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Health Effects of Temperature (Respiratory) - Summary
Climate alarmists predict rising temperatures will increase human death rates, and nary a heat wave occurs but what they are quick to blame its elevated temperatures for any excess deaths associated with it.  In this review, we thus examine what has been learned about the relationship between mortality and temperature in the real world, particularly as it applies to respiratory diseases; and in doing so, we find that the climate-alarmist contention is one hundred and eighty degrees out of phase with reality.

We begin our review with the study of Hajat and Haines (2002), who set out to determine if the well-documented relationship between cold temperatures and respiratory mortality in the elderly extends to the number of visits by the elderly to general practitioners.  To meet this objective, they employed additive models to regress time-series of daily numbers of general practitioner consultations by the elderly against temperature.  The consultation data they employed included visits to the doctor for the following respiratory complaints, as obtained for registered patients aged 65 and older from several London practices between January 1992 and September 1995: asthma, lower respiratory diseases excluding asthma, and upper respiratory diseases excluding allergic rhinitis.

The results of Hajat and Haines' investigation 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 diseases.  In addition, at mean temperatures below 5C, the relationship between respiratory disease consultations and temperature was linear, and stronger at a time lag of 6 to 15 days, such that a 1C decrease in mean temperature below 5C was associated with a 10.5% increase in all respiratory disease consultations.  Thus, in contrast to the climate-alarmist claim that warmer temperatures increase health risks, Hajat and Haines found just the opposite to be true with respect to the elderly in London.

Similar results were earlier obtained by Keatinge and Donaldson (2001), who studied the effects of temperature on mortality in people over 50 years of age in the greater London area over the period 1976-1995.  In their study, simple plots of mortality rate versus daily air temperature revealed a linear increase in mortality as the air temperature fell from 15C to near 0C.  Mortality rates at temperatures above 15C, on the other hand were, in their words, "grossly alinear," showing no trend.  In addition, low temperatures were shown to have a significant effect on both immediate (1 day after the temperature perturbation) and long-term (up to 24 days after the temperature perturbation) mortality rates.  So why are cold temperatures so deadly? Keatinge and Donaldson say it is because "cold causes mortality mainly from arterial thrombosis and respiratory disease, attributable in turn to cold-induced hemoconcentration and hypertension and respiratory infections."

In much the same vein, Nafstad et al. (2001) studied the association between temperature and daily mortality in 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 specifically associated with respiratory diseases.  The results showed that the mean daily number of respiratory-related deaths was considerably higher in winter (October-March) than in summer (April-September).  In fact, winter deaths associated with respiratory diseases were 47% more numerous than summer deaths.  As a result, Nafstad et al. concluded that "a milder climate would lead to a substantial reduction in average daily number of deaths," once again in contradiction of climate-alarmist claims to the contrary.

On the other side of the Atlantic, in a time-series analysis of both the acute and lagged influence of temperature and humidity on mortality rates in twelve U.S. cities, Braga et al. (2002) could find no clear evidence for a link between humidity and respiratory-related deaths.  With respect to temperature, however, they found that respiratory-related mortality increased in cities with more variable temperature.  This phenomenon, according to them, "suggests that increased temperature variability is the most relevant change in climate for the direct effects of weather on respiratory mortality."  This finding bodes well for a potentially warmer world; for Robeson (2002) has clearly demonstrated, based on a 50-year study of daily temperatures at over 1,000 U.S. weather stations, that temperature variability declines with warming, and at a very substantial rate, so that this aspect of altered weather in a warmer world would also lead to a reduction in respiratory-related deaths.

Dropping down to Brazil in South America, Gouveia et al. (2003) extracted daily counts of deaths from all causes, excepting violent deaths and neonatal deaths (up to one month of age), from Sao Paulo's mortality information system for the period 1991-1994 and analyzed them for effects of temperature within three age groups: less than 15 years of age (children), 15-64 years old (adults), and greater than 64 years old (elderly).  This exercise revealed that the change points (the temperatures above and below which temperature begins to impact mortality) for both heat- and cold-induced deaths were identical, i.e., 20C.  For each 1C increase above this value for a given and prior day's mean temperature, Gouveia et al. observed 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 the 20C change point, 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 are 54%, 73% and 120% greater than those due to warming.

Findings with respect to respiratory-induced deaths were similar, with death rates due to a 1C cooling being twice as great as death rates due to a 1C warming in adults, and 2.8 times greater in the elderly.  Hence, when it comes to the bottom-line reality of living or dying, it is clear that a warming of the climate would be preferable to a cooling or even no change at all, not only in Sao Paulo, Brazil, but in all the many other places of the world where similar studies have found essentially the same results as those described in this study.

