How humans healed the ozone layer
meN 1985 STORIES he discovered an area over Antarctica where the layer of stratospheric ozone, which protects the Earth from ultraviolet radiation, had become dangerously thin. That chlorine from chlorofluorocarbons (CFCs). What the “hole” showed was that this breakdown occurred at a rate that was not expected in the unique conditions of Antarctica. Two years later world leaders signed the Montreal Protocol, a treaty to do away with CFCs. In 2003 Kofi Annan, who was then the secretary general of the United Nations, announced that it was “probably the single most successful international agreement to date”.
A report published by the UN on January 9 supports that idea. It finds that 99% of banned ozone-depleting substances have been phased out. He expects the ozone layer to return to roughly its 1980 state between 2040 (across much of the world) and 2066 (over Antarctica). How will the world lead him, and what will be the consequences?
Too much ultraviolet radiation is harmful to most living things. In humans it causes sunburn in the short term, and skin cancers, cataracts and immune disorders over longer periods. It can reduce crop yield. And it is particularly harmful to organisms that live in the ocean such as fish and zooplankton, which are essential for many food chains. Reversing the depletion of the ozone layer has helped to avoid these harms. American scientists believe that 443 million cases of skin cancer will be avoided in the country by 2100 because of the Montreal Protocol.
The treaty has also helped mitigate climate change. CFCs with a strong greenhouse effect, trapping heat in the atmosphere. Estimates for the amount of temperature rise avoided by preventing them vary, but one study by Australian researchers, published in Environmental Research Letters, estimates that implementation of the Montreal Protocol will see around 1°C of additional warming by 2050. Analysis by The Economist found that the Montreal Protocol reduced emissions by 135bn tonnes of carbon dioxide equivalent between 1989 and 2013, making it the most effective policy ever to reduce global warming.
This side effect led to calls to extend the agreement. In 2016, the “Kigali Amendment” committed countries to reduce the use of hydrofluorocarbons.HFCs), the successors of CFCs by humans. Although they do not harm the ozone, most are commercial HFCs hundreds to thousands of times more warming than carbon dioxide (although they stay much longer in the atmosphere). A recent UN report estimates that compliance with the change will avoid an additional 0.3-0.5°C temperature increase by 2100.
The success of the Montreal Protocol in healing the ozone layer means that it is often seen as a template for future environmental treaties. Petteri Taalas, secretary-general of the World Meteorological Organization, recently said that “ozone action sets a precedent for climate action”. He certainly managed to overcome some of the problems that still plague climate treaties, such as how to encourage widespread compliance. (The original Montreal Protocol is one of the only international treaties to receive universal ratification—the last holdout, Palestine, was signed in 2019.) It did this, in part, through incentives such as letting by countries to trade controlled substances with other signatories. , and by paying skeptics like China and India enough money to make them think it’s worth joining.
Unfortunately, these lessons are not as useful for mitigation and climate change as one might wish. Poor countries have never relied on ozone-depleting chemicals for development the way they do on fossil fuels; rich countries did not feel that their economies were based on exploitation. The costs of moving away from them were much lower, and the companies that did had much less to lose than the oil and gas giants that have fought so hard against emissions reduction policies. And the science was less controversial. Healing the ozone layer is a major achievement, with many benefits, and should be recognized as such. But climate action problems are in a class of their own. ■