Who commission the report ? my guess is it was congress.
That's my guess... And it was a statutory requirement met by the Clinton administration...
This is from the first section of the entire report:
With this pledge, President Bush reiterated the seriousness of climate change and ordered a Cabinet-level review of U.S. climate change policy. He requested working groups to develop innovative approaches that would: (1) be consistent with the goal of stabilizing greenhouse gas concentrations in the atmosphere; (2) be sufficiently flexible to allow for new findings; (3) support continued economic growth and prosperity; (4) provide market-based incentives; (5) incorporate technological advances; and (6) promote global participation.
So, in answer to your question, I believe Bush ordered this report to be made.
Tuor