Investigate Magazine is a New Zealand publication which has been looking into the history of Kyoto and pollution credit trading:

...without Enron there would have been no Kyoto Protocol.

About 20 years ago Enron was owner and operator of an interstate network of natural gas pipelines, and had transformed itself into a billion-dollar-a-day commodity trader, buying and selling contracts and their derivatives to deliver natural gas, electricity, internet bandwidth, whatever. The 1990 Clean Air Act amendments authorized the Environmental Protection Agency to put a cap on how much pollutant the operator of a fossil-fueled plant was allowed to emit. In the early 1990s Enron had helped establish the market for, and became the major trader in, EPA's $20 billion-per-year sulphur dioxide cap-and-trade program, the forerunner of today's proposed carbon credit trade. This commodity exchange of emission allowances caused Enron's stock to rapidly rise.

Then came the inevitable question, what next? How about a carbon dioxide cap-and-trade program? The problem was that CO2 is not a pollutant, and therefore the EPA had no authority to cap its emission. Al Gore took office in 1993 and almost immediately became infatuated with the idea of an international environmental regulatory regime. He led a U.S. initiative to review new projects around the world and issue ‘credits' of so many tons of annual CO2 emission reduction.