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Health Effects of Temperature (Hot Weather) -- Summary
Climate alarmists predict global warming will increase human death rates, and nary a heat wave occurs but what they are quick to blame any concomitant excess deaths on the high temperatures associated with it.  But are such claims correct?  Would there really be more frequent and severe episodes of heat-related mortality in a warmer world?  And if there would, how would the decrease in the number of cold-related deaths that would accompany the rising temperatures compare with the number of heat-related deaths?

We begin our review of this subject with the study of Davis et al. (2002), who determined changes in the impact of high temperatures on daily mortality rates over a period of four decades in six major metropolitan areas along a north-south transect in the eastern United States.  The results of their study showed there were few significant temperature-mortality relationships for any decade or demographic group in the three southernmost cities examined, where warm weather is commonplace.  In the three northernmost cities, however, there were statistically significant declines in population-adjusted mortality rates during hot and humid weather between 1964 and 1994.

What was the reason for the declines in heat-related deaths?  In the words of the authors of the study, "these statistically significant reductions in hot-weather mortality rates suggest that the populace in cities that were weather-sensitive in the 1960s and 1970s have become less impacted by extreme conditions over time because of improved medical care, increased access to air conditioning, and biophysical and infrastructural adaptations."  They further note that "this analysis counters the paradigm of increased heat-related mortality rates in the eastern US predicted to result from future climate warming."

Expanding both the spatial and temporal scope of their analysis, Davis et al. (2003) calculated "annual excess mortality on days when apparent temperatures - an index that combines air temperature and humidity - exceeded a threshold value for 28 major metropolitan areas in the United States during the period 1964 through 1998."  They report that for the 28-city average, there were 41.0 4.8 excess heat-related deaths per year per standard million in the 1960s and 1970s, 17.3 2.7 in the 1980s, and 10.5 2.0 in the 1990s.  In analyzing these results together with various types of ancillary data, they again concluded that this "systematic desensitization of the metropolitan populace to high heat and humidity over time can be attributed to a suite of technologic, infrastructural, and biophysical adaptations, including increased availability of air conditioning."  In addition, because of their finding that "all-causes mortality during heat stress events has declined despite increasingly stressful weather conditions in many urban and suburban areas," Davis et al. but state the obvious when noting that "heat-related mortality in the United States seems to be largely preventable at present."

Continuing in much the same vein, Davis et al. (2004) examined the seasonality of mortality due to all causes using monthly data for the same cities and time period.  The results indicated, in their words, that "warmer months have significantly lower mortality rates than colder months."  Hence, they calculated that a 1C warming actually results in a net mortality decline of 2.65 deaths per standard million people.  Since the annual death rate of approximately 9500 deaths per standard million is so much larger, however, the benefits of the warming are extremely small, i.e., a reduction in the annual number of deaths of less than 0.03%, which also pales in comparison to the nearly 20% reduction in annual mortality that has occurred as a consequence of technological advancements experienced between the 1960s/70s and the 1990s.  The primary implication of Davis et al.'s findings, therefore, is that "the seasonal mortality pattern in US cities is largely independent of the climate and thus insensitive to climate fluctuations, including changes related to increasing greenhouse gases."

A decline in heat-related mortality has also been observed for North Carolina, USA, South Finland, and Southeast England for the period 1971-1997.  According to Donaldson et al. (2003), in the coldest of these three regions (South Finland, where there was no change in temperature over the study period), heat-related deaths per million inhabitants in the 55-and-above age group declined from 382 to 99.  In somewhat warmer Southeast England, where it warmed by a whopping 2.1C over the study period, heat-related deaths per million of the at-risk age cohort still declined, but this time from only 111 to 108.  Last of all, in the warmest of the three regions (North Carolina, where mean daily May-August temperature rose by 1.0C over the study period), corresponding heat-related deaths also fell, and this time from 228 to a mere 16 per million.

