During the last few decades, the U.S. West Coast caught a break from the pace of sea level rise experienced by many coastal regions around the world, but a new study warns that changes are in the wind.
In fact, an ocean-wide “regime shift” in circulation patterns across the North Pacific may already be underway — reversing a pattern of natural variability that took hold during the mid-1970s. Oceanographers are concerned that the changes they are seeing may potentially “foreshadow” a rise in sea level from Seattle to San Diego that could reach or even surpass the global rate.
Since 1976, a climate cycle known as the Pacific Decadal Oscillation, has shown a predominant pattern of winds and currents that has kept the west coast of the United States relatively cool while keeping sea temperatures along eastern Asia especially warm.
shows the opposite pattern is about to kick into place: cooler Pacific waters near Asia, and warmer waters off the US West Coast. According to researcher Peter Bromirski and colleagues at Scripps Institution of Oceanography in San Diego, there are even “indications that this is what might be happening right now.”
On a global scale, the height of the oceans has been rising about 2 millimeters or 0.08 inches per year during the 20th Century, although it jumped to 3 millimeters a year or 0.12 inches during the 1990s. These figures may not sound like much but they mean a lot if you own a house on the beach, or depend on healthy wetlands habitats, or worry about storm surges during high tides.
In any case, not all boats rise in a uniformly rising ocean — winds and currents and different temperatures of the underlying water give the sea level a patchwork quality on a regional scale.
Since about 1980, prevailing winds along the West Coast has been driving an “upwelling” circulation that brought a disproportionate volume of cool waters from the depths. “Alarmingly,” writes Bromirski and colleagues, these wind stress patterns “have dropped to levels during 2008 not observed since before the mid-1970s regime shift.”
A greater flume of underlying warm water would mean higher seas. If the pattern persists, the Scripps team warns, sea level rise along the West Coast “would have important societal impacts, affecting coastal erosion and flooding, resources, and ecosystems.”
IMAGE: Satellite-based measurements of sea-level heights illustrate the warm or positive phase of the so-called Pacific Decadal Oscillation that has been in place since the mid-1970s. CREDIT: American Geophysical Union.