July 13, 2021

Flawed Heatwave Report Leads to False Headlines in Major Media

Last week we witnessed a major failure in science communication regarding the Northwest heatwave.

A failure that misinformed you and millions of others, and a failure that highlighted glaring weaknesses in the media's ability to cover important scientific issues.  And it revealed the disappointing behavior of some members of the scientific community.

The Northwest Heatwave Attribution Study

During the last week of June, the U.S. Pacific Northwest and southwest Canada experienced the most severe heatwave on record.  So extreme that all-time high-temperature records were not only broken but obliterated.  My recent blogs describe the situation in detail.

Within a week, an international group of scientists, policy researchers, and others rushed to create and distribute an attribution analysis of the heatwave.  A study trumpeting an extreme claim in the first sentence of the report:

"Based on observations and modeling, the occurrence of a heatwave with maximum temperatures as observed in the area was virtually impossible without human-caused climate change"

As I will show below and previously demonstrated in my recent blogs, this claim is not supported in the document or by the rigorous science, and, in fact, the material in the attribution report contradicts this assertion.  I will provide substantial evidence that the heatwave attribution report, which has not been submitted for peer-review, is profoundly flawed, with serious technical and interpretative errors.

But the lack of peer review and the obvious problems with the study did not stop it from becoming front-page news in both mainstream and secondary media, including the NY Times, the Seattle Times, the Washington Post, CNN, and many more.  Some samples of the hyped headlines are shown below:

With the exception of one story in USA Today, none of the writers questioned the grand claims of the attribution study, nor noted that other scientists had differing viewpoints.  Here in Seattle, an incurious Seattle Times staff did not bother to examine contradictory evidence.  It has become clear that much of our media is more interested in promoting a political narrative than providing citizens with factual information.

As a result of the media's failure, millions of people were misinformed about the heatwave and its connection with global warming.  And such poor information undermines society's ability to deal with climate change.

A Technical Examination of The Heatwave Attribution Analysis

In the following sections, I will note a few of the major problems with this attribution study. 

I should note that this research area is one in which I have an extensive background, having published several papers in peer-reviewed journals on Northwest heatwaves.  Some of my papers are referenced in the report and one of the authors contacted me for advice and assistance.

As I shall demonstrate, the study is deeply flawed, does not support the claims in the headline bullets, and has serious scientific and other errors.  If submitted to a journal for peer review, it would be rejected.

The main findings are not supported by scientific evidence or the materials  in the report

As noted above, the first bullet of the main findings states that the heatwave was "virtually impossible without human-caused climate change."  Sounds very certain, doesn't it?  Virtually impossible.

Then read their next bullet:  

"The observed temperatures were so extreme that they lie outside the range of historically observed temperatures.  This makes it hard to quantify how rare the event was"

On one hand, they say it is hard to quantify how rare or unusual the event was, but on the other, they claim the event was virtually impossible without human-caused climate change. 

Both statements can not be true.  You can't be uncertain and certain at the same time.

But the contradictions don't end there.  In the next bullet, they state there are two possible sources of the extreme temperatures.  The first is a low probability event that was aggravated by climate change.  This is what I suggested in my blog--and I am not the only one who believes that the best science supports this hypothesis.

Their second possibility is that global warming was the essential cause of the heatwave, with "non-linear interactions" increasing the probability of extreme heat beyond the gradual increase that has been observed during the past half-century. They state that "we need to investigate" the second possibility and ADMIT that "climate models do not show it."

This is startling.  They acknowledge that for global warming to cause the extreme heatwave, non-linear interactions that amplify the global warming signal are required and further admit that such interactions are not found by the key technology for doing so, climate models

 To put it succinctly, they have no evidence that global warming played a major role in the event.

Their next claim is that the June heatwave was enhanced by 2°C by global warming, which is not out of the realm of possibility.  

But think about it.  Considering that they state that the heatwave had maximum temperatures 16-20°C warmer than normal, by their OWN ADMISSION only about 10% of the heatwave was the result of global warming.  Thus, a record-breaking, unique heat wave would have occurred without global warming.   

Imagine if they had stated that.  You would not have seen many headlines: Global warming contributed 10% of the heatwave!

