By scientists.
You make no sense.
You know the IPCC assessment backs itself up with peer reviewed literature too, so should I believe that as well?
Everything I need to know about Crichton's (lack of) authority on science I learnt from his lecture: http://www.crichton-official.com/speeches/speeches_quote04.html
Some of the worst logical arguments I have ever read. The problem I have with crichton is that he seems to have some anti-science streak. I read his book Prey. Okay it's reasonable science fiction although gets a bit proposterous in the end - more fiction than science. My gripe was that he didn't realise it was total fiction and instead was trying to make "a serious point", as if his fiction was some kind of eye opener that we should know about. All his books that I know are about scientists getting out of control with dark agendas and how we should fear what they are up to. It's like when hollywood stars think their dumb movies make some serious real world point. They don't.