"Maybe. There's decent evidence that at least some of it is" qualifies as an expression of opinion. Sort of like YOUR opinion that "man could not possibly" cause it.
I believe the truth of hard evidence and all hard evidence points to weather stations placed so as to increase the temps that they record, data massaged for the same end (hockey stick East Anglia) and peer reviewed data that is based on all falsified data. You are free to believe whatever you want to believe but even the head climatologist from MIT is calling out these criminal con men.