In the final bullet, they note that if global warming continues at an aggressive rate (their SSP8.5 heating scenario assumption), futures heatwave would be ONE DEGREE °C warmer by midcentury.  Not much compared to the amplitude of the June heatwave.  

Daily High-Temperature Trend Problem

In the next section of the report (1.2), they claim, based on widely scattered observing stations, that the daily high-temperature trends in the Pacific Northwest are higher than the global average.  This is deceptive.  First, the Earth is 72% water and daily high temperatures generally increase more slowly over water than land.  Northwest observing stations are over land.  

But more importantly, the authors of this report appear not to know that the observing locations west of the Cascade crest have experienced LESS warming than inland stations because of the marine influence.  This is obvious if you plot (see below) July/August maximum temperature trends around Puget Sound and the Columbia Basin during the period of largest global warming (1980-2020).  The temperature trend is twice as large in the Columbia Basin compared to Puget Sound (1F versus 2F).  

Puget Sound Temperature Trends

Columbia Basin Temperature Trends

Data and Methods Problems (Chapter 2)

In this section and others of the report, it is apparent that the investigators have limited knowledge of key aspects of Northwest weather.  For example (section 2.1), they suggest the importance of Lake Washington in local weather, suggesting it significantly influences the climate of Seattle (it doesn't).  They neglect the critical effects of Puget Sound, such as its substantial cooling of downtown Seattle and Seattle Tacoma Airport,

The study makes use of low-resolution Global Climate Model (GCM) simulations, which lack the resolution to get the basic aspects of Northwest weather and climate correct,  These models do not simulate the important effects of the Cascades, the BC Coast Mountains, the mountains of Vancouver Island, the Olympics and the coastal mountains.  The regional land-water contrasts in the GCMs are seriously in error and the global climate models fail to even grossly simulate the snowpack and soil moisture distributions of the region.

To make a bad situation even worse, the simulations they used are driven by an unrealistic, excessive greenhouse gas emission scenario (SSP-8.5) that leads to unrealistic warming during this century.  Furthermore, the just-released CMIP-6 global climate model simulations were used, and these projections evince unrealistic warming.

The selected emissions scenario is highly aggressive, making unrealistic assumptions (such as massive increases in coal use)

Return Time Analysis of Historical Gridded and Station Data

In the next section, the paper attempts to determine how unusual the high temperatures were during the event.  One goal was to determine the return time of the extreme heat based on past annual high temperatures; would such warmth be observed every ten years, hundred years, etc.?   This section included an extreme value analysis, in which investigators fit a Generalized Extreme Value (GEV) distribution to the observed annual high temperatures.  You can think of the GEV as a theoretical probability of temperatures occurring at various values, with the probabilities decreasing for more extreme values.

Their analyses provided an important finding:  the Northwest heatwave of last month was extraordinarily improbable EVEN IF SUBSTANTIAL GLOBAL WARMING occurred.  Global warming could not explain it.  

This study clearly showed that the heatwave was a very rare black swan event.  And this finding contradicts the headline in the first bullet of the report and in headline banners around the world.

And there is more.  They determined the probability of getting a similar extreme temperature event ANYWHERE on Earth (similar sized area, similar or greater magnitude). Importantly, they found that the probability of observing the event anywhere on Earth was MUCH higher (about 60 more chances each year because the June heatwave encompassed about 1.5% of the Earth).   The return time of a similar extreme event somewhere on the planet was between once every 1.5 to 15 years.   Thus, such black swan events occur somewhere quite frequently-- just not necessarily in the Pacific Northwest.

After this important finding was revealed, the authors made a critical admission:

"It is, therefore, conceivable that it was pure chance that it (the heatwave) happened at this location."   And they called for further research.  Wow.  

Multi-model Attribution

In many ways, this part of the report is the weakest.   They provide little explanation of their analysis approach, other than to refer to a previous paper (Kew et al. 2021) whose methodology was questioned by the reviewers of that paper (not sure how that paper even got published with those reviews).  

For some reason, they combine observations and models at the same time in their analysis, which does not make any apparent sense.  In addition to a confusing and inadequate description of their approach, they provide grand claims of global warming producing major increases in the probability of extreme heatwaves.  Such findings were inevitable considering they used models driven by unreasonable global warming inputs and the use of highly sensitive CMIP6 simulations.  