With respect to the dramatic decline in the number of heat-related deaths observed in the hottest area of the study (North Carolina), the authors attribute the reduction in mortality to "the increase of air conditioning in the South Atlantic region of the U.S.A.," where they report that "the percentage of households with some form of air conditioning in that region rose from 57% in 1978 to 72% in 1997."  With respect to the declining heat-related deaths in the other two regions, they say "the explanation is likely to lie in the fact that both regions shared with North Carolina an increase in prosperity, which could be expected to increase opportunities for avoiding heat stress."

Adaptation and technology may also help to explain the findings of Braga et al. (2002).  These authors carried out time-series analyses in 12 U.S. cities (Atlanta, Georgia; Birmingham, Alabama; Canton, Ohio; Chicago, Illinois; Colorado Springs, Colorado; Detroit, Michigan; Houston, Texas; Minneapolis-St. Paul, Minnesota; New Haven, Connecticut; Pittsburgh, Pennsylvania; and Seattle and Spokane, Washington) to estimate both the acute effects and the lagged influence of temperature on respiratory and cardiovascular disease (CVD) deaths.  Dividing the cities into two groups -- hot (Atlanta, Birmingham and Houston) and cold (all the rest) -- they found that in the hot cities, "neither hot nor cold temperatures had much effect on CVD or pneumonia deaths," although for the sub-categories of chronic obstructive pulmonary disease and myocardial infarctions there were some lagged effects.  In the cold cities, on the other hand, the authors report that "both high and low temperatures were associated with increased CVD deaths," with the effect of cold temperatures persisting for days but the effect of high temperatures restricted to the day of the death or the day before.  Of particular interest was the finding that "for all CVD deaths the hot-day effect was five times smaller than the cold-day effect."  In addition, the hot-day effect included some "harvesting," where the authors "observed a deficit of deaths a few days later," which they say they "did not observe for the cold-day effect."

An early harvesting of imminent deaths during heat waves has also been reported by Laschewski and Jendritzky (2002), who examined daily mortality rates in Baden-Wurttemberg (10.5 million inhabitants) over the 30-year period 1958-1997 to determine the sensitivity of the population of this moderate climatic zone of southwest Germany to long-and short-term episodes of heat and cold.  With respect to long-term (seasonal) outside conditions of heat and cold, the authors say the mortality data "show a marked seasonal pattern with a minimum in summer and a maximum in winter."  With respect to short-term exposure to heat and cold, they found that "cold spells lead to excess mortality to a relatively small degree, which lasts for weeks," and that "the mortality increase during heat waves is more pronounced, but is followed by lower than average values in subsequent weeks."  The authors say this latter observation suggests that people who died from short-term exposure to heat possibly "would have died in the short term anyway."

With respect to this short-term mortality displacement in the case of heat-related deaths, the authors' data demonstrate that it is precisely that, i.e., merely a displacement of deaths and not an overall increase.  They found, for example, that the mean duration of above-normal mortality for the 51 heat episodes that occurred from 1968 to 1997 was 10 days, with a mean increase in mortality of 3.9%, after which there was a mean decrease in mortality of 2.3% for 19 days.  Hence, the net effect of the two perturbations was an overall decrease in mortality of 0.2% over the full 29-day period.

In another study, Huynen et al. (2001), evaluated the impact of heat waves and cold spells on mortality rates in the entire population of Holland.  For the 19-year period 1 January 1979 through 31 December 1997, the group of five scientists compared the numbers of deaths in people of all ages that occurred during well-defined heat waves and cold spells.  Their bottom-line findings were a total excess mortality of 39.8 deaths per day during heat waves and 46.6 deaths per day during cold spells.

