Air pollution over Los Angeles neighborhoods. Photo: rushay booysen/iStockPhoto

Fighting Climate Change Isn’t an Automatic Win for Environmental Justice

Some simulated pathways for reducing emissions in the U.S. maintained or exacerbated existing racial inequities

In the United States in 2017, people of color were exposed to 10% more particulate matter air pollution compared to white people. This well-documented inequity has been baked into the fabric of American life by racist housing policies like redlining and has left a legacy of negative health outcomes for communities of color across the nation.

The kind of sweeping cuts to greenhouse gas emissions needed to fight climate change are expected to improve air quality because burning fossil fuels also produces air pollution. But a new study from researchers at the University of California San Diego’s Scripps Institution of Oceanography and School of Global Policy and Strategy shows that while reducing greenhouse gases will likely improve overall air quality, reducing emissions could maintain or even exacerbate environmental inequality.

The study, published today in the Proceedings of the National Academy of Sciences and supported by the National Science Foundation as well as the Robert Wood Johnson Foundation, used computer models to simulate more than 300 paths to reduce emissions that all achieved the U.S. Paris Climate Agreement goal of a 50-52% net greenhouse gas emissions reduction from 2005 levels by 2030. While all the simulated paths to reducing emissions improved overall air quality, some actually widened the air quality gap between people of color and white people in the U.S.

“These disparities can go up or down depending on how you implement climate policy,” said climate scientist Pascal Polonik, 2023 Scripps PhD graduate and lead author of the study. “It’s not a given that any climate policy that succeeds in reducing emissions also succeeds when it comes to environmental justice.”

For example, a simulation that prioritized emissions reductions in neighborhoods with low household income showed increased air pollution inequality, as did a simulation that achieved the cuts needed for the U.S. to meet its Paris Agreement goals in the cheapest way possible.

chart compares the air pollution exposure of different racial groups to the national average in 2017 (black shaded bar) and expresses the disparity as a percentage. The chart also displays the racial disparities in air pollution exposure for five simulated greenhouse gas emissions reduction pathways.   Image: Polonik et al. PNAS 2023
Comparison of the air pollution exposure of different racial groups to the national average in 2017 (black shaded bar) and the disparity expressed as a percentage. Chart also displays racial disparities in air pollution exposure for five simulated greenhouse gas emissions reduction pathways. Image: Polonik et al. PNAS 2023

Polonik said the study’s investigation of how the distribution of air quality might change under different climate policies was spurred by statements from the Biden administration that linked climate change and environmental justice, including the IRA and a 2021 executive order.

To explore this question, Polonik and his co-authors started with the U.S. national emissions inventory from 2017. Because pollutants, which are damaging to human health, are often released alongside greenhouse gases, the team was able to use this national emissions inventory and a computer model to create a map of air pollution in the U.S. under different climate policy implementations.

Using the Paris Agreement emissions reduction goal, the team created a set of five reduction pathways based on different organizing principles. These five pathways reduced emissions by making equal cuts across the country, by focusing on low-income neighborhoods, by achieving the emissions cuts in the least costly way possible, by prioritizing communities of color and by reducing emissions in the places with the worst air quality.

To represent an even wider array of potential climate policy scenarios, the researchers also ran an additional 300 computer simulations that randomized where the greenhouse gas reductions came from.

Next, the team took these 305 scenarios and plugged the geographic distribution of their associated emissions reductions into an air quality model that could estimate how they would impact air pollution across the country.

Once Polonik and his colleagues established the geographic air pollution consequences of each climate policy scenario, they could use census tract data to layer demographic information onto the map and then calculate how each scenario impacted the racial disparities compared to the unaltered data from 2017. For the randomized simulations, the team conducted additional statistical analyses to tease out which variables had the greatest impact on the outcome.

While no pathway completely eliminated the historical racial inequities that influence air pollution exposure, they all reduced the overall burden of air pollution. Two scenarios that are particularly relevant to real-world climate policy, however, exacerbated racial inequities. The emissions reduction simulation that prioritized low-income areas increased air pollution inequality by 0.2 percentage points and the simulation that achieved emissions reductions at the lowest cost increased inequality by 0.5 percentage points.

“The U.S. government has at times tried to use income as a way of targeting communities of color without using race or ethnicity as policy criteria,” said co-author Kate Ricke, assistant professor at the School of Global Policy and Strategy and Scripps. “Our results show how that approach can fall short when it comes to environmental justice.”

The relevance of the lowest cost approach, especially in view of the dramatic emissions cuts needed to meet the U.S. Paris Agreement goals, is more obvious: This pathway’s estimated cost was $190 billion, compared with the most expensive pathway, which costs $340 billion. 

“To some degree the U.S. might naturally prioritize what’s economically efficient,” said co-author Jennifer Burney, an environmental scientist at the School of Global Policy and Strategy and Scripps. “But if you take an entirely economical approach to reducing emissions, our study suggests that it won't just fail to rectify existing racial and ethnic exposure inequalities, it could exacerbate them.”

The only scenario that enhanced environmental equity across all groups was the one that prioritized emissions reductions in communities of color, which reduced racial inequality by 2.6 percentage points. However, the U.S. government is unlikely to use race to target disadvantaged communities in climate policy due to the risk of legal challenges, according to Polonik. 

The pathway that targeted locations with the most air pollution also reduced overall racial inequality by 1.1%, but actually increased the air pollution disparity for Hispanic communities. The scenario with equal emissions reductions across the country reduced racial inequality by 0.1%. 

Finally, the analysis of the 300 randomized pathways revealed that greenhouse gas reductions coming from the transportation sector had the greatest potential to reduce racial disparities in air pollution.

“Climate policy can absolutely be used to reduce inequity in air pollution exposure,” said Polonik. “But naive implementation of climate policy doesn’t necessarily improve environmental equity, so it’s vital to adopt an approach to reducing emissions that explicitly factors in environmental justice.”

Polonik said that an explanation of why prioritizing emissions reductions in low-income areas or why taking the cheapest approach to reducing emissions ended up increasing racial air pollution disparities was beyond the scope of this study.

“These racial inequities are deeply ingrained and have been around for a long time,” said Polonik. “You can reduce emissions in a lot of different ways and this pattern will remain. If you’re not specifically targeting environmental inequality, it’s likely to persist.”

In addition to Polonik, Ricke and Burney, School of Global Policy and Strategy Master of Public Policy student Sean Reese was a co-author of the study.

About Scripps Oceanography

Scripps Institution of Oceanography at the University of California San Diego is one of the world’s most important centers for global earth science research and education. In its second century of discovery, Scripps scientists work to understand and protect the planet, and investigate our oceans, Earth, and atmosphere to find solutions to our greatest environmental challenges. Scripps offers unparalleled education and training for the next generation of scientific and environmental leaders through its undergraduate, master’s and doctoral programs. The institution also operates a fleet of four oceanographic research vessels, and is home to Birch Aquarium at Scripps, the public exploration center that welcomes 500,000 visitors each year.

About UC San Diego

At the University of California San Diego, we embrace a culture of exploration and experimentation. Established in 1960, UC San Diego has been shaped by exceptional scholars who aren’t afraid to look deeper, challenge expectations and redefine conventional wisdom. As one of the top 15 research universities in the world, we are driving innovation and change to advance society, propel economic growth and make our world a better place. Learn more at

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