Ozone does trap heat in the atmosphere, but whether it warms or cools the surface depends almost entirely on where in the atmosphere the ozone sits. In the lower atmosphere, ozone acts like a conventional greenhouse gas, absorbing outgoing infrared radiation and warming the planet. Higher up, in the stratosphere, the relationship flips in ways that confuse even well-informed readers. The ozone layer’s role in Earth’s heat budget turns out to be one of the more counterintuitive stories in climate science, tangled up with the ozone hole, banned refrigerants, and even volcanic eruptions.
Ozone Absorbs Radiation in Two Different Ways
Ozone interacts with energy from the sun and energy radiating off Earth’s surface, but it handles these two energy streams differently. It absorbs ultraviolet light from the sun, which is why the ozone layer protects life on the ground from damaging UV rays. That absorption heats the stratosphere itself, creating the temperature inversion that defines the boundary between the lower and upper atmosphere. At the same time, ozone absorbs and re-emits infrared radiation, the heat energy that Earth’s surface sends back toward space. This second role is what makes ozone a greenhouse gas in the technical sense: it intercepts outgoing heat and redirects some of it back downward.
The balance between these two processes shifts depending on altitude, concentration, and what other gases are nearby. A molecule of ozone near the ground and a molecule of ozone 35 kilometers overhead are doing fundamentally different things to the planet’s temperature, even though they are chemically identical.
Altitude Changes Everything
Radiative calculations have shown that the surface temperature response to ozone changes depends sharply on where those changes happen. Ozone decreases above about 30 kilometers actually warm the surface, while ozone decreases in the lower stratosphere cool it. Conversely, ozone increases below 30 kilometers warm the surface.1Journal of Geophysical Research: Atmospheres. Radiative forcing of climate by changes in the vertical distribution of ozone This is not a minor bookkeeping detail. It means you cannot talk about “the ozone layer” as a single blanket that either traps heat or lets it escape. Its thermal fingerprint is altitude-dependent in a way that most other greenhouse gases are not.
The reason comes down to temperature contrasts. A greenhouse gas traps the most heat when there is a large temperature difference between the surface below it and the gas itself. Ozone in the lower stratosphere sits just above the cold tropopause, which means it is relatively warm compared to its surroundings, and it radiates energy efficiently in all directions, including downward. Remove that ozone and you lose a source of downward infrared radiation, cooling the surface. Higher up, the physics tilts differently: removing ozone at those altitudes lets more solar energy through to warm the layers below, and the infrared trapping effect at that height is smaller.
Tropospheric Ozone Is a Straightforward Warming Agent
The ozone that sits in the lowest part of the atmosphere, the troposphere, behaves much more like a typical greenhouse gas. It absorbs outgoing infrared radiation and warms the air around it. Human activities have increased tropospheric ozone substantially over the past century, primarily through emissions of nitrogen oxides, carbon monoxide, and volatile organic compounds that react in sunlight to produce ozone near the ground. This increase has contributed measurably to twentieth-century warming.2Journal of Geophysical Research: Atmospheres. Role of tropospheric ozone increases in 20th‐century climate change
Tropospheric ozone is actually the third most important greenhouse gas that humans have enhanced, after carbon dioxide and methane, when measured by radiative forcing. It does not get the same headlines because it is short-lived compared to CO₂. A molecule of tropospheric ozone typically lasts only weeks before breaking down, whereas CO₂ persists for centuries. But at any given moment, there is enough human-generated tropospheric ozone in the atmosphere to make a real difference to the global energy budget.
There is also a dynamic exchange between layers. During certain atmospheric events, ozone-rich air from the stratosphere can push down into the troposphere, temporarily boosting ozone levels in the upper troposphere and enhancing its radiative forcing there. One recent study documented that sudden stratospheric warming events over South Asia can increase upper-tropospheric ozone by as much as 290 percent within a month, with the extra ozone adding a small but measurable warming effect.3EGUsphere. Large Ozone Intrusions during Sudden Stratospheric Warmings Enhance Ozone Radiative Forcing over South Asia
Stratospheric Ozone Depletion Has Been Cooling the Planet
Here is where the story turns counterintuitive. The thinning of the ozone layer that alarmed the world in the 1980s and 1990s has not been warming the planet. It has been cooling it. Because ozone in the lower stratosphere is an effective greenhouse gas at that altitude, losing it means less downward infrared radiation reaching the surface. Detailed radiative transfer calculations found that the globally averaged forcing from stratospheric ozone loss between 1979 and 1996 was roughly −0.2 watts per square meter, a negative number meaning a cooling effect. That offset about 30 percent of the warming from increases in well-mixed greenhouse gases over the same period.4Journal of Geophysical Research: Atmospheres. Radiative forcing and temperature trends from stratospheric ozone changes
This is worth sitting with for a moment. The ozone hole, which we rightly think of as an environmental catastrophe because of the UV radiation it lets through, has been partially masking the full warming effect of greenhouse gases. As the ozone layer heals over the coming decades, that mask will come off, and a small additional warming effect will emerge. The atmosphere has been running a kind of accidental cooling experiment since the 1970s, and we are in the process of ending it.
