Turning Down The Heatwaves Transcript

Narrator:

There’s nothing new about heat waves. Except, perhaps, for the fact that people seem to have started thinking they’re new, and that they’re caused by climate change.

John Robson:

And then there are the people who think they’re caused by racism as well as climate change. But of course heat waves are nothing new. To give just one example, the European heat wave of summer 1757 resulted in the hottest July ever recorded in Paris before or since, and one of the hottest ever in Central England, prompting English novelist and politician Horace Walpole to say, after going for a walk in his garden, “I thought I should have died of it”.

Narrator:

Or to give another example, this chart of UK heat wave data from 1961 to 2020 shows that while there has been a cluster of recent years with weather above 32°C, the worst year for widespread heat was back in 1976, while the year with the most readings above 34°C was 1990.

John Robson:

We could also point to the blistering summer of 1473 in Europe, despite the onset of the Little Ice Age. Or the ancient Romans coining the term “dog days” (“dies canincula”) for the sweltering July/August weather that they had from around 250 AD to 400 AD.

So you get the idea, in case you needed any convincing that heat waves have been around since the invention of heat. But now, whenever summer begins and we get, of all things, a heatwave, it’s automatically attributed to you-know-what, and from there the finger of blame quickly points straight at you.

And you have to admit that heatwaves can feel like damnation. The air becomes hot and oppressive, moving is unpleasant, sitting still is unpleasant, and you might start thinking you’ve been condemned to the fires of hell for your carbon sins. I mean, at least in winter you can add a layer. In summer what can you do?

Well, fellow sinners, here’s something I think we can do. We can take time for some cool reasoning concerning heatwaves. I’m John Robson, and this is a Climate Discussion Nexus fact check on Climate Change and Heatwaves.

Narrator:

Are heatwaves caused by climate change? Are they becoming more common or not? What even is a heatwave?

All these questions are all linked together, because before you can answer the first two questions you need to answer the third one, because you can’t count something until you know what you’re looking for. And the problem is there’s no one single, standard definition of a heatwave.

Loosely speaking a heat wave is a period of unusually warm weather. But how warm does it have to be, or how much warmer than normal, and for how long? The UK Met Office says the heat has to last for 3 days or more, and in the UK, it has to be above a threshold that ranges from 25 to 28°C depending on the location. Meanwhile the U.S. National Weather Service says two days is enough to make it a heat wave. And the World Meteorological Organization says it’s only a heat wave if it lasts for at least five days and gets at least 5°C above the local average temperature.

As for whether they’re becoming more common, in its 2013 report, the UN’s Intergovernmental Panel on Climate Change or IPCC, said it’s likely the number of heatwaves in many parts of the world has risen since 1950. However, they also noted “confidence on a global scale is medium owing to lack of studies over Africa and South America, but also in part owing to differences in trends depending on how heatwaves are defined”

And by the way, the phrase “medium confidence” in IPCC terminology doesn’t mean they’re fairly sure. It just means it’s 50-50.

In their most recent report they were more confident of an increasing global trend. But once again only since 1950. Before that, there just isn’t enough data for most countries.

John Robson:

Of course, a trend since 1950 could be meaningful. But it could also be meaningless, if heatwaves fluctuate on a long-term basis. And mind you, we do have longer-term records from the United States. It’s one of the few places in the world that has daily temperature records from a lot of spots going back to 1900.

And those records show that heatwaves were much more severe and frequent in the 1930s. Then they fell until about 1960, and they’ve gone up since, but only a little. They’re still nowhere near where they were a century ago.

So if you just look at data for the last few decades, you might conclude, as the IPCC did, that heatwaves are getting worse. But, without long term data for other countries, we can’t say if they’ve actually become less frequent and severe globally over the last century, as they have in the United States. And we have nothing like this kind of data to tell us whether significant variations from the average were common in the 18^th century, in the 11^th century, or in the time of Socrates and Aristotle.

