July 05, 2021

Was Global Warming The Cause of the Great Northwest Heatwave? Science Says No.


Society needs accurate information in order to make crucial environmental decisions. Unfortunately, there has been a substantial amount of miscommunication and unscientific handwaving about the recent Northwest heatwave, and this blog post uses rigorous science to set the record straight. First, the specific ingredients that led to the heatwave are discussed, including a high-amplitude ridge of high pressure and an approaching low-pressure area that “supercharged” the warming. Second, it is shown that global warming only contributed a small about (1-2F) of the 30-40F heatwave and that proposed global warming amplification mechanisms (e.g., droughts, enhanced ridging/high pressure) cannot explain the severe heat event. It is shown that high-resolution climate models do not produce more extreme high temperatures under the modest global warming of the past several decades and that global warming may even work against extreme warming in our region. Importantly, this blog demonstrates that there is no trend towards more high-temperature records. Finally, the communication of exaggerated and unfounded claims by the media, some politicians, and several activists are discussed.

During the past week, the Pacific Northwest experienced the most severe heat event of the past century.  

All-time high-temperature records were broken throughout the region, often by large margins. 

Many in the media, several local and national politicians, and some activist environmental scientists have claimed that this event was "driven by" or predominantly forced by human-inspired global warming (usually referred to as "climate change").
But such global warming claims are not supported by the facts and our best scientific understanding.  
Truth and Rigorous Science About Climate Change is Necessary for Wise Decisions

In this blog, I will use observations, modeling, climatological data, and the peer-reviewed scientific literature to demonstrate that human-caused global warming played a very small role in the extreme heat event that we just experienced here in the Pacific Northwest.
I will describe the origins of a meteorological black swan event and how the atmosphere is capable of attaining extreme, unusual conditions without any aid from our species.
As you read this, consider that I have actively pursued research on Northwest heatwaves, published several papers in the peer-reviewed literature on this specific topic, and have run both weather prediction and climate models that simulate such events.  This subject is in my wheelhouse.

I also discuss the seriousness of misinformation.   You and others can not make wise decisions when the information provided to you is not based on truth and science.

This is going to be an extended, detailed blog, a necessity if you are going to truly understand the science and the situation.  Superficial, hand-waving arguments will not allow you to comprehend the truth, particularly when so many "facts" communicated in the media and among activists are inconsistent with the best science.

The Event

The maximum temperatures during the heatwave were as high as 30-40 degrees Fahrenheit above normal.    Seattle had a high of 108F,  35F above the normal high of 73F.  Quilluyte on the Washington Coast zoomed to 109F compared to a normal high of 65 (44F above normal).  Throughout the region, all-time temperature records were broken, representing the hottest day on record at many locations. 

The map below shows where the all-time temperature records were broken, mainly west of the Cascade crest.

These high-temperature records occurred in late June, which is atypically early in the summer, with previous high-temperature records occurring roughly a month later when the Pacific Northwest climatologically is at its maximum warmth.

All-Time Records for High Temperatures Broken In WA/OR (red dots)

The Global Warming Background

The Pacific Northwest is warming and human emission of greenhouse gases is probably the origin of much of it.  

To illustrate, the figure below shows the annual average high temperatures for Washington State from 1900 through 2020.  About 1.5 F of warming over 120 years.  The summer warming is nearly the same.   

Let us assume that ALL of this warming is caused by mankind's greenhouse gas emissions, although some might argue with that assumption.   The warming during the past several decades is consistent with human causation, and climate modeling supports this contention.

So if greenhouse gas warming over Washington State is 1-2F,  how can greenhouse gases cause a huge heatwave that is ten to twenty times greater?  
A very good question. 
Such a ten-times amplification of the global warming signal would require powerful positive feedbacks, which I will demonstrate below are simply not evident.  A global warming origin of increased temperature extremes would also be evident in long-term trends of extreme temperatures, but such trends do not exist.
But before we get into such things, you must understand the origins of the extraordinarily high temperatures observed earlier last week.

What Caused the Northwest Heat Wave?

A number of factors came together simultaneously to produce the extreme high temperatures over the Northwest observed last week.  

The key factor in this and previous regional heatwaves is the development of an unusually strong and persistent area of high pressure over the Northwest.   Such high-pressure areas are also called ridges and often extend vertically through great depth (10-30 thousand feet).  

The figure below illustrates what the ridge looked like at 11 AM  last Sunday around 18,000 feet above the surface (500 hPa pressure).  At this level, the ridge was the most intense ever observed over the region (will prove that later).

Map A

High-pressure areas/ridges are associated with warm temperatures during the summer.  First, high-pressure areas possess strong sinking, and sinking causes powerful warming as air is compressed as it descends to the higher pressure that exists at low levels (pressure decreases with height).  Your air pump, very warm after inflating a tire, is a good illustration of this mechanism.  

Ridges also possess southerly (from the south) flow on their western sides (apparent above), bringing subtropical warmth northwards.    

But there is more! 

The sinking air in high-pressure areas prevents clouds, thus allowing maximum solar heating (and the sun is near maximum strength now).  And on the southern side of upper-level ridges there is often easterly (from the east) wind, which can move down the western slopes of terrain barriers, producing even MORE compressional heating as the air descends the slopes.

It is no accident that every major summer heatwave in our region is associated with a ridge of high pressure.   Ridges are veritable heating machines during summer and sometimes are colloquially referred to as heat domes.  The media loves this term.   