But that is the least of it. The probabilistic approach to climate attribution is highly flawed, something I touched upon in my previous blog on the event.  If the probability of an extreme event increases from .001 to .1 percent it has gone up by 100 times, but still, the probability is still low. That is why the claims of global warming increasing the probability of a once in a thousand-year event by 150 times are so deceptive.   Furthermore,  the results of the various models they used were all over the place (their Fig. 12), with a huge range in the probabilities of the heatwave (the majority suggested it was very, very unusual).

Meteorological Analysis:  Major Deficiencies

In this section, they state 'The circulation pattern itself also appears not extremely anomalous" and that the Heat dome "is not that anomalous."    These claims are not correct.

In truth, the amplitude of the ridge of high pressure aloft was the greatest ever observed and the high pressure was in position for a very long time, allowing air plenty of opportunity to warm by sinking.   

At 850 hPa (about 5000 ft above sea level) the temperatures were not only unprecedented but extraordinarily extreme (see graphic below from Dr. Joe Zagrodnik).  And an approaching trough of low pressure played an important role in forcing strong offshore flow, but this is not mentioned in this report. I could go on, but the message is clear:  the meteorological setup was extreme and exceedingly rare, something not recognized in this work.

Global Warming and the Jet Stream,  Drought Effects

The report considers but finds no evidence for global warming causing the jet stream to experience more blocking or ridging (high pressure) events.  Record-breaking high pressure aloft played a central role in this event and without a global warming connection, the role of natural variability comes into the forefront.

Finally, the report notes that drought and dry soil conditions could have enhanced the high temperatures due to less evaporative cooling.   But they admit that soil moisture conditions and precipitation were not below normal in British Columbia, where many of the warm records occurred.  Furthermore, as described in my previous blog, moistening the soil in model simulations only cooled the region by about 1°C, a value dwarfed by the heatwave amplitude (16-20°C).

The Bottom Line:   The ominous claim in the first sentence of this report, suggesting an overwhelming global warming origin of the Northwest heatwave, was not supported by the remainder of the document.  If anything, much of the material in the report is highly suggestive of a random, black swan event that is slightly enhanced by greenhouse gas warming.

An Advocacy Document

It is clear that this attribution study was not intended to serve as an objective examination of a scientific issue (e.g., the contribution of global warming to the Northwest heatwave) but rather is an advocacy document.  

 It is easy to demonstrate this.  For example, the first section of the paper calls for immediate policy changes, including adaptation and mitigation.  The final section "Recommendations"  promotes policy changes and specific adaptation recommendations.  The inconsistency between the dramatic claims of the first sentence and the more nuanced material within the document suggests a clear intention to highlight a message that promotes notice and action.


The future of our society depends on scientists dedicated to determining truth and communicating their best estimates of truth, including the inevitable uncertainties.  Scientists, in their professional roles, should never become advocates for politicized viewpoints or actions.  

Likewise, the media in their news reporting must strive to avoid political advocacy and communicate truth, with all its uncertainties.  The media must be engaged and curious enough to not only understand the science but to actively question the reliability and rigor of scientific claims.

In the recent heatwave case, we have seen a profound failure on both sides of the equation:  scientists who created a rushed, sloppy, and flawed attribution study of the Northwest heatwave for reasons you can probably guess, and the media who headlined such poor work because it fit a comfortable, politically favored narrative.

Hopefully, this unfortunate situation will serve to encourage reform in both the scientific community and the media.   The cost to society is too great for such behavior to continue.


  1. Is it normal that clams and mussels were cooked in their shells before they were eaten?

    1. Bert.. I am not sure they were cooked...but they were killed. Quite honestly, the unbelievable severity of this event essentially proves my point. Global warming is a relentless, slow rise in temperatures, not throwing us (and poor shellfish) into a boiling caldron...cliff

    2. What contributed to the issue of benthic mortality (ie clams being heated) was the co-incidence of some of the lowest low tides of several years at the hottest part of the day, on the longest solar days. Note: low tides, long-duration solar exposure.....nothing to do with climate change. The clams were heated but the interaction of very low tides, and the longest sunny days. Nothing to d with temperatures at head height.

