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Researchers use tree rings to trace weather patterns

Tree rings continue to serve up scientific information about past weather and help scientists determine what might lie ahead.

Dave Sauchyn leads the tree ring research at the University of Regina’s Prairie Adaptation Research Collaborative. Examining the cores of trees have allowed researchers to establish short and long weather cycles on the Prairies.

“Our tree ring research continues to uncover two scales of weather cycles, one short cycle of three to eight years, which we can relate to El Nino and La Nina, plus a longer cycle with several decades of drier weather and several decades of wetter weather,” Sauchyn said.

The longer cycle is generally 60 years, with half of them wet and half of them dry.

He said a large-scale climate fluctuation called the Pacific Decadal Oscillation probably drives the longer cycle. Water in the Pacific Ocean changes from warm to cold and back again to affect North American weather.

Tree rings tell these stories because narrow rings indicate dry years and wider rings indicate wetter years.

Sauchyn and others have been examining tree rings for years, and the research has evolved.

“We are still collecting tree ring data but using a different strategy,” he said.

“We are focusing on older dead wood so that we can speak with confidence about climatic variability over the past 1,000 years.”

Researchers have pieces of wood as old as 641 AD.

“I can’t imagine a day when we’ve learned all there is to know,” he said.

“I feel like we are just scratching, or sanding in the case of wood, the surface.”

This work has allowed scientists to reconstruct all of the prairie river basin levels, which Sauchyn said tells them about the variability and reliability of water supplies.

People have only 100 years of weather measurements, and while there have been droughts, research has shown this has been one of the wettest periods.

Explorer John Palliser said in the mid-1800s that southwestern Saskatchewan and southeastern Alberta shouldn’t be settled and farmed, but it was and still is.

Sauchyn has long said that farmers must adapt to drier conditions. He studies climate more than weather, but he said the two are obviously linked.

“If climate is your personality, then weather is your mood,” he said.

“If your personality was to change, for example you switched from pessimist to an optimist, then you’re likely to be happy more often. Using that analogy, if our climate is becoming warmer, then there is likely to be more extremes of weather and water because warmer oceans produce more water vapour and warm air holds more moisture.”

Hotter, drier air masses will occur when moist air bypasses the Prairies.

Sauchyn said the natural variability of climate and extreme weather events will be different in the future because they will occur in a warmer world.

Learning as much as possible about natural variability from tree rings helps establish the basis for further research.

El Nino is part of that natural process and has affected tree growth over the past 1,000 years. It occurs when water in the Pacific Ocean is half a degree warmer than usual. The current one is 3.1 degrees warmer.

El Nino will change if the water continues to heat, which will affect future prairie weather, he said.

Extreme weather events and water levels take people by surprise, but Sauchyn said we should expect the unexpected.

“Our long climate records show us that we have not seen or measured the worst weather, and that even in the absence of climate change we can expect conditions that are more extreme than we’ve seen because they occurred in the recent past before the Prairies were settled by Europeans and before we installed weather and water gauges,” he said.

Government agencies, municipalities and the private sector all support tree ring research because they want to know how much worse it could get, he added.

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