You ask: "what's the harm in coming up with alternatives to burning oil, and to conserving?"

The question is how much to spend fighting global warming. The US should not set an expensive policy based on the worst case without an assessment of how likely it is.

"As for sudden climate change: that is a real bogeyman for the deniers. I work with some of the key people who came up with the evidence for sudden climate change and just about 3 days ago saw one of them present the record of huge changes in a couple decades: huge warmings. The earth can switch from state A to state B.... "

Yes, this seems to be the lurking disaster to be avoided at all costs. But any sensible policy needs to assess the likelihood of the disaster to figure out how much to spend preparing for it or trying to forestall it. Another black plague, a big meteorite impact, unfettered population increases, or a nuclear war could also be bad for our future as well, for example.

I'm not saying what is the right course because I'm not an expert. I'm just trying to point out that debates which do not MEASURE pros and cons can never deduce the best course of action. I think we need to get a government that people trust to be able to think practically, then trust them to choose the right actions, and take those actions.