LONDON: The ozone layer that shields us from ultraviolet radiation is also a heat trapper, and a new study warns that this double role will add more warming than policymakers previously calculated. Led by Professor Bill Collins of the University of Reading, the analysis highlights how ozone recovery and pollution together drive a hidden force of climate change.
A multi-model study shows that without strong pollution controls, ozone will add 0.268 ± 0.084 W/m² of heating between 2015 and 2050. That makes ozone the second-largest driver of near-term warming after carbon dioxide.
Researchers identified two main drivers of this increase. The first is the recovery of the ozone layer in the stratosphere as banned ozone-depleting chemicals continue to decline. The second is the build-up of ozone closer to the surface, caused by emissions of methane and nitrogen oxides from industry, vehicles, and agriculture.
Across seven advanced Earth system and chemistry models, the pattern was consistent. Roughly half of the additional warming came from the healing stratospheric layer and half from tropospheric increases. These values exceed earlier estimates because of more refined methods that account for cloud changes, water vapor, and surface reflectivity.
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Healing Ozone Also Traps Heat
Ozone acts as a greenhouse gas by absorbing infrared radiation, especially near 9.6 micrometers. Increases in the stratosphere trap more outgoing heat, but increases near the surface have a stronger effect because the air there is denser and warmer.
The Montreal Protocol successfully phased out harmful chemicals such as CFCs and HCFCs, protecting life from ultraviolet radiation. However, this success comes with a side effect: a thicker ozone layer traps more heat.
“Countries are doing the right thing by continuing to ban chemicals that damage the ozone layer,” said Professor Collins. “But while this helps repair the protective shield, our study shows that recovery will warm the planet more than we originally thought.”
The message is not to question the Montreal Protocol but to recognize the unavoidable warming it brings and to accelerate cuts to other pollutants that generate ozone near the ground.
Pollution Today, Warming Tomorrow
At ground level, ozone forms when reactive gases mix under sunlight. These gases, which include methane, nitrogen oxides, and volatile organic compounds, are short-lived. Cutting them produces quick benefits for both health and climate.
The U.S. Environmental Protection Agency (EPA) warns that ground-level ozone worsens asthma, reduces lung function, and damages crops. Professor Collins stressed: “Air pollution from vehicles, factories, and power plants creates ozone near the ground, causing health problems and warming the planet.”
Reducing these emissions provides a dual payoff: cleaner air in cities and less warming on a global scale.
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Metrics That Change the Numbers
Scientists measure climate impacts using radiative forcing. For ozone, the effective radiative forcing (ERF) since 1750 is assessed at 0.47 [0.24 to 0.71] W/m². ERF is especially important because it captures fast adjustments in clouds and water vapor, offering a more accurate picture than older metrics.
By contrast, stratospheric temperature adjusted radiative forcing (SARF) misses those rapid responses. The new study shows that for ozone changes from declining ozone-depleting substances, ERF is roughly double SARF. This means earlier policy estimates undercounted ozone’s true role in warming.
This is not just a technical distinction—it directly shapes climate projections and strategies.
Ozone Recovery Demands Pollution Cuts
According to NOAA, the stratospheric ozone layer will continue to recover for decades. The warming associated with this recovery is therefore unavoidable. That reality underscores the need to tackle tropospheric ozone by targeting its precursors.
Cutting methane reduces a major global ozone source, while controlling nitrogen oxides and volatile organic compounds lowers harmful peaks in urban regions. These steps improve public health and reduce near-term climate forcing.
Ozone Recovery Speeds Up Warming
Ozone’s shield is essential for life, but it comes with a climate cost. Recovery in the upper atmosphere and build-up near the surface will both contribute to faster warming.
The new analysis urges policymakers to update climate models with ERF-based ozone data, push harder on methane and precursor emissions, and continue supporting the Montreal Protocol.
Protecting the ozone layer remains a success story, but its climate side effects remind us that every pollutant matters. Managing ozone properly means cleaner air today and smarter climate strategies for tomorrow.
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