And now, a word from our sponsor, and yes again, that’s you. All the people out there who are already backing our work and all the people who are subscribing. More than 84,000 of you on YouTube alone, we’ve had almost 10 million views. But we need to keep up with momentum. And that’s why I interrupt to pass the hat to those of you who aren’t already backers, and say please make a pledge, one time or monthly, $3, $5, $10, whatever you can afford, so we can continue to push back against the climate cult and win this battle.

Narrator:

So let’s leave aside the question of long term trends, and try to find out why heat waves occur. While summer heat is an important factor, meteorologists tell us that the key ingredient is high air pressure.

A stable zone of high pressure can form something called an atmospheric block, which as the name suggests, sits in place blocking air flow, deflecting the winds around it, preventing them from bringing cooler air in and breaking up the high-pressure zone. Blocking events are key ingredients for allowing extreme heatwaves to form.

John Robson:

It’s not high temperature that causes a heat wave, it’s high pressure combined with atmospheric blocking. Yes, if the entire atmosphere is a degree warmer today than it was a century ago due to greenhouse gases, or indeed for any other reason, then it stands to reason that a heatwave will also be a degree warmer than it otherwise would have been. But it doesn’t mean heatwaves would be more common, or more significant departures from the average temperature, unless it can be shown somehow that a warmer average temperature, more CO2, or both, increases the likelihood of high-pressure zones, atmospheric blocking, or both.

Narrator:

If summer warmth and greenhouse gases were enough to cause heatwaves, there would be nonstop heatwaves all summer long, everywhere. But there aren’t. They’re still somewhat rare events, because the conditions that create them are rare.

As for whether those conditions are becoming more common, surprisingly, despite the common claim that heat waves will be more common under global warming, scientists believe that one of the key components of heat waves, atmospheric blocking events, will become less common under climate warming. As one study put it, “Climate models generally predict a small decline in blocking frequency under anthropogenic climate change… Enhanced warming both in the tropics and over the Arctic act to reduce the frequency of blocking”.

But people still look for a link between greenhouse gases and heat waves, and in one prominent recent case even claimed a direct cause and effect connection.

That case was the extremely intense heatwave over the Pacific Northwest region of the U.S. and Canada in late June 2021. It reached from Oregon all the way up to northern British Columbia, and inland as far as Saskatchewan, and temperature records were broken all throughout the region. In particular, the town of Lytton, BC reached 49.6°C, the highest temperature ever recorded in Canada.

The heat wave was a very severe weather event, causing forest fires, crop failures, flooding due to rapid snow melt, and extensive injuries to people, including hundreds of deaths.

John Robson:

A week after the heatwave, a team of scientists released a preliminary study in which they concluded the event was “virtually impossible” without human-caused climate change. And, of course, this claim was immediately picked up by media around the world.

But you’ll notice that it didn’t come from the “peer-reviewed” scientific literature, or after careful analysis of all the evidence. Instead, it came from a web site called “World Weather Attribution” after a hasty and preliminary glance at the data.

Now, to be clear, the Pacific Northwest heat wave was exceptionally hot. There is nothing in the hundred years or so of temperature records for that region that matches it. Well, not quite. No other heatwave got as hot at its peak. But the 2021 event only lasted for three days, at least on the West Coast, whereas other heat waves there historically didn’t get as hot, but they lasted longer.

Narrator:

In Portland, for instance, a heat wave in 1941 sent temperatures above 100°F for five full days. But the fact that the 2021 heat wave was so exceptional also makes it hard to analyse using standard statistical methods. Basically you have a sample of one.

John Robson:

Obviously, it was rare and unusual. But also, obviously, it happened, so it wasn’t impossible. Beyond that it gets very difficult to say anything definitive, and scientists themselves are reluctant to do so.

At least some of them. A few months after the heat wave, the World Weather Attribution people got around to submitting their study to a scientific journal. They sent it to one called Earth Systems Dynamics, which has the interesting practice of posting their peer review reports online. And in this case one of the reviewers apparently didn’t give it much attention, and simply said it was fine and should be published. But the other reviewer studied it closely and came to a very different position.

