Projecting Excess Mortality In 2030 With Spatially-Varying Ozone-Temperature Risk Surfaces

Abstract

Background: Temperature and ozone have a nonlinear and synergistic effect on mortality. This relationship has not previously been incorporated into the health impact assessment of climate change on the ozone-related health burden. Objective: We estimate the change in ozone-related mortality between historical (1995-2005) and near-future (2025-2035) climates using a bivariate ozone-temperature health impact function. Methods: We use climate projections to simulate air quality with varying biogenic and constant anthropogenic emissions, which limits changes in ozone concentrations to changes in climate. We estimate nonlinear, spatially-varying, ozone-temperature risk surfaces in 94 US urban areas using observed data and evaluate daily mortality attributable to ozone based on climate projections for two scenarios: exceeding 40 ppb (moderate level) and 75 ppb (US O3 NAAQS). The climate penalty on mortality burden is the change in ozone-related excess mortality between time periods. Results: The average increases in city-specific median April-October ozone and temperature between time periods are 1.02ppb and 1.94°F, respectively. When considering climate mortality attributed to ozone exceeding 40ppb increases by 7.7% (1.6%, 14.2%), and mortality attributed to ozone exceeding 75ppb increases by 14.2% (1.6%, 28.9%). The absolute increase in excess mortality is larger for changes in moderate ozone levels, reflecting the larger number of days with moderate ozone levels. Conclusions: Climate change related increases in ozone result in an increase in ozone-mortality burden. Increases across moderate ozone levels account for a larger absolute increase in burden while increases at higher levels account for a larger relative increase, even after accounting for nonlinear and synergistic effects. Disclaimer: The contents of this article should not be construed to represent Agency policy.