Back in January 2022, in a paper titled, ‘Climate-related mortality and hospital admissions, England and Wales: 2001 to 2020’, the UK’s Office for National Statistics (ONS) stated the following:

Over a 20-year period the estimated change in deaths associated with warm or cold temperature was a net decrease of 555,094, an average of 27,755 deaths per year (Table 1). A decrease in deaths from outcomes associated with cold temperature greatly outnumbers deaths associated with warm temperature.

This was, of course, a rather inconvenient truth for those wishing to push the narrative that climate change had heightened the risk of temperature-related mortality within the UK. What made it all the more awkward was the fact that an independent poll from the National Centre for Social Research (NatCen) showed that over 80% of the British public trusts the ONS, widely believing the agency to be free from political manipulation and government interference. This wasn’t a dodgy climate-denying blog blowing a hole in the climate narrative, it was a highly prestigious and trusted organisation.

So something had to be done, and it wasn’t too long before the solution was found. In 2023, the same organisation was able to publish an updated paper that told a very different story. Instead of a summary statement pointing to a steadily falling overall death rate, we had this:

There was some indication that heat-related deaths have increased over recent years; in 2022 an estimated 4,507 deaths (95% confidence interval: 3,363 to 5,587) were associated with the hottest days in England.

Yes, the takeaway message had now become the possibility of a rise in the incidence of heat-related deaths.

But this change of emphasis in an executive summary is the least of the things that should be sounding your alarm bells. The real solution to the problem lay not in a judiciously worded synopsis; the real solution lay in a new way of counting the dead.

The ONS gets creative

In 2022 the ONS embarked on a grand new scheme for analysing climate change health statistics, referred to as the Standards for Official Statistics on Climate-Health Interactions (SOSCHI) project.

SOSCHI is financed by the global charitable foundation Wellcome, and has the purpose described in a 2026 ONS bulletin. This bulletin points out that, working alongside ‘global partners’, the ONS had developed a scheme that promised ‘a transparent and globally usable framework and platform for official statistics on climate and health’. Furthermore, the ‘final outputs of the project’ include the ‘resources and tools to help stakeholders produce high-quality data and statistics, and communicate with a range of audiences’. Which all sounds great, but in practice the real significance lies in the fact that SOSCHI gave the ONS the opportunity to re-analyse the situation. As the ONS said in an August 2026 update to the mortality statistics:

This bulletin incorporates methodological, analysis code and data source improvements, which means these estimates supersede those published in our previous Climate-related mortality, England and Wales: 1988 to 2022 article.

Superseded would be understating things somewhat. What their ‘improvements’ did was reduce the ratio between cold- and heat-related deaths from what was understood to be a massive 20:1 (ref.) to a relatively modest 3.5:1 – admittedly, still an excess of cold over heat, but one that now looks much more vulnerable to rising temperatures. And this absolutely colossal adjustment to the estimates was achieved relatively easily, simply by no longer considering all deaths within a season but counting instead only those deaths associated with the top 2.5% of hottest and 2.5% of coldest days. All of which is quite convenient for those pushing the heat death narrative, because virtually all heat-related deaths will occur within the 2.5% cut-off and therefore be counted, whereas the vast majority of cold-related deaths fall outside of the 2.5% cut-off and therefore will not. To understand why, one has to appreciate differences in what epidemiologists refer to as the exposure-risk curve.

It’s an exposure thing

In epidemiology, temperature mortality is generally mapped on a U-shaped or J-shaped curve that shows how mortality changes with temperature. However, the two sides of the curve act in completely different ways for the two threats. The risk curve for heat features a steep, dramatic spike (a J-shape). Humans tolerate a range of warm temperatures well, but once a specific extreme threshold is crossed (around 29°C in the UK), mortality risk jumps suddenly due to heatstroke, dehydration, and rapid cardiovascular strain. In contrast, the exposure-risk curve for cold is a gentle, prolonged slope (a less dramatic inverse J-shape). Crucially, the risk of dying doesn’t just spike when it is well below freezing (-5°C); it begins to climb steadily at what most people would consider mild or moderately cold temperatures, such as 8°C to 12°C.

