Extreme weather attribution

NW Pacific Heatwave Attribution – Multiple Climate Model Failure

The authors describe the models used thus:

Model simulations from the 6th Coupled Model Intercomparison Project (CMIP6; Eyring et al., 2016) are assessed. We combine the historical simulations (1850 to 2015) with the Shared Socioeconomic Pathway (SSP) projections (O’Neill et al., 2016) for the years 2016 to 2100. Here, we only use data from SSP5-8.5, although the pathways are very similar to each other over the period 2015–2021. Models are excluded if they do not provide the relevant variables, do not run from 1850 to 2100, or include duplicate time steps or missing time steps. All available ensemble members are used. A total of 18 models (88 ensemble members), which fulfill these criteria and passed the validation tests (Section 4), are used.

SSP5-8.5 means Shared Socioeconomic Pathway 5 combined with RCP8.5, leading to 8.5W/m2 GHG forcing at the earth’s surface by 2100. It is a very extreme worst case emissions/atmospheric GHG concentration scenario, not at all realistic but, for the 5 years from 2016-2021, when it is used in the models, it doesn’t make that much difference from other more realistic scenarios. Where it does make a great deal of difference is in the assessment of how much more frequent such extreme heatwaves will be over the coming century, which the authors rely on to make the alarming claim that such events will happen every 5-10 years by 2100.

The authors used other models as well for simulating the historical period:

In addition to the CMIP6 simulations, the ensemble of extended historical simulations from the IPSL-CM6A-LR model is used (see Boucher et al., 2020 for a description of the model). It is composed of 32 members, following the CMIP6 protocol (Eyring et al., 2016) over the historical period (1850-2014) and extended until 2029 using all forcings from the SSP2-4.5 scenario, except for the ozone concentration which has been kept constant at its 2014 climatology (as it was not available at the time of performing the extensions). This ensemble is used to explore the influence of internal variability.

We also examine five ensemble members of the AMIP experiment (1871-2019) from the GFDL-AM2.5C360 (Yang et al. 2021, Chan et al. 2021), which consists of the atmosphere and land components of the FLOR model but with horizontal resolution doubled to 25 km for a potentially better representation of extreme events.

They describe the basic attribution procedure as follows:

As discussed in section 1.2, we analyse the annual maximum of daily maximum temperatures (TXx) averaged over 45°N-52°N, 119°W-123°W. Initially, we analyse reanalysis data and station data from sites with long records. Next, we analyse climate model output for the same metric. We follow the steps outlined in the WWA protocol for event attribution. The analysis steps include: (i) trend calculation from observations; (ii) model validation; (iii) multi-method multi-model attribution and (iv) synthesis of the attribution statement.

The first stage of the process above is known as ‘detection’, i.e. the detection of the event from observations. Observations are then compared to models to arrive at an attribution. Here is what the authors say about the detection:

The detection results, i.e., the comparison of the fit for 2021 and for a pre-industrial climate, show an increase in intensity of TXx of ΔT = 3.1 ºC (95% CI: 1.1 to 4.7 ºC) and a probability ratio PR of 350 (3.2 to ∞).

They then introduce the section on the multi-model attribution:

5 Multi-method multi-model attribution

This section shows probability ratios and change in intensity ΔT for models that pass the validation tests and also includes the values calculated from the fits to observations (Table 2). Results are given both for changes in current climate (1.2°C) compared to the past (pre-industrial conditions) and, when available, for a climate at +2˚C of global warming above pre-industrial climate compared with current climate. The results are visualized in Section 6.

Here are the results:

Note that the observed change intensity of the heatwave in the study area is 3.1C, according to observations (ERA5). The best estimate modelled change in intensity is anywhere between 0.22C and 2.6C, i.e. none of the models actually capture the observed change in intensity. The mean best estimate change in intensity of all the models is 1.77C, which is just 57% of the actual observed change. Thus, the models don’t come close to simulating actual reality. But again, this does not deter the authors from going ahead with an attribution anyway. They call it a hazard synthesis. I call it a hazardous synthesis!

6 Hazard synthesis


We calculate the probability ratio as well as the change in magnitude of the event in the observations and the models. We synthesise the models with the observations to give an overarching attribution statement (please see e.g. Kew et al. (2021) for details on the synthesis technique including how weighting is calculated for observations and for models).

Results for current vs past climate, i.e. for 1.2°C of global warming vs pre-industrial conditions (1850-1900), indicate an increase in intensity of about 2.0 ˚C (1.2 ˚C to 2.8 ˚C) and a PR of at least 150. Model results for additional future changes if global warming reaches 2°C indicate another increase in intensity of about 1.3 ˚C (0.8 ˚C to 1.7 ˚C) and a PR of at least 3, with a best estimate of 175. This means that an event like the current one, that is currently estimated to occur only once every 1000 years, would occur roughly every 5 to 10 years in that future world with 2°C of global warming.

So there you are. A highly dubious statistical analysis combined with an observation/model synthesis using models which all fail to capture the observed intensity of the actual event, which mysteriously translates into the statement that the NW Pacific heatwave would be ‘virtually impossible without climate change’ and furthermore that we can expect such intense heatwaves every 5 to 10 years by the end of the century if we don’t urgently reduce emissions. What a farce and an insult to proper science, but it did its job, i.e. generated alarming, but highly misleading headlines around the world re. the supposed irrefutable connection with this extreme weather event and man-made climate change.

Unraveling ‘Attribution’ Pseudoscience – No, the NW Pacific Heatwave Would NOT Have Been ‘Virtually Impossible’ Without Global Warming

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.

I’m claiming BS, so let’s get straight to it. First of all, this analysis was not an analysis of a heatwave in the technical sense. According to the UK Met Office:

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)

#Rep 4 – One Day Heatwave at Cambridge Botanical Gardens Made 20 Times More Likely By Climate Change, Experts Say

Posted on  by Jaime JessopIn UK Met OfficeUncategorized9 Minutes Read

I’ve already covered the attribution study recently rushed out by scientists with regard to the very hot spell of weather in June. Now most of those same scientists have published a second attribution study which focuses on the 3 or 4 very hot days in northern France and Europe and the one very hot day in the UK on July 25th. Are we going to get a ‘It was climate change wot dunnit’ attribution study every time it gets hot in summer now? Looks like it.

As usual, the global media have given maximum coverage to this additional study which supposedly demonstrates that man-made global warming had its grubby fingerprints all over the second record breaking heatwave in Europe this summer. It’s as bad as, if not worse, than the original study and of course the headline claims that climate change made Europe’s July heat wave up to 3 degrees Celsius hotter, that the heat in France and Holland was made up to 100 times more likely and that in Cambridge up to 20 times more likely is pure hype.

Atmospheric blocking caused the July heatwave, just as in June

The authors say:

In a relatively similar way to the June case, the July heat wave occurred due to a ridge across western Europe (highly amplified Rossby wave), together with a low-pressure system developing offshore the Iberian peninsula, as shown in Figure 2. This weather pattern induced intense advection of hot air from North Western Africa across Spain to France (Figure 3) and then Germany and the Benelux, eventually reaching Scandinavia a few days later. In contrast to the June heatwave, this July heatwave was accompanied by severe drought conditions in areas such as France (a majority of French territory was under drought regulation measures), which might have been a confounding factor given that dry soils are suspected to cause an additional temperature increase at regional scales due to land-atmosphere feedbacks (Seneviratne et al., 2010).

So, once again, atmospheric dynamics play a significant role in directly causing the intense heat, just as we have seen they did in 2003 and 1947, although for summer 2019, the ‘heatwaves’ have been of very much shorter duration and I can find no reports of fatalities due to heat exhaustion for that very reason.

The attribution analysis was not done for Europe: it was done using average data from France only plus five individual weather stations in France, Holland, UK and Germany

Despite headline claims that this attribution study was about heatwaves in Europe and how they have been made much more likely by man-made climate change, it was not. The claim is incorrect and highly misleading. The results of this attribution apply strictly to just five individual weather stations, plus to metropolitan France in general but, as we will see the models were pretty useless for diagnosing trends throughout France and only moderately acceptable as diagnostic tools for the individual weather stations. But it gets worse, and worse again. Firstly, here is a list of the locations:

The only country wide data, which is for France only, is the France Metropolitan Average, which only goes back as far as 1950. Therefore it doesn’t even include data from the 1947 heatwave, not to mention any other heatwaves which might have occurred in the early part of the 20th century or even further back in the 19th century. So they’re doing an attribution analysis for France based on data from the modern period only using models which are biased to produce strong warming in the modern period and amazingly they find that man-made climate change had a significant impact! Only in climate science could this be justified. Any other field and it would be laughed out of the lab.

Only in climate science would scientists select five individual locations (weather stations each encompassing a microclimate of no more than a few hundreds of square meters) and perform a supposedly ‘rigorous’ attribution analysis, then plug their findings in the media as being somehow representative of the climate of an entire continent! It gets worse though; they didn’t just pick the stations, they cherry-picked them – outrageously cherry-picked them!

The rest of the analysis is based on a set of 5 individual weather stations. We selected the stations based on the availability of data, their series length (at least starting in 1951) and avoidance of urban heat island (UHI) and Irrigation Cooling Effects (ICE), which result in non-climatic trends. The locations considered all witnessed a historical record both in daily maximum and in 3-day mean temperature (apart from Oxford and Weilerswist-Lommersum where only daily maximum temperatures set a record).

