July 20, 2023

Is Global Warming Causing Massive Heatwaves?

The media is going hyperbolic about heat waves, claiming that global warming/climate change caused by human CO2 emissions is producing a huge, sudden uptick in massive heat events.   The greatest in the historical record.  Heatwaves are all over the planet! Phoenix, Arizona is a frequently noted poster child of the new heatwave regime.

Here are a few examples of the headlines, I could provide dozens more just like it.

The Quiz

    Before I discuss the situation, let me provide two possibilities for you to consider.

(1)  Human emissions of greenhouse gases, such as CO2,  are slowly warming the planet.  During the past century the Earth has warmed by roughly 1°C and human emissions could have contributed much (but not all) to the warming.   El Nino periods contribute to temporary warming, and local warming due to urbanization (urban heat island) is also important.  Most heatwaves are predominantly natural phenomena, with minor enhancement from global warming/climate.

(2)   Heatwaves are predominantly forced by increasing greenhouse gases.  The entire planet is experiencing unparalleled heat due to human-caused climate change.  By reducing greenhouse gas emissions, heat waves could be greatly weakened or prevented.

Which do you think is the correct answer?   The one supported by observations and peer-reviewed science?

The correct answer is  (1).  Heatwaves are mainly caused by natural variability, with humans enhancing them a small amount.  Let me prove it to you and describe some of the hype and deception going on in the media and by others.

It is important to understand that current heatwaves are localized, with substantial portions of the planet experiencing cooler-than-normal conditions as well.  Most of the planet is NOT experiencing unusual warmth.

Consider the observed temperature pattern on Tuesday night at 11 PM, or more exactly the difference in the observed temperature from normal (see below).  Red areas are above normal and blue/green are below normal.

The figures shows that the Earth has BOTH heatwaves and cold waves going on at that time.  

For example, the Southwest US. is warm, while much of the eastern U.S. is colder than normal. Northern Europe is cold, while southern Italy is experiencing heat.

So heatwaves are localized (and transient) conditions and only a small portion of the globe is experiencing unusual warmth.  Greenhouse warming from greenhouse gases is much more uniform.

So what is causing the localized warming?   The answer is very evident if we plot the upper-level map (for 500 hPa, about 18,000 ft) at the same time (see below).  Blue areas indicate troughing (low pressure) and red areas indicate ridging (high pressure). 

The warm areas are closely associated with ridging aloft and cool areas with upper-level troughing.  Ridging is associated with sinking air and warming.   The opposite with troughing.  Ridges and troughs also have wind patterns that can move tropical warmyh poleward (and vice versa).

Such wave patterns are quite natural.   There is no convincing evidence that the atmosphere becomes wavier (thus with more heatwaves and cold waves) under global warming.  I have read all the literature on this and have published on the topic myself in the peer-reviewed literature.

The waviness of the upper-level flow was particularly high-amplitude this winter and spring, producing enhanced cooling in some areas and warming in others.  Such as the cool/wet conditions in California, and warmth in southern Canada.

Let me repeat:  there is no reason to think this waviness is other than the expression of the natural variability of the atmosphere.

With the general temperature of the planet slowly rising from human greenhouse gas emissions (by roughly 1°C), the heatwaves should be about 1C warmer and cold waves about 1C weaker.  

This is exactly what is observed.

By the way, extreme cold kills FAR more people each year than heatwaves, so global warming is actually reducing deaths from extreme temperatures (you won't hear much about this in the media!)

But there is something else that is enhancing warming right now.   

This spring El Nino rapidly turned on, and El Ninos warm the planet!  Below is the key marker of El Nino:  the temperature in the central tropical Pacific (the Nino 3.4 area).  A VERY rapid and early warming during April and May.

The oscillation between El Nino and La Nina (cold water), is a natural model of atmospheric variability.

Would we have had major heatwaves without human-caused global warming?  

You bet we would.  We certainly had substantial heatwaves (some as strong or stronger than this month) in the past (such as in the 1930s).  Were the heatwaves this week enhanced modestly (like 1°C) by global warming.   Quite possibly.  So a place like Phoenix would have had a high temperature of 115F instead of 117F.   Pretty much the same impacts.

