I'm a GW skeptic, a scientist, and a staunch conservative republican with a libertarian streak, so I'm not very used to being on the receiving end of arguments about how environmentalists are wrong or overboard.



I hardly suggested we remove all CO2 from the atmosphere. There is an ideal amount of the stuff for a given desired setup, different densities of CO2 are beneficial for maximizing plant growth in a greenhouse that would impair you or I. It also isn't the same for all, C4 photosynthesis plants would benefit little from higher CO2. If we lived on some airless alternate Earth somewhere under a bunch of domes, you would want higher CO2 for some crops, but not others, same as you would want higher or lower temperature, humidity, and sunlight. I doubt many of these optimal setups would match what you or I feel comfortable. I'm sure mine won't, anything over 70F is hot to me, and I prefer 60-64F. To take advantage of CO2 concentrations of 1500-2000 ppm in plant growth, you need a temperature of 80-85F and 80-100 W/sq.ft or it is wasted concentration, the plants just aren't getting enough light to take advantage. This represent our nominal 'maximum useful' because we can't turn the sun up - well, theoretically we could stick a big green film up between us and the sun at the lagrange point and some big mirrors to reflect more light down in the red range but I digress - we already know humans are nearly useless above 20,000 ppm concentrations of CO2, but recent studies have shown pretty solidly that this impairment is major even by 1000 ppm. So while people hardly pass out or turn into retards at 1000 ppm you certainly wouldn't want to be doing much thinking and decision making at it, keeping your greenhouse at that or double that is fine just so long as it isn't where you hang out to make major life decisions. It seems like anything under 600 ppm is probably just fine, but we're at 330 and we used to be 280-300.

Ignoring all other benefits or downsides, proven or probable, we can say that we can't afford for CO2 global levels to rise above 600 unless we want to start rebuilding houses to have CO2 scrubbers in them - which isn't all that serious a hurdle but I rather shudder to think of the world condition in poorer nations if they are starved, uneducated, and then made dumb by the air itself.

So, don't go assuming CO2 can be ignored or handwaved even if you don't accept any net ecological downsides to it. I tend to think we can find smart ways to handle all our problems, but I'd say being able to extract reasonably cheap energy from coal without a carbon footprint is one such, and that it is very much in our interests to find a way to adjust global CO2 levels in both directions so as to be able to find and stay at some optimized value.

I have no idea what that is and I don't think anyone currently does, it may be higher than the current value, it may be lower. It will probably change too. An economical method for adjusting it in a direction other than up would be very useful, and certainly it would be handy to have an economical method to extract energy from coal without raising atmospheric CO2 much.



No, it isn't. To assume changing the chemical makeup of something has no effect on its thermodynamic properties is to be every bit the Luddite that the anti-vaccine, anti-nuclear or anti-GMO crowds are. I do not trust a lot of the science that goes on around GW from either side, too much politics for good science, and I certainly don't approve of a lot of the suggested measures for dealing with it, but I do not believe one can casually assume dumping massive amounts of anything into the air and expect nothing to change. Thermodynamics just doesn't work that way. That doens't mean the change will be massive and catastrophically bad, it may be relatively minor, heck it might even have net advantages, but it is reckless to assume it will do nothing at all. That I happen to think it is more reckless to do anything that damages our ability to support an ever larger population at a higher individual living standard doesn't mean I stick my fingers in my ears and assume raised CO2 levels do nothing at all or blind myself that some of those effects may be very bad.