The weather stations were deliberately selected because they set record high maximum temperatures, three of them also in 3 day mean temperature, which period was coincidentally also the basis for the event attribution, seeing as the ‘heatwave’ was so damned short it was over before it almost began! The choice of Cambridge Botanical gardens is even more hilarious because, as we have seen, the UK failed to live up to the Met Office’s hype and break the national all time temperature record of 38.5C. Then Cambridge University popped up and said that their botanical gardens managed 38.7C, so the Met office jumped at the opportunity to save face and they subsequently legitimised the ‘new record’ by ‘rigorously checking it for quality control’. LOL.

This was only a few days ago. The study’s authors must have then immediately leapt at the opportunity to include Cambridge Botanical Gardens in their ‘European Heatwave Attribution Study’ and stayed up all night presumably number-crunching the data from the station to ‘prove’ beyond all doubt that climate change must have come to Cambridge BG that day! I suspect this might be why there are two stations included in the study from the UK. But it gets even worse! They chose the station simply because the Met Office belatedly declared it as setting a new national maximum temperature record – despite its apparent unsuitability as pointed out by Paul Homewood. They also chose it knowing full well that the historic data was – shall we say – less than reliable:

The Cambridge Botanical Gardens (BG) station that observed the UK record temperature of 38.7 ºC has a sizeable fraction of missing dataOn 23 July there were battery issues, this value has been estimated by the UK Met Office on the basis of their interpolation routine. For earlier years we used the values of the nearby Cambridge NIAB station with a linear bias regression T(BG) = (1+A) T(NIAB) + B, with A about 5% in summer and B -0.6 ºC in July, -0.9 ºC in August.

Can I believe what I just read? On one of the days specifically included in their event definition (July 23rd), the thermometer batteries were on the blink so the Met Office had to estimate the data for that day and the authors used a nearby station to fill in the gaps for the large chunks of historic data (going back to 1911) missing from the station! All this, just so they could include the Botanical Gardens in their study, simply because it was the site of a decidedly dodgy UK all-time maximum temperature record! If that is not an ideologically driven choice by supposedly diligent, cautious, rational, and above all unbiased scientists, I don’t know what is. But there’s more! This is the study which just keeps giving.

Like the June study, the models are crap but in this case not crap enough – simply because of the choice of locations

Figure 5 compares the GEV distribution parameters between model ensembles and observations. In general, the same conclusions hold regarding models skill as in our analysis of the June heatwave [i.e. the models are crap at simulating the actual observations]. Models have a too high variability and hence overestimate the sigma parameter, sometimes by a large amount (factor 1.5 to 2.5). This is particularly marked for the France average. However, HadGEM3-A, EC-EARTH, IPSL-CM6-LR and CNRM-CM6.1 appear to have a reasonable departure from observations. For the other models the 95% confidence intervals on the scale parameter does not overlap with the confidence interval on the scale parameter from the observations, which is our criterion for inclusion of the models in the attribution.

Note that the models perform worse when it comes to the whole of France observations, i.e. the data over a much wider area. For the individual cherry-picked stations, they perform OK (just).

For individual stations studied here shape parameters are well simulated. The discrepancy for the scale parameter is also reduced except for weather@home where variability remains too high. The difference in behavior between the France average and the stations could arise from several reasons and remains to be investigated.

The issue requires an in-depth investigation, but probable reasons may be in a difficulty of models to correctly simulate land-atmosphere interactions, resulting in a deficit of skill for the simulation of heatwaves especially in regions where evapotranspiration regimes undergo transitions from energy-limited to soil-moisture limited regimes. Preliminary investigations into the deficits of weather@home have shown that an insufficient cloud cover in the model leads to unrealistically high hot extremes and low cold extremes. Another possible cause is dynamical as France may occasionally be influenced by episodic advection of hot and dry air from Spain and North Africa leading to large excursions of temperature which models might not capture well.

Yep, blah, blah, blah, etc. etc. Finally they get to the probable real reason why there’s a difference in model performance between individual stations and whole regions – a flipping great plume of hot air from Africa caused the heatwave and made it much more likely that very hot temperatures would be experienced on said days of the heatwave! They already bloody said this is what caused the extreme temperatures!

The source of the unusual heat was North Africa, scientists say, drawn up to Europe because of high pressure to the east of the UK.

[https://thefinancialanalyst.net/2019/08/02/climate-change-made-europes-2019-record-heatwave-up-to-100-times-more-likely/]

It’s one reason why it got very hot, up to 3.5C hotter than when it last got very hot, in 2003 and 1947. Other reasons include land use, urbanisation, station siting and yes, a general long term warming trend observed in the average temperatures of European summers. But what do our intrepid ‘scientists’ do? They use models which barely fit observations and they hype their own findings by falsely informing the public that the whole of the increase in record daily max temperatures can be attributed to man-made climate change. They also tell us that man-made climate change has made it up 100 times more likely that these extremes will occur!

Geert Jan van Oldenborgh (KNMI), one of the study’s authors admits all this to Carbon Brief, but the alarmist headlines remain and none of the scientists involved seem concerned in the least about the impression given to the public, even reinforcing that impression themselves in their press interviews.

As part of the analysis, the authors also looked at how extreme the temperatures seen during the July heatwave were in comparison to those seen in the past.

The authors find that the temperatures seen during this heatwave were around 3C higher than they would have been in 1900.

This is double the heatwave temperature increase expected by climate models – which are used to make projections about future climate change, van Oldernborgh says:

The models only predict that heatwaves get warmer at about 1.5C per degree of global warming. So for every degree of global warming, they predict that heatwaves get 1.5C hotter – a little bit faster but not really exceptional.”

The world has seen around 1C of global warming so far – meaning that the models would expect heatwaves to be around 1.5C hotter today than in pre-industrial times. However, temperatures during this heatwave were actually around 3C warmer, he says:

“We really need to do a lot more serious research than we can do within one week to look at why there is such a big discrepancy between the observed trends and the modelled trends. [No. Shit. Sherlock]

“But heatwaves are very special. A lot of things come together for a heatwave – heat from the Sahara, local heating due to sunshine, the reaction of vegetation due to very hot conditions – and all these things have to be modelled right. I’m just afraid that these models that have been designed to project the average climate correctly cannot handle these very extreme situations very well.”

So what have we learnt? We’ve learned that models are rubbish at analysing the human fingerprint in extreme weather events, but that scientists still use them and express over-confidently their opinions about how climate change has significantly altered the frequency and intensity of extreme heatwaves, using those models, combined with sparse data, poor data and unsuitable data. These opinions then get relayed to the media as ‘fact’ and idiot climate activists, Greens and lefty politicians double down on ‘climate crisis deniers’ as these ‘facts’ accumulate in the public arena.

#Rep 3 – 1947: An Anti-Hysterical Perspective On Modern European Heatwaves

2003. 2018 and now 2019: very hot (record-breakingly hot) conditions affect parts of central and northern Europe, with 2003 being by far the most significant and prolonged event. Cue, climate change hysteria from the warmist media, whacko climate crisis obsessed eco-loonies and AGW-biased scientists in search of research grants, prestige and a ‘noble cause’ for which to promote urgent action. As usual though, history often tells a less sensational tale, providing perspective on the current ‘end of the world’ narrative being perpetuated by the MSM and by emotionally and psychologically damaged members of the climate change end times Twitterati. You think I’m exaggerating? I’m not.

As it happened, 25th July 2019 wasn’t the day Britain transitioned to a ‘new climate’, because the temperature record of 38.5C set in the ‘old climate’ back in 2003 was not broken (except by iffy thermometers in Cambridge Uni’s Botanical gardens, that is). But you know how it is, Little England, being the backward, rain-soaked, cake-filled, cloud-bolted little island of grey skies, xenophobes and racists that it is, can’t be expected to immediately join continental Europe in heralding the terrifying arrival of the ‘new normal’. Germany, Belgium, Netherlands and Paris all transitioned on July 25th. Boris might make matters even worse on Halloween if he takes us ‘out of Europe’ without a deal, then God only knows how long it will be before climate alarmists can say that Britain is definitely CCBAR (climate changed beyond all recognition).

July 25th, though it didn’t see the UK transition from a benign climate to something much, much more horrible, did witness a significant rift open up between different factions of the Green blob: i.e. the opportunist BBC – who’ve bought in to the climate crisis purely for ideological reasons, and because they’re rabid, globalist lefties anyway – and those nutters who genuinely believe that we are all going to die in a few years time. The latter got quite upset at those caught ‘celebrating’ the imminent ‘hottest day evah’ in Britain. They were celebrating for the simple reason that it reinforced their catastrophe narrative. The ‘serious’ fanatics really do believe that a few very hot days are a prelude to the end of the world and they really do believe that the Beeb was being outrageously flippant. It’s quite comical.

Environmentalists who criticised the BBC for tweeting enthusiastically about the ongoing heatwave have been mocked online for their hysterical reaction. 

Campaigners including the Green Party and charity WWF heaped scorn upon the Corporation for the lighthearted tone it used when reporting the heatwave on social media.

As it happens, both factions were to be bitterly disappointed. The Met Office and the BBC didn’t get to crack open the chilled Champers and the eco-loons at GreenPiss, the Green Party, XR and WWF – plus the rest of the doom-filled Thermageddon-fixated adorers of Saint Greta – didn’t get to be really, really miserable. Shame. Never mind.

But anyway, enough of the entertainment; let’s get to the boring, ‘sciency’, fact-orientated bit. Why isn’t a few extremely hot days in Europe this year proof of a climate crisis?

