Well, they tend to start off slow, asking crazy thoughts in on line chat rooms and bulletin boards. I here some even post to "answerbag".

Psychologists often say that conspiracy believers and those anxiously awaiting some type of apocalypse are really participating in a Jungian extrapolation of their own individual mortality. Having said that, I think you have misplaced global warming in this category. The scientific evidence is overwhelming. If you want proof with your own eyes, travel to Northern Canada or Alaska and look at the trees that are dying because the permafrost is melthing. Talk to the natives there whose entire villages are sinking.

Global warming is quite real, and this question is disingenous: there's a big difference between accepting the dominant explanation provided by the bulk of the scientific community, and subscribing to a lunatic fringe belief promoted by a small and eccentric group of non-experts.

I would posit that all such folks trust more in "what the government is hiding from us" than actual facts and science. I think you meant "global warming DIS-believers," since the evidence is apparent, for all those who are not part of the Bush administration. :o}

Sorry Mirage, like several others you lost me with the "global warming believers" quip. The evidence for global warming is quite convincing.

All have bought into a big hoax, in my opinion.

The common thread linking them is fairly apparent from the wording of you question. The main similarity in their thinking is that they all believe, for whatever reasons and by whatever means, that the end of the world as we know it is imminent. However, the notable similarities end there. Many different denominations believe that there is a "God", and most of those denominations have been fighting amongst themselves since the dawn of recorded history. So obviously, trying to link such large and varied groups of people in any significant way just by their sharing of one vague belief is usually foolish and innacurate. The things which distinguish each of these groups from one another are the reasons and ways they believe the world will end: Some base their beliefs on things dredged from ancient texts and concepts, some base their beliefs on things gleaned from more recent history, some base their beliefs on current events and current scientific evidence, and some just pull most of their ideas from cult leaders who assemble ideas from all over the board and twist them to serve their own personal agendas (And no, I'm not talking about Al Gore). The only sort of "Common Thread" I could imagine you're referring to would be some kind of psychological complex, and if you really tried, you could dissect every belief system on the face of the planet that way. And honestly, I believe that most of them would have roughly the same "Diagnosis". By the way, you forgot to mention fundamentalist Christians. When making a list of doomsday seers, one mustn't forget the evangelist Christians. After all, they're one of the originals.