Abstract

Climate change is likely to have serious and long-term consequences for public health. Among these are illness and mortality related to heat and worsening air quality In this study we examined the historical relationship between age- and cause-specific mortality rates and heat events at the 99th percentile of humidex values in the greater Seattle area (King, Pierce and Snohomish counties), Spokane County, the Tri-Cities (Benton and Franklin counties) and Yakima County from 1980 through 2006; the relative risk of mortality during heat events compared with more temperate periods were then applied to population and climate projections for Washington State to calculate number of deaths above the baseline (1980-2006) expected to occur during projected heat events in 2025, 2045 and 2085. We also estimated excess deaths due to ground-level ozone concentrations for mid century (2045-2054) in King and Spokane counties. Estimates were based on current (1997-2006) ozone measurements and mid-21st century ozone projections, using estimates from the scientific literature to determine the effect of ozone on overall and cardiopulmonary mortality.

For the historical heat analysis, relative risks derived for the greater Seattle area showed a significant dose-response relationship between duration of the heat event and the daily mortality rate for non-traumatic deaths for persons aged 45 and above, typically peaking at four days of exposure to humidex values above the 99th percentile. Three different warming scenarios were considered, including high, low and moderate estimates. In the greater Seattle area, the largest number of excess deaths in all years and scenarios was predicted for persons aged 65 and above. Under the middle scenario, this age group is expected to have 96 excess deaths in 2025, 148 excess deaths in 2045 and 266 excess deaths in 2085 from all non-traumatic causes.

Daily maximum 8 hour ozone concentrations are forecasted to be 16-28% higher in the mid 21st century compared to the recent decade of 1997-2006. We estimated that the total non-traumatic ozone mortality rate by mid-century for King County would increase from baseline (0.026 per 100,000; 95% confidence interval 0.013-0.038) to 0.033 (0.017-0.049). For the same health outcome in Spokane County, the baseline period rate was 0.058 (0.030- 0.085) and increased to 0.068 (0.035 -0.100) by mid-century. The cardiopulmonary death rate per 100,000 due to ozone was estimated to increase from 0.011 (0.005-0.017) to 0.015 (0.007-0.022) in King County, and from 0.027 (0.013-0.042) to 0.032 (0.015-0.049) in Spokane County. Public health interventions aimed at protecting Washington’s population from excessive heat and increased ozone concentrations will become increasingly important for preventing deaths, especially among older adults. Furthermore, heat and air quality related illnesses that do not result in death, but are serious nevertheless, may be reduced by the same measures.