These numbers indicate that a typical cold-spell day kills at a rate that is 17% greater than a typical heat-wave day in the Netherlands.  The authors also note that the heat waves of the period they studied ranged from 6 to 13 days in length, while the cold spells lasted 9 to 17 days, making the average cold spell approximately 37% longer than the average heat wave.  Adjusting for this duration differential thus makes the number of deaths per cold spell in the Netherlands fully 60% greater than the number of deaths per heat wave.  What is more, excess mortality continued during the whole month after the cold spells, leading to even more deaths; while in the case of heat waves, there actually appeared to be mortality deficits in the following month, which suggests, in the words of the authors, "that some of the heat-induced increase in mortality can be attributed to those whose health was already compromised" or "who would have died in the short term anyway."  This same conclusion -- that of "harvesting" as described above -- has also been reached in a number of other studies (Kunst et al., 1993; Alberdi et al., 1998; Eng and Mercer, 1998; Rooney et al., 1998).  It is highly likely, therefore, that the 60% greater death toll we have calculated for Dutch cold spells as compared to Dutch heat waves is a vast underestimate of the true differential killing power of these two extreme weather phenomena.

In light of these findings, the Dutch could well ask themselves if global warming would reduce thermal stress in the Netherlands, which is exactly what the senior and second authors of the Huynen et al. paper did in a letter to the editor of Epidemiology (Martens and Huynen, 2001).  Based on the predictions of nine different GCMs for an atmospheric CO2 concentration of 550 ppm in the year 2050 -- which implied a 50% increase in Dutch heat waves, but a 67% drop in Dutch cold spells -- they calculated a total mortality decrease of approximately 1100 people per year for the country at that point in time.

Yes, global warming -- if it continues, and for whatever reason -- will result, not in more lives lost, but in more lives saved.  And it's not just the Dutch that will be thus benefited; data from all over the world tell the very same story.

In the Czech Republic, for example, Kysely and Huth (2004) tested different ways of evaluating heat-related mortality over the nine-year period 1992-2000 by calculating deviations of the observed number of deaths from the expected number of deaths for each day of the year.  In doing so, they discovered that "the distribution of days with the highest excess mortality in a year is clearly bimodal, showing a main peak in late winter and a secondary one in summer."  In the case of the smaller number of summer heat-wave-induced deaths, they also found that "a large portion of the mortality increase is associated with the harvesting effect, which consists in short-term shifts in mortality and leads to a decline in the number of deaths after hot periods (e.g. Rooney et al., 1998; Braga et al., 2002; Laschewski and Jendritzky, 2002)."  Specifically, they report that "the mortality displacement effect in the severe 1994 heat waves can be estimated to account for about 50% of the total number of victims."  In other words, as they put it, "people who would have died in the short term even in the absence of oppressive weather conditions made up about half of the total number of deaths."

Similar results were obtained in China for the city of Shanghai by Kan et al. (2003), who investigated the association between temperature and daily mortality there from 1 June 2000 to 31 Dec 2001.  Their work led to the development of a V-like relationship between total mortality and temperature that had a minimum mortality risk at 26.7C.  Above this optimum temperature, Kan et al. noted that "total mortality increased by 0.73% for each degree Celsius increase; while for temperatures below the optimum value, total mortality decreased by 1.21% for each degree Celsius increase."  The net effect of a warming of the climate of Shanghai, therefore, would likely be reduced mortality on the order of 0.5% per degree Celsius increase in temperature, or perhaps even more, in light of the fact that the warming of the past few decades has been primarily due to increases in daily minimum temperatures, where the data of Kan et al. reveal mortality rates in Shanghai to be about 50% greater than they are at the typical time of occurrence of maximum temperatures.

Down in Brazil, the monotonous results repeat themselves yet again.  Working with data from Sao Paulo, Gouveia et al. (2003) determined that for each 1C increase in a given and prior day's mean temperature above the minimum-death temperature of 20C, there was a 2.6% increase in deaths from all causes in children, a 1.5% increase in deaths from all causes in adults, and a 2.5% increase in deaths from all causes in the elderly.  For each 1C decrease below 20C, however, the cold effect was greater, with increases in deaths from all causes in children, adults and the elderly registering 4.0%, 2.6% and 5.5%, respectively, which cooling-induced death rates were 54%, 73% and 120% greater than those attributable to 1C of warming.

