February 16, 2015

The Origin of this Winter's Weather Anomalies: Is There A Global Warming Connection?

In my previous blog, I talked about the anomalous and persistent high pressure/ridging that has dominated the western U.S., producing generally dry and warm conditions.  And the equally persistent, and directly connected, low pressure and cold influencing the eastern U.S.

In this blog, I will spend some time examining the claims that global warming is behind it.  A final blog will discuss the true origins of the western North American ridging.

 Hurricane Ridge (5200 ft) in Washington Olympics is snow free, while Boston has several feet.

As I explained in my previous blog, the proximate reason for the anomalous weather is clear:  the highly amplified upper-level wave pattern with a major ridge over the West Coast and a trough over the eastern U.S.   Thursday evening's  (10 PM PST) 500 hPa upper-level chart  (top figure) shows the story.  The colors are heights (like pressures) and solid lines are sea-level pressure.  Higher heights bulge up in the west and lower height over the eastern U.S.  The lower picture shows temperatures in the lower atmosphere (around 5000 ft) at the same time.  Warm (yellows) in the west, cold (blue/purple) in the east.

So the amplified waviness of the upper level flow (and the associated jet stream) is what is making it warm in the west.   It is not due to any kind of uniform global warming over the planet.   The East Coast is as anomalously cold as we are anomalously warm.

The next question is obviously: is this amplified upper level pattern and couplet of warm-west and cold-east the result of global warming due to anthropogenic greenhouse gases or is it mainly natural variability?  I believe the facts and peer-reviewed literature suggest the latter, but you be the judge from what I will present below.

The most influential paper suggesting a global warming origin is by Jennifer Francis and Steve Vavrus:

Francis, Jennifer A.; Vavrus, Stephen J. (2012). "Evidence linking Arctic amplification to extreme weather in mid-latitudes". Geophysical Research Letters

In this paper they claim that global warming will weaken the jet stream by warming the Arctic, reducing the temperature gradients that drive the jet stream.  They hypothesize that a  weakened jet stream undulates more, producing a more amplified wave pattern with more cold waves in the eastern U.S. in the winter.  The media has given this paper huge play and it has been heralded by major political figures, like the President's Science Adviser, John Holdren.  And many environmentalists want to believe this paper is correct.

Unfortunately, the paper is deeply flawed and most members of the research community acknowledge it.    First, the Francis/Vavrus method of determining the amplitude of the waves was incorrect.  Instead of measuring the daily values of wave amplitude, they mistakenly used seasonal excursions.  A paper by Elizabeth Barnes of Colorado State University did the calculation correctly and found no trends in wave amplitude.

Furthermore, there is no reason to believe the upper tropospheric jet will weaken under global warming since increased CO2 enhances warming of the upper tropical troposphere, increasing the north-south temperature gradient, thus strengthening the jet.  Combined with the weakened gradient at low levels, this appears to result in jets with little change.  In addition, even if Francis/Vavrus were right that the jet was weakening, theoretical research is emphatic that this would deamplify the wave pattern and not strengthen it.

You want more?   There is no sign that cold waves have been increasing in the eastern U.S. as Vavrus/Francis claim;  in fact, they are declining.  And global climate models run under large increases of CO2 do not show the amplification that Francis/Vavrus claim.

Anyway, this Francis/Vavrus hypothesis is clearly wrong, but the media and some environmentally minded folks can't seem to let go of it.

More recently, the media and others have liberally cited another paper by some folks at Stanford to back the global warming/West Coast ridge connection.

Written by Daniel Swain and others, this paper starts by making the case that the drought and west coast ridging is historically very unusual. This is entirely correct.   So unusual and such an outlier, that great care needed to be taken in suggesting this was the result of progressive global warming of the past decades.

