The chemicals that caused the hole in the ozone layer were also responsible for about a third of all global warming from 1955 to 2005, a study has found.


Collectively known as ozone-depleting substances (ODS), these humanmade chemicals – which include CFCs (chlorofluorocarbons) – were developed in the 1920s and 30s, and used as refrigerants, solvents and propellants.

In the 1980s, scientists discovered a gaping hole in the Earth’s ozone layer over Antarctica. This stratospheric layer of gas plays an important role in absorbing harmful ultraviolet radiation from the Sun. The hole was quickly attributed to ODS. However, less attention was paid to the possible climate impacts of these chemicals, which – like carbon dioxide – can act as powerful greenhouse gases.

Now, a study by researchers at Columbia University in New York used climate models developed at the US National Center for Atmospheric Research to study the effects of ODS. Their simulations suggest that the chemicals played an especially significant climate role in the Arctic, causing half of Arctic warming and sea ice loss from 1955 to 2005.

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The good news is that their effects are fading. In 1987, the international community came together to sign the Montreal Protocol, which aimed to protect the ozone layer by phasing out the production of ODS.

Entering force in 1989, the protocol led to atmospheric concentrations of most of these chemicals peaking in the late 20th Century. Since then, they’ve been in decline, and the ozone hole is in recovery. Last October, NASA announced that the ozone hole was the smallest it had been since its discovery, and it’s expected to be back to 1980 levels by around 2070.

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“Climate mitigation is in action as we speak because these substances are decreasing in the atmosphere, thanks to the Montreal Protocol,” said Dr Lorenzo Polvani, lead author of the study. “In the coming decades, they will contribute less and less to global warming. It’s a good news story.”

Reader Q&A: What would have happened if we’d carried on using CFCs?

Asked by: Jessica Howard, Inverness

In the late 1970s, scientists noticed levels of ozone gas (O3) dropping in the ozone layer, a region of the stratosphere some 15 to 30km above our heads. The ozone here absorbs most of the Sun’s damaging ultraviolet (UV) radiation, shielding us from UVB and UVC rays. The culprit for the disappearing ozone? Chlorofluorocarbons (CFCs), which were used in fridges, aerosols and air conditioners. As CFCs entered the atmosphere, they released chlorine atoms which broke down ozone and allowed more UV radiation through.

As rates of ozone depletion accelerated, the international community sprang into action. Effective from 1989 and signed by 197 countries, the Montreal Protocol has now phased out 99 per cent of CFCs and other ozone-depleting chemicals, with ozone levels predicted to make a full recovery by the 2050s. Without this treaty, CFCs would have continued to rise, with disastrous consequences for life on our planet.

In humans, heightened exposure to UVB radiation would have triggered a surge in incidences of skin cancer and cataracts. According to one estimate, there would have been an extra two million cases of skin cancer worldwide by 2030. By 2065, UV radiation at the planet’s surface would have reached three times its current strength, making any Sun exposure dangerous.

Overexposure to UVB radiation stunts the growth of many plants, and the resulting decline in agricultural productivity could have triggered food shortages. The radiation harms phytoplankton, too – the tiny organisms that form the basis of marine food webs – with untold consequences for wider ecosystems.

CFCs are powerful greenhouse gases, and US researchers have calculated that there would have been an additional 2°C of global warming by 2070 if CFCs had been left unchecked. This would have fuelled extreme weather such as floods, droughts, hurricanes and heatwaves.

Fortunately, this disaster scenario was averted, and today the Montreal Protocol is often heralded as the most successful piece of environmental legislation in history.

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James Lloyd
James LloydStaff writer, BBC Science Focus

James is staff writer at BBC Science Focus magazine. He especially enjoys writing about wellbeing and psychology.