Media Deception Regarding Phoenix, Arizona

The media has been particularly interested in the recent warm spell in Phoenix, in which they are headlining its record for the number of days above 110F.

As I will describe below, there is more than a little deception going on here.   The 110-degree approach is a prime example of misinformation, and the Phoenix temperature record is highly suspect because of massive development and a huge urban heat island effect.

"Cherry Picking"  Statistics

The term cherry picking can be defined (Wikipedia) as:

Cherry pickingsuppressing evidence, or the fallacy of incomplete evidence, is the act of pointing to individual cases or data that seem to confirm a particular position while ignoring a significant portion of related and similar cases or data that may contradict that position.

The media and some climate activist groups have been advertising that Phoenix has now exceeded 110F a record number of times in a row.  Thus, something unusual and scary is occurring.

But why 110F?  Did you wonder about that?    

They did this deliberately because if they had picked another temperature they would have gotten a completely different answer, one in which Phoenix was not unusually warm.

Consider a choice of two-degree difference (112F).   This year drops to 6th place!

How about something more unusual (115F)?  2023 drops to 8th place

Or let's consider more "garden variety" heat (105F).   This year remains in 8th place.

Do you feel deceived and tricked?  This was a deliberate attempt to cherry-pick statistics to push an agenda.  Not good.

But the selection of Phoenix is worse than that.

Phoenix has perhaps the most profound and rapidly growing urban heat island in the nation.

Phoenix has been one of the most rapidly growing cities in the US (see below) and all the construction (concrete, buildings, sources of heat) results in profound warming, something known as the urban heat island effect

Do you want to see Phoenix's heat island in action this week?  

Below are the temperatures on Tuesday during the late afternoon.   117F at the Phoenix airport but 111F just outside of the metro area.  This difference is quite typical for the city.

So even if there was no global warming going on, Phoenix's temperature would have substantially increased over time due to the rapid development of the city.  Such urban heat island effects seriously degrade the temperature records, producing artificial warming.

Want another example?  SeaTac Airport, whose third runway and local development have impacted (warmed) the temperature record there.

Finally, let me note that although the Earth is slowly warming from human-induced greenhouse warming, there is no evidence that heat waves are being amplified or enhanced over this base warming.   So all the panicky headlines are really without merit.  

Want to see an example of this?   Below are the annual high temperatures at Olympia, Washington, with a linear trend line added for your benefit.  Annual high temperatures have gone up about 2F, roughly the same as the global warming signal.

Claiming that a sudden and rapid increase in heat waves is occurring due to global warming may be good clickbait for the media and a potent tool for climate activists, but it is simply not true.

Finally, let me note that headlines early this month that the Earth was warmer than any period during the past 125,000 years were really nonsense.  But I will leave that discussion to another blog.


  1. We are in an era when facts don's seem to matter and societal choices are based much more on beliefs than science. The corporate-funded belief side has been winning for a long time, especially in terms of denying climate change and doing anything to stop it.

    Maybe its okay if more and more people believe that these heat waves and other severe weather anomalies are the result of climate change. This may put more pressure on corporations and governments to act. This unfortunately may be the only way in which we can do something about this.

    You are just one voice amongst many scientists, several of whom are stating that these anomalies are a result of climate change forcing.

    Certainly urban heat islands are one reason why these high temperatures may exist. Perhaps these can be categorized as "localized warming" suggesting a better urban design that doesn't heat up the local landscape. Arguing that these are not part of the global scheme may be scientifically accurate. Socially they are a disaster that magnifies or will magnify climate change.

    Bottom line is that people are suffering. Allow them to have the belief that climate change may be the cause and this may prevent much more suffering in the future, should people decide to act on it at the ballot box.

    1. "Bottom line is that people are suffering." Suffering how? People these days live a soft, privileged life and have no ideal whatsoever what suffering is. Lord help them if they ever have to face a real life challenge.

    2. Kenna Wickman writes "Allow them to have the belief that climate change may be the cause and this may prevent much more suffering in the future, should people decide to act on it at the ballot box." People have suffered throughout time, and believed the suffering had inumerable causes. The COST to everyone in society to deal with "beliefs" is overwhelming. Even thinking we can destroy modern society for the sake of beliefs, man. Why not sacrifice humans, since many seem to "believe" they are the root of the problem (sarc).

