A while ago I wrote briefly on why the Singularity might not be near and my estimates badly off. I saw it linked the other day, and realized that pessimism seemed to be trendy lately, which meant I ought to work on why one might be optimistic instead: http://www.gwern.net/Mistakes#counter-point
(Summary: long-sought AI goals have been recently achieved, global economic growth & political stability continues, and some resource crunches have turned into surpluses - all contrary to long-standing pessimistic forecasts.)
How likely is it for global warming to be an existential risk threat? This seems unlikely. It may well be that global warming will contribute to existential risk in a marginal fashion if it forces less resources to be spent on existential risk issues or makes war more likely, but that seems like a much more roundabout issue, and by that logic many other technologies would fall into the same category.
It depends what you mean by an existential threat.
I think there's a reasonable chance that global warming (combined with other factors; biosphere degradation, resource depletion, unsustainable farming, lack of fresh water, increasing war over increasingly limited resources, ect), may cause our current civilization to collapse.
If our civilization collapses, what are the odds that we'll recover, and eventually get back up to where we are now? I don't know, but if our civilization collapses and we're left without modern tools in a world in the middle of ... (read more)