The chilling effect of air pollution

University of Washington

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Clouds shade Earth from the sun and clouds containing aerosols do so even more effectively than those without. A new study from the University of Washington describes how clouds have lost reflectivity over the past few decades, increasing the amount of sunlight that reaches Earth, where it is absorbed as heat.

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Credit: University of Washington

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, published Nov. 5 in Nature Communications, 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 — fine particles that float through the atmosphere and influence both cloud cover and cloud composition.

Research showing that some aerosols are harmful drove efforts to limit particulate pollution that specifically targeted products of fossil fuel combustion. 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.

“This paper is a substantial contribution to the evidence that reductions in particulate air pollutants are contributing to accelerated warming.” said Sarah Doherty, a principal research scientist at the UW Cooperative Institute for Climate, Ocean and Ecosystem Studies. 

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.

“It is clearly a good thing that we have been reducing particle pollution in the atmosphere," Doherty said. “We don’t want to go back in time and take away the Clean Air Act.” 

Passed in 1963, the Clean Air Act marked the first of many worldwide efforts to control pollution. 

“Our goal is to understand what is driving current climate changes to estimate how much warming we will see in the future,” Doherty added. 

The Northeastern Pacific and Atlantic Oceans are warming faster than almost anywhere else on Earth, threatening fishery stocks and the health of marine ecosystems. 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.

“When you cut pollution, you’re losing reflectivity and warming the system by allowing more solar radiation, or sunlight, to reach Earth,” said lead author Knut von Salzen, a UW senior research scientist of atmospheric and climate science.

Updating aerosol formation and cloud droplet size in climate models improved simulations of cloud reflectivity — a critical variable for projecting future temperatures.

“We may be underestimating warming trends because this connection is stronger than we knew,” von Salzen said. “I think this increases the pressure on everyone to rethink climate mitigation and adaptation because warming is progressing faster than expected.”

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. 

“You could think of it as replacing unhealthy pollutant particles with another type of particle that is not a pollutant — but that still provides a beneficial cooling effect,” said Robert Wood, a UW 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; Luke Fraser-Leach at the University of Toronto; Edward Gryspeerdt at Imperial College London; Ayodeji Akingunola, Jason N. S. Cole, Ruth A. R. Digby and Michael Sigmond at Environment and Climate Change Canada

This study was funded by the University of Washington 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. 

CONTRAILS CREATED BY SHIPS

The streaks in this satellite image are from ships, which release sulfur dioxide that forms sulfate aerosols in the atmosphere. These aerosols, considered harmful to human and environmental health, reflect sunlight and make clouds more reflective as a whole. Reducing pollution, although critical, has reduced the amount of sunlight that gets reflected and accelerated warming, a new University of Washington study shows.

Credit

NASA

Aerosol particles form cloud droplets by attracting water vapor.

Credit

Knut von Salzen/University of Washington

In the absence of aerosols, each cloud droplet carries more water but when aerosols are present, the same amount of water is dispersed between many more droplets. This impacts how reflective the cloud is and how long it lasts for.

Credit

Robert Wood/University of Washington

Journal

Nature Communications

DOI

10.1038/s41467-025-65127-x 

Method of Research

Data/statistical analysis

Subject of Research

Not applicable

Article Title

Reduced aerosol pollution diminished cloud reflectivity over the North Atlantic and Northeast Pacific

Article Publication Date

5-Nov-2025

How much benefit comes from programs aimed at reducing pollution?

Wiley

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Because policies to address pollution are costly to implement and impose social burdens, it is important to understand the full benefits of pollution-reducing programs. An article in Health Economics provides compelling evidence that one such program offered considerable benefits for infant health, especially in vulnerable populations.

Based on an analysis of more than a decade of US birth records, the research shows that the Nitrogen Oxide Budget Trading Program—a cap-and-trade initiative to reduce ozone pollution—significantly improved infant health outcomes, particularly among Black, low-income, and single mothers.

The program was associated with up to a 19.5-gram higher birth weight, a 5.5% decrease in the incidence of low birth weight, and a 13% reduction in very preterm birth.

The author, Nahid Tavassoli, Assistant Professor of Economics at Austin Peay State University, considers the economic significance of the results in light of other environmental exposures and their later-life impacts.

“These findings underscore the life-saving potential of clean air regulations and offer critical insights for shaping future environmental and public health policy,” she said.

URL upon publication: https://onlinelibrary.wiley.com/doi/10.1002/hec.70047

 

 

Additional Information
NOTE: The information contained in this release is protected by copyright. Please include journal attribution in all coverage. For more information or to obtain a PDF of any study, please contact: Sara Henning-Stout, newsroom@wiley.com.