    3. The irony in your post is striking. Claiming that we live in an era where "facts don't seem to matter" and then saying that it's a good thing that people believe that these discrete temperature anomalies are directly due to climate change whether or not that is in fact the truth. What an insane take.

    4. Just like COVID vax, the fear narrative, e.g., "you're killing grandma if you don't do A, B, and C," is promulgated in order to lead us toward a technocracy (form of Marxism/fascism). The litmus test is always: Is what they are saying making me afraid? If so, question the narrative. Authoritarians always use fear. It's really that simple.

      This is not to say that we shouldn't waste resources. I enjoy driving my 100+ mpg homemade moped around town to get tasks done.

  2. Cliff, I really appreciate the way you break this issue down with real research and data. I hope that researchers like you continue to provide objective viewpoints that provide great clarity.

  3. Thank you for this, Cliff. I learned a lot from this blog. I am looking forward to your future blog about the 125,000 years claim.

  4. Also would love to hear more about what you think about the implications of that 1 degree Celsius warming... do we have to care at all? Any consequences for it that science can support? What actions do we need to take? I do understand the media is clearly making it a bigger deal than necessary to control the people, and that the government is clearly not doing any to stop global warming...but how should we actually respond? Best, Bobby.

    1. "do we have to care at all?" Never ask someone else what you are supposed to care about. Ask yourself that question then live with the answer.

    2. Excuse me? If there is a serious consequence to climate change, we should act as a society? What are we going to do individually?

  5. I'm looking forward to the post you promise in the last paragraph. I've seen the headlines but am interested in a reliable scientific take on it.

  6. Thanks Cliff. Keep up with the good science you do. Wish more scientists such as yourself would be bold enough to take on the media and activists as you do. I don't see how climate scientists can sit back and watch their work be cherry picked and misconstrued. However, if another person ever comes up to me again saying I don't believe in science because I'm not an alarmist, I will just ask them "How old is the universe again?" And walk away. If they cannot figure out I say that because it means science is never settled, they are lost cause.

  7. The last time I was in Phoenix the population was 600,000. Now from the web I get 1,651,344. I'm not sure about that last 4!

    Nice post. Thanks Cliff.

  8. This comment has been removed by the author.

  9. While broadly accurate, it might appear at least a little more honest if you didn't glibly omit the fact that while the eastern United States is indeed cooler than usual, it's also having record rain events. As I'm sure you're aware, climate change isn't purely about things getting hotter.

  10. First thanks for addressing this. Second, I think you're still downplaying it, for a couple reasons:

    1. A heatwave that's 3F hotter than "normal" can be significantly more dangerous, especially as places are reaching the limits of what humans can survive in. Breaking a wet bulb temperature where sweating can no longer cool the body, in a place without AC or other ways to cool down, can be really really dangerous. Going from 72F to 75F is not a big deal. Going from 114F to 117F very well might be.

    2. In your segment about cherry-picking, it's notable how many of those hottest days are in the last few years. You'd expect that to some degrees as temperatures creep up, but it's still pretty notable! 60% of the top 112F streaks have been in the last six years! Half of the top 115F streaks have been in the last three years! 87% of the top 105F streaks have been in the last twenty years!

    Even if heat island effects are responsible for some of this, it's still a problem!

    (also I think 110F is a natural breakpoint, in the same way that we counted the number of days over 100F each summer when I lived in Austin, it wasn't some nefarious cherry-picking)

  11. Good to offer the other side, but a key point I think you should call out is that the 1.1 C of warming you mention is really about 4 F over north america, europe and asia. Reasons are that land heats over twice as fast as the ocean, arctic amplification intensifies heat around the north pole, and then there's the conversion from Celcius to Fahrenhiet.

  12. The Phoenix-110-degree streak story seems to have originated on July 10, with an article from the Arizona Republic, which I link below. Author Jake Frederico noted the then-current 10-day streak of 110-degree days in Phoenix was the seventh longest on record and that the record was 18 days. It seems notable that the very next two days each recorded official highs of 111 degrees. If either day had peaked two degrees lower, the streak would have ended a full week short of the record. Major news sites like CNN were running the story as early the 12th as well.

