El Niño is not the last word of wisdom
El Niño, a climate phenomenon that has been much discussed lately, does not appear to be the only climate cycle. Another cycle has now been discovered at the University of Washington that extends over a significantly longer period of time. It looks like El Niño, it feels like El Niño, and if you look at the fish stocks, the water supplies or the agricultural production, you would say it's El Niño. But he isn't. In two recent studies, researchers from the University of Washington describe a longer climate cycle in the Pacific Ocean. This discovery appears to explain many of the changing environmental conditions observed across North America, particularly in the Pacific Northwest, since the late 1970s.
Scientists call this climatic phenomenon PDO (Pacific decadal oscillation). The cycle is currently in a positive phase. This, she says, could explain why ocean temperatures were higher than average on the U. S. West Coast, why winters were wetter than usual in the South, and why Alaskan salmon fishing is at an all-time high while it is at an all-time high along the rest of the West Coast record-breaking decline.
It seems like El Niño is just a small part of this cycle, says David Battisti, associate professor of atmospheric sciences at the University of Washington. He was the first to demonstrate why El Niño recurs on average every four years. According to Battisti, his new discovery affects sea surface temperatures in the North Pacific, which includes the tropics. In his opinion, this phenomenon explains many effects of regional climate changes: "And if we could predict the PDO, our weather forecasts would be much more reliable."
Nate Mantua, research fellow at the University of Washington, estimates that scientists won't be able to make accurate predictions for another five years. "Right now, the science is roughly at what we knew about El Niño 15 to 20 years ago," says Mantua. He believes a PDO forecasting system would enable long-term planning in areas such as fisheries, water supply, agriculture and energy production enable.
The discovery of the PDO was something of a scientific crime novel. With the help of high-performance computers, the researchers combed through the meteorological records of the past century in order to discover recurring patterns in climate change. In relation to the last few decades, El Niño quickly emerged as the dominant recurring pattern of climate change. But when the records were studied up to 1900, focusing on the region north of Hawaii in the Pacific basin, the PDO revealed positive and negative phases lasting between 10 and 30 years.
The researchers discovered that the PDO has been in a positive phase since 1977, apart from a few interruptions. This is characterized by cool air in the US Southeast and a trend toward dry weather over the Columbia Basin and Great Lakes. In the Northwest, winters have been largely warm and dry, water levels low because there were fewer storms than usual, and snowfall light. During the previous negative phase of the PDO, lasting from 1947 to 1976, Northwest water levels were on average 20 percent higher than between the 1920s and 1940s, with more frequent rainfall and heavier snowfalls.
The results also suggest that many Pacific salmon stocks will be affected by changes in ocean climate. This may explain why coho and chinook salmon were plentiful off the coasts of Washington, Oregon and California during the last negative phase of the PDO, when coastal ocean temperatures dropped, but stocks in Alaska were severely depleted. Since the 1970s, warmer coastal waters have reversed these conditions. However, the researchers say, the current positive streak of the PDO should reverse within the next decade and then restore favorable conditions for West Coast salmon.
Temperature fluctuations in the Pacific Ocean cause periodic changes in the atmosphere that are felt throughout North America. Because of the so-called Aleutian low, which controls the atmospheric events over the entire region, the phenomenon is particularly evident in the north-west. One of the mysteries of the PDO, Mantua says, is whether it dominates El Niño, or is a long-term response to the phenomenon. According to the scientists, the PDO represents a slower change in the ocean and atmosphere climate system across the Pacific Basin that influences the evolution of El Niño.
The frustrating thing about trying to predict the PDO is that it evolves over such a long period of time. A negative or positive phase can be over before the researchers even notice it. "We can see the phenomenon, but we can't tell what phase we're in," says Battisti. "But that's only because we don't fully understand it yet. After all, we only recently realized it existed."
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