  2. I'm definitely convinced it was a "black swan" event, and that global warming of 1 C or even 2 C pales in comparison to the magnitude of the event (16-20 C). Indeed, the temperature at my home was 18C above normal per nearby area long-term averages. I'm still not convinced, however, there's no trend in changing jet stream patterns that might create more extreme ridges or troughs. Such a trend might be subtle, develop over hundreds of years-- maybe just 200?, and there just not be enough data to see it. Or maybe I'm just brained washed by the press who hypes events as to make a perceptual but not objective trend in more dynamic weather patterns. The science side of me thinks more dynamic weather patterns (temperature extremes, pressure extremes, precipitation extremes etc.) is plausible, but has yet to see really convincing data.

    1. That is a central point I made (and parenthetically also made in the report). There is not apparent trend in the jet stream patterns. I have researched that very point myself and published on it.

  3. Thank you Cliff. It would be great if this got as much airplay as the "advocacy" attribution nonsense.

  4. I have a hard time blaming the media when they are reporting on what scientists are saying. Scientists have to get their own house in order. But it seems like the media is seizing upon any extreme weather event as evidence of climate change. Imagine living through the dustbowl years and what the media would have been saying.

  5. To me, the most surprising part of the heatwave is how well current models saw it in advance. The models getting this right implies that parameters fed into them were realistic enough for the models to handle. Nearly every AFD and media report showed skepticism, since huge anomalies often back off in time. This time they didn't.

  6. Caroline is right. But it will not happen since is does not serve big media's goals. The rest of my comments are incredibly insulting to the bulk of the human species so keeping them to myself.

  7. You are bring too nice Cliff

    "Flawed Heatwave Report Leads to False Headlines in Major Media"
    -- The word "flawed" is too weak.

    "Last week we witnessed a major failure in science communication ... "
    -- That's true from a scientific point of view.
    From a leftist political point of view, any claim. whether true or false, that supports the coming climate crisis narrative, is a success.

    The coming climate crisis claim predictions began in the late 1950s with oceanographer Roger Revelle and some associated. It accelerated in the 1970s with the unproven water vapor positive feedback effect. It became a "consensus" in 1988 with formation of the IPCC. It became hysterical, with no uncertainty at all, around 2018.

    This coming climate crisis prediction is not science -- it is a religion. So

    if there is any weather bad news, it will be attributed to climate change, with a "see, we told you so" attitude.

    Since the coming climate crisis, that never shows up, is just a belief, not created with science, facts, data and logic, it can not be refuted with science, facts, data and logic. Just like any religious belief -- it's not falsifiable.

    And remember that the climate crisis is ALWAYS coming in the future -- that's hard to refute without waiting 10 or 20 years. But 10 or 20 years later that alleged climate crisis will STILL be coming 10 to 20 years in the future. We've been hearing coming climate crisis predictions for the past 64 years, yet the predictions keep coming !

    1. And if the climate does cool in the next few decades, the claim will be that it would be even colder if it weren't for global warming.

  8. I've seen temps over 100 here, west of the crest, in the past. In fact, in decades past there some summers so insufferably hot we had a ceiling fan installed in the 90's. But weather here varies, and there was so little need for fans that masses of dust accumulated (never needed to run the thing). Since this odd event, there have been very chilly nights (in the 40's) and very moderate daytime temps "for a July."

    One recent USDA SNOTEL map has caused dramatic reporting about lack-of-snow when snow at these locations was already, seasonably, gone at the SNOTELs somewhat low elevations when the 'monster heat wave' occurred. Facts weren't checked by newspaper reporters - they're not "weather people" or atmospheric scientists. But newspaper articles will be cited as 'factual,' and it breaks my heart to see well-intentioned people reacting to "data" without understanding underlying conditions.

    Great post, by the way, prof.

  9. If the Puget Sounds Lowlands have warmed by 1F why would global warming contribute to 2C of the heatwave?

    1. The origin of the heatwave was neither in the Puget Sound Lowlands nor from global warming.

  10. You are quick to point out examples of weather events falsely attributed to climate change in the interest of preventing a disservice to science. Is it possible though that by not pointing out examples of weather events which may be explained by climate change you are also doing a disservice? Any weather event can be explained by the underlying synoptic situation, but surely there are cases where that pattern is more likely due to climate change. Just by looking at comments here, it is clear that climate deniers are assuming that you are denying that climate change is real concern. Short of showcasing examples of climate change induced events, you could avoid a disservice by pointing out what part climate change my have had in the magnitude of the recent event. For example, would it not be unreasonable to say that in the absence of human-induced climate change KSEA would still have set its all-time high record, but it probably would only have reached 104-106?