Moving across the Pacific (and equator) to Japan, Nakaji et al. (2004) evaluated seasonal trends in deaths due to various diseases, using nationwide vital statistics from 1970 to 1999 and concurrent mean monthly air temperature data.  The results of their analyses indicated that the numbers of deaths due to diabetes, digestive diseases, cerebrovascular and heart diseases, infectious and parasitic diseases including tuberculosis, and respiratory diseases including pneumonia and influenza all rise to a maximum during the coldest time of the year.  Hence, the team of nine scientists concluded that "to reduce the overall mortality rate and to prolong life expectancy in Japan, measures must be taken to reduce those mortality rates associated with seasonal differences."  Consequently, it is clear that to achieve the scientists' stated objectives, it is necessary to bring about a "reduction in exposure to cold environments," as they put it, which is precisely what global warming does, and what it does best when it warms more in winter than in summer, as Nakaji et al. have demonstrated to be the case in Japan, where warming in winter over the past 30 years was twice as great as what it was during the rest of the year.

Skipping across the vast expanse of continental Asia to Greece in south-central Europe, Bartzokas et al. (2004) "examined the relationship between hospital admissions for cardiovascular (cardiac in general including heart attacks) and/or respiratory diseases (asthma etc.) in a major hospital in Athens and meteorological parameters for an 8-year period."  This effort revealed that, over the whole year, "there was a dependence of admissions on temperature," and that low temperatures were "responsible for a higher number of admissions."  Specifically, they say "there was a decrease of cardiovascular or/and respiratory events from low to high values [of temperature], except for the highest temperature class in which a slight increase was recorded."

Concluding our round-the-world trip back in England, Kovats et al. (2004) studied patterns of temperature-related hospital admissions and deaths in Greater London during the mid 1990s.  This work revealed that for the three-year period 1994-1996, respiratory-related deaths were nearly 150% greater in the depth of winter cold than at the height of summer warmth.  Also, with respect to the heat waves that climate alarmists portray as being such ferocious killers, they found that the mortality impact of the heat wave of 29 July to 3 August 1995 (which boosted daily mortality by just over 10%) was so tiny that it could not be discerned amongst the random scatter of plots of three-year-average daily deaths from cardiovascular and respiratory problems versus day of year.  Likewise, in a study of temperature effects on mortality in three English counties (Hampshire, West Midlands and West Yorkshire), McGregor (2005) found that "the occurrence of influenza ... helps elevate winter mortality above that of summer."

In conclusion, and in light of the several studies described above, it would appear that a warmer world would be a much better world, especially with respect to the respiratory health of the world's citizens.

Bartzokas, A., Kassomenos, P., Petrakis, M. and Celessides, C.  2004.  The effect of meteorological and pollution parameters on the frequency of hospital admissions for cardiovascular and respiratory problems in Athens.  Indoor and Build Environment 13: 271-275.

Braga, A.L.F., Zanobetti, A. and Schwartz, J.  2002.  The effect of weather on respiratory and cardiovascular deaths in 12 U.S. cities.  Environmental Health Perspectives 110: 859-863.

Gouveia, N., Hajat, S. and Armstrong, B.  2003.  Socioeconomic differentials in the temperature-mortality relationship in Sao Paulo, Brazil.  International Journal of Epidemiology 32: 390-397.

Hajat, S. and Haines, A.  2002.  Associations of cold temperatures with GP consultations for respiratory and cardiovascular disease amongst the elderly in London.  International Journal of Epidemiology 31: 825-830.

Keatinge, W.R. and Donaldson, G.C.  2001.  Mortality related to cold and air pollution in London after allowance for effects of associated weather patterns.  Environmental Research 86: 209-216.

Kovats, R.S., Hajat, S. and Wilkinson, P.  2004.  Contrasting patterns of mortality and hospital admissions during hot weather and heat waves in Greater London, UK.  Occupational and Environmental Medicine 61: 893-898.

McGregor, G.R.  2005.  Winter North Atlantic Oscillation, temperature and ischaemic heart disease mortality in three English counties.  International Journal of Biometeorology 49: 197-204.

Nafstad, P., Skrondal, A. and Bjertness, E.  2001.  Mortality and temperature in Oslo, Norway. 1990-1995.  European Journal of Epidemiology 17: 621-627.

Nakaji, S., Parodi, S., Fontana, V., Umeda, T., Suzuki, K., Sakamoto, J., Fukuda, S., Wada, S. And Sugawara, K.  2004.  Seasonal changes in mortality rates from main causes of death in Japan (1970-1999).  European Journal of Epidemiology 19: 905-913.

Robeson, S.M.  2002.  Relationships between mean and standard deviation of air temperature: implications for global warming.  Climate Research 22: 205-213.

Last updated 10 August 2005