New modelling shows almost one in three Americans will routinely breathe air considered unhealthy for sensitive people by the year 2100 due to climate change, a sevenfold increase compared to the turn of the century.
The international study, led by the University of Waterloo, found that about 100 million people in the United States will live in areas where average air quality during smog season is poor enough to trigger alerts advising vulnerable people to stay indoors.
That is up from an estimated 14 million people in 2000, with most of the increase coming in California and the eastern United States. Smog season runs from the beginning of May to the end of September.
"Climate change could cause days with poor air quality to shift from rare to commonplace," said Dr. Rebecca Saari, a professor of civil and environmental engineering and the Canada Research Chair in Global Change, Atmosphere and Health at Waterloo.
"People who are especially sensitive to air pollution, including the elderly, children with asthma and those with health conditions, could face a daily coin flip, with nearly even odds of an alert every day asking them to change their behaviour to reduce exposure."
The study built on previous research that estimated the number of air quality alerts in the United States will quadruple, and that staying indoors to avoid the health risks posed by worsening air pollution due to climate change would require an additional 142 days per year by the end of the century.
The new study broadens the picture by including the impact of both ozone and particulate matter pollution, which together cause almost all air quality alerts and are the primary environmental contributors to sickness and premature death.
The research team also examined the economic costs of intensifying air pollution and the potential mitigating impacts of policies to limit it over the next 75 years.
Saari said a significant finding is that seniors benefit much, much more than other vulnerable people from steps to limit their exposure to poor air, such as staying indoors, wearing masks, and improved building filtration.
"We were surprised by how widespread and common it could be for sensitive groups to experience air that is considered unhealthy on average," said Saari. "We hope our work helps inform more targeted guidance and reinforces the need for pollution reductions and long-term adaptations such as access to clean indoor spaces."
Collaborators included researchers at Harvard University, North Carolina State University and the University of California, Davis.
Their study, Air Quality Alerts, Health Impacts and Adaptation Implications Under Varying Climate Policy, appears in Environmental Science and Technology.