In summary, the splendidly new ONS methodology treats heat and cold as if their mathematical distributions of risk are an identical mirror reflection when they are most emphatically not. The heat threat is episodic and acute, but the cold threat is chronic, acting over a wider range of temperatures and over a much longer timescale. The fact is that there are many more moderately cold days than freezing ones in a year, and the cumulative toll of sustained, mild cold on blood pressure, respiratory infections, and strokes across an entire population is massive. To a certain extent, the ONS accounts for this by applying a distributed lag non-linear model (DLNM) that attributes to a coldest day some of the deaths that occur within the following 21 days. Even so, by treating cold-related mortality as something that happens relative to a coldest 2.5% of days, most of the seasonal mortality is overlooked. This looks like an obvious error, so why is the ONS doing it? Well, it has its reasons, but are they good ones?

Taking things to the extreme

The first thing to appreciate is that these estimates are generated by models and there will always be limitations on what can and cannot be easily modelled. If one tries to encompass the full range of factors associated with cold weather, a very messy picture emerges, involving many mediators and confounders. The ONS didn’t like this. In particular, they didn’t like the idea that, in the UK, winter deaths are heavily driven by viral waves (like influenza) and seasonal changes in behaviour. The ONS argued that extending the definition of cold days to include relatively mild days makes it statistically impossible to separate a death caused by a chilly room (presumably a death due to acute hyperthermia) from a death caused by riding on public transport during a flu outbreak. To the ONS, the cold-related statistics have always been massively over-estimated by including deaths that are not truly cold-related (at least not in the same sense that deaths related to extreme heat are). As far as the ONS is concerned, the revised methods are putting right a long-standing error.

Except, there wasn’t an error to correct. You don’t have to die from acute hyperthermia in order for your death to be associated with cold (remember that ‘associated with’ had been the expression used by the ONS back in their 2022 paper). The ONS may think that they are doing the right thing by removing confounders but, by treating winter viruses as an unrelated confounding factor to be cancelled from the equation, the ONS methodology fundamentally misrepresents the biology of human exposure to cold. The ONS model tries to separate death-by-thermometer from death-by-virus, but in medicine these two things cannot be separated. Just because it is the virus that gets a mention on the death certificate doesn’t mean that the cold wasn’t an essential, underlying factor in the death.

Firstly, breathing in cold air chills the nasal passages. This directly impairs the body’s local immune response, slowing down the nasal tissue’s ability to fight off respiratory viruses. Secondly, many respiratory viruses are structurally more stable and can survive significantly longer in cold, dry air, increasing the ambient viral load in the community. Thirdly, when temperatures drop even moderately to 8°C or 10°C, people move indoors and close windows. This lack of ventilation drastically increases indoor transmission rates. Finally, living in a moderately cold home does not usually cause immediate hypothermia. Instead, it causes chronic stress on the cardiovascular system and lungs, leaving the resident highly vulnerable to the next respiratory bug going around.

None of this seems to interest the ONS. The political backdrop is such that climate change and its impact on extreme weather events has become the primary focus. Heat waves kill people due to acute heat stress, and so the only meaningful comparison in the eyes of the ONS would be a cold snap resulting in deaths caused by acute cold-stress. This is a nice, neat comparison, but one that entirely misses the point. By chasing a confounder-free indicator that can then be neatly compared to the heat-related scenario, the ONS has committed a classic statistical error: they have prioritized a notion of model integrity over real-world accuracy. They seem far more interested in seeking an extreme weather basis for mortality than they do an accurate indicator of public health. I don’t know exactly what the ONS thinks it is counting, but it is no longer the actual number of cold-related deaths suffered by the British public.

So, is the ONS still to be trusted?

At the very least, one has to say that the new ONS approach to modelling cold- and heat-related deaths is deeply flawed and highly misleading. If this level of misdirection were something that a climate sceptical organisation had engaged in, the leviathan that is the fact-checking industry would have come down on it like a ton of bricks. But this particular misdirection just happens to serve the orthodox narrative. Therefore, by definition, it can’t or won’t be branded as misinformation.

