The rise in temperatures along the U.S. West Coast during the past century is almost entirely the result of natural forces — not human emissions of greenhouse gases, according to a major new study released today in the Proceedings of the National Academy of Sciences.
The vast majority of coastal temperature increases since 1900 are the result of changes in winds over the eastern Pacific Ocean, the authors found. But they could find no evidence that those weather patterns were themselves being influenced by the human burning of fossil fuels.
Since the ocean is the biggest driver of temperature changes along the coast, the authors tracked land and sea surface temperatures there going back 113 years. They found that virtually all of the roughly 1 degree Celsius average temperature increase could be explained by changes in air circulation.
“It’s a simple story, but the results are very surprising: We do not see a human hand in the warming of the West Coast,” said co-author Nate Mantua, with NOAA Fisheries Southwest Fisheries Science Center. “That is taking people by surprise, and may generate some blowback.”