RealClimate logo

Will climate change bring benefits from reduced cold-related mortality? Insights from the latest epidemiological research

Filed under: — stefan @ 11 June 2018

Guest post by Veronika Huber

Climate skeptics sometimes like to claim that although global warming will lead to more deaths from heat, it will overall save lives due to fewer deaths from cold. But is this true? Epidemiological studies suggest the opposite.

Mortality statistics generally show a distinct seasonality. More people die in the colder winter months than in the warmer summer months. In European countries, for example, the difference between the average number of deaths in winter (December – March) and in the remaining months of the year is 10% to 30%. Only a proportion of these winter excess deaths are directly related to low ambient temperatures (rather than other seasonal factors). Yet, it is reasonable to suspect that fewer people will die from cold as winters are getting milder with climate change. On the other hand, excess mortality from heat may also be high, with, for example, up to 70,000 additional deaths attributed to the 2003 summer heat wave in Europe. So, will the expected reduction in cold-related mortality be large enough to compensate for the equally anticipated increase in heat-related mortality under climate change?

Due to the record heat wave in the summer of 2003, the morgue in Paris was overcrowded, and the city had to set up refrigerated tents on the outskirts of the city to accommodate the many coffins with victims. The city set up a hotline where people could ask where they could find missing victims of the heatwave. Photo: Wikipedia, Sebjarod, CC BY-SA 3.0.

Some earlier studies indeed concluded on significant net reductions in temperature-related mortality with global warming. Interestingly, the estimated mortality benefits from one of these studies were later integrated into major integrated assessment models (FUND and ENVISAGE), used inter alia to estimate the highly policy-relevant social costs of carbon. They were also taken up by Björn Lomborg and other authors, who have repeatedly accused mainstream climate science to be overly alarmist. Myself and others have pointed to the errors inherent in these studies, biasing the results towards finding strong net benefits of climate change. In this post, I would like to (i) present some background knowledge on the relationship between ambient temperature and mortality, and (ii) discuss the results of a recent study published in The Lancet Planetary Health (which I co-authored) in light of potential mortality benefits from climate change. This study, for the first time, comprehensively presented future projections of cold- and heat-related mortality for more than 400 cities in 23 countries under different scenarios of global warming.

Mortality risk increases as temperature moves out of an optimal range

Typically, epidemiological studies, based on daily time series, find a U- or J-shaped relationship between mean daily temperature and the relative risk of death. Outside of an optimal temperature range, the mortality risk increases, not only in temperate latitudes but also in the tropics and subtropics (Fig. 1).

Fig. 1 Exposure-response associations for daily mean temperature and the relative mortality risk (RR) in four selected cities. The lower part of each graph shows the local temperature distribution. The solid grey lines mark the ‘optimal temperature’, where the lowest mortality risk is observed. The depicted relationships take into account lagged effects over a period of up to 21 days. Source: Gasparrini et al. 2015, The Lancet.

Furthermore, the optimal temperature tends to be higher the warmer the local climate, providing evidence that humans are at least somewhat adapted to the prevailing climatic conditions. Thus, although ‘cold’ and ‘warm’ may correspond to different absolute temperatures across different locations, the straightforward conclusion from the exposure-response curves shown in Fig. 1 is that both low and high ambient temperatures represent a risk of premature death. But there are a few more aspects to consider.

Causal pathways between non-optimal temperature and death

Only a negligible proportion of the deaths typically considered in this type of studies are due to actual hypo- or hyperthermia. Most epidemiological studies on the subject consider counts of deaths for all causes or for all non-external causes (e.g., excluding accidents). The majority of deaths due to cold and heat are related to existing cardiovascular and respiratory diseases, which reach their acute stage due to prevailing weather conditions. An important causal mechanism seems to be the temperature-induced change in blood composition and blood viscosity. With regard to the cold effect, a weakening of the defense mechanisms in the airways and thus a higher susceptibility to infection has also been suggested.

Is the cold effect overestimated?

As in any correlative analysis there is always the risk of confounding, especially given the complex, indirect mechanisms underlying the relationship between non-optimal outside temperature and increased risk of death. Regarding the topic discussed here, the crucial question is whether the applied statistical models account sufficiently well for seasonal effects independent of temperature. For example, it is suspected that the lower amount of UV light in winter has a negative effect on human vitamin D production, favoring infectious diseases (including flu epidemics). There are also some studies that point to the important role of specific humidity, that, if neglected, may confound estimates of the effect of temperature on mortality rates.

Interestingly enough, there is still an ongoing scientific debate regarding this point. Specifically, it has been suggested that the cold effect on mortality risk is often overestimated because of insufficient control for season in the applied models. On the other hand, the disagreement on the magnitude of the cold effect might simply result from using different approaches for modeling the lagged association between temperature and mortality. In fact, the lag structures of the heat and cold effects are distinct. While hot days are reflected in the mortality statistics relatively immediately on the same and 1-2 consecutive days, the effect of cold is spread over a longer period of up to 2-3 weeks. Simpler methods (e.g., moving averages) compared to more sophisticated approaches for representing lagged effects (e.g., distributed lag models) have been shown to misrepresent the long-lagged association between cold and mortality risk.

Mortality projections

But what about the impact of global warming temperature-related mortality? Let’s take a look at the results of the study published in The Lancet Planetary Health, which links city-specific exposure-response functions (as shown in Fig. 1) with local temperature projections under various climate change scenarios.

