According to new research, our efforts to reduce air pollution are having an unintended consequence: they may be accelerating global warming by making clouds less reflective
The research team analysed two decades of satellite data and found that between 2003 and 2022, marine clouds over the North Atlantic and Northeast Pacific oceans became approximately 2.8% less reflective per decade.
This means less solar energy is being bounced back into space and more is being absorbed by the oceans, contributing to accelerated warming in regions already experiencing some of the fastest temperature increases on Earth.
The study attributes nearly 70% of this cloud-dimming effect to global reductions in sulfur dioxide and other aerosol particles. These fine particles, once churned into the atmosphere through industrial activities and shipping, served as nuclei around which water droplets formed in clouds. More aerosols meant more small, bright droplets that efficiently reflected sunlight.
As countries like China and the United States tightened air quality standards, atmospheric aerosol levels dropped. The result being that clouds now contain fewer but larger droplets, making them darker and less reflective. These larger droplets are also heavier and fall as precipitation more quickly, reducing overall cloud cover and longevity.
Lead author Knut von Salzen, a senior research scientist at the University of Washington. said: ‘When you cut pollution, you’re losing reflectivity and warming the system by allowing more solar radiation, or sunlight, to reach Earth.’
The findings may help explain why global temperatures in 2023 and 2024 exceeded climate model projections. The cooling effect from particulate pollution had masked warming from greenhouse gases for decades, and current models appear to underestimate the strength of this cloud-dimming phenomenon.
Sarah Doherty, a principal research scientist at the UW Cooperative Institute for Climate, Ocean and Ecosystem Studies: ‘This paper is a substantial contribution to the evidence that reductions in particulate air pollutants are contributing to accelerated warming. It is clearly a good thing that we have been reducing particle pollution in the atmosphere. We don’t want to go back in time and take away the [USA’s] Clean Air Act.’
Scientists are now exploring potential interventions, such as marine cloud brightening, which would spray seawater into the air to make clouds more reflective without introducing harmful pollutants. However, more research is needed to ensure such methods are safe and free from unintended consequences before implementation.
The full research can be read here.
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