About the Journal
Health Economics is an international health policy journal publishing articles on all aspects of global health economics. We welcome theoretical contributions, empirical studies, and analyses of health policy from the economic perspective. With a wide scope, Health Economics welcomes contributions on the valuation, determinants and definition of health, health care supply and demand, planning and market mechanisms, treatment micro-economics, and health care system performance.

About Wiley      
Wiley is a global leader in authoritative content and research intelligence for the advancement of scientific discovery, innovation, and learning. With more than 200 years at the center of the scholarly ecosystem, Wiley combines trusted publishing heritage with AI-powered platforms to transform how knowledge is discovered, accessed, and applied. From individual researchers and students to Fortune 500 R&D teams, Wiley enables the transformation of scientific breakthroughs into real-world impact. From knowledge to impact—Wiley is redefining what's possible in science and learning. Visit us at Wiley.com and Investors.Wiley.com. Follow us on Facebook, X, LinkedIn and Instagram.

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Journal

Health Economics

DOI

10.1002/hec.70047 

Article Title

New Beginnings: The NOx Budget Trading Program and Infant Health

Article Publication Date

5-Nov-2025

 

New approach expands possibilities for studying viruses in the environment

Bigelow Laboratory for Ocean Sciences

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A micrograph shows several individual microcapsules including one, brightly lit one in the lower right corner, that contains amplified DNA from a single particle.

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Credit: Brian Thompson, Bigelow Laboratory for Ocean Sciences

A new method vastly improves on the existing approach for single-cell genetic sequencing, enabling scientists to read the genomes of individual cells and viral particles in the environment more quickly, efficiently, and cost-effectively.

In a new study in Nature Microbiology, researchers from Bigelow Laboratory for Ocean Sciences and Atrandi Biosciences provide the first environmental application of the approach, which they call environmental microcompartment genomics. Sequencing the microbiome in a sample of surface seawater from the Gulf of Maine, the researchers showcased the method’s advantages compared to traditional processes, particularly for studying the diverse and complex world of marine viruses.

“This work demonstrates how we can increase the throughput of single particle genomics, increasing not just the quantity but also the quality of the data,” said Alaina Weinheimer, a postdoctoral fellow and the paper’s lead author. “You can study your whole microbe community in this comprehensive manner that has not been possible — at reduced cost without sacrificing quality.”

The traditional method, revolutionized by Bigelow Laboratory’s Single Cell genomics Center, involves sorting all the individual particles in a sample into their own well on a microplate. That enables scientists to process 384 particles in one run. The new approach increases that throughput by an order of magnitude. In the study, the researchers obtained genomic sequences from over 2,000 particles in just 300 nanoliters, or less than a millionth of a liter, of seawater.

Microcompartment genomics relies on recent advances in microfluidic technology. A sample is compartmentalized into thousands of tiny, semipermeable bubbles, each containing a trillionth of a liter of water. Single cells or particles are randomly sampled into individual compartments, and reagents are used to make lots of copies of the DNA. That amplified DNA is then tagged with a unique barcode. When the bubbles are dissolved, and all the material is combined to be sequenced, that barcode is used to stitch together corresponding sequences into a complete genome.

Though this first application uses seawater, Weinheimer said that early testing shows that the process also works on sediment and soil samples, which can be hard to study with methods that struggle to differentiate cells from non-biological particles.

The approach does not use flow cytometry, like the standard single-cell sequencing method. That means that scientists lose some of the descriptive data that flow cytometry provides, but the advantage is that there’s no size-based pre-sorting required, so any particle of any size can be sequenced.                                      

“This approach omits any size selection, so we can process everything from large microbes to the tiniest of viruses, or even free-floating DNA, simultaneously,” Weinheimer said. “You’re looking at the microbial community in a very holistic way.”

“Nature’s microbial world remains full of mysteries, due to its extreme biodiversity and the small physical scales that makes it hard to study,” added Ramunas Stepanauskas, director of SCGC and senior author on the new study. “Environmental microcompartment genomics creates completely new opportunities for the study of that world.”

This rapid, size-agnostic approach will be particularly valuable for studying viruses, which make up the vast majority of the microbes in the ocean but come in a wide range of sizes and can often be too small to isolate with a flow cytometer.

Indeed, the study highlights some of the advantages of the new approach compared to existing single-cell and metagenomic methods.

Though all of the methods the authors tested agreed in terms of the broad composition of the microbial community — providing assurances that the new method works — the microcompartment approach generated some unique insights. For example, the methods that use flow cytometry appeared to pick up more large viruses, whereas the new approach captured viruses of all sizes present in the sample. Likewise, the microcompartment approach provided genome sequences that were more complete and of higher quality than the widely used metagenomic methods.