Fig. 2 Relative change of cold- and heat-related excess mortality by region. Shown are relative changes per decade compared to 2010-2019 for three different climate change scenarios (RCP 2.6, RCP 4.5, RCP 8.5). The 95% confidence intervals shown for the net change take into account uncertainties in the underlying climate projections and in the exposure-response associations. It should be noted that results for single cities (> 400 cities in 23 countries) are here grouped by region. Source: Gasparrini et al. 2017. The Lancet Planetary Health

In all scenarios, we find a relative decrease in cold-related mortality and a relative increase in heat-related mortality as global mean temperature rises (Fig. 2). Yet, in most regions the net effect of these opposing trends is an increase in excess mortality, especially under unabated global warming (RCP 8.5). This is what would be expected from the exposure-response associations (Fig. 1), which generally show a much steeper increase in risk from heat than from cold. A relative decline in net excess mortality (with considerable uncertainty) is only observed for Northern Europe, East Asia, and Australia (and Central America for the more moderate scenarios RCP 2.6, and RCP 4.5).

So, contrary to the propositions of those who like to stress the potential benefits of global warming, a net reduction in mortality is the exception rather than the rule, when comparing estimates around the world. And one must not forget that there are important caveats associated with these results, which caution against jumping to firm conclusions.

Adaptation and demographic change

As mentioned already, we know that people’s vulnerability to non-optimal outdoor temperatures is highly variable and that people are adapted to their local climate. However, it remains poorly understood how fast this adaptation takes place and what factors (e.g., physiology, air conditioning, health care, urban infrastructure) are the main determinants. Therefore, the results shown (Fig. 2) rely on the counterfactual assumption that the exposure-response associations remain unchanged in the future, i.e., that no adaptation takes place. Furthermore, since older people are more vulnerable to non-optimal temperatures than younger people, the true evolution of temperature-related mortality will also be heavily dependent on demographic trends at each location, which were also neglected in this study.

Bottom line

I would like to conclude with the following thought: Let’s assume – albeit extremely unlikely – that the study discussed here does correctly predict the actual future changes of temperature-related excess mortality due to climate change, despite the mentioned caveats. Mostly rich countries in temperate latitudes would then indeed experience a decline in overall temperature-related mortality. On the other hand, the world would witness a dramatic increase in heat-related mortality rates in the most populous and often poorest parts of the globe. And the latter alone would be in my view a sufficient argument for ambitious mitigation – independently of the innumerous, well-researched climate risks beyond the health sector.

Addendum: Short-term displacement or significant life shortening?

To judge the societal importance of temperature-related mortality, a central question is whether the considered deaths are merely brought forward by a short amount of time or whether they correspond to a considerable life-shortening. If, for example, mostly elderly and sick people were affected by non-optimal temperatures, whose individual life expectancies are low, the observed mortality risks would translate into a comparatively low number of years of life lost. Importantly, short-term displacements of deaths (often termed ‘harvesting’ in the literature) are accounted for in the models presented here, as long as they occur within the lag period considered. Beyond these short-term effects, recent research investigating temperature mortality associations on an annual scale indicates that the mortality risks found in daily time-series analyses are in fact associated with a significant life shortening, exceeding at least 1 year. Only comparatively few studies so far have explicitly considered relationships between temperature and years of life lost, taking statistical life expectancies according to sex and age into account. One such studies found that, for Brisbane (Australia), the years of life lost – unlike the mortality rates – were not markedly seasonal, implying that in winter the mortality risks for the elderly were especially elevated. Accordingly, low temperatures in this study were associated with fewer years of life lost than high temperatures – but interestingly, only in men. Understanding how exactly the effects of cold and heat on mortality differ among men and women, and across different age groups, definitely merits further investigations.

200 Responses to “Will climate change bring benefits from reduced cold-related mortality? Insights from the latest epidemiological research”

  1. 51
    Mr. Know It All says:

    41 – MPassey

    Thanks for that info on the intermittency problem of renewables. Too many people seem to brush it off like it’s not a problem.

    It’ll be hard to beat the 2.7 cents per kWh in central Washington state where there is lots of Hydro. Renewable hydro is good steady power, but solar and wind are intermittent; and hydro is largely tapped out. If you want to get rich you need reliable cheap power:

    40 – Carrie
    Thank you for the stinging humor and insults. So, my proposed solution for the heat deaths was to power up for AC, perhaps with nukes since they don’t belch CO2. Do you have a solution?

  2. 52
    Carrie says:

    What stinging humor and insults? Getting in to the real basics of where all this data comes from is not stinging or insulting. Imagine a Military instructor saying “Do you get it?” (etc. when showing you how to clean a M16? Did you take that as insulting 24/7 too? Maybe you should put your air conditioner on and “cool down” a bit? :-)

    In the meantime try to focus and even try reading what I wrote again and then go back and what kinds of things you have been saying the “numbers” and what wrong with them in your haughty kia opinion.

  3. 53
    Astringent says:

    Kw @50, while there may (or may not?) be consensus on increase in relative humidity with global warming, it’s not the western desert climates that should worry us. You might like to read Russo et al 2017; which examines the multiplicative stress imposed by hot and humid days. While humans can survive in dry conditions at 50 degree C (though I recommend being quite rich before you make a habit of it), the danger of heat stress scales non-linearly with humidity. Their paper shows that while relative humidity played little role in the post 2000 heatwaves in Europe, if we breach a 2 degree warming limit then humidity is an issue. Without technology our human thermoregulation breaks down at temperatures as low as 35 degrees at 99% RH. At 4 degrees of warming this is likely to occur on the Eastern US seaboard with an annual probability of > 50%. Make sure you aren’t poor, homeless, or engaged in subsistence farming when that happens!