The origin of the intense ridge of high pressure of last week is fascinating.   

Our ridge appears to have originated in the far western Pacific, where a tropical disturbance rammed into the Pacific jet stream, causing high-amplitude waviness in the jet stream thousands of miles downstream to the east.  The result was a strong ridge over the Northwest, with the waviness also producing a deep trough over the central Pacific (see upper-level map on Wednesday, June 23rd, 500 hPa pressure--about 18,000 ft).

Blue and purple indicate much lower than typical pressures (troughs or lows), red indicates above-average values (ridges or highs). You can see the waviness of the atmosphere over the north Pacific from Asia to North America.

The Atmospheric Heat Supercharger

In our heatwave, there was a feature that supercharged the warming west of the Cascade crest and the coastal mountains (e.g., the Olympics):   an approaching upper-atmospheric low-pressure area (or trough) that was west of northern California in Map A above.
Our high-pressure ridge ("heat dome") had a potent supercharger.  Picture courtesy of Nick Ares.

Between the offshore trough and the ridge over the Pacific Northwest, there were strong southeasterly (from the southeast) winds that pulled up air from the warm desert Southwest.  This air subsequently descended the western slopes of the Cascades, where the air was further compressed and warmed.  

You can see this "supercharger" in action on Monday afternoon in a forecast map valid for around 5000 ft (850 hPa pressure level).  The colors indicate temperatures (darker red is warmer) and winds are also shown.  You can think of the solid lines as representing the pressure at that level. Note the low offshore and the high to the northeast.  The white arrow shows the warm southeasterly flow that descended the Cascade's western slopes.

And the impact of the supercharger is seen in the super-warm air (brown colors, 104F, and more) found downstream of the Cascades at 5 PM on Monday, June 28.

Everything had to come together just "right" to give us this extreme event.  

Record amplitude of a ridge/high pressure over our region, forced by a tropical disturbance in the western Pacific, that produced a downstream "wave train".   An environment that allowed the resulting wave to amplify.  The ridge had to be in exactly the right position relative to our terrain.  An upper-level trough had to develop in just the right location offshore and move in the optimal direction to cause strong southeasterly flow, fostering the supercharger noted above.  We needed a period when the sun was very strong.    And a summer stretch without smoke, which has a profound cooling effect.

The meteorological dice had to come up all sixes.  And they did.  

This concurrence of a number of factors coming together at one place and time was why the extreme heat occurred, with a very small assist from global warming, which added a few degrees to an already extreme event.

It is important to note that the atmosphere comes up sixes regularly, but not necessarily in the same place.  The atmosphere is churning with all kinds of variability inherent in the physics of the atmosphere (also called natural variability).  

To illustrate this to you, below is a world map of the temperature anomalies (difference from normal) just above the surface (about 800 m in elevation) on Tuesday, June 29th.  You can see our extreme heatwave (red colors),\ centered over the northwest corner of Washington.  But there are other large temperature anomalies scattered around the world, both warm and cold.    Those are overwhelming NOT the result of global warming, but of natural variability.  I could show you a similar map for a date, in say, 1940.  It would look the same (I checked).

Extreme temperatures happen all the time in a somewhat random fashion.  They just don't happen where YOU are located very frequently, because so many random mechanisms must come together at the same time to do so.

Natural Variability or Global Warming?   Dealing with Unsupported Claims

Since global warming is much smaller than the magnitude of the heatwave temperature extremes observed last week in the Northwest, those trying to ascribe the extreme temperatures to global warming must prove that global warming somehow amplifies natural variability.   

For example,  some have suggested that the key feature of last week's heatwave-- the extreme amplitude ridge of high pressure aloft-- had origins in global warming.   Others have suggested that global warming dries the soils, resulting in less evaporative cooling and warmer temperatures, thus explaining the extremes.

We will evaluate the plausibility of these various mechanisms for amplifying global warming and will show that they can not explain what happened last week.

Does Global Warming "Drought" and Dry Soils Explain the Heatwave? 

One hypothesis starts with global warming causing drought and dry soils over our region.  Then they claim that such dry soils warm the air (less evaporative cooling) enough to explain the high temperatures.  Others suggest that the drought increases high pressure as well.

For reference, the NOAA Drought Monitor graphic for June 22nd shows normal or just slightly dry conditions west of the Cascade crest (where the extreme records were broken), but "drought" conditions over the normally dry region of eastern Washington.  

The claims that the critical extreme ridge of high pressure was caused by dry conditions east of the Cascade crest are problematic for many reasons, including the fact that the origin of the high pressure can be traced to a large-scale amplification of the wave pattern over the entire North Pacific.  Similarly, the claims that dry conditions east of the Cascades were significant in creating the extreme heatwave west of the Cascade crest are also weak.   Let me prove this to you.

Model forecasts were stunningly good for this event.  Even almost a week out, model simulations correctly predicted the development of an extreme high-pressure area over the Northwest and very high surface temperatures.   Modelers like myself can "play god" with such excellent simulations, in this case, by making the soil much moister and seeing what happens.    Would the heatwave go away with the absence of drought and under moister soil moisture conditions?    You are about to find out.

Senior UW graduate student Robert Conrick re-ran the UW WRF weather forecasting model and tripled the soil moisture everywhere.  He turned the region into a veritable swamp!    And what do you think happened to the ridge of high pressure and the heat dome?   Did it disappear?  Did the heatwave go away? 

The answer: virtually nothing happened to the intense high-pressure area.  The heat dome was essentially unchanged.  Surface temperatures over BC and western WA hardly changed.

