🌍 Ozone could warm the Earth more than expected – A climate surprise

Ozone, that protective layer in the atmosphere, is often celebrated for its role as a shield against the Sun's ultraviolet rays. Yet, a recent study reveals that it could also amplify global warming in an unexpected way. Global efforts to restore this layer, although beneficial for human health, could have unforeseen consequences on our planet's climate.

Researchers at the University of Reading used computer models to simulate the evolution of the atmosphere up to 2050. They discovered that the recovery of the ozone layer, due to the gradual elimination of chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), would contribute to an additional warming of 0.27 watts per square meter. This value measures the extra energy retained by the Earth's surface, indicating that ozone would become the second largest warming factor after carbon dioxide.


Professor Bill Collins, lead author of the study, explains that banning ozone-depleting substances was a wise decision to preserve the protective layer. However, this repair leads to an increase in the greenhouse effect, as ozone also acts as a heat-trapping gas. Moreover, air pollution from human activities, such as vehicles and factories, generates ozone at ground level, worsening both health problems and warming.

The study, published in Atmospheric Chemistry and Physics, follows a scenario where air pollution controls are limited, but the Montreal Protocol is respected. The results show that the expected climate benefits from eliminating CFCs and HCFCs are largely canceled out by the warming induced by ozone recovery.

Despite this, protecting the ozone layer remains essential to avoid skin cancers and other harmful effects of UV rays. Policymakers must now integrate this new data to adjust climate change strategies, taking into account ozone's dual role as protector and contributor to warming.

Ozone: a gas with two faces

Ozone is a molecule composed of three oxygen atoms, formed naturally in the stratosphere where it absorbs the Sun's harmful ultraviolet rays. Without this layer, life on Earth would be exposed to dangerous radiation, increasing the risk of diseases such as cancer.

In the troposphere, near the ground, ozone is produced by chemical reactions involving pollutants emitted by human activities, such as nitrogen oxides and volatile organic compounds. This low-level ozone contributes to the formation of smog and worsens respiratory problems in humans.

As a greenhouse gas, ozone traps heat in the atmosphere, similar to carbon dioxide, but with varying efficiency depending on its altitude. Its impact on the climate therefore depends on its location.

Managing ozone requires balanced approaches, aiming to reduce its formation at ground level while preserving the stratospheric layer, to protect both human health and the climate.

The Montreal Protocol and its implications

Adopted in 1987, the Montreal Protocol is an international agreement aimed at phasing out ozone-depleting substances, such as CFCs and HCFCs. These chemicals, once used in refrigerants and aerosols, were responsible for holes in the ozone layer, particularly over Antarctica.

Thanks to this agreement, the ozone layer is showing signs of recovery, with a reduction in observed holes and a decrease in UV radiation levels reaching the surface. This has likely prevented millions of cases of skin cancer and other UV-related conditions.

However, the elimination of CFCs and HCFCs also has side effects on the climate, as these gases were powerful contributors to the greenhouse effect. Their replacement by other substances, such as hydrofluorocarbons (HFCs), has introduced new challenges, as HFCs are also potent greenhouse gases.

The Montreal Protocol illustrates how environmental actions can have multiple consequences, requiring ongoing vigilance and adaptations to achieve both ozone protection and climate change mitigation goals.