Observations in the stratosphere itself show the cooling clearly. Ozone depletion in the lower stratosphere produced atmospheric cooling of several tenths of a degree in the 12-to-20-kilometer altitude range over northern mid-latitudes.1Journal of Geophysical Research: Atmospheres. Radiative forcing of climate by changes in the vertical distribution of ozone When solar energetic particle events destroy ozone in the polar stratosphere, the resulting loss of shortwave heating produces cooling of 1.5 to 3 degrees at altitudes between 28 and 35 kilometers.5PubMed Central. Ozone impact from solar energetic particles cools the polar stratosphere
Ozone Depletion Also Reshapes Weather Patterns
Beyond temperature, stratospheric ozone loss has reshaped atmospheric circulation, particularly in the Southern Hemisphere. The cooling of the Antarctic stratosphere caused by ozone depletion strengthened the polar vortex and pushed the mid-latitude jet stream toward the South Pole during summer months. Multiple climate models confirm this: stronger ozone depletion in late spring generally leads to a greater poleward shift and intensification of the tropospheric jet, along with expansion of the Southern Hemisphere’s Hadley cell in summer.6Journal of Geophysical Research: Atmospheres. Impact of stratospheric ozone on Southern Hemisphere circulation change: A multimodel assessment
These circulation shifts matter because they change where rain falls, how sea ice forms, and what surface temperatures look like across a wide swath of the Southern Hemisphere. The jet stream’s poleward drift has been linked to drying trends in parts of southern Australia and changes in Antarctic sea ice distribution.7Atmospheric Chemistry and Physics. Sensitivity of the Southern Hemisphere circumpolar jet response to Antarctic ozone depletion: prescribed versus interactive chemistry As the ozone layer recovers, these circulation trends are expected to reverse, at least partially, creating a tug of war with the opposing effects of rising greenhouse gases that push the jet stream poleward for different reasons.
The Chemicals That Destroyed Ozone Were Also Powerful Greenhouse Gases
Chlorofluorocarbons and related compounds do double duty in the atmosphere. They destroy ozone, and they also trap heat. A single CFC molecule can be thousands of times more effective at absorbing infrared radiation than a molecule of CO₂. Even though CFC concentrations are measured in parts per trillion, their cumulative warming effect has been significant. As recently as 2020, emissions of ozone-depleting CFCs were equivalent to about 47 million metric tons of CO₂.8Nature Geoscience. Global increase of ozone-depleting chlorofluorocarbons from 2010 to 2020
This creates a strange accounting problem. CFCs warm the planet directly through their greenhouse effect, but they also cool the planet indirectly by destroying stratospheric ozone. The net effect of CFCs on climate has been warming, because the direct greenhouse warming from the gases themselves outweighs the indirect cooling from ozone depletion. When both effects are tallied, eliminating CFCs has been good for the climate on both counts: it stops the direct greenhouse warming and it allows the ozone layer to heal (though ozone recovery will, as noted above, slightly reduce the accidental cooling we have been getting).
The Montreal Protocol as Unintentional Climate Policy
The 1987 Montreal Protocol was designed to protect the ozone layer, not to fight climate change. But because it phased out potent greenhouse gases, it turned out to be one of the most effective pieces of climate policy ever enacted. Modeling work shows that by mid-century, the Montreal Protocol will have avoided roughly 1 degree Celsius of global average warming and 3 to 4 degrees of Arctic warming, amounting to about a 25 percent reduction in projected global warming.9Environmental Research Letters. Reduction in surface climate change achieved by the 1987 Montreal Protocol That is after accounting for the loss of the ozone-depletion cooling effect.
The climate protection already achieved by the Montreal Protocol has been estimated to be far larger than what the Kyoto Protocol’s first commitment period aimed to deliver.10PubMed Central. The importance of the Montreal Protocol in protecting climate In the United States alone, the decline in ODS emissions between 2008 and 2014 accounted for about half of the total reduction in CO₂-equivalent greenhouse gas emissions over the same period.11Geophysical Research Letters. Considerable contribution of the Montreal Protocol to declining greenhouse gas emissions from the United States The lesson is that a treaty focused on one environmental problem can quietly become one of the most important interventions for a different problem entirely.