The 1947 heatwave was more severe in Central Europe than 2003

In 2013, scientists from the Oeschger Centre for Climate Change Research and Institute of Geography, University of Bern, Switzerland analysed the heatwaves in Switzerland during 1947 using Meteo-Swiss weather records and the 20th Century Reanalysis (20CR) dataset based on NCEP. Here is what they found:

The heatwaves of 1947 can be compared with the events of 2003 in terms of intensity and duration.

The meteorological situation was characterized by a high-pressure bridge over Central Europe.

This report focuses on the heat period of 1947 in Switzerland. The summer of 1947 marked the culmination of a prolonged drought period that affected central Europe from around 1945 to the early 1950s.

The authors make it clear that it was atmospheric dynamics (circulation patterns/blocking high) which primarily caused the heatwave – just like in 2003, 2018 and now 2019.

The variability of air temperature in general and of extreme temperature events in particular is governed by atmospheric circulation. In particular, persistent high-pressure systems and associated circulation patterns may lead to positive anomalies of surface air temperature affecting a large area over prolonged time periods (Kysely and Huth, 2008). Heatwaves are often caused by quasi-stationary anticyclonic circulation anomalies or atmospheric blocking, which may be sustained or amplified by land-atmosphere feedbacks (IPCC, 2012). This is also the case for the region under study (Rüttimann et al., 2009).

Here are the anomalies over Europe in 1947 for Apr-Jun (left) and Jul-Sep (right) (Hadcrut 3) with respect to 1981-2010. You can see the heatwave was firmly centred over Central Western Europe and covered a huge area way beyond Switzerland, which country was not even at the epicentre.

In the analysis of the maximum temperature from the 14 meteorological stations, 29 July was the hottest day during summer 1947. The mean maximum temperature from all lowland (<560 m a.s.l.) stations on this date was 36.1 °C; 26.4 °C were reached at 2502 m a.s.l. In Basel 38.7 °C were measured – the highest recorded temperature during the heat period of 1947 and the highest temperature ever observed in Switzerland until 2003 (note, however, that the Wild screen used at that time in Basel was sensitive to radiation errors, see Auchmann and Brönnimann, 2012).

The heat period of 1947 can be compared with the year 2003 in terms of maximum temperatures and duration of the heatwaves. For instance, the maximum temperature anomaly, computed as departures from the 1961-1990 average, of the year 1947 amounted to 5 °C. This is only 1 °C less than for the year 2003. Another aspect is that in Basel, the threshold of 30 °C was exceeded 49 times in 1947, more often than in 2003 (41 times). 

The period of consecutive days during which the maximum temperature exceeded the 90% quantile of the summer temperature was also longer in 1947 than in 2003. During the year 1947 the longest heatwave lasted 14 days from 22 July to 4 August, whereas in 2003 only twelve consecutive heat days were recorded at the beginning of August (Z’Graggen, 2006; Beniston, 2004).

The meteorological situation during the heatwave event in 1947 analysed with the 20CR dataset shows typical features of a heatwave. The stationary high pressure system over the study region – the Central-European High – during the episode from the 22 July to 4 August 1947 is conductive for a heatwave according to Kysely and Huth (2008).

The analysis of the heatwaves in 1947 indicates that the event is comparable to 21stcentury heat periods such as the summer 2003 and that 1947 was extraordinary.

Even if the heatwave 2003 exceeded the maximum temperatures measured in 1947, in terms of the length of a heatwave and the exceedance of the 30 °C temperature threshold, the heat period 1947 was more intense.

So it’s fairly clear that:

  • 1947 was comparable to 2003 and both heatwaves were caused by very similar meteorological patterns.
  • 1947 maximum average temperatures were just 1C less than 2003
  • In terms of duration and number of days above 30C, 1947 was more intense

Given that summers in Europe have warmed significantly since 1950, it is perhaps not surprising that the daily average maximum temperature in 2003 exceeded that in 1947, but that’s the only real difference and by all other metrics, 1947 was more intense. Not forgetting also that urbanisation has increased since 1947 and land use has changed considerably, either of which may have contributed to generally higher temperatures. So, if you’re looking for the climate change signal in the heatwave of 2003, the increase in mean maximum temperature anomaly of 1C is it. Scary (not). Climate crisis (not). But Peter Stott et al say different:

Dramatically increasing chance of extremely hot summers since the 2003 European heatwave

A study by Christidis, Jones and Stott published Dec 2014 claims:

The vulnerability of European citizens was made evident during the summer heatwave of 2003 (refs 34) when the heat-related death toll ran into tens of thousands5Human influence at least doubled the chances of the event according to the first formal event attribution study6, which also made the ominous forecast that severe heatwaves could become commonplace by the 2040s. Here we investigate how the likelihood of having another extremely hot summer in one of the worst affected parts of Europe has changed ten years after the original study was published, given an observed summer temperature increase of 0.81 K since then.

Using a previously employed temperature threshold to define extremely hot summers, we find that events that would occur twice a century in the early 2000s are now expected to occur twice a decade. For the more extreme threshold observed in 2003, the return time reduces from thousands of years in the late twentieth century to about a hundred years in little over a decade.

Note the emphasis is on frequency of recurrence. Stott’s original attribution study of the 2003 heatwave categorised the event as:

 . . . . . probably the hottest in Europe since at latest ad 1500

Thereby classing it as a millennial scale event. However, we’ve just seen that 1947 was comparable to 2003 and only 1C cooler in terms of mean absolute maximum temperature. Also, the summer of 1541 was likely hotter, drier and far more intense than even 1947 or 2003. Stott paints the 2003 heatwave as some momentous event in the history of European weather and claims that, because of man-made climate change, such events are going to be ‘the new normal’ by the end of the 21st century. Stott is wrong about the uniqueness of 2003 in modern European meteorological history. 1947 was worse. 1976 was definitely worse – in the UK at least.

We’ve seen two heatwaves in Europe in 2018 and 2019, of similar intensity to 2003, but of shorter duration and impact (especially so far in 2019), with the 2018 heatwave being centred more over Scandinavia, the UK and Ireland – similar to 1976. Also, very inconveniently, many areas of Europe and Russia have experienced record summer minimum temperatures in 2019, whilst other parts were baking, but you didn’t hear about that in the media. But even so, perhaps Stotty is right about the increased probability of European heatwaves? Maybe they are becoming hotter and a lot more frequent due to man-made climate change? The climate fanatics certainly think so. To investigate this possibility though, we have to look at atmospheric dynamics, not just simple thermodynamics and, as it turns out, the answer is not that simple. Science and observations get in the way of warmist hyperbole. Bummer.

Observed 21st Century Increase of Jet Stream Blocking Events

study published in April this year states:

The summer of 2018 witnessed a number of extreme weather events such as heatwaves in North America, Western Europe and the Caspian Sea region, and rainfall extremes in South-East Europe and Japan that occurred near-simultaneously. Here we show that some of these extremes were connected by an amplified hemisphere-wide wavenumber 7 circulation pattern. We show that this pattern constitutes an important teleconnection in Northern Hemisphere summer associated with prolonged and above-normal temperatures in North America, Western Europe and the Caspian Sea region. This pattern was also observed during the European heatwaves of 2003, 2006 and 2015 among others. We show that the occurrence of this wave 7 pattern has increased over recent decades.

So what exactly has happened and can what has happened be attributed to anthropogenic influence?

Over recent decades the number of phase-locked wave-7 events (here defined as weeks with above average wave-7 amplitude within its preferred position, see figure S4) have increased significantly (95% confidence interval, figure 4(b)). Prior to 1999 there were no summers with two or more consecutive weeks of a wave 7 phase-locked circulation, but since then these have occurred (table S2). Thus, the persistence of such situations appears to have increased. In fact, the average duration has doubled from about one to two weeks per year, while the number of years with more than two events per summer shows an almost eight-fold increase (figure S7). Although the trends are always upward, i.e. independent of the amplitude threshold used, their significance is sensitive to the amplitude threshold due to the reduction in ensemble size for high amplitudes (figure 4(b)). The number of wave-7 events (i.e. weeks with a high-amplitude wave-7 irrespective of its phase position) do not show statistically significant upward trends for different thresholds used (figure 4(a)). A statistically significant upward trend in the observed amplitude of summertime wave-7 is only detected when data from the pre-satellite period is included (figure S8). The more pronounced trends in phase-locked events (figure 4(b)), compared to high-amplitude events (figure 4(a)) suggests that it is the phase-locking itself that has increasedIn general, these trends can simply reflect multi-decadal variability in the Earth system given that the satellite record is relatively shortNevertheless, an enhanced land-ocean temperature contrast as a consequence of amplified land warming provides a physical mechanism for such waves to become preferentially phase-locked. Such temperature contrast creates an increased zonal temperature gradient at the coastlines and provide a stationary vorticity source that triggers and maintains atmospheric waves [3031]. It is therefore possible that the relative position of land and ocean areas in the mid-latitudes with high values of dT/dx over the continental West-coasts could favor a hemispheric wave 7 pattern [32]. Such contrast would further be enhanced by the cooling trend of northern Atlantic sea surface temperatures linked to a slowdown of the Atlantic Meridional Overturning Circulation [33] and implicated in past European heat extremes [23] but this needs further investigation.

So, what the authors are saying here is that there is no trend in wave 7 phase locking events which would give rise to particularly hot summers in western Europe over the period of satellite observation, but that there is a very significant increase in phase locking events after 1999, which has resulted in a number of hot summers in Europe, including the very hot summer of 2003 and the memorable hot dry early summer of 2018 in north western Europe. What they say is that natural multidecadal variability may be the cause behind this change but that it’s plausible it may be due to Arctic warming, which implies anthropogenic causes (though note that this is only the case if such warming is attributable largely to anthropogenic causes).

