State of the Planet

News from the Columbia Climate School

Climate Record Suggests Drier Times for Pacific Northwest

We may think of the Pacific Northwest as rain-drenched, but new research led by scientists at the University of Pittsburgh shows that the region could be in for longer dry seasons, and is unlikely to see a period as wet as the 20th century any time soon.

The work, based on a 6,000-year climate record from a Washington lake, is reported in the Proceedings of the National Academy of Sciences. The team linked the longer dry spells to the intensifying El Niño/La Niña climate pattern and concluded that Western states will likely suffer severe water shortages as El Niño/La Niña wields greater influence on the region.

Measurement of oxygen isotope ratios (red) and grayscale (black) arranged to show drought cycle duration and intensity with 20th century wet period indicated.

For Lamont-Doherty Assistant Research Professor Pratigya Polissar, who participated in the project and grew up in Seattle, the research carries a personal message.

“We live in unusual times – that was really what I found so striking,” Polissar said. “This was in my backyard, so it was a personal interest.”

The researchers analyzed a sediment core from Castor Lake in north central Washington to plot the region’s drought history since around 4,000 BCE and found that wet and dry cycles during the past millennium have grown longer. The team attributed this recent deviation to the irregular pressure and temperature changes brought on by El Niño/La Niña. At the same time, they reported, the wet cycle stretching from the 1940s to approximately 2000 was the dampest in 350 years.

Lead researcher Mark Abbott, a Pitt professor of geology and planetary science, said those unusually wet years coincide with the period when western U.S. states developed water-use policies. “Western states happened to build dams and water systems during a period that was unusually wet compared to the past 6,000 years,” he said. “Now the cycle has changed and is trending drier, which is actually normal. It will shift back to wet eventually, but probably not to the extremes seen during most of the 20th century.”

Polissar said the influence of global climate change will increase the uncertainty for the future. “Even without anthropogenic climate change and global warming, we still need to deal with this,” he said.

Polissar helped design the research, was involved in taking cores from some other lakes nearby, and helped the team develop the methods used to construct the long-term climate record. The team included lead author and Pitt alumnus Daniel Nelson, several Pitt researchers and others from Ohio State University, Kent State University, Idaho State University and North Cascades National Park in Washington. For the full press release, click here.

Next up: Polissar says he and colleagues at other universities have put in a proposal to drill cores in the central Pacific Ocean and study the past variability of the El Niño/La Niña-Southern Oscillation.


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