Wildfire ozone pollution weakening Amazon's ability to absorb carbon

University of Exeter

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Tropical forest at Daintree Rainforest Observatory
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Credit: Alexander Cheesman

Ozone pollution released by Amazon wildfires is significantly reducing the rainforest's ability to absorb carbon dioxide from the atmosphere, new research reveals.

Ground-level ozone is formed when pollutants from sources such as wildfires react in the presence of sunlight.

This harms human health and interferes with plants' ability to absorb carbon dioxide (CO2) from the atmosphere.

This means wildfires have a double impact on our climate: both directly releasing CO2 from biomass burning and reducing the ability of remaining forests to capture and store CO2.

And the researchers – from the University of Exeter, ETH Zurich and James Cook University – warn that this year's strengthening El Niño could bring a repeat of the record damage seen in 2024.

Hidden carbon loss

The new study, published in the journal Communications Earth & Environment, calculates that fire-driven ozone damage cuts Amazon carbon uptake by an amount equivalent to around 24% of the carbon emitted by the fires themselves.

This effect is strongest during major droughts, and three of the most extreme Amazon droughts of the past three decades (1997/98, 2015/16 and 2023/24) occurred during El Niño events.

El Niño is the warm phase of a natural, recurring global climate cycle. It’s not caused by human activity, but climate change means it sits on rising baseline temperatures, making it more likely to push global temperatures to record highs and intensify extreme weather.

With forecasters warning that a strong El Niño is already developing this year – with the potential to become one of the most intense on record – the authors of the news study say we are likely to see another major spike in hidden carbon loss.

Distinct signature

"Forest fires don't just release CO2 when they burn," said lead author Dr Flossie Brown, of ETH Zurich.

"They also contribute to the rise in ground-level ozone, a pollutant that damages the leaves of surviving trees and reduces their ability to keep absorbing carbon afterwards.

"We found this hidden effect is equivalent to around a quarter of the carbon released by the fires themselves – a significant loss to the Amazon's carbon budget that hasn't previously been considered."

The researchers used nearly three decades of observations and a global vegetation model to track how ozone damage has changed from 1997 to 2024, alongside fire activity and drought.

"The Amazon droughts we studied have each left a distinct signature," Dr Brown said.

"Ozone damage during the 2023/24 drought nearly doubled compared to the average of the previous decade. Given that a comparably strong El Niño appears to be developing again this year, we're concerned we could see history repeat itself."

Solutions overlap

Almost all fires in the Amazon are started by people, either through land clearance or agriculture that escapes into standing forest. The worst ozone damage is concentrated in the "Arc of Deforestation", where agricultural land is expanding into the rainforest.

"That means the extra ozone damage we're describing is largely preventable," said Professor Stephen Sitch, of the University of Exeter.

"Reducing deforestation and forest degradation would cut direct fire emissions – but our study shows it would also protect the Amazon from this secondary, invisible source of carbon loss."

Co-author Dr Alexander Cheesman, of James Cook University, said the findings show that air pollution, land-clearing and climate change cannot be treated as separate problems in determining the future of the Amazon.

"These impacts interact and need to be considered together," he said. "But this also means that solutions may have multiple benefits. Policies that tackle deforestation and degradation address both the CO2 released directly by fires and the ozone pollution quietly eroding what's left of the forest's ability to soak it back up."

This research was funded by the Natural Environment Research Council, partly via the GW4+ Doctoral Training Partnership.

For more information about the research, visit the TropOz website: https://tropoz.org/

The paper is entitled: "Fire-derived ozone and intensifying droughts undermine the Amazon carbon sink."

Journal

Communications Earth & Environment

DOI

10.1038/s43247-026-04047-0

Article Title

Fire-derived ozone and intensifying droughts undermine the Amazon carbon sink.

Article Publication Date

7-Oct-2026

TropOz experimental facility on the Nguma-bada campus of James Cook University

Ozone damage on a Homalanthus novoguineensis leaf

Credit

Alexander Cheesman

Novel device will help show how wildfire smoke impacts wildlife

Colorado State University

Collared deer running — image:
The collar around this mule deer's neck holds sensors measuring air quality as well as physiological and location data, giving researchers insights into the animal's health and activity. Credit: Alexis Neukirch/U.S. Forest Service
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Credit: Alexis Neukirch/U.S. Forest Service

When wildfire smoke fills the air, most people can go inside to avoid it. Wildlife does not have that option, and little is known about how animals living in remote areas respond to wildfires and smoke exposure.

