Montreal Protocol on Substances that Deplete the Ozone Layer
NASA Goddard Space Flight Center
Adopted by: United Nations Environment Programme (Ozone Secretariat), under the 1985 Vienna Convention · Kind: Binding treaty · Scope: Universal · Adopted: 1987
A protocol to the 1985 Vienna Convention, adopted in 1987 and the only treaty ever ratified by every UN member state. It sets concrete, binding, staged targets for ending both the production and the consumption of ozone depleting substances, and gives developing countries longer timelines plus a dedicated Multilateral Fund to cover the cost of transition. It has been adjusted or amended six times as the science advanced, most significantly by the 2016 Kigali Amendment on hydrofluorocarbons, and it is repeatedly cited as the most successful multilateral environmental agreement ever made.
The Montreal Protocol was adopted on 16 September 1987 as a protocol to the 1985 Vienna Convention, and entered into force on 1 January 1989. It is administered by the Ozone Secretariat of the United Nations Environment Programme.
What separates it from a statement of concern is that it set concrete, binding, staged targets for ending both the production and the consumption of ozone-depleting substances. Every UN member state ultimately ratified it, which makes it the only treaty to have achieved universal ratification.
Responsibility under the Protocol scales with capacity. It distinguishes Article 5 parties, meaning developing countries, from non-Article 5 parties, meaning developed ones, giving the former a longer compliance timeline and access to a dedicated Multilateral Fund that covers the cost of transition. The obligation is the same in kind for everyone; the pace and the financing are not.
The Protocol was also built to keep tightening as the science improves. Parties meet annually, and the Protocol has been adjusted or amended six times as scientific understanding of ozone depletion advanced. The most significant of those is the 2016 Kigali Amendment, which extended the Protocol to phase down hydrofluorocarbons, substances that do no harm to the ozone layer at all but are themselves powerful greenhouse gases. That is a treaty deliberately widening its own subject matter when the evidence called for it.
The Ozone Secretariat's own framing is that the ozone layer is well on its way to recovery because of this treaty, and the Protocol is repeatedly cited as the most successful multilateral environmental agreement in history. Its principle of acting despite scientific uncertainty was carried over explicitly into the UN Framework Convention on Climate Change five years later. The full text, its annexes and all six amendments are published by the Ozone Secretariat. The Protocol's detailed substance-by-substance phase-out schedules are technical implementation rather than separate ethical commitments, and are not restated here.
Key provisions · 4 provisions
Principle 1
The Protocol set concrete, binding, staged targets to end production and consumption of ozone-depleting substances, and it is the only treaty ever ratified by every UN member state.
ozone-depletion · universal-ratification
Principle 2
The Protocol gives developing countries a longer compliance timeline and access to a dedicated fund to cover the cost of transition, scaling responsibility to a country's capacity.
common-but-differentiated · financial-support
Principle 3
The treaty is designed to tighten over time, having been adjusted or amended six times as scientific understanding advanced, most significantly to phase down the greenhouse gas HFCs under the 2016 Kigali Amendment.
adaptive-treaty · amendment
Principle 4
The Protocol is treated as proof that global environmental cooperation works, credited with putting the ozone layer on a path to recovery and with originating the 'act despite scientific uncertainty' principle later adopted by the UNFCCC.
international-cooperation · precaution