Narrator:

“Except for the relevance of the topic, I don’t see any reason for the publication of this manuscript. The quality of the study and of the manuscript is not good enough for publication in a peer reviewed scientific journal” the reviewer began.

John Robson:

The reviewer then pointed out that there are only about 72 years of daily temperature data for the whole region, so all the authors can conclude is that the heatwave was a once-in-72-year event. Maybe it’s a once-in-a-millennium event or even rarer, but we have no way of knowing. Indeed, if we had data going further back, we might find instead that it was actually a once-in-a-quarter-century event, and it’s weird that we’ve only had one in the last seven decades. We just don’t know.

To underline how unscientific this “scientific” paper was, let us share some more comments from that second reviewer.

Narrator:

“The results provide almost no valuable information, thus the conclusions make no sense. Considering the inadequate methodology and the huge uncertainties in the return periods and probability ratios, I’m afraid that the main conclusions are not trustworthy… One of the final conclusions is that ‘the event is estimated to be about a 1 in 1000 year event in today’s climate’. I point out that one cannot obtain correct return level estimates for an event occurring on average once every 1000 years based on 72 values of annual maxima… There is too much uncertainty in these results making them not very useful.”

John Robson:

Well, that’s awkward. The authors had already blasted their conclusions out to the global media and got lavish publicity for it. Faced with brutal rejection of their paper, they then wrote a response in which they conceded all the criticisms, but begged to be able to publish it anyway as long as they added in all kinds of disclaimers and caveats to the effect that they can’t really be sure if any of their conclusions are correct. And, they argued, it was important to publish a study explaining the many limitations of this kind of research.

For instance, their response contained this passage:

Narrator:

“The reviewer identified the reason for why this study was so difficult, given the extremeness of the event and the relatively small number of samples, but we see this as a strong argument to publish this manuscript in a peer reviewed journal, provided we recognize these difficulties… It is very important to publish the analysis results for this heatwave event and, especially due to the discussed challenges with fitting a distribution to the data, to point out open research questions arising through analysis of this event that need more in depth research. We show and acknowledge the limitations of the approach, and we now conclude in Section 6.1 (old Section 7.1): ‘Further research on this and other exceptional heatwaves is needed to determine whether this estimate is indeed realistic, i.e., whether or not we should reject the assumption that this heatwave occurred by chance at this location.’”

John Robson:

So, what they ended up publishing was the original analysis that the reviewer called meaningless and untrustworthy, padded with a bunch of disclaimers cautioning the reader that they really don’t know why the heatwave was so extreme, and whether the method they used, called Generalized Extreme Value or GEV analysis, actually works.

They even admitted that the weather conditions giving rise to the heat wave were not unusual, even though the resulting temperatures were, for reasons they couldn’t explain. Far from saying they had figured out the cause, and could blame the heatwave on man-made climate change, the authors now said they didn’t know why the region got so hot.

Narrator:

“Follow-up research will be necessary to investigate the potential reasons for this exceptional event and the consequences for assumptions for these fits (see also the discussion in Sects. 6 and 8). Also, further research is needed into the limitations of standard GEV analysis on annual maxima with short records and very extreme values.”

“Despite being a record, this extreme high-pressure system—a feature sometimes called a ‘heat dome’ – is not that anomalous given the long-term trend…. We conclude that the 28 June circulation is probably not exceptional, while temperatures associated with it were.”

John Robson:

Of course, it goes without saying that not one of the media outlets that reported on the original claim that greenhouse gases were behind the heatwave went back and corrected the record once this extraordinary admission by the authors was put into print. The initial claim produced a wave of hysteria and a criticism block, and the subsequent correction generated a wave of silence.

Narrator:

Scientists, meanwhile, continued to debate what had caused the extreme heat. Indeed, a little while later another team of climate scientists, led by Emily Bercos-Hickey of the Lawrence Livermore National Lab in Berkeley U.S.A., published an analysis which proposed that in addition to the high pressure zone and blocking event, an atmospheric river had made landfall over Alaska, delivering a large amount of water vapor into the Pacific Northwest, raising the humidity of the affected region and triggering a feedback loop that pushed temperatures off the charts.

