Aerosols can directly affect human health and the climate independently of CO2. They are associated with negative health impacts when inhaled, and can affect the climate by influencing temperature, precipitation patterns and how much sunlight reaches the Earth’s surface.
To study aerosols’ influence in comparison to CO2, the team created a set of climate simulations using the Community Earth System Model version 1 developed by the National Center for Atmospheric Research. They ran simulations in which each of the eight regions produced identical aerosol emissions and mapped how temperature, precipitation, and surface air quality were affected across the globe. Then they connected this data with known relationships between climate and air quality and infant mortality, crop productivity, and gross domestic product across the eight regions. In a final step, they compared the total societal costs of these aerosol-driven impacts against the societal costs of co-emitted CO2 in each of the eight regions, and produced global maps of the combined effects of aerosols and CO2. The researchers said the study is a big step forward from previous work, which either only estimated the air quality impacts of aerosols or didn’t consider their diverse global climate effects.
The outcome paints a varied and complicated picture. Emissions from some regions produce climate and air quality effects that range from two to more than 10 times as strong as others and social costs that sometimes affect neighboring regions more than the region that produced the aerosol emissions. For example, in Europe local emissions result in four times as many infant deaths outside Europe as within.
But the researchers note that aerosol emissions are always bad for both the emitter and the planet overall.
“While we might think about aerosols, which cool the climate, as having the silver lining of counteracting CO2-driven warming, when we look at all these effects in combination, we find that no region experiences overall local benefits or generates overall global benefits by emitting aerosols,” said Persad.
Researchers also said the findings create potentially new motivations for countries to cut emissions—and to care 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 switches the impact of local emissions in Europe from a net local benefit to a net cost. The study also shows that some emerging economies, like East African nations and India, might be motivated to collaborate on emission cuts since they are strongly impacted by each other’s emissions.
The framework developed in this study can also be applied to maximize societal benefits from current mitigation strategies being considered by policy makers. 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 per-capita CO2 emissions. They found the approach, while beneficial for climate stability, does not improve the mortality and crop impacts from combined aerosol and CO2 emissions because it focuses mitigation in regions that already have fairly low aerosol impacts, like the U.S. and Europe.
“By expanding societal cost calculations to include the geographically-resolved societal impacts of co-emitted aerosols, we’re showing that the incentive for individual countries to mitigate and collaborate on mitigation is much higher than if we only think about greenhouse gases,” Burney said.
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