    You might argue that the forecast accuracy is quite good, and that there was reasonable confidence when Frederico wrote about the 110-degree streak (and certainly by CNN’s story two days later) that the 18-day streak would indeed be broken if they “cherry-picked” the 110-degree threshold. But you can say the exact same thing about your blog post. You have access to even better forecasting tools than the general public. You know full well that the current heat wave in Phoenix is very likely to top the 105 and 112 streaks as well, and possibly tie the record 115 streak. Why weaken an otherwise excellent post by “cherry-picking” today as your reference date?

    I hope you'll have the courage to commit to an honest update at the end of the month. Your "they did this deliberately" language seems like something you'll want to walk back. Sooner is better than later. I include a link to the definition of "conspiracy theory" for your convenience.



  13. 110 was picked because it was a round number and that's what the public understands. It's not arbitrary. That's what the media does.

  14. Thank you. I grew up in KS Temps often soar into 100s the day I was born it was 110. Then conversely I was living there when ks hit -26. The coldest temp recorded. Some summers were mild some winter mild. Though my part of KS tended towards hot muggy summers. HmmI feel like in the 10 plus years living here here in westwrn wa there as been a lot of variation. Like those cold wet summer we sometimes have. The real kicker would be if we got another one of those summers without a summer.

  15. How can you claim that man's co2 is the cause of our warming when we are still cooler than Minoan, Roman & Medieval times?
    Thanks JK

    1. because it is simply not true, we are not cooler, but warmer already. the whole permise of this question is invalid anyway. just because it has been warm before, doesn't mean that each warming has exactly the same cause. it is like putting your house on fire and saying well, since there have been bigger natural fires in nature before, my house on fire is also due to natural causes.

    2. There have been periods in the past warmer than today in large areas of the work. The question is how much of current heat waves is caused by increasing Co2.

    3. Because Solar activity was much higher then.

  16. From what I can find, six state high temps were set in the first 23 years of the present century (including our own little Death Valley Days two years ago), and six were set (and remain) during the first 23 years of the previous century.

    Not, perhaps, all that statistically significant, but puts a bit of damper on the doomsday hype.

  17. Lake pollen studies within PNW demonstrate that the ecology in the mountains has changed significantly. Warming after the last glaciation and then steadily cooling.


    "Fossil chironomid remains recovered from lake sediments in southern British Columbia suggest Early Holocene summer temperatures at 4°C warmer than present, with the warmest temperature broadly between 11.5 and 10 ka."

  18. 6th, 8th, and 8th place..? I admit, I was tricked.

  19. Weatherman's Guide To The Sun is a great textbook that breaks away from the politicized and unfortunately internalized narrative by many humans that we are evil planet destroyers, so assuage your guilt by paying more money in taxes to government entities (aka corporations) creating this mental pollution, while they do absolutely nothing to change their behavior. Unsubscribe from the siren's song and its projections; learn how to discern actual scientific literature. Ignorance is a prison, and there are many prisoners in here defending the merits of their own psychological bars, which speaks to the power of the mind control, which will ultimately be surmounted, and relegated to history where it belongs.

  20. Here are some points offered within the context that a climate activist, Joe Biden, is now President of the United States; and that another climate activist, Jay Inslee, is now Governor of Washington State. In addition, our climate activist governor is now supported by a climate activist state legislature.

