On this day, May 8 1992, after more tense negotiations in New York, the Americans agreed to a text that would be signed down in Rio at the Earth Summit in June.
All through the “negotiations” had basically played chicken, threatening not to come to Rio if the treaty to be signed there included targets and timetables for emissions reductions by rich countries.
So, Michael Howard then the British Environment Minister had flown over to negotiate the surrender by the French/Europeans on the questions of targets and timetables. The text to be ceremoniously sighed would be a framework convention rather than one with any teeth.
And you could argue that that actually is the end of the international “policy window”, in the middle of 1992. Yes, you have have the flim-flam and the theatre of Rio and you have various states ratifying, speeches but the end of anything substantive was May 8th, a day that would live in infamy if our species had two brain cells to rub together.