Protecting the Ozone Layer: The Success Story of the Montreal Protocol

Last month, researchers announced the discovery that the mass extinction event at the end of the Devonian period, 359 million years ago, was not caused by a meteorite or a chain of volcanic eruptions, but by the disappearance of most of the ozone layer. Without the ozone layer’s protection, harmful UV-B radiation caused the collapse of forest ecosystems and devastated life on land as well as in the ocean.

Thankfully, in 2020 the ozone layer is the healthiest it has been in decades. This is somewhat of a miracle, as just thirty years ago it was rapidly shrinking due to CFCs used in refrigerators, air conditioners, and spray cans.

The recovery of the ozone layer is the result of massive international commitment and cooperation, which culminated in the adoption of the Montreal Protocol on Substances that

The hole in the ozone layer over Antarctica in September 2000 (left) and September 2019 (right). Source: NASA Ozone Watch.

Deplete the Ozone Layer in 1987, and of rapid global industrial innovation in the decades since. As former UN Secretary-General Kofi Annan said, “perhaps the single most successful international environmental agreement to date has been the Montreal Protocol.”


What is the ozone layer and why should we protect it?

The ozone layer is the part of the stratosphere where the gas ozone naturally occurs. It sits between 10 and 50 km above the Earth’s surface; passenger planes pass just underneath its lower edge. It does not actually contain very much ozone: even at its ‘thickest’ point, at 32 km, the ozone concentration is just 15 parts per million. Ozone is created by sunlight and destroyed by chemical reactions. Because the amount of sunlight is constant, if the concentration of chemicals that destroy ozone rises, more ozone is destroyed than created and the ozone layer shrinks. This is what was happening before the Montreal Protocol was adopted.

Fun fact: We are not the only ones in our solar system with an ozone layer. Mars, Venus, and at least one of Jupiter’s moons also each have one.

Besides visible light, the sun emits infrared light and UV light with different wavelengths. The most damaging type of UV light, called UV-B, is absorbed by ozone and never reaches us. UV-B is so effective at destroying DNA in living cells that it is widely used to disinfect drinking water. It kills plants, and in animals and humans, it can cause severe sunburn, skin cancer, and cataracts. If we had no ozone layer, life on earth would not be possible.

The hole in the ozone layer

In 1974, scientists Frank Sherwood Rowland and Mario J. Molina suggested that chlorofluorocarbons (CFCs), then much used as refrigerants, to make foams and in aerosol cans, could reach as high up as the stratosphere and devastate the ozone layer. Just over a decade later, in 1985, measurements from Antarctica confirmed this hypothesis. Researchers found that during every Antarctic winter a large hole appeared in the ozone layer above the south pole.

The Montreal Protocol

The world sprang into action and just two years later, in September 1987, the Montreal Protocol on Substances that Deplete the Ozone Layer was agreed. It came into force in January 1989. The treaty stipulates that the production and consumption of CFCs and other substances that deplete ozone are to be phased out, first in developed countries and later in developing countries. The Montreal Protocol and its parent treaty, the Vienna Convention for the Protection of the Ozone Layer, are the only UN treaties that have been signed by all 197 members of the United Nations.

[Fun fact: The last country to sign the Montreal Protocol was South Sudan in January 2012, just a few months after it gained independence.]

The world followed up these commitments with action: in 2020, 98% of ozone-depleting substances have been phased out. Though the hole in the ozone layer still appears between August and November, every year it gets a little smaller and closes a little sooner. In 2000, the hole reached a size of 28.5 million square kilometers, three times the size of the United States. Last year at its largest point it covered 16.3 million square kilometers. The ozone layer is expected to recover fully by 2050.


Global Consumption of Controlled Ozone-Depleting Substances (1986 =100%) Note the steep drop after the Montreal Protocol came into force in 1989. Source: UN Environment Programme, Ozone Secretariat.

This is an extraordinary success, and a great relief: without the Montreal Protocol, the Earth’s ozone layer would have likely collapsed by 2050. By 2070, the UV index on a mid-summer day in Washington, DC or Los Angeles would have been at least 30. The scale currently used by the EPA only goes up to 15, and anything over 11 is designated ‘extreme’. According to the EPA, the Montreal Protocol will help to avoid more than 1.6 million skin cancer deaths and 45 million cases of cataracts in the US.