    (1) -- Reaching Net Zero energy for the entire world requires a credible strategy for convincing China, India, and all the Third World nations to abandon their reliance on fossil fuels. No such credible strategy has been offered by the Biden Administration.
    (2) -- Joe Biden has legal authority under current law to declare a climate emergency and to issue an executive order which imposes an immediate fossil energy lockdown on the American economy. He has not done so.
    (3) -- Reaching Net Zero in the power generation sector by 2035 requires that on average, one coal-fired or gas-fired power plant must be shut down each and every month between now and the year 2035. But the current pace of plant closures is far less than the pace actually needed to achieve Net Zero in the power sector by 2035.
    (4) -- A credible energy transition plan for Net Zero electricity by 2035 must identify each and every fossil power plant targeted for closure, including its scheduled closure date. No such plan has been published by the Biden Administration.
    (5) -- Fully replacing fossil power with wind & solar power by the year 2035 on a one-for-one megawatt-hour basis is clearly impossible. A credible plan is needed which identifies which portion of the shuttered power generation is to be replaced by wind & solar, and which portion is to be covered by strictly-enforced energy conservation measures. No such plan has been offered by the Biden Administration.
    (6) -- A credible energy transition plan must also identify the most promising candidate projects for new-build wind & solar farms. That plan must include the procurement and installation of battery backup for intermittent wind and solar energy production; and for numerous and extensive upgrades to the power transmission infrastructure. No such plan has been published by the Biden Administration.
    (7) -- Roughly 3% of the CO2 emitted globally is emitted from jet airliners, of which Boeing airliners represent approximately half of the world's airliner fleet. Airbus is under pressure to produce a hydrogen-powered airliner by the mid-2030's, and might actually get there if everything goes right. In contrast, Boeing has no firm plans whatsoever to produce an emissions free jet airliner in the near to mid-term future.
    (8) -- If Jay Inslee and our state legislators are truly sincere in their climate activism, they must demand that Boeing either cease production of fossil-powered jet airliners within a decade, or else lose all the tax and financial incentives they receive for building airliners in Washington State. Neither Jay Inslee nor our climate activist state legislators have done so.
    (9) -- California has adopted a series of carbon emission regulations governing petroleum product refining which will, consciously and deliberately, result in the eventual closure of all nineteen refineries now operating in that state. Governor Jay Inslee, the state legislature, and WS-DOE could adopt similar regulations targeted at the six refineries now operating in Washington State, thus forcing their eventual closure. They have not done so.

    Here is a question for all the climate activists who read and comment on the Cliff Mass weather blog: Is your personal energy, your personal commitment to the cause, and your activist enthusiasm not better spent in convincing Joe Biden, Jay Inslee, and the Washington State legislature to walk the talk of their professed concerns about climate change?

  21. Couple of comments: whether deaths due to excessive heat or cold depends on who you listen to. NOAA says heat is worse and uses excess deaths correlated to temperature. CDC says cold is worse but they do not filter for higher deaths due to flu and pneumonia in the winter or the impact of temperature distributrion. In addition if excess deaths vs temperature the data shows a clear correlation between excess heat and deaths but looking at cold there is no correlation on a daily basis. On a monthly basis deaths are higher but that is primarily due to seasonal diseases.
    Looking at the records of temps in excess of certain threasholds note that the heat wave is not over, 20 days and counting over 110. Also the record has been broken for consecutive days with lows above 90 which causes a lot of misery for those who can't afford or don't have air conditioning . They can't cool off much at night.

    1. Concerned...there is a deep and extensive literature showing that cold waves kill more than heat waves. Do a search on google scholar if you want to read them.. I am not saying heatwaves are pleasant or that they don't kill. But cold waves are much worse. And we seen the impacts here in Seattle with numerous homeless dying of exposure during the winter...cliff

    2. "By the way, extreme cold kills FAR more people each year than heatwaves, so global warming is actually reducing deaths from extreme temperatures (you won't hear much about this in the media!)"

      I heard an interesting discussion from some 'health experts' on NPR the other day about heat deaths, and how they are grossly underreported. The supposed primarily reason is due to it (heat) not even being an option for "cause of death" records at most hospitals, etc... so they are most often reported as other reasons.

      I'm not saying that heat outnumbers cold deaths, but its probably somewhat closer than some of the data suggests.

  22. When the baseline has shift the extremes get more extreme, it doesn't seem like rocket science.

    1. Right... the extremes get slightly worse because the baseline is higher. So a heatwave where highs are 38F above normal would have been 36F above normal.

    2. As I mentioned above Cliff, the current 1.1C global change is a 4F change in northern continental latitudes, so a 38F replaces a 34F, not at 36F. Don't be sloppy with your numbers please, it undermines the points you are making.

    3. Eric...you are not correct. Our temperatures in the NW have only gone about 1 C. We are not in the arctic....cliff

  23. Professor Mass:

    Three questions:

    1. Is it likely that as our atmosphere slowly warms our oceans will also slowly warm and the El NiƱo/La Nina cycles slowly alter?