The figure below shows the height of the ridge at 500 hPa pressure (you can think of this as the pressure at around 18,000 ft.  The left side uses the actual soil moisture last week, the right side shows the same thing with TRIPLE the soil moisture.  Virtually the same heights or pressures.

What about temperatures at the surface?   Even with "biblical" moistening of the soil over the entire domain, temperatures over western Washington and British Columbia, where the heatwave was most severe, hardly changed, cooling by about 1 degrees C (about 2F) or less.

The theory of an unusually dry surface produced by global warming "drought" causing the high pressure "heat dome" or greatly warming low-level temperatures west of the Cascade crest appears unfounded.

This makes physical sense for a number of reasons.  For example,  the lush western side of the Northwest remained relatively moist into the summer.  June's rainfall was well above normal over most of the region west of the Cascade crest.  As noted in my earlier blog, the trajectories of the air reaching the surface west of the Cascade crest did not come from the surface over eastern Washington or Oregon but subsided (sank) rapidly from aloft.

But there is something else that essentially puts the silver stake into the heart of the unfounded global warming "drought" theory of this event.

Specifically, there is no observed trend towards "drought" over the Pacific Northwest as demanded by the proposed global warming origin of this event.

Below is the observed annual precipitation over Washington State since 1900.   Our region is NOT getting drier.  If anything precipitation has increased a slight amount.

And is spring drought increasing in frequency as suggested by those pushing the global warming hypothesis?  The answer is no.  Below is a long-period plot of the Palmer Drought Index, which considers BOTH temperature and precipitation.  No apparent long-term trend in spring drought...and notice how much worse it was during the 1930s and early 1940s.

So not only does the global warming drought hypothesis for the heatwave fail on a physical basis, but there is no trend in drought, which is a requirement if global warming was the explanation.  

Does Global Warming Produce Stronger Ridges of High Pressure?

Another claim, provided by Professor Michael Mann of Penn. State and published in the New York Times is that global warming produces a weakened, "lazy" jet stream that forces more wave-like undulations and thus more ridging.    This hypothesis has been thoroughly debunked in a number of papers in the peer-reviewed literature (see this article for an example or my blog).  But I need not cite others, since I and my students have investigated this very issue in research sponsored by the National Science Foundation and published the research in the peer-reviewed literature.

For example, Matt Brewer and I looked at global climate models driven by rapidly increasing greenhouse gases and found that high-pressure areas like that seen last week will WEAKEN under global warming.  Just the opposite of what Professor Mann was suggesting.

And last week I examined the frequency of high-amplitude ridging over our region from 1948 to today using NOAA reanalysis gridded data.  I found no trend in the extreme highs aloft.

As further confirmation, Dr. Joe Zagrodnik of Washington State University examined the radiosonde sounding data (balloon-launched weather stations) at Quillaytate on the Washington coast and found no upward trend in the maximum heights (that is big ridges of high pressure) at 500 hPa (around 18,000 ft) at that location.

Dr. Zagrodnk also did not find any trend in extreme high temperatures in the lower troposphere (around 5000 ft).

Bottom line: none of the claims that global warming increases ridging (high pressure)  over time are supported by data or modeling.  Unfortunately, Dr. Mann and others continue to push this unfactual narrative.

Perhaps, The Most Compelling Evidence of All

If global warming was producing extreme heatwaves in our region, such as the event last week, there would be a long-term trend towards more extreme high temperatures.  A single event does not reflect climate, only a trend or changes in long-term average do.

Well-known climatologist (and the official Alabama State climatologist) Dr. John Christy has run the numbers to determine if there are trends in record-breaking extreme temperatures in Washington State or Oregon.  

As shown below, there IS NO INCREASING TREND for more record high temperatures over our region during the past century.  In fact, the past decade (2011-2020) had no all-time records.  I suspect many of you are surprised at this, but it is true.

Average number of days with temperatures above 99F in our region? Also no trend.

These results are consistent with what others have found.  For example, the U.S. National Climate Assessment found the warmest day of the year over the Northwest actually COOLED between a historic (1901-1960) and a contemporary period (1986-2016).

I had a conversation about these findings with Dr. Nick Bond, Washington State Climatologist.  He told me he was not surprised, and that he and Associate State Climatologist Karin Bumbaco found similar results, published in a peer-reviewed paper.

You may ask why there is little or no upward trend in record high temperatures even though the region and planet are warming.   

There are a number of possibilities.  For example, natural variability may be so dominant that a small amount of global warming is hard to notice.  Or there may be climate feedbacks that work against extremes in a warming world....at least in our area.  I have been researching one of these feedbacks:  the tendency of heat-wave producing easterly flow to weaken under global warming and describe it below. And I can think of several more.

Still not convinced?  Read on.

High Resolution, State-of-Science Regional Climate Models Do Not Suggest A Global Warming Origin of the Extreme Heat

One of my major research projects (with Professor Eric Salathe of UW Bothel and supported by Amazon) has been to run high-resolution climate simulations driven by the most realistic global climate models.  And the results are very relevant for this discussion.

Below is a graphic from this work showing the extreme high temperature each year at Seattle Tacoma Airport by an ensemble of 12 regional climate simulations (12-km grid spacing---VERY high resolution for climate work) driven by a highly aggressive (and unrealistic) increase of greenhouse gas emissions (RCP 8.5).  These simulations started in 1970 and each forecast is shown by a different color. The green line is the mean of the regional forecasts and the observed highs are shown by black dots.  I have indicated SeaTac's high temperatures this year (108F, 42C) by the blue line.

