If Ze'ev Gedalof, a University of Victoria graduate student is correct, climatic changes are just starting that could lead to favorable conditions for salmon in the Pacific Northwest for the next two decades.

Studying tree rings that date back centuries, Mr. Gedalof found evidence of a climatic cycle that changes every 23 to 26 years. His statistical analysis indicates another shift is due - just about now.

"There are some signs that it's already begun," he said, referring to oceanic studies that suggest the north Pacific Ocean may be starting to cool.

Mr. Gedalof's findings are of immense importance to the Pacific Northwest, where salmon and steelhead stocks have widely been in decline since 1977.

That year is marked on the tree rings Mr. Gedalof has extracted from old growth trees from California to Alaska. The youngest tree from which he took a core sampling was 400 years old, the oldest 980 years old.

In the tree rings, which are fat or wide apart during periods of rapid growth, and tight together during lean years, Mr. Gedalof found a repeating signal of abrupt climatic change in 1977, 1946, 1923 and on nine other dates in sequence. The average range between the signs of change: 23 years.

That would make 2000 the likely year for another change, going from a relatively warm period to a cold one.

The cold cycles result in deeper snow packs, which in turn leads to increased run-off and lower temperatures in salmon streams all along the Pacific Coast. Salmon are a cold water species that have a hard time coping with low-water, warm-water conditions.

A cold phase could trigger a resurgence in Pacific salmon, agrees Mr. Gedalof.

"The North Pacific climate has been working against our recovery efforts for salmon, so a change would be welcomed," he said.

Mr. Gedalof began extracting tree trunk cores initially to study the effects of El Nino, an event which sends warm water currents into the North Pacific from near South America. Drastic declines in salmon stocks coincide with El Nino, which triggers a decline in the upswelling of deep ocean nutrients, and causes an influx of predatory fish, like mackerel, which prey heavily on young salmon.

But Mr. Gedalof's study took a change of direction when researchers from the University of Washington published an article about a climatic phenomenon known as PDO - the Pacific decadal oscillation.

Mr. Gedalof suddenly realized that the pattern he was looking at in tree rings matched perfectly with the PDO.

"I looked at trees from California to Alaska. I found that pattern at almost every one of the sites. I was able to say: 'That's big - that's not just a local phenomenon.'"

While scientists are still debating what causes the PDO, Mr. Gedalof's research provides a reliable time record of the event over the centuries.

If the pattern holds, we should be on the doorstep of a major climatic change that will lead to a resurgence of Pacific salmon stocks. In that event, the billions of dollars that have been spent from Alaska to California on improving salmon habitat may finally bring the returns that everyone has long hoped for.