Then they compared climate model simulations for a pre-industrial era and the late 20th century regarding the amplitude of west coast high pressure at particular locations and found that it had increased;  on this basis, they suggested that anthropogenic CO2 is increasing pressure/heights making extreme values more likely.    This is, of course, true.  If you warm the atmosphere, the heights of pressure surfaces (like 500 hPa) will rise.    But this says NOTHING about troughs and atmospheric ridges, because they are associated with gradients of heights, not absolute values.

Lost you on this?   A ridge or high pressure area is only important because heights or pressures are lower in adjacent areas.   So for a ridge to become important and influence the weather, height must rise more in the ridge than elsewhere.  They did not show that and to be fair to them, they admitted this in the paper and back-pedaled in their conclusions.

So basically, their work DOES NOT LINK GLOBAL WARMING to the drought or enhanced high pressure areas along the coast.  But that did not stop the media from saying so.  In fact, Stanford's PR office was pushing this angle.

 Finally, there is apaper by Wang. et. al in Geophysical Research Letters (2014) that is being heavily cited in the media as proof that mankind is enhancing the western U.S. ridging:

In this paper,  the authors come up with a "dipole index" that measures the amplitude of the trough/ridge pattern.  Their results showed that 2013-2014 was very unusual, but if you look at their graph you will see that there is absolutely no trend, as one would expect if progressively global warming was the cause:
From GRL, Wang et al., 2014, page 3222

 Then they discuss the anthropogenic influence of human greenhouse gas emissions on the dipole amplitude.  Strangely, they examine how the variance (variability) of the dipole changes in time not the critical pattern of ridging on the west and troughing in the east.  They find that using analyses based on observations (the 20th century reanalysis from NOAA) that there is little trend in variance since 1950 or since 1975 when satellite data started to become available.   So this would really indicate that the real atmosphere is not changing.

But then they ran single climate simulations with and without greenhouse gases and found the variance increases with CO2.  What these single simulations mean and their relevance to global warming's impact on the west coast ridging is uncertain, but this did not stop them from claiming:

"there is a traceable anthropogenic warming footprint in the enormous intensity of the anomalous ridging during winter 2013-2104."

The bottom line is that a careful reading of any of the papers claiming an anthropogenic origin of the amplified upper atmospheric waviness reveals that they all have major flaws.  Or the media has hyped them beyond recognition.   I don't know of any leading atmospheric scientist that is claiming such a relationship.  But that has not stopped the media from hyping the connection.

There are, in fact, a number of papers that provide a different view, that the origin is from natural variability.  For example, in the same issue as Swain et al, a paper by Funk et al looked at a large collection of climate model simulations and concluded that global warming had no impact on the  West Coast ridging:

And as I mentioned in my last blog, a report by leading NOAA scientists have said the same thing:  the West Coast ridge is probably the result of natural variability.  There is no absolute certainty, of course.

Global warming is a serious issue, but we must keep it in perspective in comparison to natural variability.

In my next blog on this topic I will examine the results of recent papers that show the dominance of natural variability in producing the West Coast ridging.

KPLU Climate Talk

If you want to hear me talk about the regional implications of global climate change in some detail, please come to my UW Kane Hall talk on March 11th.Sponsored by local public radio station KPLU, tickets for this event can be secured at this web site.

The Pacific Northwest Weather Workshop

Interested in attending the big local weather workshop of the region?  The Pacific Northwest Weather Workshop will be held in Seattle at the NOAA facility on February 27-28th.   Everyone is invited and the majority of talks are accessible to laypeople.  To attend you have to register or they won't let you in the gate.  There will be a major session on the Oso landslide.  There is a registration fee that covers refreshments and food, and special student pricing.  If interested, check out this website.


  1. All good and solid information certainly Prof. Mass. With Part 2 of your "Why is the Northwest Warm and California Dry?" post theme, and with your having said that you would be focusing on what the origin of the pattern of ridging in the west and troughing in the east is more, within it, I'm hoping that you will be covering both just why ridges (even troughs) form more basically, together with also what elements are involved toward their (the jet) becoming more amplified, also more generally.

