Climate and mortality in Australia: retrospective study, 1979-1990, and predicted impacts in five major cities in 2030

Abstract

Quantitative assessment of climatic and environmental health risks is necessary because changes in climate are expected. We therefore aimed to quantify the relationship between climatic extremes and mortality in the 5 largest Australian cities during the period 1979-1990. We then applied the relationship determined between recent climatic conditions and mortality to scenarios for climate and demographic change, to predict potential impacts on public health in the cities in the year 2030. Data on mortality, denominator population and climate were obtained. The expected numbers of deaths per day in each city were calculated. Observed daily deaths were compared with expected rates according to temperature thresholds. Mortality was also examined in association with temporal synop- tic indices (TSI) of climate, developed by principal component and cluster analysis. According to observed-expected threshold analyses, for the 5 cities combined, the annual mean excess of deaths attributable to temperature over the period 1979-1990 was 175 for the 28°C threshold. This sum of sta- tistically significant differences from the 5 cities was the greatest excess found in association with any threshold considered in the range of temperatures that occur. Excess mortality for the hottest days in summer was greater than for the coldest days in winter. Temperature-mortality relationships were lit- tle modified by socio-economic status. TSI analyses produced similar results: using this method, the cli- mate-attributable mortality in the 5 cities was approximately 160 deaths yr -1 , although this number was evenly distributed across summer and winter. Persons in the group aged 65 yr and older were the most vulnerable. After allowing for increases in population, and combining all age groups, the synoptic method showed a 10% reduction in mortality in the year 2030. We conclude that the 5 largest Aus- tralian cities exhibit climate-attributable mortality in both summer and winter. Given the scenarios of regional warming during the next 3 decades, the expected changes in mortality due to direct climatic effects in these major coastal Australian cities are minor.