Abstracts: ISEE 22nd Annual Conference, Seoul, Korea, 28 August–1 September 2010: Climate Change and Environmental Health
Deaths from heat extremes are already important in Australia, and will increase under global warming. In all, 1500 people die from heat extremes in Australian cities and this could treble by mid-century (Research Australia 2007). Many studies have quantified the increase of mortality in response to extremes of heat. Nicholls et al. (2007) found that when mean daily temperature exceeds a threshold of 30°C (mean of today's maximum temperature and tonight's minimum temperature), the average daily mortality of people aged 65 years or more is about 15%–17% greater than usual. Fewer studies have given equal attention to mortality arising from extremes of cold, which can be expected to fall under as the climate warms. The present study considered the effects of heat and cold on mortality in each capital city of Australia.
Daily all-cause mortality was modeled as a function of recent daily maximum and minimum temperatures. Linear and quadratic relative risk functions were compared. For each city, 2 threshold temperatures were estimated by maximum likelihood: one for cold and the other for heat. Variations in both thresholds and relative-risk parameters, by age-group and by season of the year, were investigated.
Different mortality-temperature response functions were found in each capital city. The increase of risk in response to cold was well modeled by a linear function (ie, constant relative risk per degree), but the effects of extreme heat increase more rapidly than this, and were better modeled as proportional to the square of temperature above the local threshold.
In assessing the likely impacts of climate change on mortality, it is important to consider local conditions which affect the susceptibility of the local population to heat. It is also important to include in such calculations allowance for the ameliorating effects of reduced mortality from cold, which is not negligible even in the warmer northern cities of Australia.