Challenges & Victories

The success of the Montreal Protocol was not guaranteed from the start. When first introduced, CFCs were hailed as a perfect refrigerant. Unlike earlier refrigerants, they were cheap, non-toxic, and non-flammable. They were used by industries all over the world, and significant amounts were present in industrial installations and homes, in air-conditioners, refrigerators, fire extinguishers, and insulation foam.

Even more challenging was the fact that the ozone layer presents a classic “Common Pool Resource Problem”: everybody needs the ozone layer, but it can only be protected if everybody cooperates. And since cooperating costs money and non-cooperation is difficult to detect, some countries or companies will be tempted to cheat. Once a few do not honor their commitments, the common pool resource continues to be depleted, which can lead to the unraveling of the entire protection plan.

How did the Montreal Protocol overcome these obstacles? The answer is partly due to fortuitous circumstances, partly due to clever design and partly due to committed negotiators.

Committed Negotiators

Most importantly, the negotiators managed to get industry on board. Some companies were concerned about the impacts of their products but did not want to be the only ones to invest in replacements. A few were already developing alternatives to CFCs and thought a ban on the rival product would be good for business. Others knew that even without an international treaty they would soon face domestic regulations on CFCs, putting them at a disadvantage internationally.

The Montreal Protocol created a global level playing field, forcing companies everywhere to start developing alternatives at the same time. It was fortunate that the damage to the ozone layer was caused by a small number of substances, the CFCs, used in only a few industrial sectors. One of the reasons the case of global warming, in general, is more complicated, is that there are so many different greenhouse gases emitted by every sector of our global economy.

Fortuitous Timing

It also helped that CFCs had been around for a while and that companies had already begun looking at cheaper, more efficient alternatives. And industry did not stop innovating or supporting the Montreal Protocol once the initial targets had been met: new, more environment-friendly refrigerants are still being developed.

Great Design

The Montreal Protocol was very cleverly designed for flexibility. The science surrounding CFCs and the ozone layer was not yet settled when negotiations began, so the treaty provided modest initial targets combined with a mechanism to ramp up ambition and phase out more substances if and when new evidence showed that was necessary. The treaty also allowed CFCs to be replaced initially by the already available, less harmful but still damaging HCFCs (hydrochlorofluorocarbons). Then it called for the phasing out of the HCFCs once better alternatives were found. A similar strategy is used by some countries to switch from coal or oil to nuclear or natural gas as steppingstones towards cleaner energy. These low initial targets combined with the long lead times for developing countries convinced all members of the UN to sign.

Other features that have contributed to the Montreal Protocol’s success include:

  • The trade provisions, allowing signatories to only trade in ozone depleting substances with other signatories. That meant that once the main CFC-producing countries had signed up, other countries faced a choice: either commit to phasing out CFCs over time or be cut off from the CFC market immediately.

  • The independent Technology and Economic Assessment Panel, which includes scientists and industry representatives, and which helps countries with their transition away from ozone-depleting substances.

  • The Multilateral Fund, which helps developing countries meet their commitments.

  • And finally, the compliance mechanism, which does not try to ‘punish’ countries that look likely to miss their targets but helps them get back on track.[1]

As a result of all these clever features, not just all developed countries but also all 142 developing countries succeeded in phasing out CFCs, halons, and other banned substances 100% by 2010.

Where do we go from here?

In recent years, the Montreal Protocol has evolved to protect not just the ozone layer, but the climate, too. In 2016, parties to the treaty adopted the Kigali Amendment, named after the Ugandan capital, where they were meeting. The Kigali amendment calls for the phasing out of hydrofluorocarbons (HFCs), refrigerants that do not harm the ozone layer but are extremely powerful greenhouse gases. The richest countries started reducing their production and consumption of HFCs in 2019 and the rest of the world will freeze their use by 2024 or 2028. The treaty still has the support of industry: high-level representatives of some of the main producers of HFCs in the world were part of the Kigali conference and supported the deal.

So, what can we learn from this success story? Firstly, that when there is scope for truly global, ‘playing field-leveling’ regulations, the industry can be persuaded to back measures that at first sight appear to go against their own interests. Secondly, that even successful, quickly adopted environmental treaties take a long time to have an effect: scientists estimate that it will take until 2050, more than 60 years after the adoption of the Montreal Protocol, for the ozone layer to fully repair itself. Thirdly, and most importantly, though, the success of the Montreal Protocol shows us that global consensus and cooperation for the benefit of the environment and ultimately, all of us, is possible. We have done it before, and we can do it again.