The Montreal Protocol on Substances that Deplete the Ozone Layer is considered the world’s most successful international environmental treaty.
Under the Protocol, nations phased out chlorofluorocarbons (CFCs) – a class of compounds that were used mostly in aerosol sprays, refrigerants, foams and as solvents, and were damaging the protective ozone layer that shields the planet from harmful ultraviolet radiation. Recent evidence shows that the ozone hole over Antarctica is beginning to repair itself because of efforts under the Protocol to reduce ozone-depleting substances.
Because ozone-depleting substances and many of their substitutes are also potent greenhouse gases, their phase-out under the Montreal Protocol is critical to international efforts to address climate change.
Following nearly a decade of talks, a landmark agreement was reached October 15, 2016, at the 28th Meeting of the Parties of the Montreal Protocol in Kigali, Rwanda, to phase down hydrofluorocarbons (HFCs), CFC substitutes that, while not harmful to the ozone layer, are a fast-growing source of potent greenhouse gases contributing to climate change. On January 1, 2019, the Kigali Amendment entered into force. The United States Senate ratified the Kigali Amendment on Sept. 21, 2022. The amendment has now been ratified by 138 parties, surpassing the 20 ratifications needed to bring it into force.
HFCs are widely used in refrigeration and air conditioning, foam blowing, and other applications. Though they now account for less than 1 percent of global greenhouse gas emissions, HFCs are extremely potent greenhouse gases whose use is projected to grow rapidly, particularly in developing countries.
The Kigali Amendment sets out a schedule of targets and timetables for all developed and developing countries to phase down their use of HFCs. The amendment links these control requirements with a renewed commitment by developed countries to provide financial support for developing countries through the Protocol’s Multilateral Fund. The agreement sets out key principles for how the fund will transition from supporting projects aimed at safeguarding the ozone layer to spurring action focused on climate protection.
Because HFCs have a relatively short atmospheric lifetime (compared to carbon dioxide), their phasedown could reduce temperature changes in 2100 by an estimated 0.5 degrees Celsius. These reductions are critical to meeting the long-term goal of the Paris Agreement to keep warming well below 2 degrees.
The Montreal Protocol is a part of the 1985 Vienna Convention for the Protection of the Ozone Layer, which commits its 197 parties to protect human health and environment against “adverse effects” of human-induced changes to the ozone layer.
The Montreal Protocol, which was adopted in 1987 and entered into force in 1989, limits the consumption and production of ozone-depleting substances. Since its entry into force, the Montreal Protocol has phased out over 98 percent of the world’s consumption of ozone-depleting substances.