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. Last Updated: 07/27/2016

Researcher Sees Major Shift in Pacific Climate




New satellite data shows the Pacific Ocean may be undergoing a dramatic climate shift - much longer-lived than any El Ni?o - that could alter global weather patterns, disrupt fish stocks and perhaps lead Southern California into decades of drier than normal weather.


The changing cycle, known as the Pacific Decadal Oscillation, was formally identified just three years ago. Scientists tracking its progression say it appears that the eastern Pacific is undergoing a significant ocean cooling trend.


Their interest was prompted by highly unusual temperatures throughout the Pacific Ocean. The most recent satellite images indicate waters along the coast of the Americas are several degrees cooler than normal while a massive horseshoe-shaped chunk of the western Pacific is abnormally warm.


"It's bigger than El Ni?o," said Bill Patzert, a satellite oceanographer at the Jet Propulsion Laboratory in Pasadena, California, who announced the findings Wednesday. "This is a very strong signal."


Records for the past century show the Pacific Ocean climate has shifted periodically every 20 to 30 years, at times ushering in prolonged shifts in U.S. rainfall patterns.


But whether it is shifting now remains an open question - and a topic of fierce debate. Leading climatologists this week said it was far too early to tell whether such a long-term shift was occurring. They warned that any predictions of drought were tenuous at best.


"Whether it's going to stick around is anyone's guess," said Nathan Mantua, a climatologist at the University of Washington and an expert on the oscillation.


Nevertheless, Patzert theorizes the changes signal the Pacific is shifting to a "cool phase" that could last for decades, bringing more rain to the Pacific Northwest and less to Southern California.


Since 1977, the Pacific Ocean climate has been in a "warm phase," marked by higher than normal rainfall in Southern California and more El Ni?o events. Historical records show a cool phase persisted between 1947 and 1977 and that a warm, wetter phase persisted between 1925 and 1945.


While the day-by-day weather effects of a shift in the oscillation are subtle, the effects are important because they are widespread and long-lasting. "Over time, these changes are huge," said Aants Leetma, director of the National Atmospheric and Oceanographic Administration's Climate Prediction Center in Washington. He added that the shift may play a role in Southern California's current dry spell and last year's mid-Atlantic drought.


Patzert's new data was beamed down from the Topex/Poseideon satellite, run by JPL and France's space agency. The satellite uses radar to measure ocean height and converts those measurements to estimates of ocean temperature. Warm water, because it expands, can be higher by several centimeters.


The images show a steady cooling of several degrees in waters throughout the eastern Pacific and abnormally warm waters in the western portion. Even small changes in ocean temperature can have massive effects on climate.


But links between the Pacific Decadal Oscillation and drought remain unproven, said Dan Cahan, director of the climate research division at the Scripps Institution of Oceanography at the University of California, San Diego.


Cahan is among a number of climatologists who argue there is not enough evidence to confirm any shift. Although fascinated by the recent ocean changes, many said the pattern could be an extended short-term event, like a La Ni?a, which cools waters in the eastern Pacific.


The pattern could even be caused by something as random as a series of storms, said David Battisti, a professor of atmospheric science at the University of Washington, who has been monitoring the changes for several months using records of sea surface temperature collected by ships and buoys, which he says are more accurate than satellite data.


The announcement by JPL scientists that the ocean is probably undergoing a long-term shift is "premature," and would require several more years of temperature records, he said. "You can't make a prediction from a snapshot."


More clear is the relationship between the Pacific Decadal Oscillation and fish stocks. After the last shift in the mid-1970s, "salmon runs in the lower 48 went to hell in a handbasket and got really good in Alaska," said Michael Mullin, who directs Scripp's Marine Life Research Group.


While it takes a few years for fish stocks to respond to oceanic changes, early indications point to a cooling trend. Columbia River Chinook runs may soon be at record levels - more evidence a Pacific Decadal Oscillation shift may have occurred, fisheries scientists say.


Long-term ocean cycles may be largely to blame for the demise of some fish populations. Analysis of fish scales left in ocean sediment finds sardine and anchovy populations underwent cycles of boom and bust long before any commercial fishing pressures.


"Fish live long enough to get through an El Ni?o, but a decades-long shift affects a whole generation," Mullin said. Fishery regulators, he said, are struggling to adjust rules "in the face of huge environmental variability we're just groping to understand."