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

July 18, 2021

By Paul Homewood



h/t Ian Magness



There have been several stories developing while I was away, so I will be picking up on some of them in the next few days.

The first concerns the Pacific Northwest heatwave:




The heatwave has quite frankly generated a hysterical reaction. Roger Harrabin says it scared him, while Matt McGrath repeats the lie that the heatwave would have been “virtually impossible” without global warming. And it’s not just the BBC; the media seems to have a collective nervous breakdown and lost its ability for rational thought.

The idea that global warming is responsible for the heatwave is patently absurd. According to HADCRUT, global temperatures have only risen by half a degree since the 1940s, so its impact on last month’s heatwave would have been tiny at the most.

Nobody is denying that the temperatures in the Pacific Northwest and Canada were extraordinarily high, but there is a perfectly rational explanation why.

Cliff Mass is one of the leading American meteorologists. As Professor of Atmospheric Sciences at the University of Washington, he has devoted most of his career to studying meteorology and climate modelling in the region.

On July 5th, he wrote a long, factual essay on the heatwave:




It is worth reading in full, but this is how he explains the actual event:


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.

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).

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).


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.

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.


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.


In other words, it was a natural weather event, albeit an extremely rare one, something you might term a Black Swan event.

Mass goes on to address what influence global warming may have had. He makes the point that there has actually been no trend whatsoever to heatwaves growing hotter in the region, something you would have thought should be occurring if global warming was a factor.




He also deals with claims that global warming has led to more intense high pressure episodes and more drought. Again he finds that the actual data shows nothing of the sort. Indeed there is solid evidence that the reverse is true.

He concludes:


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. 


All of this information is out there, so why have the BBC and the rest of out gullible media totally ignored it?

It is not even as if freak heatwaves like this have not happened before. The heatwaves of the 1930s were far more severe and affected large swathes of the US and Canada.

In Kansas, for instance, temperatures peaked in 1936 several degrees above anything seen in recent decades. And it was not just a one off event, as similar heatwaves were commonplace throughout the 1930s.




But apparently the BBC’s Environment and Science Department are no longer interested in facts!

  1. Penda100 permalink
    July 18, 2021 6:21 pm

    The BBC has no interest in providing balanced reporting on climate change/emergency. It is only interested in reporting scare stories and propaganda – a position it seems to take on an increasing number of issues. There are no so deaf as those who won’t hear or blind as those who will not see, so why go looking for evidence that disproves that which you have already decided is the only, allowed, truth?

  2. July 18, 2021 6:35 pm

    Tip : 7pm Countryfile : “Charlotte Smith investigates the environmental impact that increases in offshore windfarms are having both on land and at sea.”
    rest of crew is at Yorkshire’s Flamborough Head.

    • GeoffB permalink
      July 18, 2021 7:42 pm

      Surprise for countryfile,,, it was a critic of onshore cabling to get the power to a grid causing environmental problems by digging wide trenches 45 metres across. I guess you cannot cultivate these, why so wide was not explained maybe it is DC.

      • Ray Sanders permalink
        July 18, 2021 8:34 pm

        Hi Geoff, the reason pylons are so large is to keep a wide spacing between the cables to avoid power arcing across as a short circuit. Even if you bury cables the same thing can happen so you still have to maintain large distancing between the cables. Rather than dig down ultra deep to achieve the distance separation (i.e. the height equivalent of a pylon) they separate the cables horizontally hence the very wide track required. This is one of the many reasons why burying HT cables is so expensive – it uses up a lot of land.

    • July 18, 2021 8:47 pm

      No mention of the fact that all this intermittent (but clean and green!) and very expensive offshore wind-generated electricity with all its attendant problems, could be replaced with a few SMRs, saving consumers a fortune and doing very little damage to the environment. I wonder why this BBC obsession with white elephants (aka offshore wind)?

    • July 18, 2021 10:52 pm

      @BBCCountryfile weather forecast just now ,
      “ this weekends hot temperatures are due to changing climate “…

  3. GeoffB permalink
    July 18, 2021 7:46 pm

    Back to topic…….”Do not confuse me with the facts! My mind is made up”

  4. Broadlands permalink
    July 18, 2021 8:03 pm

    ” The heatwaves of the 1930s were far more severe and affected large swathes of the US and Canada.”

    According to NOAA’s NCEI, the maximum mean temperature for June from 1895 through 2021 in the contiguous US 48 states was 85.95°F. in 1933. (4.61°F above the 20th century mean). CO2 was pre-industrial. Man-made global warming could not have been involved.

  5. July 18, 2021 8:43 pm

    The BBC weather forecast is about the effect of “climate heating” and this weekend’s very high temperatures at….I’ll let you guess. Top marks for anyone who says Heathrow.

    • Gerry, England permalink
      July 19, 2021 2:20 pm

      Somewhere I saw mention of the source of the heat and ‘Azores High’. No doubt wasn’t the BBC as they would never refer to a weather phenomenon that has existed for no doubt thousands of years.

  6. Broadlands permalink
    July 18, 2021 9:06 pm

    Also for those who say asphalt, concrete, nearby highways and buildings. In other words the UHI… Urban Heat Island effect…rapidly becoming suburban heat.

  7. John 189 permalink
    July 18, 2021 9:24 pm

    I’m on holiday at the moment and don’t have access to my records, but I seem to recall that the last time the British Isles failed to record a summer temperature of 30 Celsius or above was in 1987. 30 C is reached or bettered most years. Any hype of the current pleasant weather is just cheap sensationalism or alarmism.

  8. Coeur De Lion permalink
    July 18, 2021 9:53 pm

    I guess this heatwave was exceptional-not seen for say 80 years. So it’s likely to be difficult for alarmists to generate fear when nothing matches it for a couple of decades. I note the trending belief in a protracted La Niña. Btw Boris’s stupid windmills are generating 1.29% of demand

  9. July 18, 2021 10:38 pm

    Yes, it was a classic jet stream blocking event with a big loop up from Mexico getting stuck on the Rockies.

    Mike Lockwood during the last solar minimum pointed out that Rossby waves get loopier during solar minimums. The last solar minimum featured the Great Moscow Heatwave of 2010, which lasted for a month – another jet stream blocking event.

    So far none of the climate activists have managed to explain how CO2 can cause this sort of thing happen every 11 years.

  10. StephenP permalink
    July 19, 2021 6:43 am

    How much of this increasing alarmist hype is being caused by the run-up to COP26?

  11. Phoenix44 permalink
    July 19, 2021 8:01 am

    Exactly the obvious point about short-lived localised events – it is extremely unlikely that in the last 150 years we have had EVERY POSSIBLE variation of weather in that locality at that time of year. Indeed for a single place in a single city on a single day, we have obviously only had at most 150 of the possible variations in weather. An analogy is that each day we throw a dice with say 300 sides. 250 of the sides have temperatures within the variation of a 100 year record but the other 50 are not and five of those 50 have extreme temperatures. I don’t need to load the dice to occasionally get extremes and every so often to get records.

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