Temperatures in the northwestern United States have been on the rise for 100 years — and, lo and behold, mankind may not be to blame, after all.

So claim the authors of a new study, published Monday in Proceedings of the National Academy of Sciences. Via the New York Times:

The analysis . . . effectively suggests that the region has warmed because ocean winds, on average, have weakened and shifted direction.
Scientists have long known that sea surface temperatures are lower when strong winds whip up ocean waves, and higher when the seas are calm. Researchers generally have assumed that the phenomenon was but one factor in that warming, and that increased levels of carbon dioxide from human activity play a major role in driving rising temperatures.
But the new analysis, which relies on wind, barometric pressure and temperature data recorded from 1900 to 2012, concludes that human activity has little impact.

“It explains practically every wiggle in the ocean temperature variations” observed from northern California up the Pacific coast to Washington, says the study’s lead author James A. Johnstone. “It’s a phenomenal correlation.”

Johnstone and his coauthor, Nathan J. Mantua, are researchers at the Joint Institute for the Study of the Atmosphere and Ocean at the University of Washington in Seattle.