This is an event that is more extreme than any in the observed record, and our research suggests that global warming is playing a role right now. — Stanford Scientist Noah Diffenbaugh
Last week, a strong storm over-rode a powerful high pressure ridge that has been deflecting moisture-loaded weather systems northward and away from the US West Coast for the better part of two years. Though some precipitation did grace the northern and mountain stretches of the drought-stricken state of California, it is no-where near enough to alleviate an epic 21+ month long drought. A drought borne of a blocking pattern that began during the winter of 2012-2013 and now threatens to extend to the end of 2014 and, possibly, beyond.
In the wake of the storm, the powerful ridge reasserted — again delaying hopes that a parched California would at last begin to receive at least a normal allotment of rain.
(Euro Model forecast shows the ridiculously resilient ridge [RRR] strongly in place off the US and Pacific Northwest coasts in the October 6 run. Image source: ECMWF.)
It is a high pressure ridge based blocking pattern that has become so persistent that researchers at Stanford University have given it a new name — the ridiculously resilient ridge or Triple R. And the Triple R, according to those same researchers has climate change based origins.
For this week, Stanford scientists published a new study that found:
The atmospheric conditions associated with the unprecedented drought currently afflicting California are “very likely” linked to human-caused climate change.
Researchers used a combination of climate models and statistical techniques to determine that large, persistent high pressure systems of the kind that have been locking California into perpetual drought are more likely in the presence of high concentrations of greenhouse gasses. They found that the ridge, which has generated year-round wildfires in California and at its peak intensity during January of 2014 stretched from Hawaii all the way to coast of the Arctic Ocean north of Alaska, was a kind of new species of extreme weather far more likely to occur in a human-warmed world.
(January 23 of 2014 weather pattern showing a moisture flow diverted from Hawaii to Alaska by the Triple R west coast blocking pattern. Image source: NASA.)
The anomalous strength of the ridge also likely played a role in the powerful polar vortex disruptions that were commonplace throughout the winter of 2014. As the ridge shoved more warm air into the polar zone north of Alaska the cold core of the polar vortex was displaced south and eastward over the Canadian Archipelago and Hudson Bay — driving extreme weather events over the central and eastern US as well as across the Atlantic and on to the UK.
The Researchers found that ridging was the overall and anomalous tendency of the pattern in this region of the northeast Pacific. They observed that the ridge remained strong throughout the winter of 2013, weakened during the summer of that year, then flared into an extreme intensity by January of 2014. Since that time, the ridge has swelled and spluttered, occasionally letting a storm or two pass but still serving as a kind of brutal sentinel to weather systems that would typically make their way to California.
The results of such a human-caused disruption of the climate are all too visible in the most recent US Drought Monitor.
(Despite tropical storms and the occasional weakness in the Triple R allowing a brief influx of moisture, 100% of California is still suffering from drought conditions with 58% percent of the state under the most extreme level of drought. Image source: US Drought Monitor)
A drought event that is the most extreme in the observed record and that is now linked to climate change by at least three major studies.
From the Stanford Study’s authors:
“We’ve demonstrated with high statistical confidence that the large-scale atmospheric conditions, similar to those associated with the Triple R, are far more likely to occur now than in the climate before we emitted large amounts of greenhouse gases,” Rajaratnam said.
“In using these advanced statistical techniques to combine climate observations with model simulations, we’ve been able to better understand the ongoing drought in California,” Diffenbaugh added. “This isn’t a projection of 100 years in the future. This is an event that is more extreme than any in the observed record, and our research suggests that global warming is playing a role right now.”