For the last few decades, sea levels of the eastern North Pacific Ocean along the west coast of North America have remained remarkably steady as other sea levels rise around the world.

That is due to the dominance of cold surface waters along the coast. According to a new study from the University of California (UC) San Diego, the cold waters on the coast will give way to warmer waters beginning this decade, which will lead to accelerated sea-level rise. The change in water temperature is related to the climate phenomenon in the Pacific Ocean known as the Pacific Decadal Oscillation (PDO).

Globally, sea levels rose about two millimeters per year in the 20th century. Starting in the 1990s the rate jumped to 3 millimeters per year, widely believed to be caused by global warming. The greatest concern for rising sea levels is their effect on beach erosion, and the devastation that can be caused to coastal developments during high tides coupled with storm surges and high waves.

Residents of the west coast have escaped that fate until now, according to researchers at Scripps Institution of Oceanography, UC San Diego. Their study shows a great shift coming in sea temperatures. "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.

The Pacific Decadal Oscillation (PDO) is thought to have begun in the 1970s. The "warm" phase we are currently in is characterized by an upwelling of cold water toward the surface of the west coast. Despite aberrations caused by El Nino, the current trend has held steady.

Bromirski and his fellow colleagues believe the cyce is shifting to its opposite "cold" phase, characterized by a decrease in upwelling, causing surface waters to be warmer. Warmer surface water equates to a rise in sea levels. They look at changing wind patterns which suggest a shift in the PDO. In the 1970s just before the current phase begun, the wind stresses reached unprecedented levels. Now it is happening again.

The researchers write, "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."