The Northwest is getting hotter, and humans are to blame

Human activity has caused the average annual temperature in the Pacific Northwest to increase by about 1.3 degrees Fahrenheit over the past century, a new report from Oregon State University shows.

"The amount of warming may not sound like a lot to the casual observer, but we already are starting to see some of the impacts and what is particularly significant is that the rate of warming is increasing," said Phillip Mote, director of OSU's Oregon Climate Change Research Institute and a study co-author.

Already, the "freeze-free" season has lengthened by two to three weeks, Mote said. That's like moving the snow line 600 feet up the mountains.

The warming trend has been accelerating over the past three or four decades.

"At the rate the temperature is increasing, the next 1.3-degree bump will happen much more quickly," Mote said.

In their study, the researchers looked at temperatures and precipitation from 1901 to 2012 in the Northwest, which includes Oregon, Washington, Idaho, western Montana and the northwestern tip of Wyoming.

They examined four factors to determine the influence of human activities: greenhouse gases and aerosols; solar cycles; volcanic eruptions; and naturally occurring phenomena such as El Niño events.

"Natural variation can explain much of the change from year to year, but it cannot account for this long-term warming trend," said co-author David Rupp, a research associate with the Oregon Climate Research Institute.

John Abatzoglou, associate professor at the University of Idaho, was lead author of the study, one of the first to isolate the role of greenhouse gases in regional warming.

The study recently was published in the Journal of Climate, a publication of the American Meteorological Society.

It was funded by the U.S. Department of Agriculture and the National Oceanic and Atmospheric Administration.

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