This week NASA's Jet Propulsion Laboratory issued a press release suggesting that changes in the Pacific Ocean are making it more likely that winter weather in much of the United States will exhibit unusual warmth alternating with sharp cold. The researchers said the pattern, prevalent this winter and last, might predominate for 20 or 30 years.
They are absolutely right. But this isn't news. Many climatologists have known about this, and have described it since the early 1990s.
My friend Dr. Bill Gray of Colorado State University was one of the first scientists to discover this phenomenon. Bill is well-known for his forecasts of hurricane activity in the Atlantic. He observed there are periods of generally active hurricane summers, and others with inactive years, lasting several decades each. Bill found that periods with El Ninos coincide with relatively quiet hurricane years, while La Nina conditions and are linked with busier years. A good place to view some of Bill's work is: http://tropical.atmos.colostate.edu/forecasts/index.html.
As I began studying these patterns, I noticed similar variations in the North Pacific. In the Pacific Northwest, we tend to get periods with mostly wetter than average years, and others with mostly dry years. The "wet" and "dry" periods typically last 20-25 years. In 1995, I publicly stated I believed we were entering a period of mostly wet years here. At the time, we had had 10 consecutive drier than average years. But since the winter of 1994-95, every year has been wet; we're now in our 6th in a row.
In addition, our winters have gotten cooler and offshore currents have gotten more favorable for our endangered salmon and other aquatic species. For more information, see http://www.ocs.orst.edu/reports/climate_fish.html and for a fairly complete analysis of the global variations, see http://www.ocs.orst.edu/reports/wet-dry.html.
Note Figure 4 in the second reference. Since 1994, we have seen a very large increase in the number of hurricanes and a preponderance of La Nina events, in addition to the shift from dry to wet years in the Northwest. We have also seen big changes in salmon returns (as described in the first article). After many years of abundance, Alaskan stocks have plummeted, while conditions in the Northwest have steadily improved. A researcher from British Columbia has stated that Alaskan salmon may be declining because of global warming, but the changes are much more consistent with a regime shift.
University of Washington researchers were discovering the decadal shift at about the same time. They gave it a name: Pacific Decadal Oscillation (PDO). Frankly, I prefer North Pacific Oscillation, but PDO seems to have come into vogue. You can read the UW report at http://www.iphc.washington.edu/staff/hare/html/decadal/decadal.html.
An interesting sidelight is that the PDO explains a great deal of the variation in global air temperatures in the last century. Take another look at Figure 4 and note how the El Nino-dominated periods (1920-45 and 1975-94) have seen global temperature increases, while the other periods have seen decreases. Few can explain why temperatures went up prior to 1945, a period with very little greenhouse gas enhancement; nor why they dropped thereafter, even though CO2 was increasing rapidly. Here's your answer and it's to be expected: the tropical Pacific is the single largest source of terrestrial heat to the atmosphere, and during El Ninos the Pacific tends to heat up. Check out John Daly's excellent article and chart at http://www.vision.net.au/~daly/soi-temp.htm.
Cooler North Pacific
Recently, we've been hearing news reports about the thinning Arctic ice (evidence, some say, of global warming). Now we hear news of a major cooling in the Bering Sea (information obtained from John Daly):
"Ice pushing much deeper south than normal has resulted in the postponement of the start of the multimillion-dollar Alaska snow crab fishery because of unusual ice buildup in the Bering Sea.
Officials of the Alaska Dept. of Fish and Game has speculated that the fishery, scheduled to open on Jan. 15, might have to remain closed until late April or May, if ice extending much farther south than normal makes most of the fishing area inaccessible.
Ice conditions are reported to be the most severe since the early 1970s, with the St. Paul Island and harbor iced in and inaccessible."
If we oversimplify, or look for trends over very short periods of time, we will come to faulty conclusions and make bad decisions. One of my favorite quotes is "there's nothing you can't prove if your outlook is only sufficiently limited" (Dorothy Sayers). When it comes to climate and ocean conditions, if we ignore long-term fluctuations, we're missing out on a big part of the picture.
All I can say to NASA is "welcome to the multi-decadal club!"
George H. Taylor
State Climatologist, Oregon
President, American Association of State Climatologists
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