You will notice two important features of these regional climate projections.  

First, and of great importance, there is little upward trend in the extreme high temperatures.  

Second, the most extreme temperatures of the ensembles over the entire period climbed to about  42C (108F).  To do so, required rare, but possible, combinations of several factors.   Improbable, but possible.   You might also notice that the climate model was typically about 1-2C to warm.  I believe that reflects the inability of even my very high-resolution simulations to properly simulate the effects of a narrow, improperly resolved cold Puget Sound. 

Could Global Warming REDUCE Heat Waves West of the Cascade Crest?

Most people assume that global warming can only increase our high temperatures, but it can do the opposite as well.  The Northwest's mountains and nearby cold water paradoxically might reduce heatwaves over the populated areas west of the Cascade crest under global warming.  

Global warming preferentially warms the interior of western North America compared to the Pacific coast (land warms up much more quickly than the Pacific Ocean).  The heating results in enhanced pressure falls over the interior (warm air is less dense than cold air), which strengthens cool, onshore flow and lessens warm easterly (offshore) flow.   Bad for heatwaves!

All the great heatwaves west of the Cascade crest occurred under strong easterly flow. 
Both global and regional climate models have shown that global warming lessens heatwave-producing easterly flow.    To illustrate this, consider the figure produced by the research done by my group with Dr. Eric Salathe of UW Bothell.  This plot shows the maximum easterly flow each year simulated by an ensemble (many forecasts) of high-resolution regional climate models.  Importantly, the mean strength of the strong easterly flow (black line) goes DOWN under global warming, working against the kind of heatwave we had last week.

The Evidence is Overwhelming

As I described above, the natural origins of the "black swan" heatwave we experienced last week can be demonstrated in a number of independent ways, from examining the origins and frequency of the ingredients (such as the high-amplitude ridge of high pressure), considering the statistics of warm temperatures  (the lack of trend in extreme high-temperature days), and through high-resolution climate modeling.

The evidence for a predominantly natural origin of the high temperatures records of last week is compelling, with global warming marginally increasing the peak temperatures by perhaps a few degrees.  Without global warming, we still would have experienced the most severe heatwave of the past century.

Politicization and Miscommunication of Science

The inaccurate information being distributed about the origins of this heatwave is very disturbing.

Some of this is being done out of ignorance or laziness, but a few individuals are deceiving the public deliberately.   Science journalism is only a shadow of what it was decades past, and a number of scientists now see social activism as more important than the determination and communication of truth.

Our nation has made costly mistakes when the truth was twisted for political reasons, such as for the Iraq war, when our nation spent trillions of dollars and initiated a war that killed hundreds of thousands of people based on misinformation about non-existent weapons of mass destruction.

We are now making similar mistakes with global warming, with politically inspired misinformation slowing realistic and life-saving steps, such as thinning our forests and restoring natural fire, or proceeding rapidly with nuclear energy.  Hyping global warming puts unrealistic and unnecessary fear into the hearts of our fellow citizens.  Unconscionable.  Global warming is an issue we can deal with, but only if truthful, factual, and science-based information is provided to decision-makers and the nation's citizens.

I have spent my life trying to understand the weather and climate of our region and it is so frustrating that the media (e.g., KNKX public radio, the Seattle Times, the Seattle Stranger) and local politicians (such as our governor) have placed such a low priority on providing accurate information regarding climate change and other environmental challenges.  

They have put political agendas ahead of truth and we are all the worse for it.


  1. Stop confusing us with the facts. And thank you for a fascinating write-up.

  2. That was fantastic, and I learned more about the interactions that influence atmospheric circulation. In particular, low pressure system off of Northern California and it's impact. Speaking of science journalism, my brother wrote for the Christian Science Monitor and retired circa 2016. MIT offered watered down classes for journalists to help them better cover their topics. Pete was an active participant. I'm so glad Pete turn me on to your blog!

  3. Cliff,thanks for presenting the facts and calling out the people spreading misinformation.Maybe one day the will acknowledge that you can not have the same CO2 level with 7.9 billion people than you had with 4.4 billion as in 1980.

    1. It's obviously true that increasing population will increase CO2 levels (without some change in lifestyles). But maybe one day you'll acknowledge that this will have an inevitable consequence i.e., increased global temperatures as a result of increased greenhouse gas production. It's pretty simple, right?

    2. I did not address any consequences,i simply stated the facts.

  4. Interesting. The Global warming effects look quite small relative to the day-to-day or year-to-year variance. Is there any evidence that the day-to-day variance is increasing... e.g. variance of highs, medians, or lows in pressure or temperatures? I'd like to calculate something like the standard deviation or perhaps a root mean squared of highs, means, or lows of temperature or pressure from year to year. There might be effects there, but with a relatively short time frame and such small effects-- it's going to be hard to show real trends. Certainly the day-to-day variance is large compared to the trend, but then is that variance changing?

  5. Alas, fireproofing forests via commercial thinning similarly falls in the category of myth. The most reliable means of wildland ignition are the logging roads that allow easy access into remote areas for fire-starting humans. Still, the prevailing politics in Washington and Oregon will hold onto this myth for about as long as West Virginia and Kentucky hold onto the myth of "clean coal." As always, money is the driver.

