Climate change behind extreme swings in western North America

Drought, floods and heat waves are becoming more common in western North America, and scientists expect the trend to continue. The culprit? A new study points to climate change.

“Our study found that extreme variability is synchronizing processes within and among ecosystems at a level not seen in the last 250 years,” Dr. Ivan Arismendi of Oregon State University said in a press release.

The bulk of research on climate change focuses on averages such as rising global temperatures, Arismendi said. He and his colleagues saw a need for more study into how climate change is affecting conditions on a smaller scale.

So they turned their focus to western North America. Led by the University of Texas Marine Science Institute, the team of scientists looked at how climate change is affecting the North Pacific High, and how that in turn is affecting ecosystems in western North America.

A subtropical “anti-cycone,” the North Pacific High is a climate pattern centered northeast of Hawaii and west of California. It shifts toward the equator in the winter. It’s connected to dry weather in the summer and fall and rainy months in the winter and spring in California.

But when the North Pacific High is strong in the winter, it disrupts the winter storm track. That leaves California and much of the surrounding western U.S. high and dry, triggering drought. And the North Pacific High has been more variable over recent years, a pattern that appears to be related to climate change.

The researchers documented North Pacific High and its effects over the past century, using everything from records to tree rings. They found that in recent decades, winter weather patterns have been swinging dramatically between extremes more frequently.

These changing wintertime conditions in western North America are having a profound effect on the plants and animals that live there. Ecosystems have been changing due to the more variable climate patterns, the researchers said.

“We’ve found that land, rivers, and oceans are all strongly related to a winter climate pattern off the western coast of North America, and that climate pattern has become more variable over the past century,” lead author Dr. Bryan Black of the University of Texas-Austin said. “This extreme variability is increasingly imprinted on these freshwater, terrestrial, and marine systems, and this has caused them to become more synchronous with one another with a number of implications for fisheries, drought, snowpack, and tree growth.”

The study has been published in the journal Global Change Biology.

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By Kyla Cathey, Earth.com staff writer