Ozone depletion was the first human threat to the global atmosphere to be recognized. It was also the first to be addressed by the international community. The results have been truly remarkable. The Montreal Protocol on Substances that Deplete the Ozone Layer, which celebrates its thirtieth anniversary this year, can claim to be one of the most successful international treaties ever struck.
It has fulfilled its original objective by putting the stratospheric ozone layer on the road to recovery. But its effects have not stopped there: it has also done more than any other measure to date to combat climate change. And it has achieved all this through a united, indeed unanimous, world community. The Montreal Protocol is the first and only treaty ever to have been ratified by every nation on Earth. This has happened not just once, but six times over, including the underlying framework convention, the protocol, and its four amendments.
In 1974, one of us (Mario Molina) and Sherwood Rowland published the results of a scientific study that concluded that chlorofluorocarbons – then widely used mainly as refrigerants and propellants – were migrating to the upper atmosphere and affecting the ozone layer which shields terrestrial life, including humans, from deadly ultraviolet radiation. If such depletion had continued there would have been catastrophic global consequences, with many millions of people contracting skin cancer and widespread damage to crops.
Many originally disputed our conclusion, but the science was later confirmed by strong experimental evidence. Consumers in Europe and North America acted quickly and boycotted the use of spray cans using chlorofluorocarbons as propellants for such products as deodorants and hair spray: at the time, every household, on average, used 15 spray cans. The chemical industry, which had initially questioned the science, began to develop replacement chemicals that were less harmful to the ozone layer. A handful of national laws were passed, and UN Environment brokered an international framework treaty, the Vienna Convention for the Protection of the Ozone Layer, in 1985.
Just months after the Convention was agreed, a scientific paper was published revealing a “hole” in the ozone layer above Antarctica so great that the scientists who found it originally thought their instruments must be faulty. The development of the Montreal Protocol to the Convention was further catalyzed by this unexpected discovery – similarly confirmed by measurements and scientific evidence that also found chlorofluorocarbons and related chemicals to be responsible.
The Protocol, also agreed under UN Environment's auspices, aimed at starting, then strengthening, protective action. Initially, its parties agreed to cut chlorofluorocarbons by 50 per cent over 12 years, but they swiftly accelerated the reduction to 75 per cent by 1998, and then 100 per cent by 1992. Success has continued to breed success. Over its 30-year history, the treaty has succeeded in reducing nearly 100 ozone-depleting chemicals by nearly 100 per cent.
The ozone layer is healing, and is likely to recover in several decades. But that is only part of the Protocol's impact. The same chemicals that attacked the ozone layer are also greenhouse gases. So, phasing them out has made a great contribution to slowing global warming.
That contribution increased markedly last year when the nations that are party to the convention agreed in Kigali, Rwanda, to amend the Protocol to phase down the use of hydrofluorocarbons, which were introduced as ozone-friendly alternatives to damaging chemicals, but are also one of the six main sets of pollutants causing global warming. Their use has been growing rapidly and, molecule-for-molecule, they are up to 4,000 times more powerful than carbon dioxide in promoting climate change.
The phasedown will reduce use of the chemicals by 80 per cent, cut emissions equivalent to 80 billion tons or more of carbon dioxide by 2050, and avoid up to a half degree Celsius of warming by 2100. That is a significant contribution to the goal of the 2015 Paris Agreement, to keep the increase in average world temperatures to well below 2 degrees Celsius, aiming for 1.5 degrees Celsius above their pre-industrial level, with no net emissions of greenhouse gases beyond mid-century.
The amendment was achieved after an eight-year campaign initiated by the Federated States of Micronesia, Mauritius, and Morocco. The amendment also eases the world's path away from fossil fuels by promoting improvement in the energy efficiency of the air conditioners, refrigerators, and other products switching out of hydrofluorocarbons. This would be perfectly practicable: when replacing other damaging refrigerants in the past, manufacturers achieved just such gains in efficiency.
Improvements in efficiency would also bring many other advantages, including reduced air pollution and improved public health. Consumers also would save money – and be better able to afford cooling – since energy use typically makes up 90 per cent or more of the lifecycle impacts of an air conditioner. National economies would also gain. Just a 30 per cent increase in the efficiency of India's units, for example, could save enough electricity to avoid having to build 140 medium sized power plants to meet peak demand by 2030. In China, moving to climate-friendly refrigerants, and boosting the energy efficiency of cooling, could together save as much energy as would be produced by eight Three Gorges hydroelectric dams.
The Montreal Protocol’s Kigali Amendment and associated energy efficiency efforts are at the leading edge of the triple-headed climate strategy that is needed to meet the Paris goals, as laid out in the recent report Well Below 2 Degrees: Fast Action Policies to Protect People and the Planet from Extreme Climate Change, published by the Committee to Prevent Extreme Climate Change, which we co-chair with Professor V. Ramanathan. This requires cutting both carbon dioxide and short-lived climate pollutants, including hydrofluorocarbons, black carbon, and methane, while also learning how to accelerate the removal of carbon dioxide already in the atmosphere.
We are rightly celebrating the achievements of the planet-saving Montreal Protocol this year. The most important tribute would be to redouble the efforts being made under it worldwide, including fast ratification and fast implementation of the Kigali Amendment, along with energy efficiency measures to double the climate benefits.