  4. 54
    jgnfld says:


    Re. baseload: Mr. KIA appears to already have forgotten the 2014 polar vortex event where the cold knocked out a large number of “baseload” coal and gas plants around the nation for a number of reasons including the fact that gas cannot “reliably” deliver both residential heat and electrical power under cold extremes.

    Nuclear plants undergo prolonged shutdowns for maintenance on an 18-24 month basis and so overcapacity needs to be planned in to take care of that.

    The automatic denier assumption that coal and gas (and nuclear) are “reliable” and that solar/wind are not is one of those denier assumptions that gets oft stated, but never examined.

  5. 55
    Romain says:

    Very interesting read.
    Looking at the error bars, it seems the results are unfortunately very dependent on the regional forecasts of the climate models.
    The only two regions where there is excess mortality for the whole confidence interval are southern and central Europe.
    Could you elaborate on that? Why the excess mortality is more certain for these two regions? Are the regional forecasts easier for the Mediterranean basin?

    Many thanks in advance,

  6. 56

    “Thanks for that info on the intermittency problem of renewables. Too many people seem to brush it off like it’s not a problem.”

    And too many people exaggerate it for ideological reasons.

    Neither response is helpful.

    I have no serious beef with nuclear power per se, but it has become painfully obvious that there is no business case for massive expansion of nuclear generation in the near term. (In the US, there’s barely a business case for keeping older reactors operating; and in fact several have been closed down for this reason.) And if there were such a case, there aren’t the skilled personnel available to do the building in the time that we have. (Or, more accurately, given needed planning and build times, *don’t* have.)

    So the choice is simplification a la Killian, renewable energy, or some of both (and including energy efficiency measures, for which there is still ample scope.) Nothing else is fast enough.

    Personally, I believe with nigel that it will have to be some of both. I don’t think the ‘strong version’ of simplification that Killian advocates will be acceptable to enough people fast enough to avoid cataclysmic disaster to humans and the environment, but neither do I think that a ‘convenience society’ like ours is apt to reach anything like sustainability just by ‘drop in’ substitutions. Structural change is needed.

  7. 57
    JCH says:

    So they factored out the socioeconomic factors between Minnesota and Iowa, or between Iowa and Missouri, or between Missouri and Arkansas, or between Arkansas and Louisiana? I do not believe that for one second.

    Let’s do another one, north to south: North Dakota has a colder climate and a lower death rate than South Dakota; South Dakota has a colder climate and a lower death rate than Nebraska; Nebraska has a colder climate and a lower death rate than Kansas; Kansas has a colder climate and a lower death rate than Oklahoma; Oklahoma has a colder climate and a higher death rate than Texas. Texas is large enough to have distinctly different climates, all of which are warmer than the other states on this ladder, and their death rate is higher than all except Oklahoma’s.

    What is the socioeconomic factor(s) that would result in South Dakotans and their balmy life saving climate overwhelming the humungous killer cold death rate of North Dakota and its freezer from heck?

  8. 58
    Mal Adapted says:


    What stinging humor and insults? Getting in to the real basics of where all this data comes from is not stinging or insulting.

    Now you’re talking! Heh. Once again, in my gratuitous (yet humble) opinion: AGW-denialism of IAT’s noxious species (and indeed, he’s far from the worst specimen) is, and should be, protected speech, but it will never be respectable. ‘Stinging’ speech is called for in response, particularly if it’s well-cited.

    A sincerely constructive word, however: I’m scarcely defending Mr. Ironically Anosognosic Typist, but IMHO we could all write more clearly if we worked at it. That’s not to say it’s easy! It’s not the writing that’s most time-consuming, it’s the rewriting, while avoiding cut’n’paste errors e.g. “cdesign proponentsists“. Being joyfully retired gives one more time, a necessary but not sufficient resource 8^} (‘}’ = ‘wavering smile of humility’). Still, even when you’re pretty sure the target of your comment won’t read all or any of it, something they tell us in writing classes is worth remembering: it’s up to the writer to make herself clear, so that it’s as easy as possible for even the lazy and/or hostile reader to ‘get’. Call it playing to the crowd, if you will.

  9. 59
    nigelj says:

    Keith Woolard @50, nobody was claiming humidity had increased. It was simply that it’s deceptive to compare death rates during a dry heatwave with a more recent humid heatwave. You went off on a huge tangent.

  10. 60
    JCH says:

    Excess winter deaths in Europe: a multi-country descriptive analysis

    Background: Winter deaths are a known health and social care challenge for many countries. A previous inter- national comparison showed significant differences in excess winter deaths across Europe in the 1990s, with the northern countries having lower excess winter mortality than those in southern Europe. Methods: The Excess Winter Deaths Index (EWDI) is the ratio of deaths in the winter period (December to March) compared with deaths in the non-winter period. Data from the Eurostat database and national registries were used to calculate the EWDI for 31 countries in Europe across the time period 2002/2003 to 2010/2011. Results: National EWDI values show heterogeneity, with a broad pattern of increasing EWDI values from northern to southern Europe and increasing mean winter temperature (r2 = 0.50, P > 0.0001). Malta, Portugal, Spain, Cyprus and Belgium all had an EWDI that was statistically significantly higher than the average EWDI for the other 30 European countries. There was no clear association between country-level EWDI and the level of inter-annual variability in winter temperature across Europe. Discussion: This article demonstrates the differences in EWDI that exist between European countries with implications for both research and policy. Many deaths may be avoidable as environmental, social and personal factors are known to contribute to winter mortality. We now need to work to better understand the causes of inter-country differences.

