The official position that human activity is likely mostly responsible for global warming gives a big boost to Leftists in the arena of public debate on environmental policy, IMO.
That said, the report merely attributes unquantified "warming" to human activity and the body of the report makes clear that science has not determined the amount of warming is due to natural causes versus human, the future trend, whether the warming is harmful and whether cutting back on fossil fuel consumption would reverse the warming. The report clearly states that the present state of the science justifies the President's position and does not support Kyoto.
Of course, this report is not a position statement, but rather is a requirement of the Rio treaty that the US bureaucracy report to the UN bureaucracy periodically on conditions in the US. This is a very low level document that is now being used for political purposes.
By taking the "most likely" line out of context the New York Times and the envirowackos spun the report, falsely claiming it supports Kyoto and falsely claiming a change in position by the administration. What chaps my keester is that Rush and other conservatives spun the story the liberal direction to make some cheap bushbash points, ignoring what the report as a whole says. And when the President and Ari reiterate the same position the Administration has had all along, Rush claims credit for moving Bush away from a position he never took! Ain't politics a grand thing!