Yes, ozone is a greenhouse gas. It absorbs infrared radiation (heat) rising from Earth’s surface and traps it in the atmosphere, working through the same basic mechanism as carbon dioxide and methane. But ozone’s role in climate is more complex than most greenhouse gases because it exists in two distinct layers of the atmosphere, and its effects depend heavily on where it is.
How Ozone Traps Heat
Like all greenhouse gases, ozone molecules absorb longwave infrared radiation emitted by Earth’s surface. Instead of letting that energy escape to space, ozone captures it and re-emits it in all directions, including back toward the ground. This warms the surrounding atmosphere. NASA describes this simply: ozone absorbs infrared radiation from Earth’s surface, reducing the amount that escapes to space.
What makes ozone unusual among greenhouse gases is that it isn’t emitted directly by smokestacks or tailpipes. It forms in the atmosphere through chemical reactions involving other pollutants, primarily nitrogen oxides (from combustion engines, power plants, and industrial processes) and volatile organic compounds (from vehicles, solvents, and even trees). Sunlight drives these reactions, which is why ground-level ozone peaks on hot, sunny days.
Two Layers, Two Different Roles
About 90% of Earth’s ozone sits in the stratosphere, roughly 10 to 30 miles above the surface. This is the “ozone layer” that blocks harmful ultraviolet radiation. The remaining ozone forms in the troposphere, the lowest layer of the atmosphere where weather happens and where we live. These two pools of ozone have had very different trajectories over the past half-century: stratospheric ozone has been depleted (largely by industrial chemicals now banned under the Montreal Protocol), while tropospheric ozone has increased due to rising pollution.
Both changes contribute to warming, but through different mechanisms. Tropospheric ozone acts as a straightforward greenhouse gas, trapping heat near the surface. Stratospheric ozone depletion, somewhat counterintuitively, also contributes to warming in certain regions by altering wind patterns and ocean circulation. A study published in Nature Climate Change found that ozone changes between 1955 and 2000 were responsible for about 30% of the heat gained in the upper 2,000 meters of the Southern Ocean. Of that warming, roughly 60% came from tropospheric ozone increases and 40% from stratospheric depletion.
How It Compares to CO₂ and Methane
Tropospheric ozone is the third most important greenhouse gas after carbon dioxide and methane in terms of human-caused warming. Under one high-emission scenario modeled by multiple research groups, ozone’s total radiative forcing (a measure of how much extra energy it traps) is projected to increase by about 0.27 watts per square meter between 2015 and 2050. That would make it the second largest contributor to additional warming over that period, with roughly half coming from recovering stratospheric ozone and half from rising tropospheric pollution.
For context, carbon dioxide’s total radiative forcing is currently around 2 watts per square meter, so ozone is a smaller player in absolute terms. But it punches above its weight relative to its concentration. Methane’s global warming potential actually includes some of ozone’s warming effect, because methane is a precursor to ozone. When methane breaks down in the atmosphere, it generates ozone as a byproduct, so part of methane’s climate impact is really ozone’s climate impact.
A Short-Lived but Uneven Threat
One key difference between ozone and the major greenhouse gases is lifespan. Carbon dioxide persists in the atmosphere for hundreds of years. Methane lasts about a decade. Tropospheric ozone breaks down in days to weeks. This short residence time means ozone never mixes evenly throughout the atmosphere. Its warming effect is concentrated near the regions where it forms, creating hotspots rather than a uniform global blanket.
Ozone concentrations vary dramatically by season, location, and altitude. Levels tend to peak in spring and summer when sunlight is strongest and temperatures are highest. Urban and industrial areas with heavy traffic and manufacturing see far more ozone formation than remote regions. This geographic patchiness makes ozone harder to track and regulate than long-lived greenhouse gases, which spread uniformly enough to be measured from a single monitoring station.
Climate Change Makes the Problem Worse
Rising temperatures and ozone pollution feed each other in a troubling loop. Higher temperatures accelerate the chemical reactions that produce ozone. They also increase emissions of natural volatile organic compounds from trees, particularly a hydrocarbon called isoprene, which fuels further ozone production. Urban heat islands intensify local ozone formation, and changing weather patterns can trap polluted air near the surface for longer periods.
Climate projections suggest that in regions where warming brings more frequent high-pressure systems with stagnant, sunny conditions, ozone episodes will become more common and more severe, even without any increase in the pollution that serves as raw material. Some modeling work has projected that both plant emissions and soil emissions of ozone precursors will rise as temperatures climb, compounding the effect of human-made pollution.
Ozone’s Hidden Impact on Carbon
Beyond trapping heat directly, tropospheric ozone undermines one of nature’s most important climate defenses: the ability of plants to absorb carbon dioxide. Ozone enters leaves through the same pores plants use to take in CO₂ and disrupts photosynthesis at the cellular level. It inhibits the key enzyme responsible for carbon fixation, forcing plants to divert energy toward repairing damage instead of growing. The result is fewer leaves, smaller root systems, reduced crop yields, and less carbon pulled out of the atmosphere.
This creates a secondary warming effect that climate models have historically underestimated. USDA research has found that models predicting how much carbon forests and crops will absorb under rising CO₂ levels tend to overestimate carbon sequestration when they don’t account for ozone damage. In other words, ozone doesn’t just warm the planet by trapping heat. It also weakens the planet’s ability to cool itself by hobbling the vegetation that would otherwise soak up carbon dioxide.