Oceanography, UC San Diego, who said that conditions dominated by cold surface waters along the West Coast could soon flip to an opposite state.

"There are indications that this is what might be happening right now," said Peter Bromirski, lead author of a study now in press in the Journal of Geophysical Research-Oceans, published by the American Geophysical Union.

Global sea level rose during the 20th century at a rate of about 2 millimeters (.08 inches) per year. That rate increased by 50 percent during the 1990s to a global rate of 3 millimeters (.12 inches) per year, an uptick frequently linked to global warming. Rising sea level has consequences for coastal development, beach erosion and wetlands inundation. Higher sea levels could cause increased damage to coastal communities and beaches, especially during coincident high tides, storm surges and extreme wave conditions.

Several state and federal agencies, led by the California Department of Boating and Waterways, funded the study. Support also came from NOAA, the National Science Foundation, and the California Energy Commission.

Scientists date the current phase of a Pacific Ocean climate cycle called the Pacific Decadal Oscillation (PDO) to the mid- to late 1970s. The current "warm" phase is characterized by the upward movement, or upwelling, of cold water toward the surface along the West Coast. Despite a few El Niño-induced surges in sea level during that time, the coastal sea level trend has mostly been steady.

When the cycle shifts to its negative "cold" phase, coastal ocean waters will become characterized more by a downwelling regime, where the amount of colder, denser water currently brought to the surface will be reduced. Resulting warmer surface water will raise sea level.

Bromirski and fellow Scripps oceanographers Art Miller, Reinhard Flick and Guillermo Auad (now at the U.S. Department of the Interior's Bureau of Ocean Energy Management, Regulation & Enforcement) studied the wind stress patterns that characterize the different phases of the PDO. Wind stresses can act to change the characteristics of the coastal upwelling/downwelling regime, i.e. suppress or raise sea level.

The authors write that the characteristics of wind stress variability over the eastern North Pacific "recently reached levels not observed since before the mid-1970s regime shift. This change in wind stress patterns may be foreshadowing a PDO regime shift, causing an associated persistent change ...that will result in a concomitant resumption of sea level rise along the U.S. West Coast to global or even higher rates."

About Scripps Institution of Oceanography
Scripps Institution of Oceanography at University of California, San Diego, is one of the oldest, largest and most important centers for global science research and education in the world. Now in its second century of discovery, the scientific scope of the institution has grown to include biological, physical, chemical, geological, geophysical and atmospheric studies of the earth as a system. Hundreds of research programs covering a wide range of scientific areas are under way today in 65 countries. The institution has a staff of about 1,400, and annual expenditures of approximately $170 million from federal, state and private sources. Scripps operates robotic networks, and one of the largest U.S. academic fleets with four oceanographic research ships and one research platform for worldwide exploration. Birch Aquarium at Scripps serves as the interpretive center of the institution and showcases Scripps research and a diverse array of marine life through exhibits and programming for more than 415,000 visitors each year. Learn more at scripps.ucsd.edu.

About UC San Diego
Fifty years ago, the founders of the University of California, San Diego, had one criterion for the campus: It must be distinctive. Since then, UC San Diego has achieved the extraordinary in education, research and innovation. Sixteen Nobel laureates have taught on campus; stellar faculty members have been awarded Fields Medals, Pulitzer Prizes, MacArthur Fellowships and many other honors. UC San Diego — recognized as one of the top 10 public universities by U.S. News & World Report and named by the Washington Monthly as No.1 in the nation in rankings measuring "what colleges are doing for the country" — is widely acknowledged for its local impact, national influence and global reach. UC San Diego is celebrating 50 years of visionaries, innovators and overachievers. 50th.ucsd.edu