The West Coast of America has been let off the hook, so to speak, over the past few decades, which has left ocean levels in the eastern North Pacific Ocean steady. However that is likely to change in the near future, says a new study.
A change in wind patterns is believed to be taking place that could cause coastal sea-level rise to accelerate, beginning anytime now.
This is the conclusion of researchers from the at Scripps Institution of Oceanography, UC San Diego, including Peter Bromirski, lead author of a study to appear in the Journal of Geophysical Research-Oceans.
The researchers believe that conditions are currently dominated by cold surface waters along the West Coast of the US, but that that could soon swap to an opposite state, resulting in rising sea levels.
During the 20th Century, global sea levels rose at a rate of approximately two millimetres (.08 inches) per year, which increased by 50% during the 1990s to a global rate of three millimetres (.12 inches) per year.
However the West Coast of America has seen steady sea levels that scientists believe is the result of the current phase a Pacific Ocean climate cycle called the Pacific Decadal Oscillation (PDO), which they date back to the late-1970s.
The current phase is a “warm” phase, and is characterised by the upwelling of cold water from the depths of the ocean to the surface along the West Coast. However, when the cycle shifts to its “cold” phase, as scientists believe it will soon do, this upwelling will drop, allowing warmer waters to congregate at the surface, resulting in rising sea levels.
Bromirski and colleagues studied the wind stress patterns that characterise the different phases of the PDO, which act to change the characteristics of the coastal upwelling/downwelling of waters, which in turn supress the increase of sea levels.
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.”