February 28, 2011 — Vol. 27 No. 9
The Pacific Northwest could be entering a period of generally drier climate where the duration of cycles between wetter versus drier conditions last 60 to 100 years, is an implication of a new study that has analyzed the region's weather patterns from the last 6,000 years.
According to a study published this week in Proceeding of the Natural Academy of Sciences, during most of the 20th century the region was in a relatively wet period compared to the last 6,000 years, and if weather patterns continue, the region is due for a prolonged dry period.
"Over the last 6,000 years droughts and wet periods have tended to come in cycles and the period of those cycles has not been constant over time," said Idaho State University biological and geosciences professor Bruce Finney. "Early in the record the duration of one wet-dry cycle was roughly every 30 to 60 years, but they have become less frequent, particularly in the last 1,000 years, occurring 60 to 100 years apart."
Finney was part of a team of researchers led by University of Pittsburgh's Daniel Nelson and Mark Abbott that produced the study "Drought variability in the Pacific Northwest from a 6,000-yr lake sediment record" by analyzing the sediment core samples from Castor Lake in Washington.
As the duration of drought and wet periods has increased, their impacts have been amplified over the last 6,000 years in the Pacific Northwest. The effects of climate change could create even more extreme periods of both types of weather patterns in the region. The change in Pacific Northwest's drought patterns in the last 1,000 years is linked to weather patterns in the Pacific Ocean, namely the El-Niņo Southern Oscillation. El-Niņo weather patterns are the result of cyclic warming and cooling of the surface of the central and eastern parts of the Pacific Ocean, creating disruptions in weather patterns over a large scale. El-Niņo patterns have intensified over the last 1,000 years, and that intensification could continue.
"The experts on El Niņo have a hard time predicting what is gong to happen to this weather pattern as human influence on climate grows stronger," Finney said. "But what our research shows is that you really need to know what El Niņo is going to do to predict the future of our climate here."
The impact of global warming on the El Niņo Southern Oscillation "will be intimately tied" to changes in the Pacific Northwest's climate and hydrology in upcoming years, the study authors conclude.
The study's authors included lead author Nelson, Abbott, Michael Rosenmeier and Byron Steinman from the University of Pittsburgh; Nathan Stansell from Ohio State University; Pratigya Polissarass from Columbia University's Lamont-Doherty Earth Observatory; Joseph Ortiz, from Kent State University; Finney; and Jon Riedel, a geologist at North Cascades National Park in Washington.