This is what the media is claiming, this is what ‘scientists’ are claiming. This is what Matt McGrath at the BBC is claiming:
The searing heat that scorched western Canada and the US at the end of June was “virtually impossible” without climate change, say scientists.
In their study, the team of researchers says that the deadly heatwave was a one-in-a-1,000-year event.
But we can expect extreme events such as this to become more common as the world heats up due to climate change.
If humans hadn’t influenced the climate to the extent that they have, the event would have been 150 times less likely.
Scientists worry that global heating, largely as a result of burning fossil fuels, is now driving up temperatures faster than models predict.
The World Meteorological Organization (WMO) has drafted guidelines on the definition and monitoring of extreme weather and climate events (WMO, 2018). The recommended definition of a heatwave is:
‘A period of marked unusual hot weather over a region persisting for at least three consecutive days during the warm period of the year based on local climatological conditions, with thermal conditions recorded above given thresholds.’In addition, the characterisation of events should consider the following aspects:
Magnitude: The departure from normal, reflecting the climatological extremity of the event.
Duration: Measuring the duration of elevated temperatures.
Extent: The geographical extent of the heatwave.
Severity: Indicating potential damages and impacts of the event.
The NW Pacific heatwave might (just) have qualified on this basis as it occurred over a large region from the 27th to 29th June, but the authors of the WWA attribution analysis have chosen instead to concentrate not on the 3-day consecutive temperatures (including the all important minimum overnight temperatures) but just on the maximum daily one day annual temperature:
Note the highlighted text. In order to get the attribution out fast (whilst the event was still fresh in the minds of the public and presumably to get maximum media attention), they chose to concentrate only on the headline maximum temperatures, which gained most attention in the press. It would have been a more complex and lengthy analysis to concentrate on 3-day temperatures consistent with the actual WMO definition of a heatwave. Also, they deliberately limited their analysis to urban areas, excluding those wild regions where the daily maximum temperatures might not have been expected to be so extreme on account of the well documented and studied urban heat island effect. Indeed, two of their chosen station locations were situated at airports serving large cities; you know, those great slabs of concrete and tarmac, flat as a pancake, where huge jets with big engines are taking off and landing daily.
Temperature observations were collected to directly assess the probability ratios and return periods associated with the event for the three major cities in the study area; Portland, Seattle, and Vancouver. Observing sites were chosen that had long homogenized historical records and were representative of the severity of the event by avoiding exposure to nearby large water bodies. Sites were also chosen to be representative of the populous areas of each city to better illuminate impact on inhabitants. For Portland, the Portland International Airport National Weather Service station was used, which has continuous observations over 1938–2021. The airport is located close to the city centre, adjacent to the Columbia River. The river’s influence is thought to be small and the water temperature is warm by June. For Seattle, Seattle-Tacoma International Airport was chosen, which has almost continuous observations 1948–2021, among the longest records in the Seattle area.
It’s odd, is it not, how they are at pains to avoid large bodies of water which might have a cooling effect, but they’re OK with choosing stations located in the middle of bloody great stretches of heat absorbing concrete and tarmac! Here’s what the cartoonist Josh has to say about that:
I’ve pointed out recently how the choice of event definition can affect the outcome of the attribution, by WWA’s own admission:
Addendum: Event definition
WWA have an article entitled ‘Pathways and Pitfalls in extreme event attribution’. They point out that the definition of the extreme event is very important in determining the result of the attribution. Defining the event is very much a choice of the people doing the analysis.
It’s almost certain that WWA will choose to define this extreme event only with reference to extreme daytime temperatures in the regional Pacific Northwest.
Was I right?
Here is the area studied:
To get an idea of just how extreme the departures were from the long term average in this study area, just look at this graph produced by the authors:
The red line is the maximum recorded temperature in any given year. The green line is the running 10 year average. Note that the series only covers from the period from 1950 (71 years). The green line is representative of the generalised warming in the study region with reference to maximum summer temperatures. As you can see, it’s of the order of 2 or 3 degrees C over the 70 year period to 2020, with annual departures from the trend line (positive or negative) amounting to no more than 4 degrees, the largest departures being negative values in the 1960s and 1970s. Then we get to 2021 and the red line jumps up 6 or even 7 degrees above the baseline! That’s huge. It just cannot be related to the observed slightly increasing long term trend. It can’t. Something else has to be in play, be it a ‘black swan’ extremely low probability event generated randomly or be it due to some very specific meteorological set up (perhaps amplified by other factors, e.g. land use, previous drought conditions), unique in the observed period.
But this does not stop the intrepid team at WWA from torturing the data to fit an extremely dubious statistical distribution. Yes, they actually squeeze this glaringly unusual and extreme departure from normal into a new statistical time series and by so doing they arrive at a highly improbable estimation of the return time for such an extreme event purportedly based upon this statistical time series. I’m actually gobsmacked. They own up to their sins in the paper, which is at least honest, but of course the media coverage (with the assent and cooperation of the authors themselves) is exceptionally dishonest, conveying the impression that this ‘scientific’ study revealed a strong link between this event and global warming.
So, as opposed to simply excluding the anomalous 2021 from the statistical analysis, they decided to try and provisionally include it, using an alternative approach, but this still didn’t give the ‘right’ answer because it implied that the event was either a ‘black swan’ with a return time of 10,000 years, even in the current climate, or that it was due to non-linear (i.e. dynamical/meteorological) effects which are not fully understood. Having to wait 10,000 years for another similar event is just not scary enough! So, the authors did this instead:
They deliberately chose an area where the heat was particularly extreme and they shoe-horned this extreme event to fit a highly improbably statistical series to arrive at a highly improbable estimate of a return time. Now, even a thousand years doesn’t sound that scary, but with projected global warming of another two degrees in 20 years time, which ‘could happen’, we could then be seeing a heatwave like this every 5 or 10 years. Friederike Otto, one of the paper’s authors, explains:
Co-author Dr Friederike Otto, from the University of Oxford, explained what the researchers meant when they said the extreme heat was “virtually impossible” without climate change.
“Without the additional greenhouse gases in the atmosphere, in the statistics that we have available with our models, and also the statistical models based on observations, such an event just does not occur,” she explained.
“Or if an event like this occurs, it occurs once in a million times, which is the statistical equivalent of never,” she told a news briefing.
This type of research, which seeks to determine the contribution of human-induced climate change to extreme weather events, is known as an attribution study.
According to the analysis, if the world warms by 2C, which could happen in about 20 years’ time, then the chances of having a heatwave similar to last week’s drop from around once every 1,000 years to roughly once every 5-10 years.
OMG, hit the panic button! We’re all gonna fry in 45C plus heatwaves if we don’t stop driving cars and get rid of our gas boilers and pay 10 times what we pay now for electricity which is produced exclusively by sustainable ‘sea breezes’ and food-crop-destroying arrays of solar panels. You see we don’t really need to travel, heat or eat, cheaply; what we do need to do is to save the damned planet from Thermageddon – and fast!
I was going to go through the entire paper in one go, exposing the bad science, bit by excruciating bit, but this is enough for now. I’ll write another post (or two) in the next day (or two)