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More cold winters of our discontent ahead
Wednesday, March 3, 1999
By TOM PAULSON
If you're unhappy with La Niña and the wet weather it brought the Pacific Northwest this year, you're not going to like the Pacific Decadal Oscillation.
Are you ready for a few more decades of wetter, colder winters?
"I'm not making a prediction," cautioned Philip Mote, a University of Washington climate researcher. "It's a suggestion . . . I suppose some would consider it a pretty bleak suggestion."
Mote and his colleagues suggest we get used to our raincoats and umbrellas. A recently discovered weather cycle known as the Pacific Decadal Oscillation, or PDO, may be shifting to its "negative" or wet phase, he says.
Unlike El Niño or La Niña, the Pacific Decadal Oscillation isn't a climate cycle that flips back and forth quickly. "It tends to persist for a long period of time in one phase or the other," Mote said. "We don't understand why."
While scientists may not fully understand the PDO, there's no question it exists. The Pacific Northwest has been in a dry phase since 1977, Mote said. The previous wet phase, with colder and wetter winters, lasted from 1945 to 1976.
"It was only this year that the Pacific's (lower) surface temperatures began to look like a wet phase PDO," Mote said. Last year's El Niño, which makes for warmer, drier winters in the Pacific Northwest, may have masked the effect of a coming wet phase.
The PDO weather pattern was discerned almost accidentally by scientists who began comparing the behavior of salmon, rivers and regional weather records.
In the early 1990s, Steve Hare was asked by Robert Francis, a UW professor of fisheries, to compare variations in the salmon population with climate variations such as El Niño.
Hare crunched some numbers and noticed another climate cycle that differed from El Niño -- flipping back and forth over decades -- and he found that it matched cyclic variations in the salmon population.
Hare, who now works as a biologist for the International Pacific Halibut Commission, learned that another scientist studying climate change, Yuan Chang, had separately identified the same pattern. Chang now works for The Boeing Co.
"We all got together and ended up naming this climate pattern the Pacific Decadal Oscillation, PDO for short," Hare said.
Pretty Darn Obnoxious might be how others translate the acronym.
"The most compelling evidence for a transition back to the wet phase of the PDO is stream flow in the Columbia River," Mote said. Since the year 1900, he said, high stream flow on the Columbia has corresponded with the wet phase of the PDO.
In 1996-97, he said, there was high stream flow on the Columbia. In the winter of 1997-98, Mote said, we should have had below-average stream flow because of El Niño but flow was about normal. Perhaps, he said, the wet phase PDO effect counteracted the warmer, drier El Niño.
Another hint that we're entering a wet phase, Mote said, is the abrupt decline recently in the Alaskan salmon population as the cooler northern ocean waters shift the fish populations south. That's a wet phase indicator as well, he said.
"We have had phenomenal changes in climate in the last few years," agreed Nate Mantua, a climate scientist at the UW's Joint Institute for the Study of Atmosphere and Ocean and one of those who with Hare first described the PDO.
"The north Pacific has gone from warm PDO conditions to cool PDO conditions," Mantua said. "The big question is whether what happened in the north Pacific is really going to get stuck in this cool PDO phase. . . . We don't know enough yet to say if that's the case."
This weather pattern has a more lasting and profound effect on the Pacific Northwest than does the El Niño/La Niña cycle, Mantua said, yet much less is known about it.
But the signs are lining up, Mote said. The salmon and the rivers appear to be a warning that the region has "shifted into the wet phase a couple of years ago."
P-I reporter Tom Paulson can be reached at 206-448-8318 or tompaulson@seattle-pi.com
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