What a US Ozone Study Reveals About the True Cost of Wildfire

✅ Key Takeaway: Wildfire smoke has reversed a decade of US clean-air progress, adding 300-plus ozone deaths a year, while UK statutory evidence shows our wildfire risk rising fastest on open habitats.

In Canada's record-breaking 2023 fire season, ground-level ozone breached US federal air-quality standards for around 148 million people, close to 44% of the population of the continental United States. The smoke responsible had, in many cases, drifted in from fires hundreds or thousands of miles away.

A new study in the journal Science finds this was no one-off. Wildfire smoke has reversed roughly a decade of progress on ozone pollution across much of the United States, and the consequences reach far beyond the fireline.

Researchers led by the University of Iowa mapped surface ozone (ground-level ozone, the main ingredient in smog) across the continental US from 2003 to 2024. Tighter limits on vehicle exhaust and industry had driven ozone steadily down for years.

After about 2015 the trend flipped, with ozone climbing again across much of the Midwest and West. When the team removed wildfire from their analysis, the decline returned, which is how they identify fire as the main driver of the reversal.

The annual rise is small but relentless, averaging about 0.13 parts per billion a year between 2015 and 2024. The researchers attribute more than 300 additional premature deaths a year in the US since 2013 to wildfire-driven ozone, a pollutant linked to respiratory and cardiovascular disease.

How the researchers built the picture

The study's value is in its resolution. The team trained deep-learning models (artificial-intelligence systems that find patterns in large datasets) on satellite observations and readings from about 1,000 ground monitoring stations, producing a daily, gap-free map of surface ozone at one-kilometre scale spanning more than two decades. The work was funded by NASA.

Surface ozone is not emitted from any tailpipe or chimney. It forms when sunlight reacts with other pollutants in the air, which is why cleaning up traffic and industry once brought it down. The new problem comes from a source those controls do not touch.

Smoke does not stay near the fire

The finding most relevant to land managers is how far the damage travels. Burning vegetation releases carbon monoxide, which can move thousands of miles downwind before reacting to form ozone.

A fire in California or western Canada can therefore degrade air over states that never saw a flame. For surface air quality, the study finds this ozone effect is generally larger than that of black carbon (the soot also carried in smoke).

This sits against a worsening fire regime. North American wildfire seasons are lengthening, and Canada recorded its worst seasons on record in both 2023 and 2025. The authors expect the ozone burden to climb further if those trends hold.

The UK relevance: a real threat on the habitats we manage

The specific figures here are American and cannot be applied directly to Britain. The rate of increase, the death toll and the exposed population reflect North American conditions, and the paper makes no claim about UK moorland or any fire-management method.

What does carry across is the principle the study quantifies so clearly: a large wildfire is not only a local emergency but an air-quality and public-health event that reaches well beyond the burn.

That principle lands squarely on British uplands. Parliament's own science advisers identify wildfire as an increasing climate-change risk, flagged in both the 2022 UK Climate Change Risk Assessment and the 2023 National Adaptation Programme.

The Met Office projects that 2°C of warming would roughly double the frequency of dangerous summer fire weather. And the burden is concentrated where it matters most to our members: between 2009 and 2021, open landscapes such as heath, peat and grassland accounted for around 70% of the area burned by wildfire in England while making up only about 30% of incidents.

The driver of fire severity is well understood. As the National Fire Chiefs Council and landowners told the House of Lords in June 2025, the larger the share of fuel load (the vegetation and organic matter available to burn) left unmanaged, the bigger the fire and the greater the damage. On that point the parliamentary evidence is blunt: land management is critical.

What this means for the uplands

For estate owners, gamekeepers and upland managers, the study matters not as a UK statistic but as a measure of what is at stake. It puts hard numbers on the cost that fuel-heavy, unmanaged landscapes invite: smoke that sickens people far downwind and erases years of air-quality investment.

Britain's fire risk is rising fastest on exactly the open habitats that active management has long maintained. The case for keeping fuel loads in check, by the methods the evidence supports is only reinforced by a study like this.