Take home message: no increase in blocking over the period of satellite observations, only a 21st century increase which may be due to natural causes or possibly anthropogenic influence. More research needed.

1947 was a circulation-induced heatwave analogous to modern heatwaves

An interesting new study looking at 1947 as an analogue of more recent European heatwaves was published in May this year and Friederike Otto is among the authors. It’s rather better science, I must say, than the shockingly poor event attribution which was plugged by the media as ‘proof’ that the recent record breaking heatwave in France was man-made, which she also co-authored. The abstract says:

The science of extreme event attribution has rapidly expanded in recent years, with numerous studies dedicated to determining whether and to what extent anthropogenic climate change has increased the likelihood of specific extreme weather events occurring. However, the majority of such studies have focussed on extreme events which have occurred in the recent past (usually within the past 10 years) while minimal research efforts have considered the multitude of high-impact extreme climatic events which occurred throughout the instrumental record.

Using a reanalysis-based dataset, our results show changes in the frequency of 1947-like extreme heat throughout the twentieth century to be highly sensitive to methodological choices, particularly in the context of disaggregating dynamic and thermodynamic changes in the risk of extreme heat. Evidence also suggests clear decadal variability in the occurrence of circulation patterns conducive to the 1947 heatwaves.

The authors make the clear distinction between dynamic and thermodynamic influences when considering attribution of extreme events like European heatwaves:

Since European heatwaves are known to preferentially occur in the presence of specific summertime atmospheric circulation states (Cassou et al. 2005; Pfahl and Wernli 2012; Sousa et al. 2018; Jézéquel et al. 2018b), it is important to understand how dynamic and non-dynamic processes leading to heatwaves are each affected by anthropogenic climate change. Consequently, a second topic of recent research for the attribution community has concerned the extent to which changes in the likelihood of a particular extreme event occurring can be further separated into dynamic and thermodynamic contributions (Trenberth et al. 2015; Shepherd 2016; Otto et al. 2016; Harrington 2017).

The authors then define the 1947 European heatwave and identify it as the focus of their study:

This study focuses on the anomalously hot summer of 1947 over Central Europe as a case study to examine the time-evolution of attribution statements, as well as the efficacy of circulation analogues as a tool for probabilistic event attribution. As discussed extensively in Grütter et al. (2013, hereafter G13), the summer of 1947 was a period of pronounced heat over large regions of Central Europe, and occurred during the middle of a five-year period of drought which affected the region between 1945 and 1949 (Hirschi et al. 2013).

The period of April-September 1947 witnessed record-breaking rainfall deficits over Switzerland, which by some estimates were up to twice as severe as for the summer of 2003 (Calanca 2007). This widespread dryness helped to exacerbate the favourable meteorological conditions for extreme heat in Central Europe: in this case, such conditions were characterised by a persistent high-pressure system over Central Europe and several low pressure systems forming to the west of the British Isles contributing to significant heat advection from the south-west. The severity and length of this anomalous heat during the summer of 1947 lead to widespread forest fires in Germany, as well as a near-total loss of crops across Switzerland (Grütter et al. 2013).

The above graphic shows the absolute Jul-Aug temperature anomalies in Europe in 1947 compared to the 1901-2000 base period.

Obviously not a flash in the pan. A very significant meteorological event which, as we have already seen, is comparable to, and even more severe in retrospect than 2003. Emissions of greenhouse gases had yet to take off in 1947 and it was 11 years before direct measurements of atmospheric CO2 began at Mauna Loa. It’s quite likely that CO2 has increased by more than 100ppm since 1947 and that atmospheric concentrations of GHGs were far closer to pre-industrial concentrations when Europe experienced this very significant mid 20th century heatwave. It therefore defies reason that radiative forcing from GHGs could have played any significant role in that event.

The authors of the study were interested in the evolving probability of “witnessing circulation features similar to those which coincided with the 1947 heatwave through the twentieth century”. Here is what their analysis revealed:

Clear multidecadal variability. The authors state that “there is no clear positive trend through time in the likelihood of witnessing daily circulation patterns like those of the 12 days of the 1947 extreme heatwave” and furthermore that there are “some individual decades—like the 1940s in Fig. 4d—which can show statistically significant probabilities of witnessing 1947-like MSLP patterns”.  The authors further state:

Up until the 1940s—and to a lesser extent for those 20-year periods ending in the 1970s—the probability of witnessing 12-day MSLP sequences analogous to the 1947 heatwave event was substantially lower than average. Meanwhile, for every 20-year period since 1976–1995, there are substantive increases in the likelihood of witnessing such circulation analogues, with probability ratios reaching between three and six for in the most recent decades. While these results appear to qualitatively resemble corresponding changes in the Atlantic Meridional Oscillation over the same period (Sanderson et al. 2017), decomposing the relative effects of low-frequency modes of variability versus changes to European aerosol or greenhouse gas emissions (King et al. 2016; Undorf et al. 2018) is beyond the scope of this analysis.

So what we have here is the high likelihood that multidecadal variability is dictating the probability of circulation patterns occurring which would result in extreme heatwaves in Europe like 1947, 2003, and 2018. But dynamics are only one side of the equation. What about absolute temperatures?

For the case of general summertime temperatures, a clear warming signal is found through the twentieth century, with increases of more than 2 °C for the twenty-year period ending in 2014 relative to the start of the 1900s. We also find for any given time period, the average of the analogue temperatures to be approximately 2 °C warmer than the corresponding mean of all daily temperatures (black line in Fig. 5a–c), an inflation consistent with previous studies (Jézéquel et al. 2018b). This is clear evidence to support the notion that extreme summertime temperatures in 1947 were more likely to occur in the presence of the corresponding MSLP patterns which were also present.

The conclusion is plain: summers in Europe have got warmer due to the secular trend in warming experienced by most of the globe, but the probability of extreme summer heatwaves occurring due to particular circulation patterns shows no overall trend in the 20th century but is most likely controlled by multidecadal variability (the AMO). The authors clearly state that “no added increase in temperature anomalies is found associated when constraining on the circulation features of the 1947 heatwave, beyond the warming trends which are apparent for all summertime temperatures over the twentieth century.” Thus, Stott’s assertion that the probability of summers like 2003 and 2018 occurring has dramatically increased and will continue to do so, because of anthropogenic global warming, such that they become ‘the norm’ at the end of the 21st century is highly suspect and probably simply WRONG. If generalised warming continues, summer heatwaves will probably continue to set records but there is little evidence to suggest that they will become more frequent.

The authors do at least consider the possibility that thermodynamics have played a part in the late 20th/early 21st century increased probability of European heatwaves, but then say that dynamics could equally have been responsible:

A further consideration is whether or not warming-driven changes to background circulation patterns should be considered as part of the analogue analysis a priori. Jézéquel and colleagues (2018b) argue that mean changes to both Z500 and MSLP fields generally constitute a thermodynamic signal, and thus any overall trend in Z500 or MSLP through time should be removed before an analogue analysis to infer dynamical changes to the likelihood of extreme heatwaves is performed. While such an approach would be reasonable to account for the overall thermodynamic increase in tropospheric depth when considering Z500 trends, mean changes to MSLP could equally reflect dynamically driven changes in the prevalence of blocking high pressure systems in general, and thus could be argued as a dynamical signal (Smoliak et al. 2015; Parsons et al. 2016; Harrington et al. 2016; Lehner et al. 2017; Gibson et al. 2017; Woollings et al. 2018).

They leave open at least the possibility that anthropogenic influence may play a role in the evolution of the dynamical patterns conducive to extreme heatwaves – but don’t sound too hopeful:

In reality, no metric will serve as a perfect proxy for the weather systems conducive to an extreme heatwave event. Therefore, any attempt to look at changes in the frequency of witnessing such weather regimes—which one might consider to reflect the ‘dynamical’ component of a probability ratio—will in fact just be a partial representation of the ‘true’ role of human influence on circulation changes conducive to heatwave occurrence, with the remainder instead being (perhaps mistakenly) ascribed as a thermodynamic component of the probability ratio.

Then there’s land use changes, which have nothing to do with radiative GHG forcing of climate:

There are also further complicating aspects to the binary narrative of either thermodynamic or dynamic changes to the atmosphere combining to influence the likelihood of an extreme heatwave occurring. One example is the role of land-use changes and land–atmosphere feedbacks. Antecedent soil moisture anomalies can modulate the potential severity of a heatwave (Seneviratne et al. 2010), and these processes can be further influenced by anthropogenic changes to land use over the twentieth century unrelated to climate (Cook et al. 2009; Lejeune et al. 2018). Such issues have not been addressed in this analysis, and warrant further consideration.

In conclusion:

A warming world might influence how often weather patterns conducive to exceptionally hot weather will occur over Central Europe (Jézéquel et al. 2018a; Woollings et al. 2018), as well as how warm summertime temperature maxima will reach. However, our results show further work is needed to properly quantify the uncertainty of these changes, both to understand the evolution of changes in the past and as warming continues into the future.

Do you think there is any ch

2003. 2018 and now 2019: very hot (record-breakingly hot) conditions affect parts of central and northern Europe, with 2003 being by far the most significant and prolonged event. Cue, climate change hysteria from the warmist media, whacko climate crisis obsessed eco-loonies and AGW-biased scientists in search of research grants, prestige and a ‘noble cause’ for which to promote urgent action. As usual though, history often tells a less sensational tale, providing perspective on the current ‘end of the world’ narrative being perpetuated by the MSM and by emotionally and psychologically damaged members of the climate change end times Twitterati. You think I’m exaggerating? I’m not.

