90% is a YOTA number from the IPCC. I have heard it bandied about by many people in the last several years. I am sure they used some really scientific process to come up with it though. "Hey, Michael, what do you think the chance that humans caused this warming we haven't actually found is?"
Michael: "I am 90% sure it's humans causing the terrible things out there. Who else could it be? The dolphins? It has to be someone. Can't blame the sun can we, that's like a Gazillion miles away!"
I certainly wouldn't bet my life savings (or house) on it! Especially as I suspect it'll start to creep down the way over the coming years.
Reminds me of the old cartoon of the guy wandering along the street with a sandwich board declaring "The end of the world is nigh on..
1 Jan 1968 (crossed out)
14th June 1975 (crossed out)
31st July 2015