Patri Friedman has written the most interesting thing I’ve read on global warming in years:

I think humans naturally tend to a more anthrocentric viewpoint, where civilization arose because we had evolved enough to create it. It is fascinating and somewhat disturbing to think that we may have had the capacity for tens of thousands of years, but the weather just wasn’t cooperating.

By the way, this same climate theory suggests that the greatest danger from global warming may be global cooling. That is, anthropogenic climate increases could hasten the onset of the switch in climate modes, changing ocean circulation and plunging us into an ice age. How credible such a theory is depends on your time scale. It is certainly tempting to look at the history of human civilization and dismiss a climate pattern that has never been seen, but if you zoom out an order of magnitude, you’ll find that such weather is the historical norm, not the exception.

It will be quite ironic if we go through the switch, and CO2 emission becomes a positive externality, subsidized for its useful warming characteristics.