  11. 61
    Victor says:

    On the European heat wave of 2003:

    “As seen in Figure 1 below for June, July, and August of 2003, Europe was definitely ground-zero for what is certainly an extreme event. However, it is interesting that far more than half the planet is portrayed in green tones indicating below normal temperature anomalies at that time. Europe was simply located in the wrong place at the wrong time, but it is immediately obvious that the heat wave was anything but global in nature.”

  12. 62
    Hank Roberts says:

    > Keith Woollard

    You can look this stuff up, you know, rather than asserting your disbelief that something does not exist. Just put your belief into a search engine and find out.


    finds, among much else

    … Climate models that assume that future relative humidity will remain constant predict greater increases in the Earth’s temperature in response to increased carbon dioxide than models that allow relative humidity to change. The constant-relative-humidity assumption places extra water in the equation, which increases the heating.

    Many have questioned whether this prediction of a wetter future atmosphere is right, including Dessler and Minschwaner. “There’s no theoretical, simple line of reasoning that should say that it [relative humidity] should be constant,” says Ian Folkins, an associate professor of atmospheric sciences at Dalhousie University …

  13. 63
    zebra says:

    Hank Roberts 62,

    I think Keith is trying to emphasize the difference between relative and absolute humidity.

    I would agree, intuitively, that making a claim about “global relative humidity” doesn’t make a whole lot of sense.

    I suggest looking up the definitions before trying to interpret the scientific papers.

  14. 64

    And here’s the very model of a modern (Victor) strawman:

    “…it is immediately obvious that the heat wave was anything but global in nature.”

    It has been quite clear to all concerned that it wasn’t a ‘global’ heatwave. That’s why it’s always described as ‘European’.

    However, 2003 was pretty toasty as a year–at least, by the then-prevailing standards:

    And that’s the point; an increasingly warmer planet means increasingly severe and frequent heatwaves which develop in particular places. Like, right now, the Southeastern USA. Heat indices pushing 110 yesterday, today, and expected to be the same tomorrow. Hopefully, nobody dies.

  15. 65
    Keith Woollard says:

    JCH@57, Surprisingly (and this may come as a shock to you) there are other countries in the world, and occasionally they do science

  16. 66
    Keith Woollard says:

    Nigelj@59, this whole article is about whether climate change decreases life expectancy, and the worldś great anonymous statistician was trying to confirm this by saying Florida is worse than Nevada. The clear inference from what he/she said was that a more humid climate is harder for humans to cope with. I was just commenting that there is no suggestion in any published research that relative humidity is modeled to increase.

  17. 67
    Hank Roberts says:

    63 zebra says:
    20 Jun 2018 at 4:18 AM

    I suggest looking up the definitions

    The terms are defined, you’d find that at the links I provided above about climate models that do, or don’t, include changes in RH.

  18. 68
    JCH says:

    Winter Season Mortality: Will Climate Warming Bring Benefits?


    Extreme heat events are associated with spikes in mortality, yet death rates are on average highest during the coldest months of the year. Under the assumption that most winter excess mortality is due to cold temperature, many previous studies have concluded that winter mortality will substantially decline in a warming climate. We analyzed whether and to what extent cold temperatures are associated with excess winter mortality across multiple cities and over multiple years within individual cities, using daily temperature and mortality data from 36 US cities (1985-2006) and 3 French cities (1971-2007). Comparing across cities, we found that excess winter mortality did not depend on seasonal temperature range, and was no lower in warmer vs. colder cities, suggesting that temperature is not a key driver of winter excess mortality. Using regression models within monthly strata, we found that variability in daily mortality within cities was not strongly influenced by winter temperature. Finally we found that inadequate control for seasonality in analyses of the effects of cold temperatures led to spuriously large assumed cold effects, and erroneous attribution of winter mortality to cold temperatures. Our findings suggest that reductions in cold-related mortality under warming climate may be much smaller than some have assumed. This should be of interest to researchers and policy makers concerned with projecting future health effects of climate change and developing relevant adaptation strategies.

  19. 69
    Hank Roberts says:

    In recent years, a few well-known scientists have rejected the assumption of stable relative humidity, however, and we’re now in the middle of a dust-up in the field.

  20. 70

    #62, 63–But the constant relative humidity assumption doesn’t seem to be that far off, as I understand it. For example:

    During 1976–2004, global changes in surface RH are small (within 0.6% for absolute values), although decreasing trends of −0.11% ∼ −0.22% decade−1 for global oceans are statistically significant. Large RH increases (0.5%–2.0% decade−1) occurred over the central and eastern United States, India, and western China, resulting from large q increases coupled with moderate warming and increases in low clouds over these regions during 1976–2004.

    There is also a rather nuanced discussion in Chapter 2 of AR5 (WG 1), which I won’t try to summarize here.

