We begin our review of the effects of cold temperatures on human health and mortality with the study of Keatinge and Donaldson (2001), who examined the effects of temperature, wind, rain, humidity and sunshine during high pollution days in the greater London area over the period 1976-1995 to determine what weather and/or pollution factors have the biggest influence on human mortality.  The results of their complex analysis were truly astounding: "no pollutant in that analysis, SO2, CO, or smoke, was associated with a significant (P < 0.05) increase in mortality."  There was, however, a "large, delayed increase in mortality after low temperature," which was "specifically associated with cold and is not due to associated patterns of wind, rain, humidity, [or lack of] sunshine."  Indeed, cold alone was found to be responsible for the excess deaths, although there was a small but "short-of-statistical-significance" increase in mortality with smoke, which the authors suggested might possibly have been due -- if it really occurred (which is highly questionable) -- to the effects of PM10 (particulate matter of 10-micron diameter).

So how does cold kill?  According to Keatinge and Donaldson, "cold causes mortality mainly from arterial thrombosis and respiratory disease, attributable in turn to cold-induced hemoconcentration and hypertension [in the first case] and respiratory infections [in the second case]."  Such a cause-and-effect relationship has been demonstrated by Nafstad et al. (2001), who studied the association between temperature and daily mortality for citizens of Oslo, Norway over the period 1990 to 1995.  Because Norwegian law requires that all deaths be examined by a physician, who diagnoses the cause of death and reports it on the death certificate, the authors were able to categorize and examine the effects of temperature on mortality from (1) respiratory diseases, (2) cardiovascular diseases and (3) all diseases (excluding deaths caused by accidents, poisoning, suicide, or other non-normal causes).  The results of Nafstad et al.'s analysis showed that the average daily number of deaths in all three categories was higher in winter (October-March) than in summer (April-September).  For respiratory diseases, winter deaths were 47% more numerous than summer deaths; while for cardiovascular diseases and the all-disease category, winter deaths were 15% more numerous than summer deaths.  Based on these findings the authors conclude that "a milder climate would lead to a substantial reduction in average daily number of deaths."

Similar findings have been noted by other authors.  In a brief review of Sudden Cardiac Death (SCD) and Acute Myocardial Infarction (AMI) in Israel and elsewhere, Behar (2000) reports that "most of the recent papers on this topic have concluded that a peak of SCD, AMI and other cardiovascular conditions is usually observed in low temperature weather during winter."  As one example, he cites an Israeli study (Green et al., 1994), which revealed that between 1976 and 1985, "mortality from cardiovascular disease was higher by 50% in mid-winter than in mid-summer, both in men and women and in different age groups."  And this occurred in spite of the fact that summer temperatures in the Negev, where much of this work was done, often exceed 30°C, while winter temperatures typically do not drop below 10°C.

Deaths related to coronary artery disease in California were also shown to be higher in winter than in summer.  According to Kloner et al. (1999), who examined all 222,265 death certificates from Los Angeles County for deaths caused by coronary artery disease as a function of month of the year from 1985-1996, "even in the relatively mild climate of southern California, there is a seasonal variability to coronary death, with rates in December and January 33% higher than in June through September."  They additionally noted that studies from a number of other locations have also determined that deaths due to coronary artery disease are more prevalent in the colder winter months of the year than they are in the warmer summer months.

In a slight twist to the studies above, Hajat and Haines (2002) set out to determine whether or not the well-documented relationship between cold temperatures and cardiovascular/respiratory mortality in the elderly extends to the number of visits by the elderly to general practitioners.  To accomplish this objective, they used general additive models to regress time-series of daily numbers of general practitioner consultations by the elderly against temperature.  Consultation data included visits to the doctor for the following respiratory and cardiovascular complaints, as obtained for registered patients aged 65 and older from several London practices between January 1992 and September 1995: asthma, lower respiratory disease excluding asthma, upper respiratory disease excluding allergic rhinitis, and cardiovascular disease.

The results of their analysis showed that the mean number of consultations was higher in cool-season months (October-March) than in warm-season months (April-September) for all respiratory and cardiovascular diseases.  In addition, at mean temperatures below 5°C, the relationship between respiratory disease consultations and temperature was linear, and stronger at a time lag of 6 to 15 days, such that a 1°C decrease in mean temperature below 5°C was associated with a 10.5% increase in all respiratory disease consultations.

Low temperatures were also determined to significantly increase stroke occurrence in Russia.  According to Feigin et al. (2000), "the risk of [ischemic stroke] on days with low ambient temperature is 32% higher than that on days with high ambient temperature."  Elsewhere, Keatinge et al. (2000) evaluated mortality deviations from a base level as temperatures rose and fell by 0.1°C increments in north Finland, south Finland, southwest Germany, the Netherlands, Greater London, north Italy, and Athens, Greece, in people aged 65-74, finding that "all regions showed more annual cold related mortality than heat related mortality."  In fact, over the seven regions studied, annual cold related deaths were nearly ten times greater than annual heat related deaths.

In contrast to the results discussed above, Goklany and Straja (2000) report that there were no trends in deaths due to either extreme heat or cold in the entire U.S. population over the period 1979-1997, even among the older more susceptible age groups, i.e., those aged 65 and over, 75 and over, and 85 and over.  However, deaths due to extreme cold still exceeded those due to extreme heat by 80% to 125%.  As for why there is an absence of statistically significant trends in U.S. death rates attributable to either extreme heat or cold, the authors state that this observation "suggests that adaptation and technological change may be just as important determinants of such trends as more obvious meteorological and demographic factors."

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.  These cities were divided into two groups: hot (Atlanta, Birmingham and Houston) and cold (all the rest).

Results of their analysis showed 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 deaths during heat waves has also been reported by Laschewski and Jendritzky (2002), who examined daily mortality rates of people 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.

Last of all, Gemmell (2001) conducted a detailed analysis of the answers of 858 respondents to a pertinent health and housing survey conducted in 1991.  The response rate to this survey was 82%, while the average age of respondents was 59 years.  Gemmell's analysis showed that "over and above socioeconomic factors and house conditions, inadequate home heating is associated with poor health in those aged 55-60."  He says, for example, that "respondents who reported feeling cold in winter 'most of the time' were over three times more likely to suffer from a limiting condition and almost five times as likely to report 'fair' or 'poor' self assessed health."  Also noted was the fact that "living in a cold house will almost certainly exacerbate existing conditions and may lead to early mortality."

How can we stem the ugly tide of premature death associated with unseasonably low temperatures? In the words of the author, "affordable efficient methods of home heating could help reduce the number of people living in homes that are detrimental to their health."  So also would increases in minimum air temperatures help in this regard; while anything that tended to make methods of home heating more expensive would be counterproductive.

On this basis, the Kyoto Protocol and other such regulatory schemes clearly have three strikes against them: (1) their stated objective of combating global warming, which is expressed most prominently in the form of elevated minimum temperatures, (2) their inclination to make fossil fuel use more costly, and (3) the fact that this policy will hurt most those who can least afford to heat their homes, i.e., the world's poor and elderly.

So it has ever been; and so, it seems, it shall ever be: the poor and the aged are the ones who suffer most.  And unless enough good people step forward to do something about it, the cycle will not be broken.  Global warming and heat waves are clearly not the health hazards they are made out to be.  Global cooling and cold spells, on the other hand, are a much more clear and present danger.

References
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