    1. Thinning forests certainly works. It's been done in Northern Arizona to great effect. Forest management in the western US has lacked for a century and is exacerbating the intensity of fires. I won't disagree that ease of access is a factor, but not the overwhelming issue.

    2. At the time Europeans began coming to what was to be called America the trees in the Eastern United States were very wide apart. It was said one could drive a wagon through the forests. The reason was that the Native Americans routinely started fires to thin out the underbrush. Forest fires were common, but not the huge conflagrations we now seem to routinely have. There is no reason to believe that thinning forests can't be done now. What the costs are I don't know.

    3. Lightning is a huge cause of ignition of wildfire in the Cascades in Washington and Oregon. I think it may be responsible for many more wildfires than those human caused

  6. Thank you. A very thorough and moderately lay explanation. However I don't see any attribution/relation for the PDO, ENSO, jet stream excursions, etc.

  7. As always, I appreciate your desire to let the truth speak, even if it doesn't line up with "our agendas." Just emailed the ST on an article that was just published today tying the heat wave to climate change. Ugh.

  8. Great stuff and thanks.We have enough real to worry about without amplified rumors. That said, re warming, how about the higher lows? Seems hard freezes used to be regular and are now unusual in town.

  9. A few points:

    1) The Scientific American article (https://www.scientificamerican.com/article/unprecedented-heat-wave-in-pacific-northwest-driven-by-climate-change) that you have a screenshot of at the top (but don't link to for people to read for themselves), actually credits the same thing you do for this high-pressure ridge, a tropical cyclone in the Pacific. Their point is that as the oceans warm, that will cause more cylones like this one, which will cause more heat events like this one. Do you disagree?

    2) You say that "those trying to ascribe the extreme temperatures to global warming must prove that global warming somehow amplifies natural variability", but that's not true. You don't need to increase variability to significantly increase the likelihood of extreme temperates, if temperatures on a given day/week/month follow something like a normal distribution. For example, using the average July highs from 2012-2015, we get an average of 79F and a standard deviation of 7.5F. If that average goes from 79F to 81F, the chance of a 3-sigma event (101.5F) sometime in July more than doubles! It goes from ~4.0% to ~9.6%, and that's with NO increase in variability. Small changes in averages can result in big changes in the rate of what were previously (dangerous and damaging) outlier events.

    3) The "Total number of stations with temperatures about 99F in our region? Also no trend" graph totally has a trend, and it's upwards.

    4) If you look at the hottest days in Seattle history (https://www.seattleweatherblog.com/temperature-stats), 5 of the last 10 are in the last 20 years, and 8 of the last 10 are in the last 30 years.

    5) The idea that Global Warming can be declared the cause of a specific and individual weather event is basically a straw man -- it's the classic difference between weather and climate. The question isn't whether this specific event was "caused" by climate change, but rather whether climate change will make events like this more likely. And the answer to that question, based on what I can tell, is likely yes.

    Finally, it would be great if you used your platform to warn more about the dangers of climate change and what our state (and the country, and the world) will have to deal with if we don't change our trajectory. As it stands, you spend far more time telling people that specific events AREN'T directly attributable to climate change than you do trying to educate people about what climate change WILL do. Which feels pretty irresponsible to me. The risks involved in people maybe overstating the causality of these kinds of weather events isn't even in the same ballpark as people not understanding the dire climate changes that are predicted, and what we'll need to do to mitigate them.

    1. "educate people about what climate change WILL do"

      Cliff doesn't have a crystal ball. How would he or anyone else know what "climate change" WILL do? Herein lies the problem.. people don't like uncertainty, and they will go to any length to fool themselves in an attempt to eliminate it. In Cliff's case, you have it completely backwards - Cliff is being entirely responsible by NOT making claims about things he can't know. But, that's not the drama people crave, so he is likely to be largely tuned out. This is the human condition.

    2. I totally agree with your last point.

    3. I was going to make a similar comment re the poor logic of Cliff's statement that ... "those trying to ascribe the extreme temperatures to global warming must prove that global warming somehow amplifies natural variability"

      I look forward to Cliff's resonse on that point as well as your other points.

      That said, just as I don't like Cliff's mind-probing in determining what other people are "trying to ascribe," I'm not sure about your (plausibly deniabe?) implication of intent behind the missing link (no pun intended) and conclusion that Cliff's being irresponsible. He clearly thinks that he's helping society to respond to the risks of global warming by focusing on what he considers to be the best take on the evidence. Imo, rhetorical posturing and personalizing the science is sub-optimal, whether it comes from Cliff or those who disagree with his analysis.

    4. Quality response. Thank you, Chris.

    5. Regarding Point #2, I can't tell whether you're earnest or obfuscating. Cliff, if I'm interpreting correctly, is saying that 110° this year as about as likely as 108° was before man perturbed the system. You're not disagreeing, just saying that adding 2° changes the odds by a factor of two, so the odds of any given anomalous temperature are affected a lot by climate change, even if the peak temperature is not. Cliff is not contesting that POV.

      It amazes me that few seem able to separate and appreciate the two perspectives, and would rather argue with Cliff.

