re: To your last two sentences:
"Yup. US leadership might have done wonders."
I agree. US leadership was lacking in the 90s when the treaty was consolidated. The admin back then did not push it through the Senate (thankfully) or earlier, properly use its influence to form a saner treaty (regretably). This century, the new administration has opposed blithely joining the fait accompli, a wise move as we can see from the ongoing comic Kyoto fiascoes in NZ, Canada and Europe.