Larry,

Just because we can't control all climate factors is a reason not to bother with one we can?

Your water example is one case of a positive feedback loop. Water vapor is a greenhouse gas and warming Earth will generate more water vapor causing further warming. Water vapor being a greenhouse gas is no reason to ignore global warming.

You have pointed out several examples of climactic instability which support my point that climate is not inherently stable. You are also correct that we do not know the causes of all of these. However, a recent hypothesis that release of methane hydrates after mild warming then causes much greater warming can explain these wild swings and also indicates why it is important for us not to trigger even mild warming.

It is also certain that humans can survive global warming. That is not the main issue for me. It is the lives and property lost due to the side effects of global warming (worse storms, higher sea levels, crop failures, loss of arable land, and possible increase in tropical diseases.) I'm sure the industrialized world will be able to handle much of these potential impacts with low levels of fatality, but the potential costs seem far higher to me than preventive measures. Countries where populations can not move freely or rapidly or shift both agricultural and industrial production rapidly will be much harder hit. Toxic pollution is and was a greater threat IMO, but that doesn't mean GW is a threat to be ignored.

Regards,
Mark