Screenshot_2019-07-28 James Murray on Twitter

As it happened, 25th July 2019 wasn’t the day Britain transitioned to a ‘new climate’, because the temperature record of 38.5C set in the ‘old climate’ back in 2003 was not broken (except by iffy thermometers in Cambridge Uni’s Botanical gardens, that is). But you know how it is, Little England, being the backward, rain-soaked, cake-filled, cloud-bolted little island of grey skies, xenophobes and racists that it is, can’t be expected to immediately join continental Europe in heralding the terrifying arrival of the ‘new normal’. Germany, Belgium, Netherlands and Paris all transitioned on July 25th. Boris might make matters even worse on Halloween if he takes us ‘out of Europe’ without a deal, then God only knows how long it will be before climate alarmists can say that Britain is definitely CCBAR (climate changed beyond all recognition).

July 25th, though it didn’t see the UK transition from a benign climate to something much, much more horrible, did witness a significant rift open up between different factions of the Green blob: i.e. the opportunist BBC – who’ve bought in to the climate crisis purely for ideological reasons, and because they’re rabid, globalist lefties anyway – and those nutters who genuinely believe that we are all going to die in a few years time. The latter got quite upset at those caught ‘celebrating’ the imminent ‘hottest day evah’ in Britain. They were celebrating for the simple reason that it reinforced their catastrophe narrative. The ‘serious’ fanatics really do believe that a few very hot days are a prelude to the end of the world and they really do believe that the Beeb was being outrageously flippant. It’s quite comical.

Environmentalists who criticised the BBC for tweeting enthusiastically about the ongoing heatwave have been mocked online for their hysterical reaction. 

Campaigners including the Green Party and charity WWF heaped scorn upon the Corporation for the lighthearted tone it used when reporting the heatwave on social media.

As it happens, both factions were to be bitterly disappointed. The Met Office and the BBC didn’t get to crack open the chilled Champers and the eco-loons at GreenPiss, the Green Party, XR and WWF – plus the rest of the doom-filled Thermageddon-fixated adorers of Saint Greta – didn’t get to be really, really miserable. Shame. Never mind.

But anyway, enough of the entertainment; let’s get to the boring, ‘sciency’, fact-orientated bit. Why isn’t a few extremely hot days in Europe this year proof of a climate crisis?

The 1947 heatwave was more severe in Central Europe than 2003

In 2013, scientists from the Oeschger Centre for Climate Change Research and Institute of Geography, University of Bern, Switzerland analysed the heatwaves in Switzerland during 1947 using Meteo-Swiss weather records and the 20th Century Reanalysis (20CR) dataset based on NCEP. Here is what they found:

The heatwaves of 1947 can be compared with the events of 2003 in terms of intensity and duration.

The meteorological situation was characterized by a high-pressure bridge over Central Europe.

This report focuses on the heat period of 1947 in Switzerland. The summer of 1947 marked the culmination of a prolonged drought period that affected central Europe from around 1945 to the early 1950s.

The authors make it clear that it was atmospheric dynamics (circulation patterns/blocking high) which primarily caused the heatwave – just like in 2003, 2018 and now 2019.

The variability of air temperature in general and of extreme temperature events in particular is governed by atmospheric circulation. In particular, persistent high-pressure systems and associated circulation patterns may lead to positive anomalies of surface air temperature affecting a large area over prolonged time periods (Kysely and Huth, 2008). Heatwaves are often caused by quasi-stationary anticyclonic circulation anomalies or atmospheric blocking, which may be sustained or amplified by land-atmosphere feedbacks (IPCC, 2012). This is also the case for the region under study (Rüttimann et al., 2009).

Here are the anomalies over Europe in 1947 for Apr-Jun (left) and Jul-Sep (right) (Hadcrut 3) with respect to 1981-2010. You can see the heatwave was firmly centred over Central Western Europe and covered a huge area way beyond Switzerland, which country was not even at the epicentre.

Screenshot_2019-07-28 Microsoft Word - Paper08_Heatweave_12dec2013_korrigiert doc - GB2013_G89_08 pdf

In the analysis of the maximum temperature from the 14 meteorological stations, 29 July was the hottest day during summer 1947. The mean maximum temperature from all lowland (<560 m a.s.l.) stations on this date was 36.1 °C; 26.4 °C were reached at 2502 m a.s.l. In Basel 38.7 °C were measured – the highest recorded temperature during the heat period of 1947 and the highest temperature ever observed in Switzerland until 2003 (note, however, that the Wild screen used at that time in Basel was sensitive to radiation errors, see Auchmann and Brönnimann, 2012).

The heat period of 1947 can be compared with the year 2003 in terms of maximum temperatures and duration of the heatwaves. For instance, the maximum temperature anomaly, computed as departures from the 1961-1990 average, of the year 1947 amounted to 5 °C. This is only 1 °C less than for the year 2003. Another aspect is that in Basel, the threshold of 30 °C was exceeded 49 times in 1947, more often than in 2003 (41 times). 

The period of consecutive days during which the maximum temperature exceeded the 90% quantile of the summer temperature was also longer in 1947 than in 2003. During the year 1947 the longest heatwave lasted 14 days from 22 July to 4 August, whereas in 2003 only twelve consecutive heat days were recorded at the beginning of August (Z’Graggen, 2006; Beniston, 2004).

The meteorological situation during the heatwave event in 1947 analysed with the 20CR dataset shows typical features of a heatwave. The stationary high pressure system over the study region – the Central-European High – during the episode from the 22 July to 4 August 1947 is conductive for a heatwave according to Kysely and Huth (2008).

The analysis of the heatwaves in 1947 indicates that the event is comparable to 21stcentury heat periods such as the summer 2003 and that 1947 was extraordinary.

Even if the heatwave 2003 exceeded the maximum temperatures measured in 1947, in terms of the length of a heatwave and the exceedance of the 30 °C temperature threshold, the heat period 1947 was more intense.

So it’s fairly clear that:

  • 1947 was comparable to 2003 and both heatwaves were caused by very similar meteorological patterns.
  • 1947 maximum average temperatures were just 1C less than 2003
  • In terms of duration and number of days above 30C, 1947 was more intense

Given that summers in Europe have warmed significantly since 1950, it is perhaps not surprising that the daily average maximum temperature in 2003 exceeded that in 1947, but that’s the only real difference and by all other metrics, 1947 was more intense. Not forgetting also that urbanisation has increased since 1947 and land use has changed considerably, either of which may have contributed to generally higher temperatures. So, if you’re looking for the climate change signal in the heatwave of 2003, the increase in mean maximum temperature anomaly of 1C is it. Scary (not). Climate crisis (not). But Peter Stott et al say different:

Dramatically increasing chance of extremely hot summers since the 2003 European heatwave

A study by Christidis, Jones and Stott published Dec 2014 claims:

The vulnerability of European citizens was made evident during the summer heatwave of 2003 (refs 34) when the heat-related death toll ran into tens of thousands5Human influence at least doubled the chances of the event according to the first formal event attribution study6, which also made the ominous forecast that severe heatwaves could become commonplace by the 2040s. Here we investigate how the likelihood of having another extremely hot summer in one of the worst affected parts of Europe has changed ten years after the original study was published, given an observed summer temperature increase of 0.81 K since then.

Using a previously employed temperature threshold to define extremely hot summers, we find that events that would occur twice a century in the early 2000s are now expected to occur twice a decade. For the more extreme threshold observed in 2003, the return time reduces from thousands of years in the late twentieth century to about a hundred years in little over a decade.

Note the emphasis is on frequency of recurrence. Stott’s original attribution study of the 2003 heatwave categorised the event as:

 . . . . . probably the hottest in Europe since at latest ad 1500

Thereby classing it as a millennial scale event. However, we’ve just seen that 1947 was comparable to 2003 and only 1C cooler in terms of mean absolute maximum temperature. Also, the summer of 1541 was likely hotter, drier and far more intense than even 1947 or 2003. Stott paints the 2003 heatwave as some momentous event in the history of European weather and claims that, because of man-made climate change, such events are going to be ‘the new normal’ by the end of the 21st century. Stott is wrong about the uniqueness of 2003 in modern European meteorological history. 1947 was worse. 1976 was definitely worse – in the UK at least.

We’ve seen two heatwaves in Europe in 2018 and 2019, of similar intensity to 2003, but of shorter duration and impact (especially so far in 2019), with the 2018 heatwave being centred more over Scandinavia, the UK and Ireland – similar to 1976. Also, very inconveniently, many areas of Europe and Russia have experienced record summer minimum temperatures in 2019, whilst other parts were baking, but you didn’t hear about that in the media. But even so, perhaps Stotty is right about the increased probability of European heatwaves? Maybe they are becoming hotter and a lot more frequent due to man-made climate change? The climate fanatics certainly think so. To investigate this possibility though, we have to look at atmospheric dynamics, not just simple thermodynamics and, as it turns out, the answer is not that simple. Science and observations get in the way of warmist hyperbole. Bummer.

