A new and most likely controversial analysis of Pacific Ocean weather patterns concludes that a century-long trend of rising temperatures in the American Northwest is largely explained by natural shifts in ocean winds, not by human activity.

The analysis, published on Monday in the prestigious peer-reviewed journal Proceedings of the National Academy of Sciences, 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.