2 May 2011
WASHINGTON—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 a new study that says 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,” says Peter Bromirski, a researcher at Scripps Institution of Oceanography, UC San Diego, and lead author of a study now in press in the Journal of Geophysical Research–Oceans, a journal of the American Geophysical Union.
Global sea level rose during the 20th Century at a rate of about two millimeters (0.08 inches) per year. That rate increased by 50 percent during the 1990s to a global rate of three millimeters (0.12 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.
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 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.”
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.
Joint Press Release
Kathleen O’Neil, +1 202 777 7524, [email protected]
Robert Monroe or Mario Aguilera
+ 1 (858) 534-3624, [email protected]
As of the date of this press release, the paper by Bromirski et al. is still “in press” (i.e., not yet published). Journalists and public information officers (PIOs) of educational and scientific institutions who have registered with AGU can download a PDF copy of this paper.
Or, you may order a copy of the paper by emailing your request to Kathleen O’Neil at [email protected]. Please provide your name, the name of your publication, and your phone number.
Neither this paper nor this press release are under embargo.
“Dynamical Suppression of Sea Level Rise Along the Pacific Coast of North America: Indications for Imminent Acceleration”
Peter D. BromirskiIntegrative Oceanography Division, Scripps Institution of Oceanography, UCSD, La Jolla, California, USAArthur J. MillerCASPO Division, Scripps Institution of Oceanography, UCSD, La Jolla, California, USAReinhard E. FlickCalifornia Department of Boating and Waterways, Scripps Institution of Oceanography, UCSD, La Jolla, California, USAGuillermo AuadCASPO Division, Scripps Institution of Oceanography, UCSD La Jolla, California, USA; now at Bureau of Ocean Energy Management, Regulation and Enforcement, Herndon, Virginia, USA