Federal Coordinating Lead Author:
Christopher G. Nolte, U.S. Environmental Protection Agency
Chapter Lead:
Christopher G. Nolte, U.S. Environmental Protection Agency
Chapter Authors:
Patrick D. Dolwick, U.S. Environmental Protection Agency
Neal Fann, U.S. Environmental Protection Agency
Larry W. Horowitz, National Oceanic and Atmospheric Administration
Vaishali Naik, National Oceanic and Atmospheric Administration
Robert W. Pinder, U.S. Environmental Protection Agency
Tanya L. Spero, U.S. Environmental Protection Agency
Darrell A. Winner, U.S. Environmental Protection Agency
Lewis H. Ziska, U.S. Department of Agriculture
Review Editor:
David D'Onofrio, Atlanta Regional Commission
USGCRP Coordinators:
Ashley Bieniek-Tobasco, Health Program Coordinator
Sarah Zerbonne, Adaptation and Decision Science Coordinator
Christopher W. Avery, Senior Manager

Air Quality

Unless offset by additional emissions reductions of ozone precursor emissions, there is high confidence that climate change will increase ozone levels over most of the United States, particularly over already polluted areas, thereby worsening the detrimental health and environmental effects due to ozone. The climate penalty results from changes in local weather conditions, including temperature and atmospheric circulation patterns, as well as changes in ozone precursor emissions that are influenced by meteorology. Climate change has already had an influence on ozone concentrations over the United States, offsetting some of the expected ozone benefit from reduced precursor emissions. The magnitude of the climate penalty over the United States could be reduced by mitigating climate change.

Climatic changes, including warmer springs, longer summer dry seasons, and drier soils and vegetation, have already lengthened the wildfire season and increased the frequency of large wildfires. Exposure to wildfire smoke increases the risk of respiratory disease, resulting in adverse impacts to human health. Longer fire seasons and increases in the number of large fires would impair both human health and visibility.

Climate change, specifically rising temperatures and increased carbon dioxide (CO2) concentrations, can influence plant-based allergens, hay fever, and asthma in three ways: by increasing the duration of the pollen season, by increasing the amount of pollen produced by plants, and by altering the degree of allergic reactions to the pollen.

The energy sector, which includes energy production, conversion, and use, accounts for 84% of greenhouse gas (GHG) emissions in the United States as well as 80% of emissions of nitrogen oxides (NOx) and 96% of sulfur dioxide, the major precursor of sulfate aerosol. In addition to reducing future warming, reductions in GHG emissions often result in co-benefits (other positive effects, such as improved air quality) and possibly some negative effects (disbenefits) (Ch. 29: Mitigation). Specifically, mitigating GHG emissions can lower emissions of particulate matter (PM), ozone and PM precursors, and other hazardous pollutants, reducing the risks to human health from air pollution.


Projected Changes in Summer Season Ozone

The maps show projected changes in summer averages of the maximum daily 8-hour ozone concentration (as compared to the 1995–2005 average). Summertime ozone is projected to change non-uniformly across the United States based on multiyear simulations from the Community Multiscale Air Quality (CMAQ) modeling system. Those changes are amplified under the higher scenario (RCP8.5) compared with the lower scenario (RCP4.5), as well as at 2090 compared with 2050. Data are not available for Alaska, Hawai‘i, U.S.-Affiliated Pacific Islands, and the U.S. Caribbean. From Figure 13.2 (Source: adapted from EPA 20171).

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