"There is no liberal spin on the fact that the Administration is accepting the premise that human activity is likely mostly responsible for global warming." Yes, there is. The document, which you may want to peruse, is a low level bureaucratic report, the likes of which are reproduced by the hundreds if not thousands annually on a galaxy of subjects. The report does not purport to speak for President Bush or his White House staff. To the extent the report mentions the President, it reaffirms his announced policy.
It's like in the movie Fort Apache. While Col. Thursday (Henry Fonda) treats the Indian Agent, a renegade whisky and gun runner, as "a representative of the United States Government," he sure doesn't regard him as as spokesman for President Grant.
If Ari Fleischer had said exactly what you just said, I would agree with you.
He didn't though. He flat out said this was the President's position.