It was almost inevitable that, rather than pounce upon the startlingly dubious methodology undermining the ONS analysis, the Guardian instead would report upon the latest ONS figures by taking them entirely upon trust. For the Guardian, there was a ‘National Scandal’ to be reported but it wasn’t the entirely unacceptable approach taken by the ONS that was scandalous in their view, it was what the new (albeit entirely misleading) figures purported to say about ‘the rising toll of climate crisis’. And more to the point, the Guardian was more than happy to report the ONS’s own spin:

James Tucker at the ONS said: “Our results show that the gap between heat- and cold-related deaths has narrowed in recent years as the proportion of heat-related deaths has increased.”

Perhaps he should have said instead that, over the years, a degree of narrowing of the gap between heat- and cold-related deaths is to be expected, but the only way to explain this particularly dramatic narrowing is to look toward the ONS’s creative accounting and an almost scientifically fraudulent redefinition by the ONS of what it means to cause a particular category of death.

So, no I don’t think they can be trusted any more, and I think it may also be wise to revisit that NatCen poll, with its suggestion that the ONS is free from political manipulation.

16 Comments

  1. Thanks John. It’s impossible to overestimate the damage to science (& human knowledge in general) involved in messing around with statistics on mortality. Death stats are in principle one of the most reliable sources of information for historians & social scientists, because everyone dies, and their death is legally recorded.

    The Guardian is of course at the forefront of this effort to change history, biology and physics. They’ve started on the heatwave stats too, recording as a climate disaster the 3,000 deaths attributed to the hot summer in France, while failing to note that there were officially 30,000 deaths from the 2003 heatwave. A ten-fold improvement in health care and heat death mitigation wouldn’t fit the narrative.

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  2. Geoff,

    Agreed. When the statistics are more than just raw data, but data processed using models with parameters (such as the shape of a Poisson distribution used in a DLNM) one has to wonder to what extent the outcome is an artifact of the modelling rather than a feature of the real world. And when trends in the data emerge, one has to wonder whether this is a real world trend or one caused by altering model parameters from one analysis to the next. We’ve been here before, of course. I seem to remember some pretty dodgy statistical manoeuvres during Covid, and the ONS was no stranger to such controversy. Don’t get me wrong. DLNMs are a useful tool in a modeller’s armory and modelling is not inherently wrong. But we have to remain aware of the difference between map and territory.

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  3. It’s curious that the National Record of Scotland still produces the statistics that the ONS has given up on. Here’s a figure for the underlying causes of excess deaths in winter 24-25.

    These are real climate deaths. Deaths from the extremes of heat and cold might be better recorded as weather-related. Of course, everyone dies, so it’s not clear to me what the point is of trying to squeeze the balloon like this. If one of the heatwaves killed me, I probably wouldn’t have made the start of the new school year if there hadn’t been any heatwaves at all. Ditto the folks dying over winter in the above figure: how many would have survived another trip around the sun? How many people are being killed, who let’s say had another decade in them absent the inclement weather?

    I’ve been trying to construct my own national excess winter mortality figures. Calculating the England and Wales excess mortality using the Scottish method did not give me numbers that matched the tail end of the ONS-published EWM stats. Will update in due course, if I find a solution.

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  4. “..when trends in the data emerge, one has to wonder whether this is a real world trend or one caused by altering model parameters..”

    This is a prime reason for altering model parameters, including such basic things as definitions of time periods, age cohorts etc., as little as possible.

    On the 80% public confident in the ONS: Few people know what it is, and this mirrors the famous annual “trust” survey, where doctors & scientists are always rated highly, and politicians the lowest of the low. One year a doctor was convicted of killing 200 patients, I believe, & the stats didn’t blink.

    Which leads me to think that we’re looking in the wrong place when we measure popular esteem for institutions. The public trusts the people it needs to feel are trustworthy. We know what politicians get up to, & we know they’re the only professionals we can get rid of. The public knows nothing of Poisson distributions, & can only hope that they’re doing it right.

    If we could look at the opinions of the 1% of the population who know a Poisson distribution from a Filet de Sole Meunière, we might find (à la Kahan) that scepticism is rifer where you wouldn’t expect. The fish rots from the head, and all that.

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  5. Jit,

    I have a certain amount of sympathy for the ONS because I think all they are trying to do really is identify a purely climate-related signal from the noise created by all the other factors that contribute to mortality. However, I would have a great deal more sympathy if they were to avoid making press statements that are clearly designed to be narrative-friendly. What they have done, under the auspices of SOSCHI, is introduce a radically new approach to the categorisation of causations, and the least they could do is make this the headline, rather than feed the Guardian.  Also, if they are to filter out a climate signal, I think there are better ways of doing it, but that would require developing a sophisticated causal model, and I don’t think the ONS has the appetite for that. They seem to think that focussing upon extreme weather and using a suitably tuned DLNM is the way forward.

