Future of Canadian Air Quality and Related Health Benefits from Climate Change Mitigation

Abstract

Air pollution has been recognized as the world’s largest environmental health risk. Climate change is expected to exacerbate air pollution. Mitigating the “climate penalty” of climate change on air quality yields air quality-related “co-benefits” by protecting human health. This study quantifies Canada’s air quality-related co-benefits from reducing greenhouse gases under different policy scenarios. It achieves this by adapting the MIT-IGSM-CAM-Chem-BenMAP framework for use in Canada. This integrated framework was used to analyze the all-cause premature mortality and economic impacts due to changes in fine particulate matter (PM2.5) and ground-level ozone pollution in Canada under climate change and climate policy at mid- and end-of-century in comparison to the beginning of century. Modelled air quality concentrations were validated with Canada’s National Air Pollution Surveillance program station data, resulting in acceptable relative errors of 66% and 47% for ground-level ozone and PM2.5, respectively. Without climate policy, ozone concentrations in Canada will generally decrease, with the exception of the Greater Toronto Area, while the PM2.5 concentrations will increase over the century. The impact of the increase in PM2.5 greatly outweighs the impact of the decrease in ozone, leading to an overall increase in excess annual premature mortality between 1,300 (95% confidence interval: 880, 1,700) and 3,000 (1,500, 4,500) for mid-century, and between 2,800 (1,900, 3,700) and 6,500 (3,300, 9,700) in 2100, under the reference scenario. This corresponds to economic damages between 16 (1.5, 44) billion and 21 (2.0, 5.8) billion dollars (2021 CAD) for mid-century, and between 45 (4.3, 120) billion and 90 (8.5, 250) billion dollars for end-of-century. Climate policies consistent with the Paris Agreement are expected to increase mean ozone concentrations slightly while greatly decreasing mean PM2.5 concentrations in key urban areas including Toronto, Montreal, Calgary, and Vancouver. This leads to a net decrease in annual premature mortality between 590 (370, 810) and 1,500 (690, 2,200) for mid-century, and between 1,800 (1,200, 2,300) and 4,800 (2,200, 7,000) for end-of-century, using the American Cancer Society Study and the Harvard Six Cities Study as the PM2.5 health impact function, respectively. Using the American Cancer Society Study as the PM2.5 health impact function, this yields annual air quality co-benefits between 8.3 (0.78, 22) billion and 11 (1.0, 29) billion dollars for 2050, and between 32 (3.0, 87) billion and 66 (6.2, 180) billion dollars by 2100. The yields increase using the Harvard Six Cities Study as the PM2.5 health impact function, ranging between 21 (1.8, 59) billion and 28 (2.5, 80) billion dollars for 2050, and between 79 (7.0, 220) billion and 160 (14, 460) billion dollars by 2100. This represents a near doubling of the current annual air quality burden in Canada, estimated at $50 billion. These co-benefits do not represent the main goal of climate policy, and but they still serve to slightly offset compliance costs. When compared to the cost of implementing the policies, the benefits have the potential to offset between 1% and 6% of annual GDP loss. This is lower than the potential for 5% to 17% cost offset in the case of the United States, as the policy cost for Canada is a higher fraction of its GDP due to its emission intensive economy.