Paper Reviewed
Johnstone, J.A. and Mantua, N.J. 2014. Atmospheric controls on northeast Pacific temperature variability and change, 1900-2012. Proceedings of the National Academy of Sciences USA 111: 14,360-14,365.

Johnstone and Mantua introduce their analysis by writing - in the journal Proceedings of the National Academy of Sciences USA - that the "Northeast Pacific coastal warming since 1900 is often ascribed to anthropogenic greenhouse forcing," but they go on to demonstrate that this attribution is almost certainly incorrect. This they do by working, as they describe it, with "several independent data sources to demonstrate that century-long warming around the northeast Pacific margins, like multi-decadal variability, can be primarily attributed to changes in atmospheric circulation."

More specifically, the two researchers demonstrate how "sea level pressure reductions and related atmospheric forcing led to century-long warming around the northeast Pacific margins, leading to circulation changes that they say "are estimated to account for more than 80% of the 1900-2012 linear warming in coastal northeast Pacific sea surface temperature and US Pacific Northwest (Washington, Oregon, and northern California) surface air temperature." And at the same time, they also demonstrate that "an ensemble of climate model simulations run under the same historical radiative forcings fails to reproduce the observed regional circulation trends."

These results - quoting Johnstone and Mantua once again - suggest that "natural internally generated changes in atmospheric circulation were the primary cause of coastal Northeast Pacific warming from 1900 to 2012 and demonstrate more generally that regional mechanisms of inter-annual and multi-decadal temperature variability can also extend to century time scales." And, therefore, as they write in their paper's concluding paragraph, "based on the strong, physically realistic correlation between large-scale sea level pressure and sea surface temperature indices from 1900 to 2012, we conclude that dynamical forcing accounts for virtually all of the observed warming in Northeast Pacific Arc sea surface temperature over the 1900-2012 period as well."