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  6. Geoff,

    “The public trusts the people it needs to feel are trustworthy.”

    So true.

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  7. On average, sadly, about 1500 people die in the UK every day. Some of these deaths will be sudden and unexpected, but the majority will be of the elderly and terminally ill, many of whom will certainly die within the next few days, or even hours. As a nation, how much are we prepared to spend to defer by a few days the death of someone who is unlikely to have a very good quality of life?

    This is a question that should have been asked during Covid, but apparently never was.

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  9. Hi John, thanks for your really informative analysis. 👍

    “In summary, the splendidly new ONS methodology treats heat and cold as if their mathematical distributions of risk are an identical mirror reflection when they are most emphatically not. The heat threat is episodic and acute, but the cold threat is chronic, acting over a wider range of temperatures and over a much longer timescale.”

    To reinforce your point, there are Heating Degree Days (HDD) and Cooling Degree Days (CDD), which are quantitative weather and energy metrics used to measure how much, and for how long, outside air temperatures deviate from a standard baseline temperature. Respectively, they can plausibly be deemed proxies for Cold-related deaths and Heat-related deaths 

    The two key facts from the Grok Q&A below are the bold, italicised sentences:

    1. A “standard” UK annual total often cited for normalisation is 2,463 HDD (to 15.5°C)

    2. Annual UK CDD totals are far lower than HDD (typically tens to a few hundred, depending on base and location)

    When asked “For the UK, will you concisely explain Heating and Cooling ‘Degree Days’?”, Grok informs:

    Heating and Cooling Degree Days (HDD/CDD) measure how much and for how long outdoor temperature sits below or above a “base” (balance-point) temperature. They are used in the UK to estimate weather-driven heating or cooling demand and to weather-correct energy use. The base temperature is the outdoor temperature at which a building theoretically needs neither heating nor cooling, because internal gains (occupants, lights, equipment, solar) already keep it comfortable. 

    Heating Degree Days (HDD)

    HDD accumulate only when the outdoor temperature is below the base.

    The conventional UK base is 15.5°C. This assumes a desired indoor temperature of roughly 18.5–21°C and that internal gains typically contribute about 3–5.5°C. 

    The Met Office also uses 15.5°C for national climate statistics. 

    Simple daily approximation: if the day’s mean outdoor temperature is 10°C, that day contributes 15.5 - 10 = 5.5HDD. Published UK figures usually use a more refined Met Office method based on daily maximum and minimum temperatures. 

    A “standard” UK annual total often cited for normalisation is 2,463 HDD (to 15.5°C); actual regional averages typically range from about 1,800 in the milder south-west to 2,600+ in northern Scotland. 

    Cooling Degree Days (CDD)

    CDD accumulate only when the outdoor temperature is above the cooling base.UK cooling demand is smaller and less standardised than heating:

    Met Office climate monitoring uses a 22°C threshold. 

    For building energy analysis, 15.5°C is common for summer-only cooling and 5°C for year-round cooling (e.g. shops or data centres). 

    Annual UK CDD totals are far lower than HDD (typically tens to a few hundred, depending on base and location).Modern well-insulated buildings often have a lower heating base (e.g. 10°C) because they lose less heat; the “right” base is building-specific rather than a single national figure.

    https://x.com/i/grok/share/12838d070919490ba6edd5bd87bdf6c2

    VESMA produces much useful Degree Day data and explanations. And, gives free access to anyone interested in the data for their location (Britain, maybe UK)

    https://www.enmanreg.org/freedd/

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  10. I see that Paul Homewood has had an article on this subject published at the Daily Sceptic:

    https://dailysceptic.org/2026/09/03/ons-caught-peddling-fake-heatwave-deaths-scare/

    Whilst I share many of his concerns, I think his take on it is simplistic. Even though there is a lot of spin involved whenever the ONS talks to the media, to dismiss the new analysis as a ‘cover up’ does little to recognise the full range of motives behind the ONS approach. There is much in it that is misguided and misguiding, but to state categorically that mischief is the driving force may be going too far. If we overplay the conspiracy card, we become easier to ignore.