Observed 21st Century Increase of Jet Stream Blocking Events

study published in April this year states:

The summer of 2018 witnessed a number of extreme weather events such as heatwaves in North America, Western Europe and the Caspian Sea region, and rainfall extremes in South-East Europe and Japan that occurred near-simultaneously. Here we show that some of these extremes were connected by an amplified hemisphere-wide wavenumber 7 circulation pattern. We show that this pattern constitutes an important teleconnection in Northern Hemisphere summer associated with prolonged and above-normal temperatures in North America, Western Europe and the Caspian Sea region. This pattern was also observed during the European heatwaves of 2003, 2006 and 2015 among others. We show that the occurrence of this wave 7 pattern has increased over recent decades.

So what exactly has happened and can what has happened be attributed to anthropogenic influence?

Over recent decades the number of phase-locked wave-7 events (here defined as weeks with above average wave-7 amplitude within its preferred position, see figure S4) have increased significantly (95% confidence interval, figure 4(b)). Prior to 1999 there were no summers with two or more consecutive weeks of a wave 7 phase-locked circulation, but since then these have occurred (table S2). Thus, the persistence of such situations appears to have increased. In fact, the average duration has doubled from about one to two weeks per year, while the number of years with more than two events per summer shows an almost eight-fold increase (figure S7). Although the trends are always upward, i.e. independent of the amplitude threshold used, their significance is sensitive to the amplitude threshold due to the reduction in ensemble size for high amplitudes (figure 4(b)). The number of wave-7 events (i.e. weeks with a high-amplitude wave-7 irrespective of its phase position) do not show statistically significant upward trends for different thresholds used (figure 4(a)). A statistically significant upward trend in the observed amplitude of summertime wave-7 is only detected when data from the pre-satellite period is included (figure S8). The more pronounced trends in phase-locked events (figure 4(b)), compared to high-amplitude events (figure 4(a)) suggests that it is the phase-locking itself that has increasedIn general, these trends can simply reflect multi-decadal variability in the Earth system given that the satellite record is relatively shortNevertheless, an enhanced land-ocean temperature contrast as a consequence of amplified land warming provides a physical mechanism for such waves to become preferentially phase-locked. Such temperature contrast creates an increased zonal temperature gradient at the coastlines and provide a stationary vorticity source that triggers and maintains atmospheric waves [3031]. It is therefore possible that the relative position of land and ocean areas in the mid-latitudes with high values of dT/dx over the continental West-coasts could favor a hemispheric wave 7 pattern [32]. Such contrast would further be enhanced by the cooling trend of northern Atlantic sea surface temperatures linked to a slowdown of the Atlantic Meridional Overturning Circulation [33] and implicated in past European heat extremes [23] but this needs further investigation.

So, what the authors are saying here is that there is no trend in wave 7 phase locking events which would give rise to particularly hot summers in western Europe over the period of satellite observation, but that there is a very significant increase in phase locking events after 1999, which has resulted in a number of hot summers in Europe, including the very hot summer of 2003 and the memorable hot dry early summer of 2018 in north western Europe. What they say is that natural multidecadal variability may be the cause behind this change but that it’s plausible it may be due to Arctic warming, which implies anthropogenic causes (though note that this is only the case if such warming is attributable largely to anthropogenic causes).

Take home message: no increase in blocking over the period of satellite observations, only a 21st century increase which may be due to natural causes or possibly anthropogenic influence. More research needed.

1947 was a circulation-induced heatwave analogous to modern heatwaves

An interesting new study looking at 1947 as an analogue of more recent European heatwaves was published in May this year and Friederike Otto is among the authors. It’s rather better science, I must say, than the shockingly poor event attribution which was plugged by the media as ‘proof’ that the recent record breaking heatwave in France was man-made, which she also co-authored. The abstract says:

The science of extreme event attribution has rapidly expanded in recent years, with numerous studies dedicated to determining whether and to what extent anthropogenic climate change has increased the likelihood of specific extreme weather events occurring. However, the majority of such studies have focussed on extreme events which have occurred in the recent past (usually within the past 10 years) while minimal research efforts have considered the multitude of high-impact extreme climatic events which occurred throughout the instrumental record.

Using a reanalysis-based dataset, our results show changes in the frequency of 1947-like extreme heat throughout the twentieth century to be highly sensitive to methodological choices, particularly in the context of disaggregating dynamic and thermodynamic changes in the risk of extreme heat. Evidence also suggests clear decadal variability in the occurrence of circulation patterns conducive to the 1947 heatwaves.

The authors make the clear distinction between dynamic and thermodynamic influences when considering attribution of extreme events like European heatwaves:

Since European heatwaves are known to preferentially occur in the presence of specific summertime atmospheric circulation states (Cassou et al. 2005; Pfahl and Wernli 2012; Sousa et al. 2018; Jézéquel et al. 2018b), it is important to understand how dynamic and non-dynamic processes leading to heatwaves are each affected by anthropogenic climate change. Consequently, a second topic of recent research for the attribution community has concerned the extent to which changes in the likelihood of a particular extreme event occurring can be further separated into dynamic and thermodynamic contributions (Trenberth et al. 2015; Shepherd 2016; Otto et al. 2016; Harrington 2017).

The authors then define the 1947 European heatwave and identify it as the focus of their study:

This study focuses on the anomalously hot summer of 1947 over Central Europe as a case study to examine the time-evolution of attribution statements, as well as the efficacy of circulation analogues as a tool for probabilistic event attribution. As discussed extensively in Grütter et al. (2013, hereafter G13), the summer of 1947 was a period of pronounced heat over large regions of Central Europe, and occurred during the middle of a five-year period of drought which affected the region between 1945 and 1949 (Hirschi et al. 2013).

The period of April-September 1947 witnessed record-breaking rainfall deficits over Switzerland, which by some estimates were up to twice as severe as for the summer of 2003 (Calanca 2007). This widespread dryness helped to exacerbate the favourable meteorological conditions for extreme heat in Central Europe: in this case, such conditions were characterised by a persistent high-pressure system over Central Europe and several low pressure systems forming to the west of the British Isles contributing to significant heat advection from the south-west. The severity and length of this anomalous heat during the summer of 1947 lead to widespread forest fires in Germany, as well as a near-total loss of crops across Switzerland (Grütter et al. 2013).

Screenshot_2019-07-29 Circulation analogues and uncertainty in the time-evolution of extreme event probabilities evidence f[...]

The above graphic shows the absolute Jul-Aug temperature anomalies in Europe in 1947 compared to the 1901-2000 base period.

Obviously not a flash in the pan. A very significant meteorological event which, as we have already seen, is comparable to, and even more severe in retrospect than 2003. Emissions of greenhouse gases had yet to take off in 1947 and it was 11 years before direct measurements of atmospheric CO2 began at Mauna Loa. It’s quite likely that CO2 has increased by more than 100ppm since 1947 and that atmospheric concentrations of GHGs were far closer to pre-industrial concentrations when Europe experienced this very significant mid 20th century heatwave. It therefore defies reason that radiative forcing from GHGs could have played any significant role in that event.

The authors of the study were interested in the evolving probability of “witnessing circulation features similar to those which coincided with the 1947 heatwave through the twentieth century”. Here is what their analysis revealed:

Screenshot_2019-07-29 Circulation analogues and uncertainty in the time-evolution of extreme event probabilities evidence f[...] (2).png

Clear multidecadal variability. The authors state that “there is no clear positive trend through time in the likelihood of witnessing daily circulation patterns like those of the 12 days of the 1947 extreme heatwave” and furthermore that there are “some individual decades—like the 1940s in Fig. 4d—which can show statistically significant probabilities of witnessing 1947-like MSLP patterns”.  The authors further state:

Up until the 1940s—and to a lesser extent for those 20-year periods ending in the 1970s—the probability of witnessing 12-day MSLP sequences analogous to the 1947 heatwave event was substantially lower than average. Meanwhile, for every 20-year period since 1976–1995, there are substantive increases in the likelihood of witnessing such circulation analogues, with probability ratios reaching between three and six for in the most recent decades. While these results appear to qualitatively resemble corresponding changes in the Atlantic Meridional Oscillation over the same period (Sanderson et al. 2017), decomposing the relative effects of low-frequency modes of variability versus changes to European aerosol or greenhouse gas emissions (King et al. 2016; Undorf et al. 2018) is beyond the scope of this analysis.

So what we have here is the high likelihood that multidecadal variability is dictating the probability of circulation patterns occurring which would result in extreme heatwaves in Europe like 1947, 2003, and 2018. But dynamics are only one side of the equation. What about absolute temperatures?

For the case of general summertime temperatures, a clear warming signal is found through the twentieth century, with increases of more than 2 °C for the twenty-year period ending in 2014 relative to the start of the 1900s. We also find for any given time period, the average of the analogue temperatures to be approximately 2 °C warmer than the corresponding mean of all daily temperatures (black line in Fig. 5a–c), an inflation consistent with previous studies (Jézéquel et al. 2018b). This is clear evidence to support the notion that extreme summertime temperatures in 1947 were more likely to occur in the presence of the corresponding MSLP patterns which were also present.

The conclusion is plain: summers in Europe have got warmer due to the secular trend in warming experienced by most of the globe, but the probability of extreme summer heatwaves occurring due to particular circulation patterns shows no overall trend in the 20th century but is most likely controlled by multidecadal variability (the AMO). The authors clearly state that “no added increase in temperature anomalies is found associated when constraining on the circulation features of the 1947 heatwave, beyond the warming trends which are apparent for all summertime temperatures over the twentieth century.” Thus, Stott’s assertion that the probability of summers like 2003 and 2018 occurring has dramatically increased and will continue to do so, because of anthropogenic global warming, such that they become ‘the norm’ at the end of the 21st century is highly suspect and probably simply WRONG. If generalised warming continues, summer heatwaves will probably continue to set records but there is little evidence to suggest that they will become more frequent.

