The strongest point he makes is this:
Our influence on climate may be inadvertent, but it is a milestone in civilization's progress. We have, for the first time, the technological capacity to noticeably alter climate on a global basis within a person's lifetime. History suggests that our expanding population and increasing technological ability will cause this capacity to grow with time, not decline. If not because of greenhouse gas emissions, it will be because of something else, such as changes in land coverage or the acidification of the ocean. The question now is: Should we strive to channel this capacity to our benefit, or should we struggle perpetually to avoid having any impact, for better or worse?
It seems plausible, but it's so impractical as to be silly.
It's ridiculous to talk about human activity bringing the system under control any time soon. At the moment we are utterly out of control. We have not demonstrated a capacity for postindustrial civilization to reach any stable operating point. It may be possible to do that sometime in the distant future, but for now we have to slow the huge input that is in process, to reach something like a quasiequilibrium.
It's like having a barely conscious drunk at the wheel of the car and arguing that in principle the car could get to Myrtle Beach. (I assume for the purpose of the analogy that you are in North America but not in South Carolina.) Yes it might, but the immediate issue is pulling off to the side of the road without major incident.
Gail is ridiculously optimistic about climate models (and presumably the poor sod has to run his climate models under Microsoft operating systems... I actually know someone who tried to do this once... He didn't fare well...) but that is the least of his problems. Look at his conclusions.
Before we picked a climate, we would need to evolve the political, commercial, and academic institutions to get us there. International institutions, in particular, would need to be strengthened to support the inevitably global solutions. The new technical discipline Earth systems engineering would have to be expanded and countless practitioners trained. We would have to develop complex new computer models, not only to forecast climate but also to understand how today's costs should be balanced against tomorrow's benefits. The private sector would need to envision climate change as opportunity, not impediment. The complete transition will take decades, if not centuries, but it can be accomplished in small steps.
The risks, of course, would be enormous. Virtually no significant technological breakthrough has ever occurred that nations did not find a way to apply to warfare, and the possibilities of global-scale climate alteration for military purposes would be staggering. Even putting those aside, the temptation of nations to use climate to gain economic advantage will be great. All human institutions suffer from mismanagement to some extent—those associated with climate will be no different. Any approach to climate management would have to be very robust to compensate for such failings.
Some may argue that humankind will never be able to manage projects that are so big and risky. Much the same was said about nuclear weapons, yet civilization has so far succeeded in controlling their enormous risk. In the case of climate change, the risks of not acting—relying on the belief that human climate influence can be eliminated soon and forever-after avoided—could be even more dangerous.
I am sorry to say to those of you still running "Windows" that people who think exactly this clearly designed your computer's software.
Meanwhile Hank Roberts has a rather more insightful approach to geoengineering on the globalchange list.