Climate Shift Signals Higher Sea-levels on U.S. West Coast

SAN DIEGO, California, May 5, 2011 (ENS) – A change in wind patterns that could cause an accelerated rise in West Coast sea levels beginning this decade has been measured by researchers at Scripps Institution of Oceanography at the University of California, San Diego.

Sea conditions dominated by cold surface waters along the West Coast could soon “flip to an opposite state” says Peter Bromirski, an associate project oceanographer at Scripps. “There are indications that this is what might be happening right now.”

Bromirski is the lead author of a study now in press in the “Journal of Geophysical Research-Oceans,” that measured the changes in wind stress patterns linked with changes in sea levels along the West Coast of North America.

Oceanographer Peter Bromirski on a Pacific Ocean beach (Photo courtesy UCSD)

Bromirski and fellow Scripps oceanographers Art Miller, Reinhard Flick and Guillermo Auad studied the wind stress patterns that characterize the different phases of a Pacific Ocean climate cycle known as the Pacific Decadal Oscillation.

The scientists date the current phase of the Pacific Decadal Oscillation, or PDO, to the mid-1970s. During the past three decades since the current PDO phase began, West Coast sea level trend has mostly been steady in a warm phase. The only exceptions have been fluctuations associated with the warming El NiƱo climate pattern in the eastern tropical Pacific Ocean.

It may sound contradictory, but Bromirski says the current “warm” phase of the PDO is characterized by the upward movement, or upwelling, of cold water toward the surface along the West Coast.

When the PDO cycle shifts to its negative “cold” phase, coastal ocean waters will be characterized by a downward movement, or downwelling, where the amount of colder, denser water brought to the surface will be reduced. The resulting warmer surface water will raise coastal sea levels, he says.

Wind stresses can change the characteristics of the coastal upwelling and downwelling regime, that is they can suppress or raise sea level.

In their paper, 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,” the authors write.

Global sea levels rose during the 20th century at a rate of about two millimeters (.08 inches) per year.

That rate increased by 50 percent during the 1990s to a global rate of three millimeters (.12 inches) per year, an uptick linked to global warming.

The authors warn that 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 the National Oceanic and Atmospheric Administration, the National Science Foundation, and the California Energy Commission.

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