    1. Mike... I said that..both in this blog and my previous one on the heat wave. I explicitly note how much I thought was global warming: 1-2F..cliff

  11. First there is a need to preface this comment by placing some emphasis on it not being a defense of the media.

    The media is a private enterprise for the most part. BUSINESSES!

    Its job is to:
    1) Make money.
    3) Inform.

    Again, its first and foremost activity is to MAKE MONEY, which is why businesses exist. There is no "4) Be truthful" included on the list. All of these media outlets via for clicks, views etc and the reality is they have to distinguish themselves in order to establish a particular niche. In the USA its very easy to make money by playing to the prevalent toxic political environment, identity politics, fear mongering, tribalism and echo chambers. Again there is no requirement that anything be peer reviewed or vetted in any way...let alone ethical. And why should it be? People will believe what they want to believe and its very profitable to dish out exactly what they want to hear in order to reinforce those beliefs. The constituency of the USA really isn't interested in learning anything new or compromising. So, business caters to that.

    Honesty, truth and empirical are boring and unprofitable. So completely laying this at the feet of the media and the politicians is not 100% accurate as they just serve up what the public want. The public at large is the real villain here, and the frontier culture of rugged individualism that gives very little leeway for objective reason.

    1. You are spot on with this commentary!..But you are way too nice..."The frontier culture pf rugged individualism" can be better referred to as "stupidity"! and stupidity has clearly manifested itself in what is left of our culture.

    2. Good post. I would go further and suggest that quite often even responses to potential threats such as COVID are shaped to some degree by a desire people have for some drama in their lives.

  12. They say the Sahara once had trees

  13. Grade of this Study in today's Atmos Sci 101 class is an F. Grade of this same study in today's Journalism 101 class is an A+.

  14. I'd be interested to know whether, as I suspect, summer rain has decreased in the NW. Fairly
    frequent rain, I understand, is the most important natural control on fires.

  15. Let me offer up my version of Occam's razor: Do not attribute to conspiracy what can be accounted for by incompetence. I am suggesting that your disdain for the local newspaper's "promoting a political narrative" may be overstating the case. Could not mere incompetence of investigative journalism be an adequate explanation?

    1. Indeed: incompetence does prevail at the Seattle Times. Maybe that is because it is an inherited an privately owned newspaper where the inherited rich owners like to purvey their wares...no thought required... just inherited wealth of the liberal elite of Seattle

  16. Cliff, you've written before of the pricision of you and your team's local weather prediction models and I've been impressed. Have you offered this capability to help the authors of this study and/or others to improve their studies? It seems like that would benefit them, you, and us.

  17. An excellent piece of honest reporting.
    I wonder if the UW College of Environment and the Department of Atmospheric Sciences will ensure it gets circulated to all students, faculty and those who might wish to learn that science is more than getting WaPo as your information source.

  18. Dr. Mass, do you think we need to move away from fossil fuels, or is that not a factor?

    1. I do think we need to move away from fossil fuels. Renewables are a start but we require nuclear as well...fission or fusion. But we need to make this transition in a smart, deliberate way.

  19. Why not publish a rebuttal? A blog post is just a blog post without peer review (which is what you blame the authors for).

  20. I wonder what you're thoughts are not just on a single, rare, extreme, weather event, but the number of them occuring within a short period of time. For example, we've had at least 2 almost unprecedented events back to back- the Labor Day wind event and this extreme heat wave. How do the extreme weather events of the past 20 years hold up to expected amounts of extreme events? It seems like they are getting more frequent, and perhaps there is a climate instability connection to not the single events, but them as a whole. It feels like we've been in extreme conditions for the last 20 years now.

  21. We get extreme events occasionally. That is the way of the atmosphere. No evidence that there is a trend in extreme weather events... we just forget the earlier ones. The Columbus Day Storm (62) was an extreme windstorm/low. We had extreme atmospheric rivers during the 80s and 90s, extreme snowpack in 1998.