    (Scroll to page 206.)

  21. 71
    nigelj says:

    Keith Woolard @66, I will briefly expand on my interpretation. Tamino was pointing out the difference in numbers of deaths between the two heatwaves of 1976 and 2003 was due to humidity in the recent event, not “societal changes”. I just don’t think he was arguing humidity is getting worse as such. My take is he was saying look hard at the physical differences.

    If anything societal changes would presumably include better health care and air conditioning in recent years which should lead to less deaths, which clearly didn’t happen so provides even more evidence that the 2003 event was very powerful.

    But I agree with you that nobody is totally sure whether relative humidity would increase and the evidence is mixed. But look at it this way with more water vapour in the atmosphere even relative humidity is more likely to increase than stay the same. You are gambling that it won’t increase. The sceptical side of the debate is gambling that everything will be less extreme than even middle range model estimates. Good luck with playing with that loaded revolver.

  22. 72
    Victor says:

    64 Kevin McKinney: And that’s the point; an increasingly warmer planet means increasingly severe and frequent heatwaves which develop in particular places. Like, right now, the Southeastern USA. Heat indices pushing 110 yesterday, today, and expected to be the same tomorrow. Hopefully, nobody dies.

    V: From GEOPHYSICAL RESEARCH LETTERS, VOL. 33, L23709, doi:10.1029/2006GL027470, 2006
    “Was the 2003 European summer heat wave unusual in a global
    Thomas N. Chase,1 Klaus Wolter,2 Roger A. Pielke Sr.,3 and Ichtiaque Rasool4

    “We place the European summer heat wave of 2003 in
    the context of other extreme summer tropospheric
    temperature events from 22N to 80N since 1979, as
    well as globally using annual averages. The analysis is
    performed in terms of standard deviations (SD) exceeded
    and correlations between regional extremes and
    temperatures at larger spatial scales. As has been pointed
    out previously the heat wave was statistically unusual and
    was a deep tropospheric phenomenon. In this analysis we
    also find the following. (1) Extreme warm anomalies
    equally, or more, unusual than the 2003 heat wave occur
    regularly. (2) Extreme cold anomalies also occur regularly
    and occasionally exceed the magnitude of the 2003 warm
    anomaly in terms of the value of SD. (3) There is a
    correlation between global and hemispheric average
    temperature and the presence of warm or cold regional
    anomalies of the same sign (i.e., warmer than average years
    have more regional heat waves and colder than average
    years have more cold waves). (4) Natural variability in the
    form of El Nin˜o and volcanic eruptions appear to be of
    much greater importance in causing extreme regional
    temperature anomalies than a simple upward trend in
    time. Extreme temperature anomalies in the wake of the
    1997 – 98 El Nin˜o were larger than the anomalies seen in
    summer 2003 both in area affected and SD extremes
    exceeded. (5) Regression analyses do not provide strong
    support for the idea that regional heat waves are increasing
    with time.”

  23. 73
    Al Bundy says:

    Nigelj: Nobody is making a case that renewable electricity will be cheaper in the short term

    AB: Not going to the doctor when you have cancer is cheaper in the short term, too. The deaths due to increased heat are decades after you’ve saved a buck. There will never be a time when humanity won’t be better off ignoring the global cancer…. this year.

  24. 74

    KW, #65–

    Keith, no-one to my knowledge is claiming, nor expecting, relative humidity to increase.

    The point is rather that, where RH already commonly reaches 95% levels for significant stretches of time during the year, relatively small increases in mean temperature–you know, the quantity that *is* projected to increase–may reliably be expected to kill increasing numbers of people who are unable to find ‘cool shelter’ for one reason or another.

    I trust the ‘Astringent’ link to Russo (2017) will help clarify, if needed:

  25. 75
    Hank Roberts says:

    But see citing papers for subsequent comment on any particular scientific paper that you find copacetic to your views.
    Search Scholar for the DOI, use a verbatim limit under Tools

    You may find support for what you believe.
    Or not, of course. For example:

  26. 76
    nigelj says:

    Victor @72, cherry picking again. You mention one research paper on the 2003 heat wave which is cherry picking. What’s more, it has a notorious climate sceptic among the authors, Roger Pielke so I’m underwhelmed. The following published research papers found the 2003 heatwave was related to agw climate change:

    Human contribution to the European heatwave of 2003, Peter A. Stott, D. A. Stone, M. R. Allen, Nature.

    Daniel Mitchell, Clare Heaviside, Sotiris Vardoulakis, Chris Huntingford, Giacomo Masato, Benoit Guillod, Peter Frumhoff, Andy Bowery, David Wallom, and Myles Allen. Attributing human mortality during extreme heatwaves to anthropogenic climate change. Environmental Research Letters, 2016.

    Other research links other heatwaves to climate change. The last IPCC report found good evidence that heatwaves have increased in frequency and this is probably the largest concern of all. They reviewed all the available research, as opposed to cherry picking like you consistently do. They also look critically at the quality of the research, unlike you.

    Heres a nice summary of the issues from “Global warming is increasing risk of heatwaves”:

  27. 77
    nigelj says:

    Al Bundy @73 yes good advice, but getting the world coordinated to deal with a complex future risk such as climate change is like herding cats. How does this change, short of a massive sudden climate shock next week?

