Researchers Find Northeast Pacific Surface Warming (1900-2012) Caused By Changes in Atmospheric Circulation, NOT Manmade Forcings

UPDATE:  See the update at the end of the post.

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This is a revisit of a paper already discussed in the WUWT post Surprising PNAS paper: CO2 emissions not the cause of U.S. West Coast warming.  We’re revisiting it because it relates to the record high global surface temperatures in 2014.  There already has been and there continues to be a lot of misinformation about those record highs in the months to come, so this is another post intended to counter that misinformation.

The extraordinary sea surface temperatures of the Northeast Pacific are known to be responsible for the record high global surface temperatures in 2014.  (See the post Axel Timmermann and Kevin Trenberth Highlight the Importance of Natural Variability in Global Warming… and the post On The Recent Record-High Global Sea Surface Temperatures – The Wheres and Whys.  A well-timed paper reveals that the warming of sea surfaces in that region is governed not by manmade greenhouse gases but by changes in atmospheric circulation.

The paper is Johnstone and Mantua (2014) Atmospheric controls on northeast Pacific temperature variability and change, 1900–2012.  In addition to the abstract, the PNAS webpage includes an introductory paragraph titled “Significance”.  It reads:

Northeast Pacific coastal warming since 1900 is often ascribed to anthropogenic greenhouse forcing, whereas multidecadal temperature changes are widely interpreted in the framework of the Pacific Decadal Oscillation (PDO), which responds to regional atmospheric dynamics. This study uses several independent data sources to demonstrate that century-long warming around the northeast Pacific margins, like multidecadal variability, can be primarily attributed to changes in atmospheric circulation. It presents a significant reinterpretation of the region’s recent climate change origins, showing that atmospheric conditions have changed substantially over the last century, that these changes are not likely related to historical anthropogenic and natural radiative forcing, and that dynamical mechanisms of interannual and multidecadal temperature variability can also apply to observed century-long trends.

Let me amend the opening sentence: “Northeast Pacific coastal warming since 1900 is often ascribed to anthropogenic greenhouse forcing…” but not any longer.

Let’s also repeat that last sentence (my boldface), because it’s important.

It presents a significant reinterpretation of the region’s recent climate change origins, showing that atmospheric conditions have changed substantially over the last century, that these changes are not likely related to historical anthropogenic and natural radiative forcing, and that dynamical mechanisms of interannual and multidecadal temperature variability can also apply to observed century-long trends.

The abstract of Johnstone and Mantua (2014) is also important because it highlights another climate model failure.  They even use the word “fails” (my boldface and caps).

Over the last century, northeast Pacific coastal sea surface temperatures (SSTs) and land-based surface air temperatures (SATs) display multidecadal variations associated with the Pacific Decadal Oscillation, in addition to a warming trend of ∼0.5–1 °C. Using independent records of sea-level pressure (SLP), SST, and SAT, this study investigates northeast (NE) Pacific coupled atmosphere–ocean variability from 1900 to 2012, with emphasis on the coastal areas around North America. We use a linear stochastic time series model to show that the SST evolution around the NE Pacific coast can be explained by a combination of regional atmospheric forcing and ocean persistence, accounting for 63% of nonseasonal monthly SST variance (r = 0.79) and 73% of variance in annual means (r = 0.86). We show that SLP reductions and related atmospheric forcing led to century-long warming around the NE Pacific margins, with the strongest trends observed from 1910–1920 to 1940. NE Pacific circulation changes are estimated to account for more than 80% of the 1900–2012 linear warming in coastal NE Pacific SST and US Pacific northwest (Washington, Oregon, and northern California) SAT. An ensemble of climate model simulations run under the same historical radiative forcings FAILS to reproduce the observed regional circulation trends. These results suggest that natural internally generated changes in atmospheric circulation were the primary cause of coastal NE Pacific warming from 1900 to 2012 and demonstrate more generally that regional mechanisms of interannual and multidecadal temperature variability can also extend to century time scales.

I enjoy studies that point out climate model failings.

Johnstone and Mantua also provided sea surface temperature data as part of their Supplementary Information.

Bottom line:  From 1900 to 2012, there is no evidence that manmade greenhouse gases had any influence on the sea surface temperatures of the Northeast Pacific.

Now, because of a prolonged weather event in the Northeast Pacific, which was strong enough to be reflected in sea surface temperatures globally, the chicken littles of our world are doing what they do best…whining about problems that exist only in their illogical, not-too-fertile imaginations.

POSTSCRIPT

I suspect that someone is bound to say something to the effect of: well this is only a small part of the global oceans.

For nearly six years, we’ve been illustrating, animating and describing how data indicate coupled ocean-atmosphere processes are responsible for the rise in ocean heat content since the mid-1950s and the warming of sea surfaces during the satellite-era.  If this is still news to you, see the introductory discussion in the free illustrated essay “The Manmade Global Warming Challenge” (42MB) and the blog post Answer to the Question Posed at Climate Etc.: By What Mechanism Does an El Niño Contribute to Global Warming?

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UPDATE: Jim Johnstone, one of the authors of the paper, has joined us on the thread at WUWT and provided a link to his webpage.  There you can find a link to the paper discussed on this thread.  Also see his comment here for an update on the recent unusual warming event in the extratropical North Pacific. Thank you, Jim.