    Some extremes should lessen under global warming, some increase. Lot of nuance here.

  22. Re: the killed marine life...the maximum heat wave also hit when tidal ranges were at their monthly extreme, meaning that at low tide more marine life was exposed to the air for a longer time....Thank you Cliff for taking the time to discuss this. The degree to which everything has become weaponized in search of narrative support is frightening. It might be helpful to remind people every now and then that, according to out understanding of glaciations and orbital cycles, we are approaching the end of this current interglacial, after which temperatures will drop considerably....

    1. "the maximum heat wave also hit when tidal ranges were at their monthly extreme"
      An interesting observation that is worthy of further investigation.

  23. In my comments related to the July 5 post I mentioned the possibility that the record breaking heatwave might to some degree be related to ozone loss since when there is low stratospheric ozone more intense solar radiation heats up the Earth. Because of this when an ozone depleted air mass moves over an area it to some extent allows for higher temperatures than would otherwise be possible. Since air masses in which ozone is significantly depleted are over an area for a limited amount of time, the higher temperatures allowed for this are only allowed for a limited amount of time. Since many other factors also contribute to whether the higher temperatures allowed for actually occur, this further decreases the influence on average temperatures of the possibility for higher temperatures. This might partly explain why as discussed in the article that I included a link to along with my previous comments that while Australia has warmed by just over one degree C since 1910, the frequency of extreme heat events has greatly increased since the Antarctic ozone hole was discovered in 1985 while the frequency of temperatures being extremely above normal is greatest in the spring as ozone depleted air masses move north from Antarctica.

    The influence of the possibility of higher temperatures on average temperatures is further reduced by that additional ozone depletion corresponds to additional cooling of the stratosphere which can extend well into the troposphere. Since rapid ozone loss occurs when the sun is near the horizon as it first reaches areas that have been dark all winter while a large part of the limited amount solar radiation is reflected off of snow, cooling of the upper troposphere because of ozone loss is much greater than any heating of the earth that occurs until later when ozone depleted air moves south. Since this allows for ozone loss to continue to cool the troposphere for an extended period of time without being offset by that more intense solar radiation heats up the lower part of the troposphere, a large enough amount of ozone loss could significantly cool the troposphere at lower levels.

    Last year a record was set for the most ozone loss ever in the Arctic as discussed in this article: https://www.severe-weather.eu/global-weather/rare-ozone-hole-arctic-polar-vortex-fa/. The article from last year includes "It is a rather rare occurrence to see a large area of sustained ozone depletion depletion over the Arctic regions during the late winter/ early spring season. But this year records were broken as an unusually large area of ozone depletion formed." If it is eventually found that this is related to a trend, it might be that as is the case in Australia the frequency of extreme heat events will also increase in the northern hemisphere.

  24. I really don't understand your very elegant debating points. You really don't need to be a climate scientist to understand what's happening. 30-50 years ago in the northwest we didn't have smoke seasons from fires all over the world every summer. Ask any farmer and they will tell you the weather is changing, getting warmer . Check out the ice at the poles, the glaciers on our mountains and yes honestly count the more frequent occurrence of weather extremes. It's not rocket science, it's common sense. Global warming's effects are multiple and and happening all over the world and seems certain to kill people in the not so distant future. Debating whether any single event meets your own strict causal criteria iis not seeing the forest through the trees.

    1. Sounds like you haven't looked at Cliff's data. It's important to look at original reports not just "scientific" summaries.

  25. Dr. Mass,

    Most people feel through personal observation that the weather is changing. I’m pretty sure the psychology of “feel” is strongly biased towards memory of unusual observations rather than average conditions. Given that the average change in climate is very small, are there statistical studies of the frequency and magnitude of record testing weather events? How much more or less likely are we to have record testing weather today as compared to past periods?

  26. Courageous blog, willing to stand up! Well done.

  27. An outstanding blog by a man of courage!

  28. https://climate.gov/news-features/event-tracker/preliminary-analysis-concludes-pacific-northwest-heat-wave-was-1000-year

  29. I thought it was interesting that during the interview with a NOAA employee, he pointed out that massive urbanization was a contributing factor (i.e. heat island effect) to temps in the cities.


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

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