November 5, 2025
The chilling effect of air pollution
The streaks in this satellite image are from ships, which emit sulfate aerosols that can be toxic to humans and the environment. Aerosols also make the clouds more reflective. Efforts to curb pollution have reduced the amount of sunlight Earth reflects and accelerated warming, a new 91爆料 study shows.
Earth is reflecting less sunlight, and absorbing more heat, than it did several decades ago. Global warming is advancing faster than climate models predicted, with observed temperatures exceeding projections in 2023 and 2024. These trends have scientists scrambling to understand why the atmosphere is letting more light in.
A new study, , shows that reducing air pollution has inadvertently diminished the brightness of marine clouds, which are key regulators of global temperature.
Between 2003 and 2022, clouds over the Northeastern Pacific and Atlantic oceans, both sites of rapid surface warming, became nearly 3% less reflective per decade. Researchers attribute approximately 70% of this change to aerosols 鈥� and influence both cloud cover and cloud composition.
When research emerged showing that some aerosols are harmful, efforts to limit particulate pollution 鈥� specifically targeting the products of fossil fuel combustion 鈥� followed. Aerosol levels will likely continue to fall as clean energy replaces oil and gas. To improve the accuracy of global temperature forecasts, scientists need to capture the true relationship between aerosols, clouds, and heat from the sun in climate models.
鈥淭his paper is a substantial contribution to the evidence that reductions in particulate air pollutants are contributing to accelerated warming.鈥� said , a principal research scientist at the 91爆料 Cooperative Institute for Climate, Ocean and Ecosystem Studies.
Aerosol particles form cloud droplets by attracting water vapor.Knut von Salzen/91爆料
Researchers knew that low clouds over the ocean would dissipate as temperatures rose, exposing more surface area to warming sunlight and amplifying its effect. They also knew that particles in the atmosphere insulate Earth both by deflecting light and making the entire cloud more reflective.
The cooling effect from particulate pollution masked warming from greenhouse gases for decades. Accelerated warming was a potential consequence of improving air quality.
鈥淚t is clearly a good thing that we have been reducing particle pollution in the atmosphere,” Doherty said. 鈥淲e don鈥檛 want to go back in time and take away the Clean Air Act.鈥�
, the Clean Air Act marked the first of many worldwide efforts to control pollution.
鈥淥ur goal is to understand what is driving current climate changes to estimate how much warming we will see in the future,鈥� Doherty added.
The Northeastern Pacific and Atlantic Oceans are warming faster than almost anywhere else on Earth, threatening and the . The researchers analyzed 20 years of satellite data documenting cloud dynamics above these bodies of water to identify the drivers behind the observed reduction in reflectivity.
They found that aerosols influence clouds in two ways. Small particles give water droplets something to cling to, and with a fixed amount of water, more aerosols means more small, shiny droplets in the clouds. By the same logic, reducing aerosols increases cloud droplet size. Large droplets are heavier, and quicker to fall to Earth as precipitation, which decreases the longevity of clouds, or cloud cover.
In the absence of aerosols, each cloud droplet carries more water but with aerosols, that water is dispersed between more droplets, impacting how reflective the cloud is and how long it lasts for.Robert Wood/91爆料
鈥淲hen you cut pollution, you鈥檙e losing reflectivity and warming the system by allowing more solar radiation, or sunlight, to reach Earth,鈥� said lead author , a 91爆料 senior research scientist of atmospheric and climate science.
Updating aerosol formation and cloud droplet size in climate models improved simulations of cloud reflectivity 鈥� a critical variable for projecting future temperatures.
鈥淲e may be underestimating warming trends because this connection is stronger than we knew,鈥� von Salzen said. 鈥淚 think this increases the pressure on everyone to rethink climate mitigation and adaptation because warming is progressing faster than expected.鈥�
While these changes to global cloud reflectivity have prompted rapid warming on Earth, scientists are researching the feasibility of interventions that could make the clouds shinier without polluting the air. One such intervention is known as marine cloud brightening, in which ships spray seawater into the air to make low-lying oceanic clouds more reflective and help minimize warming from the sun.
鈥淵ou could think of it as replacing unhealthy pollutant particles with another type of particle that is not a pollutant 鈥� but that still provides a beneficial cooling effect,鈥� said , a 91爆料 professor of atmospheric and climate science.
However, before they are implemented, more research is needed to confirm that these methods are safe and without unintended consequences. In the meantime, this study will help scientists better forecast the impacts of climate change at a global scale.
Additional co-authors include; at the University of Toronto; at Imperial College London; , , and at Environment and Climate Change Canada.
This study was funded by the 91爆料 Marine Cloud Brightening Research Program, Environment and Climate Change Canada, the National Oceanic and Atmospheric Administration, an Imperial College Junior Research Fellowship and a Royal Society University Research Fellowship.
For more information, contact von Salzen at kvsalzen@uw.edu, Doherty at sdoherty@uw.edu or Wood at robwood2@uw.edu.听