The authors do at least consider the possibility that thermodynamics have played a part in the late 20th/early 21st century increased probability of European heatwaves, but then say that dynamics could equally have been responsible:

A further consideration is whether or not warming-driven changes to background circulation patterns should be considered as part of the analogue analysis a priori. Jézéquel and colleagues (2018b) argue that mean changes to both Z500 and MSLP fields generally constitute a thermodynamic signal, and thus any overall trend in Z500 or MSLP through time should be removed before an analogue analysis to infer dynamical changes to the likelihood of extreme heatwaves is performed. While such an approach would be reasonable to account for the overall thermodynamic increase in tropospheric depth when considering Z500 trends, mean changes to MSLP could equally reflect dynamically driven changes in the prevalence of blocking high pressure systems in general, and thus could be argued as a dynamical signal (Smoliak et al. 2015; Parsons et al. 2016; Harrington et al. 2016; Lehner et al. 2017; Gibson et al. 2017; Woollings et al. 2018).

They leave open at least the possibility that anthropogenic influence may play a role in the evolution of the dynamical patterns conducive to extreme heatwaves – but don’t sound too hopeful:

In reality, no metric will serve as a perfect proxy for the weather systems conducive to an extreme heatwave event. Therefore, any attempt to look at changes in the frequency of witnessing such weather regimes—which one might consider to reflect the ‘dynamical’ component of a probability ratio—will in fact just be a partial representation of the ‘true’ role of human influence on circulation changes conducive to heatwave occurrence, with the remainder instead being (perhaps mistakenly) ascribed as a thermodynamic component of the probability ratio.

Then there’s land use changes, which have nothing to do with radiative GHG forcing of climate:

There are also further complicating aspects to the binary narrative of either thermodynamic or dynamic changes to the atmosphere combining to influence the likelihood of an extreme heatwave occurring. One example is the role of land-use changes and land–atmosphere feedbacks. Antecedent soil moisture anomalies can modulate the potential severity of a heatwave (Seneviratne et al. 2010), and these processes can be further influenced by anthropogenic changes to land use over the twentieth century unrelated to climate (Cook et al. 2009; Lejeune et al. 2018). Such issues have not been addressed in this analysis, and warrant further consideration.

In conclusion:

A warming world might influence how often weather patterns conducive to exceptionally hot weather will occur over Central Europe (Jézéquel et al. 2018a; Woollings et al. 2018), as well as how warm summertime temperature maxima will reach. However, our results show further work is needed to properly quantify the uncertainty of these changes, both to understand the evolution of changes in the past and as warming continues into the future.

Do you think there is any chance at all that the world’s media will convey this non-alarmist message to the public and do you think little Greta, who knows all about the ‘science’ of the ‘climate crisis’, will tweet the good news to her thousands of followers on Twitter? Any chance that Rupert Read of XR will go on telly and announce “OK, maybe we do have a bit more than 18 months to save the planet”? Any chance at all that the scientists involved in these studies will go public and explain that extreme heatwaves in Europe and beyond are not necessarily due to fossil fuel burning, in fact rather more likely due to natural variability? Not bloody likely!

ance at all that the world’s media will convey this non-alarmist message to the public and do you think little Greta, who knows all about the ‘science’ of the ‘climate crisis’, will tweet the good news to her thousands of followers on Twitter? Any chance that Rupert Read of XR will go on telly and announce “OK, maybe we do have a bit more than 18 months to save the planet”? Any chance at all that the scientists involved in these studies will go public and explain that extreme heatwaves in Europe and beyond are not necessarily due to fossil fuel burning, in fact rather more likely due to natural variability? Not bloody likely!

#Rep 2 – What The Media Didn’t Tell You About The ‘Man-Made’ June 2019 European Mini Heatwave – Climate Models FAILED To Make The Link

Posted on  by Jaime JessopIn Uncategorized13 Minutes Read

The guys and gals at World Weather Attribution have pulled a white rabbit out of the hat yet again to confirm to a breathlessly waiting queue of climate activists, alarmists and media hacks their worst suspicions – yes, humans did indeed make the recent June heatwave in France much more likely and more intense. Peter Stott is one of the authors of the retrospective rapid extreme weather attribution study. Quite why, I’m not sure because he already knew that it was climate change wot dunnit before the heatwave actually happened! Was it tea leaves, Tardis or entrails I wonder which bestowed this remarkable foresight upon Peter? Actually, Peter would make quite a good Doctor, don’t you think? Perhaps he should think about auditioning for the BBC.

Joking aside, let’s get to the serious stuff. Let’s actually examine the study which headlines across the world declared was proof positive that the European heatwave was man-made. Did the writers of those headlines actually read the study? I doubt it somehow. Most of them were probably just briefed by the scientists involved or they got their info second hand from other media sources.

What the papers say

So before getting into the nitty gritty, let’s look at a few of those official tweets, headlines and media stories which have promoted the idea that your SUV, washing machine and toaster were responsible for France baking in extreme high temperatures for three days from June 26-28.

CNN headline says:

Climate crisis made European heat wave ‘at least’ five times more likely

In the text, Friederike Otto, another of the above study’s authors, is quoted as saying:Acting Director of the Environmental Change Institute at Oxford University Friederike Otto, who contributed to the research, told CNN that the findings give the most conservative assessment of the impact of human activity on the heatwave.“It’s important to stress the ‘at least’. It’s likely to be much higher but this is hard to quantify. Our best estimate is that it’s 100 times more. We give the most conservative estimate,” Otto said.

Scam (Scientific American) reports:

For one group of climate scientists, the event presented a rare opportunity: to rapidly analyse whether the cause of the heatwave — which made headlines around the world — could be attributed to global warming. After a seven-day analysis, their results are in: climate change made the temperatures reached in France last week at least five times more likely to occur than in a world without global warming.

The scientists with the World Weather Attribution Project decided to take action when they saw the heatwave coming and ended up performing a real-time analysis while at a climate conference in Toulouse, France.

“Some say the uncertainties are too big,” says Otto. “There are indeed caveats, mostly to do with imperfect climate models. But even with large uncertainty bars we think it is useful to provide quantitative evidence for how climate change is affecting extreme weather,” she says.

Using their models, the researchers calculated that the average temperatures reached over the three hottest days in France — around 28°C — were at least five times more likely to happen because of climate change.

But in a second analysis that looked at historical temperature records over the past century rather than models, the team calculated that the likelihood of such a heatwave in June has in fact increased 100 times since around 1900, owing to the combined influence of climate change and other factors such as air pollution.

Here’s what the British version of Scam, New Scientist, tweeted:

The Graun’s headline and sub-heading says:

Climate change made European heatwave at least five times likelier

Searing heat shows crisis is ‘here and now’, say scientists, and worse than predicted

Underneath, we read:

The record-breaking heatwave that struck France and other European nations in June was made at least five – and possibly 100 – times more likely by climate change, scientists have calculated.

Such heatwaves are also about 4C hotter than a century ago, the researchers say. Furthermore, the heatwaves hitting Europe are more frequent and more severe than climate models have predicted.

Dr Friederike Otto, of the University of Oxford, one of the scientists behind the new analysis, said: “This is a strong reminder again that climate change is happening here and now. It is not a problem for our kids only.”

The researchers, many of whom happened to be at a conference on extreme events and climate change in Toulouse, then used temperature records stretching back to 1901 to assess the probability of a heatwave last month and in the past. They also examined climate change models to assess the impact of global heating.

Global heating caused by human activities made the French heatwave at least five times more likely, said Otto, based on combining the observations and climate models. Analysis of the observations alone indicated the heatwave was at least 10 times more likely than a century ago, and potentially 100 times.

However, these bigger increases in probability may result in part from changes in land use, soil moisture and irrigation, the growth of towns and cities, and air pollution, all of which can affect temperature.

You get the idea. We’re all going to fry, not boil slowly, like frogs in a gently heated saucepan, but like prawns, flash-fried in a wok, via heatwaves so intense that not even the climate models predicted just how intense they would be. The climate crisis is happening here and now.

The World Weather Attribution rapid attribution study

So what does the attribution study actually say? Well, in summary, at the beginning, it states:

The observations show a very large increase in the temperature of these heat waves. Currently such an event is estimated to occur with a return period of 30 years, but similarly frequent heat waves would have likely been about 4ºC cooler a century ago. Climate models have systematic biases in representing heat waves at these scales and show smaller trends, more year-on-year variation and fewer really severe heat waves than the observations. Combining models and observations we conclude that the heat wave was made at least 5 times more likely.

Why did the heatwave occur?

The authors tell us:

The heat wave occurred rapidly after a rather cool period in the early phase of June. This sudden change was mostly due to the specific dynamical conditions that were present, with a mid-tropospheric “cut-off low” system that formed off the coast of the Iberian peninsula (see the 500 hPa map on 27/6/2019 in Figure 2a). This system created a transport of heat from low-level Saharan air, and induced extreme temperatures at 850 hPa (Figure 2c) and in mountainous areas, such as 29°C at 1600-1800m in the Alps. These dynamical conditions, transporting hot Saharan air or air arising from the Iberian Peninsula are unusual (see analysis below). In particular the fact that the resulting transport of air masses remained at a very low level across the Mediterranean sea over five days was very unusual.

So it’s clear. The reason the heatwave occurred was because of a rare meteorological set of events, precipitated as we have already noted by what is known as a phase-locked wave 7 pattern of the northern hemisphere jet stream which is currently in an exaggerated wavy (meridional) configuration.