Colorado State University researchers have developed an air quality monitoring device that can be paired with systems that track wildlife location and physiological data to learn how smoke impacts wildlife health and behavior. The smoke logger is an open-source tool that will allow wildlife researchers everywhere to answer questions that previously couldn’t be answered and gather data that can be used to better protect wildlife. The smoke logger design and programming are now freely available with publication of initial results in Methods in Ecology and Evolution.

“Wildfire is now a chronic problem in North America. We all are experiencing these massive smoke plumes that can negatively affect air quality for weeks at a time,” said CSU Professor George Wittemyer, who led the project with U.S. Forest Service wildlife ecologist Mark Ditmer and CSU postdoctoral researcher Adam Parlin. “We're interested in how wildlife adjusts its behavior relative to smoke exposure, and it wasn't possible to know until now.”

As wildfires increase in frequency, size and severity, smoke plumes that impact air quality for an extended time are a new stressor for wildlife, Wittemyer added, and air quality typically is not monitored in wilderness areas. The small, affordable smoke logger the team has developed can be attached to animal-borne collars to record the concentration of hazardous particles animals are breathing.

“We know relatively little about the impacts of wildfire smoke on the behavior of animals in the field, especially how free-roaming wildlife respond to severe smoke events,” said Parlin, who designed the smoke logger while he was a postdoctoral researcher in the Department of Fish, Wildlife and Conservation Biology. “These units provide one avenue to better understand the consequences from wildlife’s perspective – such as identifying refugia during smoke events – that can provide actionable insights for conservation and management.”

Wildlife studies – especially those that capture, collar and recapture animals – are resource intensive, and many of them already track health data, like heart rate, in addition to GPS coordinates. These data combined with smoke logger data will reveal new information about wildlife welfare and activity.

The team is partnering with researchers across the western U.S. to piggyback on studies tracking cougars, deer and elk, and they stationed sensors in the habitat of the endangered Sierra Nevada fisher, a small mammal related to weasels, to better understand the air quality in their range. Those results will be published in future studies.

They encourage researchers with projects where wildlife collars are recovered to partner with them to add smoke loggers to their sensor packages. Or, for about $100 in materials per unit, researchers can assemble their own smoke loggers by downloading the free, open-source design and programming.

Initial deployment on mule deer revealed that air quality differed by an order of magnitude – 10 times either more or less – between the deer-borne sensors and the closest monitoring stations, indicating the highly localized nature of air quality and the need to monitor individual animals to understand their exposure and response. Deer monitored in Colorado and Utah this year were not exposed to unhealthy levels of wildfire smoke, but testing showed that the sensor is sensitive enough to register minimal air pollution spikes from traffic for urban-dwelling deer.

"That was eye-opening for us and shows how variable air quality is at a microscale,” said Wittemyer, a professor in the Warner College of Natural Resources.

The U.S. Environmental Protection Agency monitors air quality in populated areas across the country through the AirNow network. The wildlife-worn sensors will fill gaps in data and deliver further health insights for people exposed to smoke too.

To design an affordable tool, the team repurposed a low-cost, commercially available sensor similar to the ones used by the PurpleAir monitoring network. The sensors use a laser to measure microscopic particles known as particulate matter 2.5 because they have a diameter of 2.5 micrometers or less. These particles are detrimental to cardiovascular and respiratory health.

The solar-powered smoke logger is designed to be worn on a collar by medium and large animals and must be recovered for the data to be downloaded. Transmitting data would be costly and would drain the device’s battery, limiting its lifespan, and there is no connectivity for transmission in wildlands. Instead, air quality data is recorded and stored every 30 minutes.

Ditmer said a stronger understanding of how smoke impacts wildlife health will improve conservation planning and allow prescribed burns to be timed to reduce risk to wildlife.

“Prescribed fire is an important tool for managing forests in the face of increasingly severe wildfires, and understanding when and where smoke actually reaches wildlife could help managers plan burns that meet forest-management goals while reducing exposure during sensitive periods or in important habitats,” he said.

Former CSU postdoctoral researcher Adam Parlin assembles a smoke logger that will be attached to a wildlife collar, so researchers can study the impacts of wildfire on wildlife. Courtesy of Adam Parlin/Colorado State University

Credit

Adam Parlin/Colorado State University

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