Although international bans on ozone-depleting chemicals such as CFCs have aided the layer's recovery, combined effects with air pollution mean ozone could add 40% more warming than earlier predictions suggested.
A University of Reading study projects that from 2015 to 2050, ozone will contribute 0.27 watts per square meter (Wm-2) of additional warming. This makes it the second most important driver of climate change by mid-century after carbon dioxide, which is forecast to add 1.75 Wm-2.
Professor Bill Collins, lead author, said: "Countries are doing the right thing by continuing to ban chemicals called CFCs and HCFCs that damage the ozone layer above Earth. However, while this helps repair the protective ozone layer, we have found that this recovery in ozone will warm the planet more than we originally thought.
"Air pollution from vehicles, factories and power plants also creates ozone near the ground, causing health problems and warming the planet."
The study, published in Atmospheric Chemistry and Physics, used atmospheric simulations to assess changes expected by 2050. The models assumed weak enforcement of air pollution controls but a full phase-out of CFCs and HCFCs under the 1987 Montreal Protocol.
Results show that halting CFC and HCFC production brings less climate benefit than anticipated. These gases are greenhouse agents, but their removal is offset because a healing ozone layer contributes warming that cancels much of the expected climate gain.
While cutting air pollution can reduce surface ozone locally, the recovery of the stratospheric ozone layer will proceed for decades regardless, creating unavoidable additional warming.
Despite this, scientists stress that ozone protection remains vital for human health, shielding against skin cancer and UV radiation damage to ecosystems. The findings indicate climate policy must adapt to reflect ozone's greater warming role.
Research Report:Climate forcing due to future ozone changes: an intercomparison of metrics and methods
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