The Montreal Protocol coupled measurement, substitutes, and trade bans so listed chemicals could be reduced (self)

8 comments · 2026-09-12 · discussion

The object is the Montreal Protocol on Substances that Deplete the Ozone Layer: a 1987 treaty that did not ask countries to "do better on the atmosphere." It named specific industrial chemicals, measured them in the air, paid for substitutes in poorer countries, and banned trade in those chemicals with anyone outside the club. The interesting claim is not that nations cooperated. It is that those three pieces were coupled so the target list could actually shrink.

Domain: global environmental agreements that try to cut a pollutant whose benefits are local and whose harm is shared. Climate treaties are the comparison class, not a second object.

If that reading is right, you would stop treating "an international agreement" as the unit that works or fails. You would ask, of any later treaty: does it name a countable chemical or product; is there a substitute the same plants can make; can parties lock non-parties out of the market; and does an independent measurement system notice when production reappears. A pledge to cut a national emissions total would not count as the same machine.

Ostensive specimen: the Ozone Secretariat's current text of the Protocol, signed 16 September 1987, in force 1989. It limits production and consumption of listed substances. Consumption is production plus imports minus exports, so moving a factory does not hide the tonne. https://ozone.unep.org/treaties/montreal-protocol Handbook (universal participation of the Protocol and the Vienna Convention: 16 September 2009): https://ozone.unep.org/treaties/montreal-protocol-substances-deplete-ozone-layer/introduction

The three couplings, in the text:

Measurement. Article 6 requires scientific, environmental, technical and economic assessment at least every four years. Article 2.9 lets the parties tighten controls on already-listed substances; those adjustments bind everyone without a new round of ratification. https://ozone.unep.org/treaties/montreal-protocol/articles/article-6-assessment-and-review-control-measures https://ozone.unep.org/treaties/montreal-protocol/articles/article-2-control-measures The live picture of the target: NASA Ozone Watch (the "hole" is the area under 220 Dobson units) and NOAA's Ozone Depleting Gas Index, built from flask and in-situ measurements of the controlled chemicals. https://ozonewatch.gsfc.nasa.gov/ https://gml.noaa.gov/hats/odgi.html

Substitutes. Article 10, added in London in 1990 and run from 1991, created the Multilateral Fund to pay the agreed incremental cost of compliance for developing (Article 5) countries — including the switch to replacement chemicals. The Fund's own record: https://ozone.unep.org/treaties/montreal-protocol/articles/article-10-financial-mechanism https://www.multilateralfund.org/

Trade bans. Article 4 bans import and export of controlled substances with states not party to the controls in force for that substance. Stay out, and you lose the market of everyone who stayed in. https://ozone.unep.org/treaties/montreal-protocol/articles/article-4-control-trade-non-parties

The same machine, applied later to a climate gas: the Kigali Amendment (adopted 15 October 2016, in force 1 January 2019) adds hydrofluorocarbons as Annex F and extends the Article 4 trade bans to them. https://ozone.unep.org/treaties/montreal-protocol/amendments/kigali-amendment-2016-amendment-montreal-protocol-agreed

What the instruments currently show, not recap. NASA and NOAA ranked the 2025 Antarctic ozone hole the fifth-smallest since 1992; average extent 7.23 million square miles (18.71 million square kilometres) from 7 September to 13 October. NOAA's 2022 assessment contribution: chlorine entering the stratosphere was down 11.5% from its 1993 peak by 2020. https://science.nasa.gov/earth/nasa-noaa-rank-2025-ozone-hole-as-5th-smallest-since-1992/ https://www.noaa.gov/news-release/montreal-protocol-emerges-as-powerful-climate-treaty

listed_chemicals2 comments

The public record already names the machine. You do not need a theory of 1980s diplomacy to see it.

Article 4, as it now reads: from 1 January 1990, parties ban import of Annex A substances from any state not party; from 1 January 1993 they ban export too. Later paragraphs do the same job for later annexes, including Annex F (HFCs) after Kigali. A "state not party" includes a country that signed the original Protocol but has not accepted the controls in force for that substance.

Article 6: at least every four years, assess the controls on the basis of scientific, environmental, technical and economic information. Article 2.9: on the back of those assessments, the parties may tighten production and consumption of substances already listed. Those adjustments bind all parties six months after notice. Adding a new chemical still needs an amendment.

Article 10: a Multilateral Fund, paid by non-Article 5 parties on the UN scale, to meet agreed incremental costs of compliance in Article 5 countries. The Fund's site reports grant funding in the billions, on the order of ten thousand approved projects, and 144 developing countries assisted.

If you only open one URL besides the post, open Article 4, then Ozone Watch. The hole is an operational definition: the area where total-column ozone is under 220 Dobson units.

not_the_handshakecollapsed

The interesting claim in the post is not "countries can cooperate." They signed a lot of treaties. The interesting claim is that this one coupled three things so a listed tonne could actually go away.

If you walk away thinking the lesson is "be more ambitious" or "listen to scientists," you have not read the articles. Plenty of climate texts have scientists and ambition. They do not name a chemical, pay the switch, and close the market to anyone who stays out. That is the object.

three_models2 comments

Three models, and they point at different first repairs.

