Revisiting The Exceptional Pacific North West Heatwave Part 2

Reconfiguring The Impossible

Extreme weather attribution ‘scientists’, who would have us all believe that heatwaves, storms, floods and deluges all bear the unmistakable fingerprint of man-made global warming, have a problem: many of these events are ‘statistically implausible’ (even impossible) in today’s warmer climate. This means that attributing the event to a rise in local ambient average temperature of 1 or 2 degrees is also implausible or impossible.

Nicholas Leach is a postdoctoral researcher in climate science at the University of Oxford and he recently published this article at the Conversation:

‘Statistically impossible’ heat extremes are here – we identified the regions most at risk

He starts off talking about the Pacific NW heatwave in June 2021:

In the summer of 2021, Canada’s all-time temperature record was smashed by almost 5℃. Its new record of 49.6℃ is hotter than anything ever recorded in Spain, Turkey or indeed anywhere in Europe.

The record was set in Lytton, a small village a few hours’ drive from Vancouver, in a part of the world that doesn’t really look like it should experience such temperatures.

Lytton was the peak of a heatwave that hit the Pacific Northwest of the US and Canada that summer and left many scientists shocked. From a purely statistical point of view, it should have been impossible.

I’m part of a team of climate scientists who wanted to find out if the Pacific Northwest heatwave was unique, or whether any other regions had experienced such statistically implausible events. And we wanted to assess which regions were most at risk in future. Our results are now published in the journal Nature Communications.

Leach outlines just why the event was statistically impossible:

One of the most important questions when studying these extreme heatwaves is “how long do we have to wait until we experience another similarly intense event?”. This is a challenging question but, fortunately, there is a branch of statistics, called extreme value theory, that provides ways in which we can answer that exact question using past events.

But the Pacific Northwest heatwave is one of several recent events that have challenged this method and should not have been possible according to extreme value theory. This “breakdown” of statistics is caused by conventional extreme value theory not taking into account the specific combination of physical mechanisms, which may not exist in the events contained in the historical record.

Note my bold. Something other than the local rise in mean temperature (climate change) is causing these events. As we saw in Part 1, in the case of the Pacific NW, the main driver was atmospheric circulation, followed by soil moisture deficit. ‘Global warming’ contributed just roughly 6% to the observed remarkable anomalous high temperatures. As I say, this is a problem if you’re trying to claim that these extreme heatwaves are being caused by ‘global heating’. You end up lying to the public, which is what attribution scientists and the media have been doing. But they know that sooner or later, the gaff will be up and they’ll end up with egg on their faces, just like NASA scientist Gavin Schmidt in Part 1. Science marches on. It will not be denied.

Hence this latest effort from Leach. But he’s not serious. He’s twisting the facts, claiming on the one hand that these events are statistically impossible but that they are paradoxically becoming more frequent and widespread, and then attempting to shoehorn them into an absurd new theory of how global warming is making the statistically impossible suddenly possible because ‘non linear effects’, or something. He doesn’t give much away in his Convo article though, merely saying this:

The first is that statistically implausible heatwaves can occur anywhere on the Earth, and we must be very cautious about using the historical record in isolation to estimate the “maximum” heatwave possible. Policymakers across the globe should prepare for exceptional heatwaves that would be deemed implausible based on current records.

Perhaps he was too embarrassed. You have to look at his recent study to see what he’s up to, suggesting that regions which have not so far not experienced these ‘statistically implausible’ heatwaves should prepare to do so, whilst tenuously suggesting that some ‘non-linear effect of climate change’ is at work, without explaining what that might be, but definitely giving the impression that it’s climate change which we should be worried about with reference to these ‘statistically implausible’ events. Incidentally, the paper is co-authored by Julia Slingo, infamous former chief scientific officer at the Met Office, who liked to say that ‘all the evidence points to’ global warming being the cause of UK floods. The abstract sets the scene:

Heatwaves are becoming more frequent under climate change and can lead to thousands of excess deaths. Adaptation to extreme weather events often occurs in response to an event, with communities learning fast following unexpectedly impactful events. Using extreme value statistics, here we show where regional temperature records are statistically likely to be exceeded, and therefore communities might be more at-risk. In 31% of regions examined, the observed daily maximum temperature record is exceptional.

The objective is clearly alarmist:

The aim of this study is to identify which regions globally have perhaps been lucky not to have experienced higher temperature extremes so far. We argue that these regions may be particularly vulnerable to the impacts of a record heatwave because there has been no need for adaptation thus far.

They go on to talk about the Pacific NW heatwave:

In June 2021, western North America experienced a record-breaking heatwave. In Lytton, British Columbia, temperatures of 49.6 °C were observed on June 29th, breaking the previous record by almost 5 °C²⁸. The heatwave was associated with an unusual circulation pattern, with a blocking anticyclone leading to a stagnant warm air mass²⁹.

A rapid attribution study found the event was so far beyond what had been previously observed that it was deemed virtually impossible without climate change³⁰.

What they don’t make clear is that the event was virtually impossible even with climate change. I explained this in the post here:

Leach, Slingo et al say that we should expect regions which have not so far experienced ‘statistically implausible’ heatwaves to experience one soon, but they handwave as to the reason why:

The 2021 western North America heatwave is exceptional, almost 2 °C beyond any other region (Figs. 2a, 3b). But it is not the only region displaying a record event beyond the statistical fit; we find the current record is exceptional in 41 of the 136 regions, ~31% of the land surface (Fig. 2b). These implausible regions are spread across continents and latitudes—there is no apparent spatial discrimination. The events are also spread across the assessed time period but with more events in the later decades, possibly caused by greater availability of satellite data but potentially also by a non-linear signature of climate change (Fig. 3).

They don’t know basically. But they are fixated on climate change, so have a stab in the dark by suggesting a “non linear signal of climate change”.

We know what caused the extreme high temperatures in the Pacific NW heatwave and it wasn’t global warming - it was largely atmospheric dynamics with a significant contribution from depleted soil moisture. What we don’t know is whether changes in regional or global atmospheric circulation brought about by either solar variability and/or internal multidecadal variability are contributing to making these exceptional events more likely by altering the dynamics. What we don’t know is if changing land use and urbanisation are making these exceptional events more likely and more extreme. What we don’t know is if there is a link between record breaking temperatures and the fact that many of them seem to be measured at airports! That’s what scientists should be looking at, not obsessing about proving a link with global warming which doesn’t exist.