  2. With all due respect, and little understanding of meteorology (I am a scientist - an ornithologist at WWU), it seems to me that the uncertainties on both sides of this argument should lead us to conclude "We just don't know what role of climate change has in this persistent ridging pattern" rather than guessing one way or the other. We will know better in 50 years or so, or maybe sooner as our meteorology gets better.

  3. That whole thing begs the question, if the ridging (warming here) is not a global warming effect, what is? i.e. How do we differentiate "natural variation" from global warming and, further, how do we differentiate "global warming" from the effects of humans on global warming? There ya go, Cliff, looks like you'd be set for a series of blog topics with those.

    There seems to be some dramatic warming going on, but historically (say over 10s and 100s of thousands of years, I've been told it's "not that warm" and that the global warming is in fact "natural variation" and that human efforts will do little to stop it.

    1. 'begs the question' doesn't mean what you think it means ...

    2. 'begs the question' doesn't mean what you think it means ...

  4. We are adding energy to the system, to say that AGW doesn't have some play in what is occurring seems not to take this into account.
    If we are adding energy into the system, then any weather, or over time, climate, is effected by the CO2 we add.

  5. Weather is clearly a hugely complex system with large stochastic components. The difficulty is whether we can associate a short-term or small-extent phenomenon to a gradually increasing forcing function that (at least until recent times) was dwarfed by the stochastic components. Won't that always be impossible? At least until the effects are so widespread in time and space that reversing the effects will be hopeless? How sensitive are we (currently) to being able to detect global warming? Can we say that if we can't discriminate its effects that "there's still time"?

  6. Thanks for providing a good summary for laypeople on this current research. I've heard of all these different papers that reached different conclusions but I had no idea what any of them actually said.

    Just one question: you said in a paragraph about the Francis/Varvus paper that global warming may amplify the jet stream in the future, and also that weaker jet stream has less waviness, so would this mean that there is a possible mechanism for global warming to cause stronger jet stream waves?

    I'm also confused about the link between global warming and the temperature gradient between the poles and the equator, since you mentioned a stronger gradient due to tropical warming, but I remember hearing that the gradient will be lower because the warming happens faster at the poles.

  7. The weather in New England proves that God is an Indianapolis Colts fan.

  8. I rode my bike 21 miles yesterday in a short sleeve t-shirt. We're just beyond halfway into February. It's usually April the first time I do this, or late March if I take the bike east of the crest.

  9. It's as if The Great Red Spot of Jupiter has found a new home here on Earth and settled right over the Northwest.

  10. Related to shidots last point, I am a long time reader of your blog and don't think I've ever seen you address what's happening in the arctic. Not just the loss of sea ice -- which gets most of the media attention -- but also the overall dramatic temp anomalies. And the decreasing snow cover trend on surrounding land areas.

    Surely this has some impact on temp gradients? Do you believe these changes are also due to natural variability?

    - Douglas

  11. Michael Synder: I'm not sure we are adding energy to the system, but rather adding a green house gas to the system, which will theoretically increase solar energy retention. The extent to which humans are contributing to energy retention, and the extent to which we can reduce that seems to be the big unanswered question.

  12. Douglas,
    Global warming preferentially warms the poles. The part driven by greenhouse gases is not natural variability. This will weaken the low level temperature gradients. On the other hand, the upper tropospheric temperature gradient will be enhanced by increasing greenhouse gases. So the net tropospheric gradient may not change much. My point is you have to be careful about simple arguments like those offered in Francis and Vavrus. They might seem plausible to laymen, but the real world is more complicated...cliff

  13. It seems to me there are at least four characteristics of this anomaly that we need to understand in a historical context before we could make any claim one way or another about this system is affected by global warming:

    Frequency: The only characteristic that seems to be tested in the papers cited.
    Duration: Ideally this would be the percentage of time during the rainy season that the system is in an effective blocking position (for the high pressure pole of the dipole)
    Intensity: This would be the absolute pressure differential between the high pressure of this system and the surrounding pressure systems.
    Scale/Spread: Ideally this would be the geographic extent of pressures intense enough to act as a block to storm systems.
    Position: As we've seen this year, the position of this high pressure can make a big difference as to how much precipitation can occur.

