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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