Extreme temperature variation as an effect of climate change has recently been linked to an increase in mortality. However, the shape of the graphical relationship between temperature and mortality has been varied across studies. Iñiquez et al. (2010) studied the shape of the association between temperature and mortality in 13 Spanish cities. Using data from areas with a wide range of climatic and socio-demographic conditions the authors calculated the temperature value linked with minimum mortality (MMT) and the slopes before and after the turning point. A V-shaped temperature-mortality relationship was found for most cities, with higher MMTs in cities with warmer climates. The effects of heat and cold also depended on climate—effects were greater in hotter cities but lesser in cities with more variability. Additionally, the authors fou— Carolyn Campbell nd that the effect of heat was greater than the effect of cold on mortality.
Iñiguez, C., Ballester, F., Ferrandiz, J., Pérez-Hoyos, S., Sáez, M., López, A., 2010. Relation between temperature and mortality in thirteen Spanish cities. International Journal of Environmental Research and Public Health 7, 3196–3210.
The relationship between temperature and mortality has been the subject of numerous studies, displaying a V, U, W, or J-shaped curve. The shape of the relationship is likely to vary from city to city as it depends on many factors including climate, socio-economic condition, and age. Therefore, Iñiquez et al. concluded that it was important to incorporate information from several locations and to consider all available factors that might confound the relationship. The authors aimed to determine the temperature at which mortality is lowest, study the effects of temperature changes below and above that value, detect if there is a specific effect on various causes or ages, and express possible patterns between cities.
The study utilized daily information from 13 Spanish cities: Barcelona, Bilbao, Cartagena, Castellón, Gijon, Huelva, Madrid, Oviedo, Seville, Valencia, Vigo, Vitoria, and Zaragoza. Mortality was calculated as the daily number of deaths occurring in each city. Daily mean temperature and daily mean humidity were obtained from the Meteorological Service in each city. Air pollution (or in its absence, black smoke or suspended particles), daily incidence of influenza, and calendar variables were considered potential confounders. The authors used a Poisson generalized additive model to explore the shape of the relationship. Explicative models for each outcome and city were constructed.
The authors found a significant relationship between temperature and mortality in nine of the 13 cities. Mortality due to specific causes and mortality in the elderly were also significant in Madrid, Barcelona, Valencia, Seville, and Zaragoza. The relationship was V or U-shaped suggesting a rise in the death rate when the weather gets colder or hotter than the comfort band, with the largest effects for cardio-respiratory deaths. Victoria and Oviedo were the only exceptions, with a linear negative relationship between temperature and mortality. The temperature associated with minimum mortality (MMT) for total mortality varied between cities and tended to increase with mean temperature. Additionally, in general the effect of heat was greater than the effect of cold and was positively correlated with the temperature of cities for specific causes of mortality and mortality in the older population.
The increase in number and intensity of unusual hot or cold episodes due to global warming will have an important effect on health. The authors found that changes in heat had a steeper slope than changes in cold, indicating that total mortality will likely increase with climate change. The implementation of alert systems or health education as well as ambient corrective actions may help to avoid or mitigate the effects of temperature variation proposed by this study.