  28. 78
    John Pollack says:

    Astringent @53 I agree entirely that the danger of heat stress increases rapidly with humidity. This is best represented by wet bulb temperature, but this is rarely reported (at least in the U.S.) so dew point is a reasonable proxy for extreme humidity. That said, your assertion that a 4C temperature rise would regularly result in temperatures of 35C with 99% humidity on the Eastern U.S. seaboard makes no meteorological sense. That’s a 35C dew point. Right now, dew points top out at about 27C in the most humid conditions, and even in a 4C warmer world, that would be about 31C. There are other places with higher dew points, especially the monsoon region of southeast Asia, and especially the vicinity of the Persian Gulf. These are the places that would first see a temperature/humidity combination that is lethal to the general population, especially those who had to do physical labor outdoors.

    I am not trying to minimize the situation, just be realistic. Before heat stress becomes generally lethal, there would be widespread suffering. Any power outage would be an emergency for those used to air conditioning. That could easily apply to the eastern U.S., and a lot of other places.

  29. 79
    zebra says:

    #70 Kevin,

    “not far off”

    Two different issues.

    Locally, as your reference notes, we have cases where RH has increased. For the purpose of this topic (health impacts), that’s what matters. If the global mean is relatively constant, then somewhere else RH has declined. (One might also infer that extremes of RH have become more frequent.)

    The value of mean global RH relates to the forcing question with water vapor as a GHG.

  30. 80


    I’m presuming that the near-balance for areas of increasing RH is the smaller decreasing trend over the oceans (obviously a much larger area). (And why is that happening anyway, I can’t help but wonder?) So for the health issue, maybe RH increases or flatlining are the order of the day, except for sailors.

    You are right of course that the radiative forcing is another important issue here, albeit not the focus of attention for this thread.

  31. 81
    Steven Emmerson says:

    Victor@72, There have been two IPCC Assesssment Reports since that paper. The latest concludes

    Human influence on the climate system is clear. It is extremely likely (95-100% probability) that human influence was the dominant cause of global warming between 1951-2010.

    The authors would know about Chase et alii‘s paper.

  32. 82
    Michael Sweet says:

    People discussing humidity need to understand the difference between relative humidity and absolute humidity. The absolute humidity is the amount of water in the air. The relative humidity is the percent of the maximum absolute humidity that is actually in the air.

    Looking each up on GOOGLE the citations I find disagree whether or not relative humidity will change due to AGW. There is agreement that absolute humidity will increase in a warmer world, the question is how much.

    That is: absolute humidity is expected to increase as temperatures increase. It may not increase enough for the relative humidity to stay the same, but absolute humidity will increase.

    As Tamino pointed out, even a small increase in absolute humidity in a hot location like Florida (where I live and work outside every day) is unbearable to anyone (or their animals) exposed for long periods of time. Anywhere in the humid tropics is susceptible to overheating with a small increase in temperature and absolute humidity. It is irrelevant if the relative humidity drops, if the absolute humidity increases it is more deadly.

    Criticizing Tamino as being anonymous is disingenuous, everyone knows his real name. It has even been posted on WUWT.

  33. 83
    Keith Woollard says:

    Michael @ 81… I had high hopes for your comment, the first three paragraphs were perfect and then it all fell to pieces.

    It is relative humidity that is the issue. If the body’s sweat can’t evaporate you don’t get the cooling effect.

    I don’t know Tamino’s real name, nor do I feel inclined to research to find it. All I know is he is one of the world best statisticians, because someone on this site told me that.

  34. 84
    Mr. Know It All says:

    Let’s have a quick review of 7th grade engrish.

    Apparently, 70K heat-related deaths is estimated to be the TOTAL number of deaths, not an ADDITIONAL number of deaths. If the number is the “total”, don’t use the word “additional” unless normally there are 0 heat-related deaths. If normally there are 50,000 and in 2003 there were 70,000, then 20,000 additional deaths occurred in 2003, not 70,000. Agreed?
    OK, engrish refresher is over. :)

    I have a question: what would be a “normal” or “typical” or “ballpark” number of deaths that occur in a European summer?

    54 – jgnfld
    Yes, nukes and FF power plants have to undergo plant maintenance, which can be planned for, and worked around by the grid operators. Examine these facts: Solar goes out reliably once per day, and if it’s cloudy, more than that. Wind goes out when the wind quits, but it’s not predictable when that will occur. Grid operators, and their customers, don’t like that.

    For those who want more info on the relationship between relative humidity and absolute humidity, temperature, etc a psychrometric chart is useful. Here is a tutorial with a link to free software. I have not used the software.

    Trane has a psychrometric chart you can download – not sure if it is free or not:

    And they have printed ones, for various temperature ranges, altitudes, etc.

    Carrier may have a better selection of paper charts:

  35. 85
    Astringent says:

    @78 John Pollack

    Thanks for the correction John, I can see that I misinterpreted some of the numbers in Russo’s paper. Still don’t fancy living somewhere that’s hot and humid today – let alone in a hotter world!

  36. 86
    zebra says:

    #82 Michael,

    “understand the difference”

    Yes, I and others have already pointed that out. However, it is also necessary to be disciplined in using the terms. You say:

    As Tamino pointed out, even a small increase in absolute humidity in a hot location like Florida (where I live and work outside every day) is unbearable to anyone (or their animals) exposed for long periods of time. Anywhere in the humid tropics is susceptible to overheating with a small increase in temperature and absolute humidity. It is irrelevant if the relative humidity drops, if the absolute humidity increases it is more deadly.