    2. Is there evidence, and if so, what are the data, that atmospheric warming is related to recent flooding events globally, or are they, while spectacular and attention grabbing, within historic records of such phenomena?

    3. Last, is PBS falling prey to current media speculation?https://www.pbs.org/newshour/science/summer-of-record-breaking-heat-paints-story-of-a-warming-world-scientists-say

  24. Are marine heat waves, such as what is happening in Florida, also normal? It will be interesting to see if the coral survives.

  25. Heatwaves like the one we had a few years ago would not be possible without global warming so off course global warming is increasing the number of heatwaves. They tried to re-create the Great Northwest Heatwave with pre-industrial CO2 levels and the computer models couldn't do it. I don't belive its as simple as heatwaves are 2 or 3 degrees F hotter than they used to be I suspect that a weaker jet stream is getting stuck in extreme configurations making heatwaves several degrees hotter and cold snaps 3 or 4 degrees colder. You do have a valid point about the urban heat island and when considering whether the Pheonix heat is record setting we need to look at rural weather stations as well. I'm a construction worker and I don't understand how Pheonix can grow so quickly. I would never do construction work in Arizona, Doing construction work in Seattle is bad enough because they often refuse to run the A/C in these new buildings so if its 80 outside its dusty and 90 or 95 inside and they won't let us crack a window. I've heard that in arizona you get paid alot less, you have to work in 120 degree buildings, you often have to work at night/don't see much of you're family and they are very stingey about water breaks. If I were a construction boss in Arizona I'd build the outer the outer shell of the building and HVAC system in the cool season and do the electrical/plumbing/painting in the hot season with the A/C running but I don't think its done that way.

    1. They are very possible...just slightly worse because of global warming.

  26. There is an old saying that goes if you throw a frog in a pot of water and heat it up slowly, it won't jump out until it's too late.
    There's a new saying that goes if you throw a bunch of frogs in a pot of water and heat it up slowly, they'll argue about if it's really getting that much warmer and won't jump out until it's too late.

    1. Good. I like it even though I'm a skeptic. (a skeptic, not an unbeliever).

  27. Whoops! The media's stampede to report this July as hottest month on record before it's over made me ask you about it before it's over. You can wait till it's over :) .
    I *would* like to hear your view on claim June was warmest June ever.

    1. When they say "ever" it is usually the last 30-40 years...which is not ever!

  28. Cliff, I agree with most of what you're saying about global warming. But I've lived in the Seattle area for 45 years now, and can remember telling my friends and family back East that we rarely if ever needed air conditioning here. Now, it seems that we do, for extended periods of time every summer. This to me seems like substantial (albeit anecdotal) evidence that the effects of global warming are somehow greater than the data suggest. Perhaps the data, and the processes for collecting same, need a review?

    1. Well, temperatures are about 2F warmer than 45 years ago...perhaps that is what you are sensing. I suspect you are living in a different place now..which could explain things as well.

  29. I'm curious, Cliff. What would be a handful of indicators, measurements or observations that you would need to see before you'd say Global Warming/Climate Change had become a serious, even existential problem?

    1. Existential problem? Evidence of feedbacks or amplification that could not be handled by mankind. Right now deaths from extreme weather is DOWN 95%. If the trend reversed and there were rapid increases in loss of life

    2. Thanks Cliff. You might be interested in checking out consensus.com results: https://bit.ly/3OsutGz

    3. Such a "consensus" approach is meaningless. Not the way science is done. Often the consensus is wrong... has happened again and again.

  30. Cliff, you may be right on these particular points, but what exactly is this "agenda" you think is being pushed? The media hypes all kinds of stories/issues because doing so gets clicks. That, I'll give you and no one likes that. But beyond that, I don't buy that there's any other agenda here. And as far as it goes, I don't mind a bit of media hype on this issue if it gives people and/or governments a sense of urgency regarding anthropogenic climate change.

  31. Cliff - thought you might find this article interesting. https://azfreenews.com/2023/07/city-of-phoenix-knew-its-cool-pavement-would-make-people-hotter/


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

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