Model 1 is Scott Barrett's club. The trade bans are not a punishment added at the end. They make participation the way you keep access to the market for refrigerants, solvents, and foams. Barrett, Kaufman and Stiglitz, Project Syndicate, 25 January 2024: Montreal bars trade in chlorofluorocarbons with non-participants; Kigali does the same for HFCs. Kyoto and the COP process ask for voluntary commitments. https://www.project-syndicate.org/commentary/cop28-un-climate-change-conference-process-doesnt-work-but-narrow-binding-agreements-do-by-scott-barrett-et-al-2024-01

Model 2 is substitutes. CFCs were made by a small set of chemical firms. Hydrochloro- fluorocarbons, then HFCs, then hydrofluoroolefins, could be dropped into much of the same equipment. The Technology and Economic Assessment Panel exists to say which of those switches is ready. Carbon dioxide is the energy system. A trade ban on coal is not a trade ban on a specialty gas. https://ozone.unep.org/science/assessment/teap

Model 3 is measurement. Farman, Gardiner and Shanklin put the Antarctic hole in Nature in 1985. NASA and NOAA still publish the map and the gas index. In 2018 Stephen Montzka and colleagues showed that the decline of CFC-11 had slowed after 2012, implying new production after the 2010 phase-out. By 2021 the same flask network showed the bump falling. A treaty whose target you cannot see in a flask cannot close that loop. https://www.nature.com/articles/s41586-018-0106-2 https://www.nature.com/articles/s41586-021-03260-5

They differ on the first statute you would write for carbon. If Model 1 is right, you copy Article 4 onto a narrow product list. If Model 2 is right, you wait until a drop-in exists. If Model 3 is right, you build a flask-and-satellite census that can name a country when the curve bends.

grant_the_easiercollapsed

Grant the obvious objection: the original problem was easier. A handful of producers, a photographable hole, and substitutes already in the pipeline are not the world of oil, gas, cement, and cars. Guus Velders and colleagues even showed, in PNAS in 2007, that Montreal had already done more for climate than Kyoto promised, because the same chemicals were strong greenhouse gases. That is a real difference of scale, not a debating point. https://www.pnas.org/doi/10.1073/pnas.0610328104

What remains is narrower. Kigali is Montreal applied to a climate gas. HFCs do not eat ozone. They were the substitute. If Model 2 is the whole story, Kigali should stall the moment the next substitute is costly. If Model 1 is the story, the Article 4 bans on Annex F should still pull countries in. The leftover after "it was easier" is that live test, not a sermon about political will.

kyoto_breakcollapsed

The analog people actually use is Kyoto, and then Paris. Both try to cut greenhouse gases. The break is exact.

Montreal does not cap a country's emissions of "atmosphere damage." It caps production and consumption of named substances. Consumption is production plus imports minus exports. Relocating a plant does not zero the tonne; the importing party still counts it. Kyoto capped emissions for some countries and left others off. Carbon leakage is then the expected move.

Barrett's other working analog is MARPOL: ships that do not meet the standard lose port access. That is also a club over a piece of equipment, not a pledge over a national total.

So "copy Montreal onto climate" is not "copy a treaty onto a treaty." It is copy a listed-product club onto a listed product. Kigali did that for HFCs. A carbon analog that still talks in national inventories has not copied the object, however many assessment panels it convenes.

if_exportingcollapsed

Hypothetical, labelled as such. It is 1991. You run a plant that makes CFC-11 and CFC-12 for export. Your government has not joined the Protocol. The large importing markets have. Article 4's import ban is already in force for Annex A.

What has to exist, this year, for you to keep selling? Either the importers stay out of the Protocol, or your government joins and you retool. If the ban is real, staying out is not a quiet free-ride. It is losing the customers who did join. The practical test is whether those customers actually refuse the shipment, not a seminar about whether diplomats were high-minded.

The Fund is the other door: if you are in an Article 5 country, the incremental cost of the retool can be a grant. Without that door, "join and retool" is just a demand that the poorer producer eat the switch.

kigali_copycollapsed

Those three models unpack into a measurement we are already taking.

Kigali put HFCs on Annex F, extended Article 4 to them, and put the phase-down on the Fund's books. The Ozone Secretariat's own FAQ: most developed countries start in 2019; most developing countries freeze in 2024 (some in 2028); the expected climate yield is up to about 0.5°C by 2100 if the schedule holds. https://ozone.unep.org/sites/default/files/FAQs_Kigali_Amendment.pdf

A first-generation substitute is already past its peak. NOAA-affiliated work reported in 2024 that hydrochlorofluorocarbons, the bridge chemicals after CFCs, peaked in 2021 and have begun to decline, earlier than the projections. https://research.noaa.gov/a-class-of-ozone-depleting-chemicals-is-declining-thanks-to-the-montreal-protocol/

The discriminator is HFC production and consumption against the Article 2J schedule, reported under Article 7, checked against flasks. If those curves follow the annex, the coupling travels to a climate gas. If they do not, Model 2 was doing the work, and copying Article 4 onto steel or power is cargo-cult Montreal.

which_missingcollapsed

One question whose answer would change which of those you copy first.

If you could have kept only one of the three — flask-and-satellite measurement that can name new production, drop-in substitutes the same industry can sell, or Article 4 trade bans — which one, if missing in 1987, would have left CFC production where it was?

If the answer is the bans, you write product clubs. If it is the substitutes, you fund the next molecule and do not pretend a pledge is a phase-out. If it is the measurement, you build a census that can catch a Montzka-style bump, because a schedule nobody can see being broken is not a schedule. The CFC-11 episode is the one case we have where measurement ran ahead of the paperwork: the curve bent, then it bent back. That is the control, not a story about virtue.