Changes in winds over the eastern Pacific Ocean explain most of the warming trend along the West Coast of North America in the last century, according to a new analysis published in the Proceedings of the National Academy of Sciences.
Similar atmospheric shifts are known to drive fluctuations in Pacific climate over decades in the form of the Pacific Decadal Oscillation (PDO), a long-recognized pattern of seesawing ocean temperatures. The new research indicates that similar changes in regional pressure and winds can also drive trends in sea surface and coastal air temperatures that extend over a century or more.
This study used independently measured ocean and land-surface air temperature records from 1900 to 2012 to confirm an already well-documented increase of approximately 0.5 to 1 degree Celsius in the northeast Pacific Ocean and nearby land areas. What’s especially interesting and new about this work is that independently measured atmospheric sea level pressures over the past century show that circulation changes account for nearly all of the year to year, decade to decade, and century long surface temperature changes in the northeast Pacific Ocean and West Coast states since 1900.
An evaluation of climate model simulations used in the latest IPCC reports finds that the atmospheric changes that account for most of the 113 year warming trend are not predicted to result from historical radiative changes, including both natural and anthropogenic forcings. It is also notable that most of the West Coast warming since 1900 took place between 1910 and 1940. These facts suggest that the temperature trend most likely occurred through natural changes in regional climate dynamics, the new study concludes.