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  11. John,

    Thank you for the balance, both in your essay and in your comments under it.

    Given the impact of the changes made by the ONS, and the way in which such changes support the establishment climate crisis narrative, I think it is reasonable for us to be suspicious regarding ONS motivation.

    However, in the absence of a smoking gun, I think you are wise to avoid paranoid conspiracy theories.

    Still, these changes are very convenient for those peddling climate hysteria, and they do clearly present a highly misleading picture….

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  12. Mark,

    “However, in the absence of a smoking gun, I think you are wise to avoid paranoid conspiracy theories”.

    Indeed, but I think there are two things going on here.

    Firstly, even with the new way of counting, the latest ONS bulletin shows that the overall death rate is still falling. Back in 2022, that was seen by the ONS as a highly relevant statistic worthy of mention in executive summaries. Now it isn’t. Nothing is said of this continued falling death rate – certainly not to the Guardian. What the ONS says instead is that the gap between cold- and heat-related deaths is falling and this is due to a rise in heat-related deaths. No mention is made that the drop in cold-related deaths is actually greater, and no mention is made that this fall provides a better explanation for the narrowing gap. This oversight seems disingenuous to say the least, and it does nothing to engender trust. Concentrating upon a smaller rising risk at the expense of a larger albeit falling risk is a political decision, not a scientifically justified one. It exploits the fear of the future whilst turning a blind eye to a present-day reality that represents a greater immediate risk. Furthermore, it is one thing to predict that the net risk will rise in the future and quite another to give the false impression that it is already rising today.

    Secondly, the change in the way deaths are counted is a big deal because it dramatically changes the statistical landscape, making the narrative of a current rising risk easier to sell (under the new counting system the gap has been reduced to an extent that there have even been recent years when the heat-related deaths have actually outnumbered the cold-related). This new methodology is preferred by the ONS and its ‘global partners’ because everything but the impact of extreme weather is stripped away, and the powers that be seem to think this is has to be the focus. But the fact remains that it also results in the vast majority of the cold-related health burden being overlooked. You can call this a cover up if you want, but I think it is not that straightforward. Even so, it is a radical change to the way in which health risk is framed, and this change of framing should have been prominently emphasised in the executive summaries and made a headline subject for the benefit of the likes of the Guardian. Failure to draw attention to the full implications of such a profound change of policy is yet another economy with the truth that erodes trust.

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  13. John – well put in your comment above.

    Mark – “However, in the absence of a smoking gun, I think you are wise to avoid paranoid conspiracy theories“

    I agree with both comments, but can’t help but notice ONS stats presentation just happen to fit nicely into the NZ is a good thing for the UK narrative (more will die from heat related causes in the future. No, It’s happening now, and will get worse unless we change our behaviour now) is the message I read into this ONS and its ‘global partners’ report.

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  14. Aircon is frowned on in the twisted minds of net zero fanatics. Even a plug-in fan is suspect. Useless trying to reason with that sort of mentality but it goes right up to government.

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  15. Dfhunter,

    “It’s happening now, and will get worse unless we change our behaviour now) is the message I read into this ONS and its ‘global partners’ report.”

    Yes, that is the message they want you to take away. Unlike we sceptics, who resort to making factually correct statements in order to promote the ‘wrong’ ideas (so-called malinformation), the likes of the ONS are happy to make factually incorrect statements as long as they promote the ‘right’ ideas (the noble lie). On this occasion, the noble lie is that global warming is already leading to a rise in temperature-related mortality. To reveal that it isn’t might lead people to conclude that global warming isn’t such a bad thing – and we wouldn’t want that!

    That said, I cannot ignore the extent to which there is legitimacy in the ONS’s new methodology – or at least a legitimacy in what they were trying to achieve. Take, for example, a relatively mild winter accompanied by a particularly virulent strain of the flu virus, or a particularly ineffective vaccine. These are confounders that are going to distort the climate-related mortality statistics, and that is what the ONS is trying to strip away. The fact that their solution also strips away the majority of the cold-related health risk seems of little concern to them, and one can’t help but wonder whether that lack of concern forms part of the noble lie.

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