Air Pollution can amplify negative effects of climate change

The impacts of air pollution on human health, the economy and agriculture differ dramatically depending on where on the planet the pollutants are emitted, according to a new study that could incentivize certain countries to cut climate-altering emissions.

Air Pollution can amplify negative effects

Led by the University of Texas at Austin and the University of California at San Diego (United States), the study, published in the journal 'Science Advances, is the first to simulate how aerosol pollution affects both the climate and the air quality in places around the world.

Aerosols are small solid particles and liquid droplets that contribute to smog and are emitted from industrial factories, power plants, and vehicle exhaust. They affect human health and agricultural and economic productivity in unique global patterns compared to carbon dioxide (CO2) emissions, on which efforts to mitigate climate change are focused.

Although CO₂ and aerosols are often emitted at the same time during the combustion of fuel, the two substances behave differently in Earth's atmosphere, said co-lead author Geeta Persad, an assistant professor at the UT Austin Jackson School of Geosciences.

"Carbon dioxide has the same impact on the climate no matter who emits it," she Persad said. "But these aerosol pollutants tend to stay concentrated close to where they are emitted, so the effect they have on the climate system is very patchy and depends a lot on where they come from."

CO2 is warming the planet

The researchers found that, depending on where they are emitted, aerosols can worsen the social costs of carbon, an estimate of the economic costs greenhouse gases have on society, by up to 66 per cent. The scientists looked at eight key regions: Brazil, China, East Africa, Western Europe, India, Indonesia, the United States and South Africa.

"This research highlights how the harmful effects of our emissions are often underestimated," said Jennifer Burney, co-senior author and Marshall Saunders Chancellor's Endowed Chair in Global Climate Policy and Research in the UC San Diego School of Global Policy and Strategy. "CO2 is warming the planet, but it's also emitted with a bunch of other compounds that directly affect people and plants and cause climate change in their own right."

The work, which was supported by the National Science Foundation, represents a collaboration between Persad and Burney, who are physical scientists, and a group of economists and public health experts. Coauthors include Marshall Burke, Eran Bendavid, Sam Heft-Neal of Stanford University, and Jonathan Proctor of Harvard University.

Aerosols can directly affect human health and the climate independently of CO2. They are associated with negative health impacts when inhaled, and can affect climate by influencing temperature, precipitation patterns, and the amount of sunlight that reaches the Earth's surface.

New motivations for countries to cut emissions

The researchers also said the findings create potentially new motivations for countries to cut emissions and worry about other countries cutting emissions. For example, the study found that adding aerosol costs to CO2 costs could double China's incentive to mitigate emissions. And it changes the impact of local emissions in Europe from a net local benefit to a net cost. The study also shows that some emerging economies, such as East African nations and India, might be motivated to collaborate in reducing emissions, as they are heavily affected by each other's emissions.

The framework developed in this study can also be applied to maximize the societal benefits of current mitigation strategies that are being considered by policymakers. For example, the researchers applied it to the "fair share" approach laid out in the Paris Climate Agreement in which all countries target the same CO2 emissions per capita. They found that the approach, while beneficial for climate stability, does not improve mortality and crop impacts from combined aerosol and CO2 emissions because it focuses mitigation on regions that already have fairly low aerosol impacts, such as the USA and Europe.

"By expanding the social cost calculations to include the geographically resolved social impacts of co-emitted aerosols, we are showing that the incentive for individual countries to mitigate and to collaborate on mitigation is much greater than if we only think about greenhouse gases, Burney said.

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