    6. Chris....let me respond to your points.
      1. The headline speaks for itself, claiming the climate change drove the heat wave. This is demonstrably untrue as demonstrated in my blog
      2. The threshold approach you suggest is flawed. You establish an arbitrary threshold and assume a distribution with a highly skewed tail and if you warm the situation, you get a big increase in percentage across the threshold. This is meaningless for a number of reasons. The heat wave event is hardly changed but you get huge percentile increases. The impacts are essentially the same and most of the cause is still natural variability. And most of these analyses assume that the distribution is the same, which is not true. I have shown this in published work.
      3.You are not looking at my figure (99F) carefully. There is no trend during the past 50 years when global warming is evident.
      4. The Northwest is certainly warming, but record temperatures are not trending up. That is my point. And you need to be careful about looking at single stations. Seattle observations have moved during the period and record and urbanization is substantial. Furthermore, the airport location is problematic because of the third runway and sensor changes.
      5. We agree. One should never claim the GW produces a single event. That is the essential message of my blog
      Finally, I disagree with your philosophy at the end...that overwarning is not a problem I think it is a big problem. Society makes bad decisions. People are needlessly made fearful. And much more.

    7. Cliff -

      Are you saying the following comment isn't true?:

      "You don't need to increase variability to significantly increase the likelihood of extreme temperates,.."

      Are you repeating that ONLY through an increase in variability can there be an increase in the likelihood of extremes? That doesn't seem logical.

    8. I did not say anything about that comment. You can increase extremes in a number of ways.

  10. Unfortunately, two dice have almost 3 percent chance of coming up double sixes. Way too large to describe what happened. By my estimates, this event has about 30 chances in a million of happening. That’s akin to rolling FIVE dice and they all come up sixes.

    1. michael how did you get 30 chances in a million? The dice discussion was a metaphor...cliff

    2. Maybe he's never played Yahtzee!

    3. The 108F seattle temperature on June 28 is about 4 to 5 standard deviations above the average high T for that date, as I explained in an email to you yesterday, Cliff. Four standard deviations corresponds to 30 chances in a million, which is the same as rolling five or six dice and they ALL COME up sixes.

    4. Michael....there is a problem with your calculation. We really don't know the standard deviation. Our observational record is too short to secure realistic information at the tails. If we had an observational record of say, several thousand years, we would have better sampled the extremes and would observe such extremes occasionally. A hint that is is true comes from the ensemble climate simulations that include many members. Occasionally one member goes to an extreme that is not observed....cliff

  11. I realize Pacific influences were pretty much shut down during this event. But I remember your spring maps, showing how La Nina was collapsing, with a warmer plume of water coming in from the western Pacific. Is it possible that plume contributed to the heat to some small extent? (Not, of course, by increasing temperatures, but by failing to cool as much as normal, to the extent Pacific winds had any impact?)

  12. Simply, the confluence of factors that mechanistically explain this heat wave are going to happen more often.
    And also very unfortunate is the upcoming age of growing energy poverty that we are on the verge of entering.

    1. "Simply, the confluence of factors that mechanistically explain this heat wave are going to happen more often."

      I guess you didn't read the article. Cliff's lengthy and detailed post explains precisely why your statement is categorically NOT the logical conclusion!

      What is your opinion of the average reading comprehension skill level these days?

  13. It is my personal opinion that some combination of natural and anthropogenic climate change processes has baked at least two degrees of warming above pre-industrial by the year 2100 into the earth's climate system. So, how did I arrive at this conclusion?

    A long-standing principle of debate is that the more assumptions you have to make to prove your argument, the weaker is your argument. Today's computerized climate prediction models contain hundreds of assumptions large and small concerning the physics of how the earth's climate system actually operates.

    For purposes of argument, I replace those many assumptions with just one very large and comprehensive maxi assumption. 'The 1850-2019 HADCRUT4 Global Mean Temperature record includes the combined effects of all natural and anthropogenic climate change processes as these have evolved through time over the past one-hundred seventy years. Similar processes will operate from 2020 through 2100.'

    The illustration presented below, dated April 15th 2020, contains a single-page graphical analysis for predicting where global mean temperature, as measured by HADCRUT4, will likely end up by the year 2100.

    Beta Blocker's Year 2100 GMT Prediction Envelope

    URL: https://live.staticflickr.com/65535/51295091190_94386cc94a_o.png

    Figure 1 contains the pattern analysis used as the basis of my year 2100 prediction envelope. Figure 2 describes the prediction envelope in greater detail, as follows:

    + 2.7 C Scenario: The 1975-2019 trend line of +0.19 C/decade continues uninterrupted from 2020 to 2100. (Less likely to occur, IMHO)

    + 2.0 C Scenario: The past pattern of GMT trends which occurred between 1850 and 2019 remains fully operative. (More likely to occur, IMHO)

    + 1.3 C Scenario: The linearized long term trend of +0.05 C/decade for the period of 1850-2019 dominates through 2100. (Less likely to occur, IMHO)

    + 0.6 C Scenario: A moderate GMT cooling trend of -0.06 C/decade starting in 2020 continues past 2050 and dominates through the year 2100 and beyond. (Less likely to occur, IMHO.)

    In my humble opinion, the 'more likely' GMT pathway between 2020 and 2100 is the one most consistent with the historical pattern of warming, then cooling, then warming which occurred in an ever-upward stepwise progression between 1850 and 2019. In other words, it is the pattern which most closely resembles the HADCRUT4 pattern between 1850 and 2019.

    As one who is a lukewarmer in the climate change temperature prediction debates, my bet is on the + 2.0 C scenario as the one most likely to occur. However, other outcomes certainly remain possible, even if I judge them to be less likely.

    Here is the bottom line question as it concerns the value of today's mainstream climate models:

    For purposes of public policy decision making, do the computerized climate models with their vast complexity and their many physical assumptions, large and small, have any more useful predictive power than does my very simple single-page graphical analysis?