Event definition

We defined the event as the highest 3-day averaged daily mean temperature in June (TG3x). The daily temperature is taken as the average over France and at the city of Toulouse in southern France.

As the intense heatwave only really lasted three days, this would seem to be an obvious choice, though it doesn’t qualify as a heatwave according to the WMO’s definition:

The World Meteorological Organization defines it [a heatwave] as five or more consecutive days during which the daily maximum temperature surpasses the average maximum temperature by 5 °C (9 °F) or more.

The short duration reflects the fact that there were apparently no deaths reported attributable directly to heat exhaustion or hyperthermia. For comparison, 15,000 people died during the prolonged heatwave of 2003.

What observational temperature dataset was used?

For the average over France we use the official Météo France definition, which is the average over 30 long-term homogenised stations. Unfortunately, this series is not public but the area average of the E-OBS daily mean temperature over metropolitan France gives virtually identical results. This time series shows previous hot events around 1950, one in 1976, and further ones in 2005 and 2017, in addition to the present event, which set a record for June of 27.5 °C (the 2003 heat wave was more intense but occurred in August, not June). The 10-yr running mean (green line) shows a combination of the increasing trend due to greenhouse gases and a cooling phase around 1980 mainly due to air pollution (aerosols).

The dataset which can’t be examined because it is not public goes back only as far as 1947 and is virtually identical to another set of observations which cover metropolitan France. Hmm. UHI bias anyone? Here is the graph of the time series which the authors used:

Note how the authors attribute the ‘warming trend’ to anthropogenic GHGs and explain away the mid 20th century cooling to anthropogenic aerosols. By doing so, they have virtually done the attribution study for observations there and then – it’s all anthropogenic according to them. No confirmation bias there then! Rational people with a fair knowledge of climate change and its causes would look at that graph and note that it could actually be the truncated part of a cycle – a natural cycle – with mid 20th century cooling, pre 1950 warming and post mid 70s rapid warming at least partly explained by natural internal variability. rational people would also note that there’s not much of a warming trend across the entire (somewhat short) series and that it is only June 2019 which stands out. Similar heat events occurred at the beginning of the series and indeed the June 1976 heat spike occurred right at the end of the mid 20th century cooling, when the authors contend that aerosols were masking the GHG warming. So according to their analysis, 1976 3 day June temperature would have been even hotter still, maybe hotter than 2019, when atmospheric CO2 concentration was around 330ppm vs. 410ppm in 2019!

Note also that the hottest 3 day max June temperature was about 25.5C in 1947 and showed no increase before 2017, which year it edged up to about 26.3C, then leapt to 27.5C this year apparently. This, we’re told, is climate change in action. But where did the 4C figure come from?

How the attribution study estimated 4C anthropogenic warming of 3 day June heatwaves

Simple really. They used the 3-day max series from 1947-2018 and plotted it against the Hadcrut 4.6 anomaly for western Europe during June July August and then drew a linear trend line through the highly variable data. Then they extrapolated the linear trend back to 1900 when anthropogenic warming was thought to be negligible. Hence they ended up with 4C of 3-day heatwave warming (since 1900) which they attributed in its entirety to GHGs released since 1900!

We fit a Generalised Extreme Value distribution (GEV) to the French series (figure 5). The trend is included by allowing for a shift in proportion to the European summer temperature. This gives a good description of 3-day heat in France. We extrapolated the linear relationship found to 1900 to obtain an estimate of the total warming since a time when anthropogenic influences were small

The mean observed summer land temperature warming in western Europe according to Hadcrut 4.6 is about 2C apparently, so how to explain the 4C 3 day heatwave warming? The authors write:

This implies a much higher warming trend in France in June compared to that of the average European land summer temperature, which has warmed by about two degrees. More research is needed to understand this feature, but a major factor in the difference is likely the amplification that soil moisture drying contributes to temperature means and extremes in regions with transitional climate between dry and wet conditions. This effect is known to be strong in southern France and other regions with Mediterranean climate and is getting stronger in mid-latitude regions with global warming (because of decreased evaporative cooling if soil moisture levels become limiting for plants’ transpiration; e.g. Seneviratne et al, (2010), Mueller and Seneviratne (2012). Nonetheless, the derived value is particularly high compared to the warming in the European land and could also be affected by additional contributing factors or reflect some shortcomings of the analysis. For instance, the fit was derived from 60 years of data (Figure 5, left) and it is possible that there could be non-linearities in the relationship, e.g., because of a threshold behaviour which could imply a different relationship to European temperatures earlier in the century compared to the derived relationship. In addition, the role of soil moisture feedbacks could be different for means vs extremes, both in France as well as for the European temperatures (since it may also play an amplifying role during extreme conditions in more northern regions). It should be noted that the strength of the feedback may also depend on the month considered (e.g. likely stronger drying at the end of the summer season). Other processes that could also contribute are landscape changes or specific dynamical conditions occurring during hottest extremes in France, which could include hot advections from Spain or Sahara, making the underpinning physical processes different for mean vs extreme cases.

A lot of uncertainties and unknowns and caveats in there, very few of which found their way into the media reports and which the authors themselves – more especially Friederike Otto – appeared not to be too concerned about expressing, preferring instead to concentrate on the climate crisis narrative.

What did the study say about dynamics (i.e. meteorological effects/the jet stream)?

Basically, it concluded that the dynamical set up which is the direct cause of the heatwave cannot be attributed to climate change.

We do not identify a trend. This analysis thus does not suggest a strong role of climate change in this dynamical aspect of the extreme June heat.

They conclude that the meteorological situation was highly unusual in June 2019 but that no trend can be observed in the data going back to 1949.

What do the climate models tell us about the attribution of the European heatwave?

The fundamental basis of an extreme weather attribution study is a comparison between a world without added GHGs and just natural climate variability and a world with added GHGs as simulated by running climate models. Comparing natural to anthro model runs in the context of the observed event should enable an estimate of the influence which GHGs have played. That’s the whole point of the exercise. So what did the climate models used in this study reveal? Nothing, basically, they were useless, not fit for purpose!

Before undertaking the attribution analysis using climate models we have to evaluate whether the models readily available to us are fit for purpose and represent the statistics of the TG3x June event well. We considered the following models to investigate the changes in heat waves in France (Table 1)

Taking the two tests together we find that only one model ensemble or single model (barely) passes the test that the fit parameters of the tail of the distribution have to be compatible with the parameters describing the observations; a situation similar to the one encountered for area-averaged heat waves in the eastern Mediterranean (Kew at al, 2019). A more careful study would also investigate whether the observational analysis did not introduce biases in the fit values for the observations.

For a single station, Toulouse, we find similar results: the two models that do not have an incompatible scale parameter (Figure 11) have incompatible shape parameters (Figure 12), so here no model passes the formal tests. From the analyses for the shape parameter, we see that the CMIP5 multi-model ensemble actually has some overlap with the observations (Fig. 11), however it is outside the range of the observed scale parameters (Fig. 10). Hence, we are formally left for the present analysis with no suitable climate models or model ensembles to do the attribution (though we did not check the suitability of each single CMIP5 models and cannot exclude that some might be suitable for both parameters).

Got that? No models were found to pass the suitability tests so the attribution analysis could not be done. So what the hell did they do?

Having thus no well suited models from the analysed sample for the investigated event and locations at this stage, we decide not to give a synthesised overall result drawn from observations and models as in previous studies (refs) but still proceed with analysing all models, noting that the results are only indicative at best when drawing conclusions.

Can you believe that? Presumably so desperate to a get a non peer reviewed attribution study out in the public domain as quickly as possible they went ahead and did it anyway, using models which they knew were not suitable for the purpose! It worked though didn’t it. They got the global headlines they wanted – but the analysis is total BS, based on using models which are, by the authors own admission, not fit for purpose.

Then comes the pièce de résistance of this French heatwave study, the glacé cherry on top of the BS cake:

For the average over France we find that the probability has increased by at least a factor five (excluding the model with very strong bias in variability). However, the observations show it could be much higher still, a factor 100 or more. Similarly, the observed trend in temperature of the heat during an event with a similar frequency is around 4 ºC, whereas the climate models show a much lower trend.

Let’s deconstruct this short, innocent looking paragraph. Using models which are total crap, they find the probability of such a heatwave occurring has increased by a factor of five due to climate change. Looking at the observations (which prove nothing about attribution), they conclude that it could be as much as a factor of 100! Using the ‘observed trend’ of 4C (which is not an observed trend, it’s a linear extrapolation) the authors go public and declare that heatwaves in France are 4C hotter, implying this is due to climate change and furthermore state that an increase in probability of 5 times is a “conservative estimate” and the “best estimate” is 100 times. This “best estimate” appears to have been plucked out of the blue with no reference to the climate model runs (which cannot be relied upon anyway), simply by looking at 60 years of observations with limited amounts of data on similar heatwaves and extrapolating this back to a point 118 years ago when it is assumed that anthropogenic forcing of climate started, assuming also that anthropogenic aerosols were responsible for mid 20th century cooling.

The estimated 4C warming since 1900, which the climate models comprehensively failed to simulate, giving much lower warming generally, was used as the benchmark for the “best estimate” of the increased probability of the heatwave occurring, i.e. 100 times more likely. It’s hard to stress just how wrong this is. It’s attributing observed changes to man-made climate change using no evidence whatsoever other than the mere fact of the observations themselves. Astonishingly bad science and deliberate deception of the public in my opinion.