Temperature, temperature extremes, and mortality: a study of acclimatisation and effect modification in 50 US cities

Abstract

Objectives: The authors examined the increase in mortality associated with hot and cold temperature in different locations, the determinants of the variability in effect estimates, and its implications for adaptation. Methods: The authors conducted a case-crossover study in 50 US cities. They used daily mortality and weather data for 6 513 330 deaths occurring during 1989-2000. Exposure was assessed using two approaches. First, the authors determined exposure to extreme temperatures using city-specific indicator variables based on the local temperature distribution. Secondly, they used piecewise linear variables to assess exposure to temperature on a continuous scale above/below a threshold. Effects of hot and cold temperature were examined in season-specific models. In a meta-analysis of the city-specific results, the authors examined several city characteristics as effect modifiers. Results: Mortality increases associated with both extreme cold (2-day cumulative increase 1.59% (95% CI 0.56 to 2.63)) and extreme heat (5.74% (95% CI 3.38 to 8.15)) were found, the former being especially marked for myocardial infarction and cardiac arrest deaths. The increase in mortality was less marked at less extreme temperatures. The effect of extreme cold (defined as a percentile) was homogeneous across cities with different climates, suggesting that only the unusualness of the cold temperature (and not its absolute value) had a substantial impact on mortality (that is, acclimatisation to cold). Conversely, heat effects were quite heterogeneous, with the largest effects observed in cities with milder summers, less air conditioning and higher population density. Adjustment for ozone led to similar results, but some residual confounding could be present due to other uncontrolled pollutants. Conclusions: The authors confirmed in a large sample of cities that both cold and hot temperatures increase mortality risk. These findings suggest that increases in heat-related mortality due to global warming are unlikely to be compensated for by decreases in cold-related mortality and that population acclimatisation to heat is still incomplete.

Climate change impacts on extreme temperature mortality in select metropolitan areas in the United States

“…This study specifically addresses mortality associated with extremely hot and cold days. By isolating the effect of single days of extreme cold temperatures the study results should not be affected by confounding factors related to generally higher wintertime mortality rates such as increased respiratory infections and cardiovascular disease (Medina-Ramon and Schwartz 2007;Mercer 2003). Several recent literature reviews suggest that the factors leading to these higher wintertime mortality rates are unlikely to be sensitive to climate warming (Ebi and Mills 2013;Kinney et al 2012), and therefore the changes in cold mortality identified by this study are likely to compose the majority of the changes in winter-time deaths resulting from warming.…”

“…We incorporate the criteria for extremely hot and cold days and the city-specific mortality results from Medina-Ramon and Schwartz (2007). Specifically, Medina-Ramon and Schwartz (2007) calculated the daily mortality impact for combinations of extremely cold and hot days in 50 cities using local mortality and weather data from 1989 to 2000.…”

“…Generally, we applied temperature anomalies derived from IGSM-CAM to a baseline period of observed daily minimum and maximum temperatures for weather station data for each city using the SimCLIM program (Warrick 2009;CLIMsystems 2010). Data from weather stations originally used in Medina- Ramon and Schwartz (2007) were incorporated where possible. Otherwise, we relied on data from the closest station with a complete baseline record (defined below).…”

“…The public health risks of extreme temperature days have long been recognized and, tragically, repeatedly demonstrated. As such, the future risk of climate-driven changes in the number and intensity of these days has been a topic of focused research for more than a decade (e.g., Kalkstein and Greene 1997;McGeehin and Mirabelli 2001;Basu and Samet 2002;Medina-Ramon and Schwartz 2007;Kinney et al 2008;Bell 2009, 2011;Huang et al 2011;Sheridan et al 2012;Zanobetti et al 2012).…”

Differential and combined impacts of extreme temperatures and air pollution on human mortality in south–central Canada. Part II: future estimates

“…There is a growing consensus that global climate change will adversely affect human health as the intensity and frequency of heat waves and high air pollution episodes are projected to increase under future climate scenarios, (e.g., Last and Chiotti 2001;Riedel 2004;Meehl and Tebaldi 2004;Medina-Ramón and Schwartz 2007). As IPCC (2007) pointed out, increased heat waves could increase risks of human mortality and morbidity, with very likely likelihood of occurrence in the middle to late of this century (90% to 99% probability).…”