    I doubt we have the detailed historical records to get much clarity as to whether the current system is anomalous in regard to these attributes. The point however is that the forcing produced by global warming could affect systems in many different ways which could have just as great an effect on the bottom line (in this case precipitation) as the frequency of these synoptic scale occurrences.

    I'm sure this is already well understood, but we can't really expect to get "purple tornadoes" from climate change (effects that jump off the page as wholly attributable to global warming), but rather this might manifest itself as small changes to historically consistent dynamics that add up to a big problem.

  14. Cliff -

    Something I've been mulling over and would be very curious to see/hear your thoughts on...

    Given the minimal-at-best snowpack in the Cascades, will the lack of sun-reflecting and insulating snow cause the ground to warm up quicker and lead to a warmer, earlier summer? Will it have the opposite effect since those rays won't be reflecting and warming the atmosphere?

    Just curious if we have enough information at this point to speculate on what the effect of little-to-no snowpack on our glorious PNW Summertime will be.

  15. California's drought has begun to recede. The reservoirs are in significantly better shape than they were a year ago. Reservoirs are not the whole story, but they are a leading indicator in both directions.

    This is good news. And while I'm on the subject, it's worth mentionting that the droughts of 1977 and 1924 were much worse, as were several droughts in the 1800s.


  16. Thanks for a thorough post and discussing some of the recent research. Some of your counterpoints on the current research leave me scratching my head. Also, why did you not mention the significant paper released last week showing a much greater probability of heat/drought in the Southwest and Central Plains?

    If the ridging is natural variability, fine. The wildly increasing temps in CA the last two years do not seem like natural variability, and they are an ominous jump from a long-term, upward trend. The whole argument about natural variability vs human-linked variability becomes a little silly as the oceans and atmosphere continue to warm, and snowpack slowly goes away regardless of ridging or troughing.

    Thanks for your posts and the opportunity to discuss.

  17. I'm not sure how far back California climate records go, but historical accounts can supplement the scientific record. In"A History of California, The American Period" by Robert Glas Cleland, Ph.D, (1922), the author describes a devastating drought that afflicted California in 1829, 20,000 cattle dead in the southern ranges and 12,000 dead at the Mission Santa Barbara alone.

    A drought in 1856 "caused a good deal of temporary discomfort to the cattle owners." The season of 1860-61was "unusually dry" and "cattle died by the hundreds for lack of grass and water."

    This was followed by the winter of 1861-62 when rain fell "without interruption for nearly a month" and "floods which resulted from this storm drowned hundreds of cattle in the lowlands."

    Then came the "great disaster" of the drought of 1863-64 which killed half to three quarters of the cattle in the Los Angeles county and ruined many ranchers.Starting in the fall of 1863, almost no rain fell, water holes dried up, grass did not sprout in the winter, and the cattle ate all the food supply. According to the author, this drought brought an end to the cattle raising era in California, and ushered in a more diversified industry that included agriculture.

    Although I am not a scientist, it seems that today's events are not too different than these historical accounts, which would seem to suggest that today's events are within the realm of natural variability, and I wouldn't presume they are the effects of man-made global warming, although I am certain man-made global warming is in the offing.

  18. fascinating little disagreement. I noticed elsewhere that your disagreement with JF et al goes back to 2012. I can't find much else disagreement other than your own. Is it true that ".... the paper is deeply flawed and most members of the research community acknowledge it. "? Can you substantiate this?

