Why the Protocol is cited
It is cited because it worked, and because it worked quickly. Within a generation of the first measurements, production of the controlled substances had collapsed, the stratospheric trend had reversed, and a risk that was genuinely civilisational in scope had been converted into a long but manageable recovery.
It is also cited because it is the only clean example. Every other candidate treaty is either too recent to judge, too partial to count, or too obviously dependent on circumstances nobody could reproduce deliberately.
The conditions that made it tractable
Four conditions did most of the work. The causal chain was short and physically legible. The number of producing firms was small and concentrated in states with strong regulatory capacity. Substitutes were technically available and commercially attractive within the compliance window. And the harm was vivid, undisputed, and attributable to a specific class of molecules.
Remove any one of these and the Protocol becomes a much harder negotiation. Remove two and it is not obvious that it concludes at all.
What did not transfer
The features usually held up as the transferable lessons — differentiated obligations, a financial mechanism, adjustment procedures that avoid re-ratification — are real institutional achievements, and they have been transferred. They have not produced comparable results, which suggests they were the enabling machinery rather than the cause.
The cause was the underlying tractability of the problem. Institutional design can exploit tractability; it cannot manufacture it. Treating the Protocol as a template rather than as a case study has cost the field a good deal of time.
Reading across to other risks
For risks with long causal chains, diffuse sources, and contested attribution, the Protocol offers a warning more than a model: it shows how much of the outcome was determined before the negotiation began.
The useful question is therefore not how to replicate the Protocol but how to increase tractability deliberately — by narrowing the class of actors that matter, by making the causal chain measurable, and by ensuring an acceptable substitute exists before compliance is demanded. That is an agenda for the years preceding a treaty, not for the treaty itself.
Placeholder text — the body of this note is indicative and awaits final copy.