Rising CO₂ Is Speeding Up Ozone Recovery
There is another twist in the relationship between ozone and climate. Carbon dioxide, the main greenhouse gas driving surface warming, cools the stratosphere. A greenhouse gas warms the lower atmosphere by trapping outgoing heat, but in the upper atmosphere, the extra CO₂ radiates energy to space more efficiently than the thin air around it can absorb, resulting in net cooling at those altitudes. That stratospheric cooling turns out to be good for ozone. The chemical reactions that destroy ozone run slower at lower temperatures, so as CO₂ cools the stratosphere, the ozone destruction cycles weaken and ozone recovers faster.12Advances in Space Research. Greenhouse gases and recovery of the Earth’s ozone layer
In the upper stratosphere, this effect is straightforward: greenhouse-gas-induced cooling causes ozone levels to bounce back to 1980 values decades before the ozone-depleting substances themselves have fully cleared the atmosphere.13Geophysical Research Letters. Impacts of climate change on stratospheric ozone recovery But the picture is messier at lower altitudes and different latitudes. In the tropical lower stratosphere, increasing CO₂ speeds up the overturning circulation and reduces ozone production, actually delaying recovery there. At high northern latitudes, the timing of recovery shifts seasonally: spring and summer recovery slows because of enhanced chemical ozone loss on cold polar clouds, while fall and winter recovery speeds up because of increased downwelling of ozone-rich air.14Journal of Geophysical Research: Atmospheres. The impact of increasing carbon dioxide on ozone recovery
Ozone’s Role at the Tropopause Boundary
One of the more specialized but important aspects of ozone’s thermal role involves the tropopause, the boundary between the troposphere and the stratosphere. The temperature at this boundary matters enormously for climate because it controls how much water vapor enters the stratosphere. Warmer tropopause temperatures let more water vapor through, and water vapor is itself a potent greenhouse gas, so even small changes here get amplified.
Ozone radiative heating plays a surprisingly large role in setting tropopause temperatures. Modeling work has found that the ozone radiative effect may explain about half of the roughly 10-kelvin spread in cold-point tropopause temperatures across current climate models.15Journal of Geophysical Research: Atmospheres. On the relative importance of radiative and dynamical heating for tropical tropopause temperatures In other words, how well a climate model handles ozone at the tropopause partly determines how well it handles the water vapor feedback that drives long-term warming projections. Ozone is not just a passive greenhouse gas at this altitude; it actively shapes one of the key feedback loops in the climate system.
Volcanoes, Geoengineering, and Ozone Disruption
Major volcanic eruptions inject sulfate aerosols into the stratosphere, and these particles interact with ozone in two distinct ways. They provide surfaces for chemical reactions that accelerate ozone destruction, and they absorb and scatter radiation in ways that heat the lower stratosphere and alter circulation patterns.16Atmospheric Chemistry and Physics. The impacts of volcanic aerosol on stratospheric ozone and the Northern Hemisphere polar vortex: separating radiative-dynamical changes from direct effects due to enhanced aerosol heterogeneous chemistry The net effect depends on how much chlorine and bromine are already in the stratosphere from human-made chemicals. After the eruption of Mount Pinatubo in 1991, when stratospheric halogen levels were near their peak, the ozone losses were substantial. As halogen levels decline in the coming decades, future eruptions of similar magnitude should cause less ozone destruction.
Stratospheric aerosol injection, a proposed geoengineering technique that would deliberately mimic volcanic cooling by spraying sulfate particles into the stratosphere, raises similar concerns. Modeling shows that the injected aerosols heat the tropical tropopause, increasing the amount of water vapor entering the stratosphere. That extra water vapor accelerates ozone destruction through hydroxyl-driven catalytic cycles, potentially causing significant ozone depletion even in a future where halogen levels are low.17Environmental Research Letters. The impact of geoengineering aerosols on stratospheric temperature and ozone Additional work has confirmed that chlorine activation on geoengineering aerosol surfaces could reduce ozone in the lowermost stratosphere at mid-latitudes, though the magnitude is small under projected future halogen scenarios.18Atmospheric Chemistry and Physics. Potential of future stratospheric ozone loss in the midlatitudes under global warming and sulfate geoengineering
The geoengineering question ties the ozone-heat story into a knot: the whole point of spraying aerosols is to cool the planet by reflecting sunlight, but if the aerosols also thin the ozone layer, you lose one of the atmosphere’s natural mechanisms for absorbing and redistributing solar energy. Any future deployment of stratospheric aerosol injection would need to account for these ozone side effects, which would shift the atmosphere’s thermal profile in ways that partially undercut the intended cooling.
How Solar Variability Feeds Into the Picture
The sun’s output is not perfectly constant. Over its roughly 11-year sunspot cycle, the amount of ultraviolet radiation reaching the stratosphere changes, and because ozone formation depends on UV light, ozone concentrations in the upper stratosphere rise and fall with the solar cycle. More UV means more ozone production and more direct heating of the stratosphere; less UV means less of both. Chemistry-climate models have confirmed that variations in solar spectral irradiance have a significant impact on stratospheric temperatures and ozone mixing ratios.19Atmospheric Chemistry and Physics. Quantifying uncertainties of climate signals in chemistry climate models related to the 11-year solar cycle – Part 1: Annual mean response in heating rates, temperature, and ozone
These solar-driven ozone fluctuations are relatively small compared to the changes caused by CFCs or volcanic eruptions, but they introduce a natural oscillation in stratospheric temperatures that can propagate downward and influence surface weather patterns. Researchers are still working out how large those surface effects are and how they interact with the longer-term trends from greenhouse gas increases and ozone recovery. The solar cycle adds noise to an already complicated signal, making it harder to isolate the thermal fingerprint of ozone changes from everything else happening in the atmosphere.