    Full Disclosure: I post as 'Beta Blocker' on Watts Up with That and on Climate Etc. I post as Betah Blocher on other climate change forums because most of these don't allow 'Beta Blocker' as a user name. I've spent thirty-five years in nuclear construction and operations. The bulk of my occupational radiation exposure has come from beta/gamma sources, hence my internet handle is Beta Blocker.

    1. Nobel Economic Lauriat Nordhaus projects optimum 2100 economic efficiency with a 3.5 C temperature increase.

  14. Cliff, i have seen commentary that the record-breaking heat wave in Lapland was from the same high pressure ridge (or jet stream wave) that affected us. can you speak about that event ?

  15. I think the last big rain in westernwa was about June 7. No rain on the horizon. For whatever reason, it looks like a dry summer. Also, observing grass growth over the past decades, it appears to me the grass freezes less mid winter. How many days does the high stay under 32 freezing anymore? It seems to me the climate has shifted two weeks to a month earlier for spring and summer warmth and dry out.

  16. Liked your article very much, but a couple of things: First, the graph of temperatures >99 degrees DOES show an increasing trend. Second, Of course there are fewer record highs now than there were. Back when there were far fewer temperature recordings it would have been much easier to achieve a record, either hot or cold. Imagine how many records would have been set in the second year of recording, versus how many would have been set in the 100th year.

  17. The downside to collecting so much data about the extremely complex system that is our atmosphere is that anyone can take that data and present it such that it shows whatever they want to believe...or what they want others to believe.

    There are also many assumptions being made that drastically change the outcome. Are all the assumptions correct? Only time will tell.

    There are those that will question every prediction for our shared climate/weather future that does not agree with their own personal expectations. Some predictions will be proven grossly inaccurate, some not so much.

    At some point, we have to decide which group we want to be part of.

    The group that forces the "end of the world at any moment" thinking on anyone who will listen. The group that uses the basic human instinct of self preservation as a weapon against those who are susceptible to that way of thinking. The group that over dramatizes events or outright tells lies to keep the fear going as long as possible.

    OR, the group that recognizes that the world is not going to end at any moment. The group that speaks calmly and does not play on people's fear. The group that does their best do convey reality as they understand it and does not cry wolf every moment of every waking hour. The group that has hope for the future.

    I choose the latter. From this layman's viewpoint and my own personal observations, I choose to side with Cliff and his peers that tell us that we must make changes to preserve some semblance of our way of life. The group that has hope for our shared future.

  18. Bjorn Lomborg approves of this posting.

  19. There was a comment by Chris yesterday that referred to the bulk of the hottest days in Seattle occurring in recent years. The problem I see with the "Seattle" temperature record is the thermometer is located between three taxiways, which are located between the center and western ("third") runways of SeaTac Intl Airport. It is there because pilots want to know the temperature on the runway. The construction of the third runway destroyed thousands of trees, required 130,000 cubic yards of concrete and 35,000 tons of asphalt to give us an 8,500' x 150' x 17" blob of pavement directly west of the SeaTac AWOS. I view any temperature record from SeaTac ("Seattle") since the third runway opened in 2008 as juiced.

    1. There were plenty of other thermometers all over the Seattle area, including Seattle itself, that had equal, or higher, temps.

  20. Natural variation can be extreme. On January 31, 1966 I was camping with my Boy Scout troop near Huntsville, Alabama. The weather report said the temperatures would be cold, possibly 18 degrees. In fact, the temperature in Huntsville that night was -21 degrees and the valley we camped in was -27 degrees the all time record low for Alabama. Areas surrounding were not as cold, but still very cold. I have never been so cold in my life, we were unprepared. It was awful. Again, the point is natural variability can be extreme. I doubt Huntsville has seen temperatures below zero before or since.

  21. Correction: The KSEA site is actually an ASOS.

  22. Did the recent volcanic eruptions contribute to the "Number of factors coming together" by way of changing air currents aloft.
    Thank you.

  23. I appreciate the science in your post, but context matters, too. You gloss over your own statement, "The Pacific Northwest is warming and human emission of greenhouse gases is probably the origin of much of it." This is the key point in climate discussions. And it's not just the Pacific Northwest. And it's on track to warm much more. And there is good science to support devastating consequences from that.

    Oddly, you seem to talk about climate only when you are denying that it affects one event or another. If climate change is as real as you admit it is, it must be affecting something.

  24. I will send my comment again as I did not see it posted, and maybe it is not worth posting.
    I analyzed the temperature record from the WSU Tree Fruit Research Center in Wenatchee, which has a record beginning about 1940 and continuing to the present time. The recording station has been in a semi-orchard environment for all of this record so should not have been affected by "heat island" issues. A NWS Western Region Technical Memorandum was published in 1993 showing the highest and lowest temperatures for each day of the year for the period from 1940 to 1993. I have updated this from 1994 to the present time. Here is what I have found regarding record daily high and low temperatures. Beginning in 1991 and through 2020 there were 157 times that a record high was equaled or exceeded, with 30 days seeing the record equaled or exceeded more than once. There were 80 times that the record low was equaled or exceeded with 9 days seeing this exceeded more than once. So about twice as many record high temperatures were set from 1991 to 2020 as record low temperatures. I divided this time period into two 15-year periods, 1991 to 2005 and 2006 to 2020. There were 55 record highs occurring in the 1991-2005 period and 102 record highs in the 2006 to 2020 period. There were 50 record lows set in the 1991-2005 period and 30 set in the 2006-2020 period. There have already been 7 record highs set in 2021. This seems to indicate a trend toward increasing number of record highs at least for this period.

