Questionable evidence of natural warming of the northwestern United States

Johnstone and Mantua (1) claim that changes in atmospheric circulation were the primary cause of the observed warming of sea surface temperature around the northeastern Pacific margins and surface air temperature (SAT) in Northern California, Oregon, and Washington from 1901 to 2012. The results of Johnstone and Mantua’s report contradict our previous finding (2) that anthropogenic forcing was the leading contributor to century-scale warming in the northwestern United States. Johnstone and Mantua’s results (1) are potentially important; however, we suspect that their results depend on the choice of sea-level pressure (SLP) data, as their conclusions are predicated on a long-term decrease in SLP over the northeastern Pacific.