    I don't mean to be pissy, just that blogs are so typically "opinion" or "assertion" with no mechanism offered for the reader to verify one way or the other. It leaves the reader no option but to either trust or not trust, essentially on faith. That of course is the great thing about consensus. If you trust the institution, then a consensus within the intstitution gives us "best known".

    So is your opinion best known of is Jennifer francis at this point?

  19. The poles warming is going to be the driving force so don't plant your citrus trees yet. We are a long way from being a frost free zone. Alaska is in a profound transition it seems. Human caused? I'll defer to the 97% of climate scientists who say this is the case.

  20. Hi Cliff -- I'd like to suggest that the information you are working from is woefully out of date. A great deal of research on this topic has been published recently, and I suggest you spend a bit of time getting yourself up to speed. Here is a partial list of some of the relevant work:

    Tang et al, 2013: Cold winter extremes in northern continents linked to Arctic sea ice loss. Environmental Research Letters, 8, 014036.

    Cohen et al, 2014: Recent Arctic amplification and extreme mid-latitude weather. Nature Geoscience, doi:10.1038/ngeo2234. Note: this paper includes a very nice schematic of the mechanism.

    Kim et al, 2014: Weakening of the stratospheric polar vortex by Arctic sea-ice loss. Nature Communications, doi:10.1038/ncomms5646.

    Mori et al, 2014: Robust Arctic sea-ice influence of the frequent Eurasian cold winters in past decades. Nature Geoscience, doi:10.1038/ngeo2277.

    Feldstein and Lee, 2014: Intraseasonal and interdecadal jet shifts in the northern hemisphere: The role of warm pool tropical convection and sea ice. Journal of Climate, doi:10.1175/JCLI-D-14-00057.1

    Coumou et al, 2014: Quasi-resonant circulation regimes and hemispheric synchronization of extreme weather in boreal summer. PNAS, doi:10.1073/pnas.1412797111.

    Francis, J.A. and S.J. Vavrus, 2015: Evidence for a wavier jet stream in response to rapid Arctic warming. Environmental Research Letters, 10, doi:10.1088/1748-9326/10/1/014005. Available here: http://iopscience.iop.org/1748-9326/10/1/014005/article, and a summary here: http://environmentalresearchweb.org/cws/article/news/59831.


  21. Jennifer,
    I have read all the papers you cited. I hate to pile on regarding your work, but these papers are highly speculative and provide hypothetical mechanisms that are not supported by reality. Cold waves are not increasing. There is no evident of secular changes in midlatitude wave amplitudes as you suggest. GCMs do not show what you are suggesting. The tropics dominate the plantetary circulation, not the relatively small polar regions. The big energy fluxes into the system are in the tropics, not the polar regions. I wish I could be more encouraging, but I think the melting arctic is the tail, not the body of the dog...cliff

  22. Cliff, is it just you that has a problem with the work of JF and others? Has there work been demonstrated to be flawed or only asserted to be flawed?

    I'm sure you have noticed that 95% of your audience here is inexpert, that is we are in no position to vaidate either your opinion or JF. We can only trust by way of the consensus opinion of you and your peers, and then ideally by reprodicability. That essetially is how and why we filter out the opinions of various outliers like Roy Hansen, Lindzen and others. We are in no position to rate their work- that is up to you guys. You sort it out and give us a consensus opinion.

    Mabe there is no solid consensus or trend in verification, I don't know and frankly its not for me to decide. I'd say that stands for most here. So whats the word and who is the "majority of rersearchers" who support your position?

  23. Jennifer cannot be right because the jet streams became more zonal up to about 2000.

    Our CO2 emissions continued rising throughout and so cannot account for the reversal in the trend of jet stream behaviour.

    This is a far more likely explanation:


  24. Rather than arguing about whether this anamoly or that is caused by man-made global warming, the general public would probably be better off trying to figure out how to better deal with extreme weather before it happens so we don't end up like the California ranchers of the 1860s.


Please make sure your comments are civil. Name calling and personal attacks are not appropriate.

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