The impact of climate change and emissions control on future ozone levels: Implications for human health

Abstract

Overwhelming evidence has shown that, from the Industrial Revolution to the present, human activities influence ground-level ozone (O₃) concentrations. Past studies demonstrate links between O₃ exposure and health. However, knowledge gaps remain in our understanding concerning the impacts of climate change mitigation policies on O₃ concentrations and health. Using a hybrid downscaling approach, we evaluated the separate impact of climate change and emission control policies on O₃ levels and associated excess mortality in the US in the 2050s under two Representative Concentration Pathways (RCPs). We show that, by the 2050s, under RCP4.5, increased O₃ levels due to combined climate change and emission control policies, could contribute to an increase of approximately 50 premature deaths annually nationwide in the US. The biggest impact, however, is seen under RCP8.5, where rises in O₃ concentrations are expected to result in over 2,200 additional premature deaths annually. The largest increases in O₃ are seen in RCP8.5 in the Northeast, the Southeast, the Central, and the West regions of the US. Additionally, when O₃ increases are examined by climate change and emissions contributions separately, the benefits of emissions mitigation efforts may significantly outweigh the effects of climate change mitigation policies on O₃-related mortality.

Keywords: Climate change; Emissions; Mortality; Ozone; Pollution; Predictive modeling; Public health.

Fig. 1.

Study methods flow. Flow of study methods depicting both dynamical and statistical results. Isolation of O₃ attributable to emissions accomplished by taking the difference between the two illustrated downscaling methods. Excess deaths calculated by source for climate change only, and combined climate and emissions changes. Isolation of O₃ attributed to emissions is achieved by taking the difference between the two methods.

Fig. 2.

Average annual change in tropospheric O₃. Changes in O₃ concentrations between 2000s and 2050s. (A) O₃ difference from combined climate change and emissions under RCP4.5; (B) O₃ difference from combined climate change and emissions under RCP8.5; (C) O₃ difference from climate change under RCP4.5; (D) O₃ difference from climate change under RCP8.5; (E) O₃ difference from emissions only under RCP4.5; and (F) O₃ difference from emissions only under RCP8.5. Numbers represent US Climate Regions as defined by the National Climatic Data Center: 1. Northeast, 2. Southeast, 3. East North Central, 4. Central, 5. West North Central, 6. South, 7. Southwest, 8. Northwest, and 9. West (NCDC/NOAA, 2013).

Fig. 3.

Change in mortality: RCPs 4.5 and 8.5 using ICLUS A2 Scenario. Annual averaged, county-level excess mortality normalized by population. RCP4.5 (low emissions scenario) and RCP8.5 (high emissions scenario) results displayed by contributing source (combined effects, climate change and anthropogenic emissions). The combined effects represent the effects of both climate change and emissions.

Fig. 4.

Sample of results: California case study. Annual averaged, county-level changes In O₃ and excess mortality normalized by population depicted for the state of California under RCP8.5.