    This is confusing.

    RH will increase if:

    1. Temp is lower, AH is constant.
    2. AH is higher, temp is constant.

    RH will decrease if:

    1. AH is lower, temp is constant.
    2. Temp is higher, AH is constant.

    And, of course, various other combinations of numerical changes in both are possible.

    To elaborate on my earlier comments, the simple point is that it isn’t simple. You have to look at specific locales in both space and time, and the actual numbers.

  37. 87
    Veronika says:

    A few comments on some of the health-related issues that came up:

    @# 55: You asked about the uncertainties in the mortality projections as shown by the error bars in Fig. 2. The sources of these uncertainties are indeed the variability in temperature projections (5 GCMs were considered here), but also the unprecise estimates of the exposure-response relationships. Interestingly, the latter are in most cases the dominant source of uncertainty, related to the extrapolation of the curves into a range of temperatures that have rarely or not at all been observed in the past.

    One would need to check whether this is precisely the case for southern and central Europe. But because there are these two sources of uncertainty, the relatively more precise estimates of increased heat-related mortality in these regions do not necessarily reflect that climate models agree more strongly on temperature changes there.

    @ #38, #57, #60: Life expectancies are of course determined by a myriad of factors. So, indeed you cannot just compare life expectancies across latitudes and conclude on the influence of climate. But if you fit exposure-response functions, aiming to separate the effect of temperature from other determinants of mortality risk, you find indeed that there is a general tendency – at least in the temperature zone – of warmer locations showing relatively higher cold risk that cooler locations. I can myself provide anecdotal evidence of “suffering” more from cold in winter in southern Sevilla, where few of the houses have central heating, than in northern Berlin, where pretty much all of the houses are centrally heated.

    The big question is of course how these relationships will evolve in the future. As climate change progresses Berlin will move towards the temperature distribution of today’s southern Europe. But houses – at least for some time – will keep the infrastructure of today. So, it is unlikely that Berlin would concurrently move to higher relative cold risk. Interestingly, studies looking how cold risks have changed over time in different countries during the last decades have rarely found evidence of a consistent trend.

  38. 88

    The relative humidity is

    RH = pH2O / es

    where pH2O is the water vapor partial pressure, and es is the saturation pressure. The latter relates to temperature in a complicated way via the Clausius-Clapeyron relation.

  39. 89
    Michael Sweet says:

    It is not confusing. Changes in the relative humidity do not matter. Only changes in the absolute humidity matter (dew point is essentially the same as absolute humidity so changes in the dew point can be used instead).

    All climate models predict increases in global absolute humidity. This increase has been measured. Globally heat is more deadly today than it was 40 years ago.

    It is not necessary to consider different locations differently. If the absolute humidity has increased, heat is more deadly. Over the entire globe absolute humidity has increased. There might be a very few locations where absolute humidity decreases, but most areas of the globe, and the global average, will increase.

  40. 90

    #74, KIA–

    Apparently, 70K heat-related deaths is estimated to be the TOTAL number of deaths, not an ADDITIONAL number of deaths. If the number is the “total”, don’t use the word “additional” unless normally there are 0 heat-related deaths. If normally there are 50,000 and in 2003 there were 70,000, then 20,000 additional deaths occurred in 2003, not 70,000. Agreed?

    No, not agreed. 70,000 is not the total mortality, it is the mortality *above* what would have been expected, and which is attributed to the heat. Hence “additional.”

    At least, that is how I understand it.

  41. 91

    #84, KIA (again)–

    Solar goes out reliably once per day, and if it’s cloudy, more than that.

    Actually, no–cloud reduces energy yield by varying amounts, but not to zero. Output can be quite significant on cloudy days.

    Wind goes out when the wind quits, but it’s not predictable when that will occur.

    Actually, it is pretty predictable on short timescales, and there is a large market for same-day forecasts. Since a common structure is to bid 15-minute blocks of power, even a forecast 30 minutes out is pretty useful to grid operators.

    Random example, in operation at an Indian hybrid wind-solar farm:

    Every 90 minutes, the Hitachi solution sends Atria detailed energy generation data that forecasts how much energy will be produced over the next 24 hours. The forecast error is required to be within 15%. Hitachi has achieved this goal and we continue to improve.

  42. 92
    Carrie says:

    84 Mr. Know It All,

    a PS you should also note that the mortality spike from heat waves continues for about 3 months after the end of the extreme heat. It’s another real world variation that precludes 100% accuracy and certainty of numbers across all regions and nations.

    Yes, if you think this means there is a delayed effect on human health from heat waves you’d be correct. How well such delayed deaths are captured in the source data is unknown from region to region, because it is a value judgment made at the coal face by medical staffers (I believe). Now how well this is reflected in different studies and data summaries is another matter.

    The accumulated knowledge of heat wave mortality is however overwhelming in it’s conclusions and what that means. This summary by Veronika being one such example.

  43. 93
    zebra says:

    #89 Michael,

    “changes in the relative humidity do not matter”

    I agree. But that’s because it is a poor metric; you need to have more complete information.

    My critique has to do with imprecision of language. It is correct that global AH will increase, and that it is a “bad thing” for many reasons. But, when it comes to mortality and morbidity due to heat stress, the effects is a local one dependent on other factors as well.

