Temperature Variation and Mortality

Extreme temperature variation has been linked to an increase in human mortality; moreover there is evidence that the effect of temperature is influenced by socioeconomic and socio-demographic factors. Burkart et al. (2011) studied the effect of temperature and thermal atmospheric conditions on all-cause and cardiovascular mortality in Bangladesh. In particular, the authors investigated the differences in mortality rates between rural and urban areas. Generalized additive models (GAMs) were fitted separately for rural and urban areas, and breakpoint models were used to determine mortality at certain temperature thresholds. In most cases a V-shaped temperature-mortality relationship was observed, with a greater increase in mortality in urban areas.—Simone Berkovitz

Burkart, K., Schneider, A., Breitner, S., Khan, M., Kramer, A., Endlicher, W., 2011. The effect of atmospheric thermal conditions and urban thermal pollution on all-cause and cardiovascular mortality in Bangladesh. Environmental Pollution 159, 2035–2043.

Most studies have identified increasing mortality levels at relative high and low temperatures, shown by U and V shaped curves. Moreover, other research indicates that socioeconomic and socio-demographic factors influence the effects of temperature. It has been observed that the effects of heat are stronger in cities with milder climates, high population density, or high levels of urbanization. Previous research on the relationship between temperature and mortality has been conducted in industrialized nations, however the effects on less developed tropical nations have been largely ignored. Therefore, Burkart et al. studied the impact of temperature on mortality in Bangladesh, taking into consideration all relevant meteorological and physiological variables. In addition, the authors compared the effects of temperature on urban and rural populations.

The study used meteorological data comprising daily mean and extreme temperature, humidity, wind speed, and cloud coverage values, collected from 26 sites across Bangladesh. Three thermo-physiological indices (TPIs) were calculated in order to look at human thermoregulation, which is determined by metabolic heat production and energy transfer with the outside environment. Heat Index (HI) combines air temperature and humidity and was used to asses temperatures above 26ºC and humidity above 40%. The physiological equivalent temperature (PET) is the temperature of a typical indoor setting when the human body is balanced with the same core and skin temperatures. The third index used was the universal thermal climate index (UTCI), which measures heat transfer occurring inside the human body. With the exclusion of accidental, infant, and maternity related deaths, crude death rates and age adjusted mortality rates were determined by daily deaths in rural and urban areas. The authors used Poisson generalized additive models to explore the relationship between daily death counts and ambient temperature, HI, PET, and UTCI. In order to emphasize urban and rural differences, separate models were constructed.

The authors found a clear relationship between thermal conditions and mortality; an increase in mortality was observed for both high and low temperatures in both rural and urban areas. For all-cause mortality, a V-shaped temperature mortality relationship was observed. The effect of heat on cardiovascular mortality, however was only observed in urban areas, while in rural areas a decrease in mortality with heat was seen. The heat effects, above a certain temperature threshold, were observed to be stronger than the cold effects. In addition, the effects were more pronounced in urban areas.

Climate variability and extreme hot or cold temperatures as a result of global warming will influence mortality rates and overall human health. The authors found that the effects of heat were stronger, which suggests that more deaths will occur with global warming. The effects were also greater in urban areas compared to rural areas, which is either due to more heat exposure or modified health or age patterns. Socioeconomic factors could also explain this difference. These findings suggest that underdeveloped urban areas will experience greater mortality from global climate change.

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