    1. Unknown... these periods are too short. Look at the last century--or from 1940 if that is all you have. Plot the annual high temperature records. Keep in mind that many records occurred in the 1930s and late 1800s, so using a short record, you are missing them.

  25. What devastating consequences are you talking about? I have repeatedly blogged about the impacts of the warming in the region. I am trying to promote a realistic view of the impacts, which are generally modest.

    1. Maybe I'm on your do not approve list or something, but I thought my question was pretty appropriate here:

      What is modest about the extinction of salmon and Southern Resident Orcas?

      Do you have any non-anthrocentric sense of consequences?

    2. When I said "devastating consequences", I was not referring specifically to the PNW, but to the planet.

    3. Colin, the near-extinction of northwest salmon is due to habitat destruction, dams, over-fishing, farmed salmon disease, and competition with other fish stocks that have been bred by man. It's not because of climate change. Mr. Mass has kept a level-headed tone in the debate, and others should too. ("Do you have any non-anthro...." is what I'm referring to)

  26. I'm much more interested in knowing when the next heat wave is coming, and which areas will be most affected. Looking forward to reading about that soon.

  27. Impressive analysis, Cliff. I hope it's correct. I sent this post to Michael Mann. Maybe you two could do a panel discussion.

  28. "We are now making similar mistakes with global warming, with politically inspired misinformation slowing realistic and life-saving steps, such as...proceeding rapidly with nuclear energy." Gen IV nuclear uses existing nuclear waste for fuel.

    Americans are great at avoiding catastrophes they can see coming. With both Republicans like Ted Cruz and Democrats like AOC in favor of nuclear, so Isaac Molitch's "upcoming age of growing energy poverty that we are on the verge of entering" will never happen.

    1. Those who believe in the most dire projections of climate change seem to employ the most rhetoric and personal and political attacks aimed at those who see modest effects to climate or even no effect. But this tone really hurts the cause, and will discourage a true scientific inquiry.

  29. This comment has been removed by the author.

  30. BRAVO and Amen. Thank you for your unrelenting commitment to actual facts and analysis. So true that science journalism is not what it once was. One has only to look at Science News magazine. Anecdotally, my memory tells me that, during the 32 years I've lived in Olympia, there have been three episodes of 100+ F. heat, in 1998, 2009, and 2021. In some summers, I haven't even gotten my fan out of its storage box. And yet, I keep hearing politicians and news media saying that "it gets worse every year." This is simply not true! I guess it becomes true if you repeat it enough times so that people believe it.

  31. Hi Cliff - How much is measurement error an issue in these historical temperature records? That is, I imagine the technology has improved over time and that older measurements are more likely to have erroneously given extreme values. If so, this would tend to obscure seeing an increase in extreme heat over time. - Thanks

  32. A study found that cosmic rays might be causing a significant amount of ozone depletion according to this article:

    This might at least partly explain the recent heat wave since more intense solar radiation heats up the Earth as ozone depletion increases. Since the same input of solar radiation causes higher temperatures when dry air is heated than when air with higher humidity is heated, it seems as if an even greater input of solar radiation would increase the tendency for dry air to heat in the Southwest along with the tendency for a strong upper level ridge to be partly over the Southwest and influence weather in the Northwest. This tendency might also possibly be related to that last year after the largest amount of ozone loss that ever occurred in the Arctic it was the hottest summer of all time in a large part of the Southwest.

    While Australia has warmed by only just over one degree C since 1910, the frequency of extreme heat events is greatly increasing as discussed in this article:

    Since 1985 was the year that the Antarctic ozone hole was discovered and since the frequency of temperatures being extremely above normal is greatest in the spring as ozone depleted air masses move north from Antarctica, ozone loss could be at least part of the reason for the trend that is clearly indicated by the graph which is included in the article.

  33. It hardly matters to our marine, forest, and human ecosystems if just 10% or 100% of the unprecedented, devastating heat wave was caused by global warming or not. As you’ve correctly stated before single events are not proof of climate change. What matters is that it dealt a significant blow to our already stressed forests and intertidal biomes, and puts yet another nail in their coffin. What matters now is that we shutdown the fossil fuel industry and start to dramatically reduce our greenhouse emissions. The heat wave is a signal, a warning, that if we continue to live the way we do, we and all plants and animals will struggle to exist.

    1. we certainly need to increase use of renewables and bring on massive nuclear. We can't "shutdown the fossil fuel industry" without a viable, read to go, replacement. You will kill many people if did that...cliff

    2. There is no culture that is going to stay intact and functional for anything even approaching the half life of nuclear waste. Creating big amounts of it is literally borrowing against the future.
      I'm for a slow transition to renewable energy, which is looking possible now that utility scale battery tech appears to be doable. You're absolutely right we can't abruptly stop using fossil fuels, because it would lead to economic collapse.

  34. All of these folks using the "standard deviations" and "odds" of this weather happening, then attributing this scant CHANCE of it to anthropomorphic climate change...I wonder if they looked at the last 25 election cycles, only to realize that Biden's electoral victory is statistically on shakier ground than 115 degree temps in Portland.


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

New Podcast: Showers, Warm Up and Winds on the Eastern Cascades Slopes

  Cold, moist unstable air has been moving into the region on Saturday, with the showers obvious on the high-resolution visible satellite im...