Addressing air pollution in Europe and North America could inadvertently weaken the Atlantic Meridional Circulation (AMOC), a crucial ocean current influencing Europe’s climate.

Air pollution, including smog and soot, claims approximately 7 million lives annually and contributes to widespread health issues. Interestingly, aerosols, which are tiny particulate pollutants like sulfur dioxide, can reflect sunlight, making clouds brighter and reducing surface heat absorption.

Recent research indicates that reducing air pollution from maritime sources and other sectors could accelerate global temperature increases. “If we cut back on aerosols, we will start to see the extent of warming,” says Michael Diamond from Florida State University.

Historically, scientists’ insights into aerosols’ climatic impact have relied on global simulations akin to those used for examining the greenhouse effect. These models suggest that “higher aerosol levels cool the North Atlantic surface and strengthen the AMOC,” according to Robert Allen from the University of California, Riverside. Conversely, if global aerosol emissions are reduced, the Earth’s surface may warm, weakening the AMOC.

Nonetheless, these simulations often overlook the regional characteristics of air pollution. Unlike greenhouse gases, which linger in the atmosphere for years, most aerosols dissipate within a week, meaning their climatic effects typically manifest close to their source, revealing the complex consequences of pollution reductions.

To gain deeper insights into the impacts of clean air initiatives, Allen and his team employed eight distinct climate models to assess how changes in regional aerosol emissions impact both local and global climates. The models evaluated AMOC strength under high-emission scenarios established by the Intergovernmental Panel on Climate Change and reformulated these scenarios with enhanced air quality regulations.

The findings indicate that if greenhouse gas emissions continue to rise but aerosol pollutants decrease, the AMOC could weaken by a third by mid-century compared to scenarios where aerosol levels remain elevated.

While Allen’s research does not delve into the regional weather implications of AMOC weakening, previous studies suggest that such a decline could lead to adverse outcomes, including increased droughts across Europe, exacerbated sea level rise in northeastern North America, and disruption of global monsoons and rising temperatures in Northern Europe.

Allen’s analysis revealed that the most significant impact on AMOC would stem from reduced aerosol levels in Europe and North America. However, he noted that air quality improvement initiatives in East Asia are also proving impactful. Cleaner air in East Asia is affecting global temperatures—despite their short lifespan, aerosols can travel long distances and mask warming effects wherever they reach, potentially leading to further weakening of the AMOC.

“To improve air quality, we must acknowledge that there will be associated climate changes,” Allen states. “To achieve clean air while minimizing our climate impact, we must simultaneously reduce other greenhouse gases like CO2 and methane.”

Diamond echoes this sentiment, stating, “When considering clean air policies, it’s vital to concurrently address decarbonization strategies.”