A similar analysis with respect to only cardiovascular deaths actually found no evidence of heat-induced deaths in adults, but the familiar 2.6% increase in deaths for each 1C decrease below 20C.  In the elderly, however, a 1C warming above 20C led to a 2% increase in deaths; but a 1C cooling below 20C led to a 6.3% increase in deaths in this age group, or more than three times as many cardiovascular-related deaths due to cooling than to warming in the elderly.  Findings with respect to respiratory-induced deaths were similar.  Death rates due to a 1C cooling were twice as great as death rates due to a 1C warming in adults, and 2.8 times greater in the elderly.

Clearly, when it comes to the bottom-line reality of living or dying, warming is much to be preferred to cooling, not only in Sao Paulo, Brazil, but in all of the many other places of the world where similar studies have found the very same thing [see also, in this regard, Health Effects (Temperature -- Cardiovascular, Cold Weather, and Respiratory) in our Subject Index].  Some people, however, simply refuse to see the truth and actually promulgate a blatant falsehood in this respect, the most egregious examples of late being the many climate-alarmist commentaries on the European heat wave of August 2003.

A prime example is the commentary of Larsen (2003), who in the opening sentence of a copyrighted report for the Earth Policy Institute declares that the heat wave claimed an estimated 35,000 lives, while stating in the story's subtitle that "far greater losses may lie ahead."  Then, after rehashing some of the particulars of the meteorological event and reciting a bit of heat wave lore, Larsen concludes with the statement that "we can say with confidence that the August heat wave in Europe has broken all records for heat-induced human fatalities," and that "for many of the millions who suffered through these record heat waves and the relatives of the tens of thousands who died, cutting carbon emissions is becoming a pressing personal issue."

In analyzing these claims, we first consider what typically happens during the other extreme of the year, i.e., the cold of winter.  According to the UK Department of Health, as cited by McGregor et al. (2004), average winter excess mortality in a normal year in the UK alone is identical to what is claimed by Larsen to have required a heat wave of unprecedented proportions over all of Europe to produce.  In fact, there is voluminous evidence, cited in our second Major Report - Enhanced or Impaired? Human Health in a CO2-Enriched Warmer World - that normal cold annually kills far more people than does even unseasonable warmth almost everywhere in the world.  Consequently, if people truly believe that rising atmospheric CO2 concentrations are responsible for global warming, which is predicted to be most strongly manifest in minimum temperatures in winter in the world's coldest climates, they should actually welcome the ongoing upward trend in the concentration of this trace constituent of the atmosphere, rather than have "cutting carbon emissions" become "a pressing personal issue," unless, of course, something other than the truth is driving their agenda.

Climate-alarmist claims about heat waves are seen to be even more outrageous when other elements of the aerial environment are considered.  Stedman (2004), for example, analyzed the impact of air pollutants during the 2003 heat wave in the United Kingdom and determined that 21-38% of the total excess deaths claimed to be due to high temperatures were actually the result of elevated concentrations of ozone and PM10 (particulate matter of diameter less than 10m).  Likewise, Fischer et al. (2004) determined that 33-50% of the deaths attributed to the same heat wave in the Netherlands were caused by high ozone and PM10 concentrations.

Simultaneously, over in the Czech Republic, Kysely and Huth (2004), as we have already noted, found that a large portion of the mortality increase that is often attributed to heat waves is actually due to a harvesting effect, "which," in their words, "consists in short-term shifts in mortality and leads to a decline in the number of deaths after hot periods."  Consequently when the heat wave harvesting effect is added to the air pollution effect described by Stedman and Fischer et al., it can be appreciated that the death toll ascribed to the unseasonably warm temperatures of the 2003 European heat wave was vastly overstated in all of the climate-alarmist-inspired press reports of the high-temperature episode, and that the true death toll of the unusual weather event literally pales in comparison to the number of deaths that occur with little notice or fanfare throughout each and every normal winter.

In conclusion, if we are truly concerned about temperature-related mortality, it is cold weather upon which we should be focusing our attention, not hot weather; and in this regard, a little global warming could do a lot to alleviate the problem, as could improved standards of living throughout the less-developed world, for prosperity - and the technological advancements that come with it (primarily heating followed by cooling) - can do even more.

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