The scientists also found that many of the viral genomes identified using the new approach belonged to a family of viruses called Naomiviridae that have only been recently cultured and have such an unusual DNA structure they can be excluded using other methods.

“This group of viruses was the most abundant in our dataset, and we found evidence that it may infect the most abundant bacteria in the ocean, but we would have missed it entirely with other methods,” Weinheimer said. “We’re showing that there’s a lot that can still be discovered about the viral community that’s currently invisible to us that we’re starting to unlock with these new methods.”

The work was funded by the National Science Foundation, Simons Foundation, and the Research Council of Lithuania. Co-authors include scientists at Vilnius University and Atrandi Biosciences in Lithuania, as well as several Bigelow Laboratory researchers, including Brian Thompson, Julia Brown, Jacob Munson-McGee, Greg Gavelis, Corianna Mascena, and Nicole Poulton.

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Journal

Nature Microbiology

DOI

10.1038/s41564-025-02167-5 

Method of Research

Data/statistical analysis

Subject of Research

Cells

Article Title

Single-particle genomics uncovers abundant non-canonical marine viruses from nanolitre volumes

Article Publication Date

5-Nov-2025

New modelling shows difficult future for the Great Barrier Reef under climate change

University of Queensland

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Bleached coral in the Pacific Ocean.

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Credit: Professor Peter Mumby

The most sophisticated modelling to date forecasts that under the current global emissions pathway the Great Barrier Reef could lose most of its coral by the end of the century, but curbing climate change and strategic management will help coral resilience.

A research team led by The University of Queensland simulated different future climate scenarios driven by a range of plausible global emissions trajectories.

Dr Yves-Marie Bozec from UQ’s School of the Environment said the comprehensive modelling of individual corals included their ability to adapt to warmer water, large-scale reef dynamics and their interconnections on ocean currents.

“We ran all of those factors with the most up to date climate projections – and the news was not good,” Dr Bozec said.

“We forecast a rapid coral decline before the middle of this century regardless of the emissions scenario.

“Corals may partially recover after that, but only if ocean warming is sufficiently slow to allow natural adaptation to keep pace with temperature changes.

“Adaptation may keep pace if global warming does not exceed 2 degrees by 2100.

“For that to happen, more action is needed globally to reduce carbon emissions which are driving climate change.”

The ecosystem model, ReefMod-GBR, simulated the lifecycles of multiple coral species on 3,806 individual reefs.

Each modelled reef had tailored environmental settings including water quality, larval connectivity with neighbouring reefs, outbreaks of the coral-eating Crown of Thorns starfish and the risk of cyclones and coral bleaching until 2100.

Professor Peter Mumby said the model was tested extensively against long-term historic monitoring of the Great Barrier Reef to ensure it was as accurate as possible.

Professor Mumby said it showed that the rate of global warming was critical.

“We saw that many reefs could persist under the Paris Agreement target of 2 degrees of warming,” he said.

“However, higher emissions leading to faster temperature rises would drive most reefs to a near collapse.”

The study has a glimmer of hope, even on the current emissions trajectory.

“Importantly, reefs in areas where the water doesn’t heat up so dramatically because it is well mixed, fared better than others,” Professor Mumby said.

“And the better-connected reefs with good access to larval replenishment from other nearby reefs were healthier.

“This shows management efforts to safeguard strategic parts of the coral reef network have a tangible benefit in promoting reef health.

“Reef management remains vitally important even on our current emissions trajectory.”

“The window for meaningful action is closing rapidly but it hasn’t shut,” Dr Bozec said.

“Reducing global emissions and addressing local stressors can still make a difference.”

Executive Director of the Reef Restoration and Adaptation Program, Dr Cedric Robillot said the collaborative research within the program shows that the local response of marine ecosystems to ocean warming is complex and nuanced.

“These findings confirm our understanding that coral reefs and the communities they support are facing an existential threat,” Dr Robillot said

“We must curb greenhouse gas emissions drastically, redouble our current management efforts, and develop new interventions to assist coral reefs while ocean warming is gradually arrested.”

The research is published in Nature Communications.

This work was funded by the Reef Restoration and Adaptation Program, a partnership between the Australian Government’s Reef Trust and the Great Barrier Reef Foundation. It was completed with collaborators at CSIRO and The Australian Institute of Marine Science.

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Journal

Nature Communications

DOI

10.1038/s41467-025-65015-4 

Method of Research

Computational simulation/modeling

Subject of Research

Not applicable

Article Title

A rapidly closing window for coral persistence under global warming

Article Publication Date

5-Nov-2025

COI Statement