    For example, it is not the case that locally increasing AH in a cold dry place (Antarctica as an extreme example) will have significant negative physiological effect– it may be a slight benefit, actually.

    And in other more common situations, a humid air mass can lower temperatures, which mitigates any adverse effects. This happens all the time.

    See #78 John Pollack. You have to look at the numbers. And you have to distinguish between weather and climate, and means and extremes, and so on.

  44. 94
    Mr. Know It All says:

    92 – Thomas, I mean Carrie:
    Approximately how many heat related deaths occur in a “normal” summer in Europe?

    For those who want more solar power, it’s almost free now. As they say in investing circles: BTFD!

  45. 95
    NonScientist says:

    Thanks for the various responses to my post. At the moment, health issues prevent me from composing anything resembling coherent further posts, I’ll add a substantive reply if/when I can. — Best to All

  46. 96
    nigelj says:

    M Sweet, thank’s for posting that research article. Very sobering and convincing.

  47. 97
    nigelj says:

    Zebra @93, yes higher humidity has both costs and some benefits, and would be regional in the sense of being more in coastal areas. However the affects of higher humidity and temperatures can be lethal, and the benefits of some humidity are only less skin irritations and other minor benefits, so don’t lose sight of that.

    I’m not sure what examples you have of humid air masses causing temperatures to drop, perhaps you mean evaporation. Humid air masses normally bring hot humid weather where I live, and this seems like the significant thing.

    Iran had a deadly serious killer heatwave caused specifically by humid air masses combined with high temperatures causing the wbt to be about 35 degrees. These sorts of things will increase in number with climate change, and many coastal tropical and poor areas are vulnerable, and will have to devote scarce resources to air conditioning.

  48. 98
    Adam Lea says:

    Someone has brought up the 2010 Russian heatwave.

    There appears (from a quick search) to be contradictory papers on the role of anthropogenic climate change on that heatwave:

    “We conclude that the intense 2010 Russian heat wave was mainly due to natural internal atmospheric variability.

    “For July temperature in Moscow, we estimate that the local warming trend has increased the number of records expected in the past decade fivefold, which implies an approximate 80% probability that the 2010 July heat record would not have occurred without climate warming.”

    From these two papers, there were two news articles making apparently opposite claims:

    The Guardian article does at least link to the papers it references.

    I appreciate that the truth is a bit more complicated than just picking out a sentence in the abstract, and it looks to me like one is looking at internal atmospheric dynamics, and the other is looking at likelihood of breaking high temperature records given natural variability superimposed on a warming trend, but the problem is, any media outlet with an agenda can pick and choose what reference it likes that supports its agenda. How is the general public expected to get their heads around it all? It is not realistic to expect individuals to trawl through scientific papers themselves, trying to piece together the best estimate of the truth from many sources, they just don’t have the time.

  49. 99
    Brian Dodge says:

    It was more than 70,000 excess deaths. How much more is unknown precisely. If there hadn’t been a huge number of deaths in August, drawing attention to the problem, a lot of the earlier excess deaths wouldn’t have been noticed – an indicator that Global warming is the culprit.
    There’s more -RTFP
    “More than 70,000 additional deaths occurred in Europe during the summer 2003. Major distortions occurred in the age distribution of the deaths…..,”
    “The southeastern boundaries of the mortality crisis are poorly defined, as it was not possible to obtain the necessary data from Bosnia-Herzegovina and Serbia. These limitations probably lead to an underestimation of the real death toll in Europe due to the summer of 2003, as Bulgaria, Greece, Romania, and the south of the Balkans may have been affected by excess mortality.”
    “a series of minor mortality crises throughout Europe, occurring almost unnoticed, led to a significant cumulative number of victims in comparison to the huge number of victims due to the August heat wave. Global warming may constitute a new threat to health in an aged Europe that may be difficult to monitor at the level of a country or of a major city only.”
    A 3 sigma event in Davis CA , summertime mean 33 C, sigma 2.8 C would be a killer at 30%RH(Wet Bulb >35C). If the distribution of temperatures in Davis has shifted like that shown in Hansen’s graph, what used to be a rare 3 sigma event (0.03%? If I read the chart right – ), now has a 7%+ probability, because the mean has shifted, and the Standard Deviation has increased.

  50. 100

    Adam, #96–

    In my opinion you’ve just put your finger on a real problem that is fundamental to attribution studies, which is that there is often not a well-defined framework for which question or questions are attempting to be answered. It’s been pointed out before that in the case of the Russian heatwave, it’s not contradictory to say that one the one hand, the internal dynamics are still within historical bounds, but on the other that shifting norms also shift probabilities of such heatwaves occurring. We need, I think, a clarification of what attribution really means, and what it really requires. At present, I think quite a few papers are still talking past each other in this fashion.

    I remember the case of extreme precipitation flooding in (IIRC) Colorado a few years ago, which was studied in the BAMS annual extreme events issue; the researchers found that there was no human fingerprint, based on the result that modeled trends showed a *decreasing* probability of such events occurring under warming. Logical, of course. But it nagged at me a bit: what about the internal dynamics of the event itself? Was it, for instance, associated with unusually warm temperatures and large amounts of precipitable water vapor? Or with slow storm tracking?

    In other words, might there be other aspects of the probabilities that might be worth considering in this context beyond simple modeled frequency, such as shifts in the intensity PDF?

    Conceptual clarity is really needed–though perhaps there are developments in that regard that I’m unaware of?