Climate policy tradeoffs may reduce air quality gains and global health outcomes

A new study published in The Lancet Global Health reveals a previously underappreciated tension at the heart of international climate negotiations: policies designed to protect developing countries from bearing an unfair share of the cost of cutting carbon emissions could inadvertently deprive those same countries of millions of life-saving air quality improvements. The leaders of the study also identify a promising way to resolve this dilemma.

The study, conducted by researchers at The University of Texas at Austin, Emory University, Princeton University, and collaborators across six countries, modeled multiple approaches to achieving the Paris Agreement's target of limiting warming to two degrees Celsius to assess policy impacts on emissions, air quality, health outcomes, and economic welfare across 178 countries through the end of the century. The researchers found that climate action consistent with the two-degree-Celsius target would avoid more than 13.5 million premature deaths from air pollution between 2020 and 2050 - overwhelmingly in low- and middle-income countries (LMICs). However, the total amount and distribution of those health gains would depend critically on how the global mitigation burden is shared.

Under a least-cost approach - where emissions are cut wherever it is cheapest to do so - LMICs shoulder a significant share of the mitigation effort but also reap the largest air quality benefits. Under an equity-based approach - where wealthier nations take on more of the burden - LMICs pay less, but nearly four million fewer premature deaths are avoided in those countries, because less fossil fuel reduction occurs where air pollution is worst.

"We show that there is a difficult tension between international distributive climate justice and the goal of saving lives via air pollution co-benefits," said Mark Budolfson, associate professor of philosophy and geography and the environment at The University of Texas at Austin, and co-lead author of the study. "Within the current Paris Agreement climate regime involving Nationally Determined Contributions to global emissions reductions, shifting mitigation from poor countries to rich countries has the perverse effect of reducing the number of lives saved via air quality improvements in poor countries - possibly by millions."

The researchers also tested a scenario that resolves this tradeoff: an equity-based climate regime in which LMICs invest their mitigation cost savings into conventional air pollution controls, such as end-of-pipe technologies targeting soot, sulfur dioxide, and other pollutants, for example in the smokestacks of power plants. This "Equity + Air Quality" scenario emerged as the most favorable overall, delivering both the fairness benefits of shifting climate costs to wealthier nations and the full life-saving potential of cleaner air in the developing world. Critically, the study found that for almost all LMICs, the savings from reduced climate mitigation costs more than cover the expense of these additional air quality measures.

"There is an urgent need to design justice-centered climate mitigation regimes to ensure that developing countries do not miss an opportunity to realize transformative reductions in air pollution," said Noah Scovronick, another co-lead author of the study. "We identify one attractive way of navigating this tension."

The findings have direct relevance for future rounds of climate negotiations in which countries will update their emission-reduction pledges. The authors note that while their equity-based scenario approximates the principle of "common but differentiated responsibilities" enshrined in the Paris Agreement, the air quality dimension has been underrepresented in those discussions.

"Our research shows the benefits of looking at development and climate policy together," said Navroz K. Dubash, professor at Princeton University. "Designing policy to proactively address trade-offs between limiting emissions in an equitable manner while addressing air pollution yield the best outcome."

"Understanding the complex trade-offs involved between different climate mitigation strategies is politically important, but analytically challenging," co-lead author Wei Peng, assistant professor at Princeton, added. "We need new modeling frameworks that can evaluate policy choices and their impacts across geographic scales and across climate, health, and cost dimensions."

The study used a chain of state-of-the-art models - including the Global Change Analysis Model (GCAM) for energy and emissions, GEOS-Chem for atmospheric chemistry, and the GIVE model for climate damages - to trace the links from policy choices through emissions, air quality, health outcomes, and economic welfare across 178 countries through the end of the century.

The study was funded by a United States National Science Foundation grant (#2420344), with Budolfson as Principal Investigator. In addition to Budolfson, other co-lead authors include Noah Scovronick, Navroz K. Dubash, Wei Peng, Jinyu Shiwang, Maddalena Ferranna, Fabian Wagner, and Frank Errickson.