Rising temperatures on the West Coast of the United States may be largely due to winds, and not man-made global warming, according to a new study.

Increasing temperatures along the American Pacific Coast over the last century has led to infestations of pine beetles and other pests. Since the start of the 20th century, temperatures in Oregon and California have risen. The conditions have also delayed seasonal ice melt, and made wildfires more common, leading to widespread environmental damage.

University of Washington researchers investigated whether the effect was caused by global warming, or if another cause could be leading to greater temperatures. Most environmental scientists are blaming man-made global warming for the conditions.

"There does seem to be a tendency for any [century-long] trend in temperature -- a warming trend -- to be interpreted in terms of human effects. We looked to see if we could verify that," James Johnstone of the University of Washington said.

Nathan Mantua worked with Johnstone, as the two researchers compared air sea-level pressures with water temperatures recorded over the course of the 20th century. The two discovered that a change in prevailing winds always preceded changes to surface water temperatures.

"The most straightforward explanation is that changes in the wind have forced the changes in the temperature," Mantua told the press.

When winds are calm, ocean surface temperatures rise, and they fall again when average wind velocities increase. This relationship has been well known to scientists for quite a while, and the effect was thought to play a small role in warming in the Pacific states. Most of the effect was thought to be caused by anthropogenic climate change. Johnstone and Mantua revealed the change was nearly entirely due to winds.

The Pacific Decadal Oscillation drives changes in surface temperatures on the surface of the ocean. These trends flip once every 20 or 30 years, an effect first discovered by Mantua.

Researchers are quick to point out that other climatic effects in the northwest, such as a recent massive drought, might be due to global climate change. These events are contingent on conditions over a much larger area than ocean temperatures on the surface.

Global warming effects on the Pacific northwest are mitigated by large spiral currents in the ocean, which tend to draw heat west across the water body.

Investigation of the role of prevailing winds on rising temperatures on the western coast of the United States was profiled in the journal Proceedings of the National Academy of Sciences of the United States of America.