Wildfires in the Amazon have consequences that go far beyond the destruction of vegetation. A new study has uncovered a less visible threat: ozone produced during these events also harms trees that survive the flames, damaging their leaves and making it harder for them to absorb carbon dioxide (CO2).
This effect can go unnoticed when attention focuses solely on the direct damage caused by fire. Yet it represents an additional loss for the rainforest’s carbon balance and can become more severe during periods of intense drought.
Researchers from the University of Exeter, ETH Zurich and James Cook University published their peer-reviewed study in the journal Communications Earth & Environment on October 7, 2026.
Amazon wildfires and human responsibility
Almost all fires in the Amazon are started by people, mainly to clear land for agriculture and cattle ranching. However, these fires can get out of control and spread into surrounding areas of rainforest, destroying vast stretches of woodland.
Wildfires release CO2 into the atmosphere, but their effects do not end when the flames die out. They also produce pollutants that contribute to the formation of tropospheric ozone. This ozone occurs in the troposphere, the lowest layer of the atmosphere, which extends from the Earth’s surface upwards.
Unlike ozone in the stratosphere, which protects us from much of the sun’s ultraviolet radiation, tropospheric ozone is harmful to human health and vegetation. It damages the leaves of surviving trees and reduces their ability to absorb CO2. In this way, wildfires not only release carbon by burning forests but also make it harder for the surviving rainforest to absorb some of that carbon.
The threat to surviving trees
Tropospheric ozone pollution damages tree leaves and reduces the efficiency of photosynthesis, the process through which trees absorb CO2. As a result, even areas that have not been directly burned can lose some of their ability to remove carbon from the atmosphere.
The researchers estimate that this additional reduction in carbon uptake is equivalent to around 24% of the carbon released directly by wildfires. Flossie Brown, the study’s lead author from ETH Zurich, explains that the consequences of wildfires go beyond the emissions produced by combustion:
Forest fires don’t just release CO2 when they burn. 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.
To investigate this phenomenon, the team analyzed observations covering the period from 1997 to 2024 and used a global vegetation model. This allowed them to examine the relationship between wildfires, ozone damage and the Amazon’s ability to absorb CO2. The results also showed that the impact is not constant: it can become more severe when climatic conditions are particularly harsh.
El Niño and droughts can worsen the impact
Although human activities play a major role in many Amazon wildfires, climatic conditions can intensify their effects. Severe droughts put vegetation under greater stress and can worsen the damage suffered by the rainforest.
One important factor is El Niño, the warm phase of a natural climate phenomenon that alters weather patterns in different parts of the world. It is not caused by human activity, but global warming raises baseline temperatures and can intensify some of its effects.
Three of the most severe Amazon droughts in recent decades — in 1997–1998, 2015–2016 and 2023–2024 — coincided with El Niño events. During the 2023–2024 drought, ozone-related damage almost doubled compared with the average for the previous decade.
The researchers warn that a strong El Niño event could once again create conditions that are damaging to the rainforest. However, this climate phenomenon should not be confused with the cause of deforestation: it can intensify the damage, while logging and burning associated with human land use remain fundamental factors that can be directly addressed.
Protecting the Amazon requires a joined-up approach
The findings show that the impact of wildfires extends far beyond the CO2 they release as forests burn. Ozone pollution also weakens surviving trees and reduces the Amazon’s ability to remove carbon from the atmosphere. When this effect coincides with extreme climatic conditions, the consequences for the rainforest can be even more severe.
Stephen Sitch, from the University of Exeter, highlights that reducing deforestation and forest degradation would not only cut direct wildfire emissions but also protect the rainforest from this additional loss of carbon:
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.
As Alexander Cheesman, from James Cook University, points out:
These impacts interact and need to be considered together.
The conclusion is clear: protecting the Amazon means not only preventing more trees from burning, but also preserving the ability of the surviving rainforest to continue absorbing CO2. This requires action to tackle deforestation while also taking the effects of air pollution and climate change into account. Ignoring any of these connections means overlooking part of the problem.
Bottom line: Amazon wildfires are weakening the rainforest’s ability to absorb carbon, as ozone pollution damages trees that survive the flames.
Source: Fire-derived ozone intensifies carbon loss in Amazon forests under extreme droughts
Read more: Will El Niño become supersized? What experts are saying
Read more: How does smoke from wildfires affect birds?
The post Amazon wildfires hide another threat to the rainforest first appeared on EarthSky.