John Robson:

A blocking event isn’t rare, nor is an atmospheric river. But the two happening at the same time over the same region apparently is. And climate change, the authors said, was irrelevant. Yes, the heatwave could be viewed as “virtually impossible” without global warming. But it was virtually impossible with it as well. Sometimes weird things happen.

The Berkeley team even went out of their way explicitly to reject even the heavily qualified conclusions of the World Weather Attribution study, referenced here as “Philip et al. 2021”.

Narrator:

“Given that an in-sample GEV distribution is a poor fit to the [temperature] data and that the combined effects of the atmospheric blocking pattern and anomalous Atmospheric River were likely very rare if not unique, we conclude that there should be little confidence in attribution statements based on in-sample GEV formulations. Philip et al. (2021) argued that the temperatures reached during the PNW heatwave were “virtually impossible” without climate change.” However “no statement about the role of greenhouse gases should be made from this technique. The statistical analysis presented here only supports an attribution statement that these temperatures were virtually impossible under any previously experienced meteorological conditions, with or without global warming.”

John Robson:

These authors did figure that greenhouse gases may have added 1°C to the peak temperatures of the heat wave. But that’s all they thought climate change contributed. Then another study by a team of Swiss climatologists and statisticians showed that that the method of analysis used by the World Weather Attribution crowd exaggerates the rarity of major events generally by overestimating the so-called “return period”. That’s the gap between the times when such events could be expected to happen.

Narrator:

“The tendency to overestimate the return period of observed extreme heatwave events may fuel the impression that seemingly impossible heatwave extremes are currently clustering at an unprecedented rate.”

John Robson:

Still another analysis took note of the fact that, while the Pacific Northwest heat wave was a rare event, the world is a big place. So, even if an event is rare in one place, over the course of a hundred years it’s to be expected that there will regularly be rare events taking place somewhere.

For instance, if you pick up a coin the odds of tossing heads 20 times in a row is just under 0.0001%. So you could say it was “virtually impossible”. But if a million people around the world were tossing coins every day, we’d expect a run of 20 heads somewhere at least once a day.

So, on the basis of sound statistical analysis this last study’s authors said that in the absence of physical evidence linking the heat wave to climate change, it was just plain old bad luck. No, really. Those are their words:

Narrator:

“Assuming a similar event does not occur in the near future, and without a clear physical link to climate change, the most likely explanation remains that the weather event itself was ‘bad luck.’ While climate change added additional warming to the picture (approximately 1.5°C since 1960), the event would have been severe even without the climate change signal.”

John Robson:

Again, there was no worldwide press coverage for any of these later studies. As the old saying goes, a headline about heatwaves can get all the way around the world before the truth has got its flip flops on. But the truth, like the proverbial tortoise, plods on and ultimately wins the race as the hare gets distracted.

What the real scientific studies showed was that the headline saying the heat wave was “virtually impossible” without manmade climate change should have added that it was also virtually impossible with it. So, it was a very rare fluke. But given the combination of circumstances it would have happened and been extremely severe with or without global warming, man-made or natural.

Now it’s safe to predict that there will be a heatwave somewhere around the world next year, maybe even an extreme one. The basic weather pattern giving rise to it, atmospheric blocking and a stable high-pressure ridge, will be behind it, but there may be other factors amplifying the warmth, such as extra humidity, or dry soils, or something else.

Cautious scientists will wait until they have sufficient data before drawing any firm conclusions. But it’s also safe to predict that the ambulance-chasing hares at websites like World Weather Attribution will rush straight to the microphones to blame you and your gas stove for the whole thing.

It's not science, it’s advocacy, and the best response is to stay cool and tune it out, because heatwaves may be bad luck, but believing nonsense is a bad choice.

For the Climate Discussion Nexus I’m John Robson, and that’s our CDN Fact Check on heatwaves.