One recent Schroeder post you might be interested in is "Colonizing Alpha-Centauri: the least and most we can do"</u>. Written in the immediate aftermath of the discovery of Alpha Centauri Bb, Schroeder argues here that even in the case of that planet being the only one in the entire Alpha Centauri system, it might still provide the anchor for a human civilization in-system.
If your idea of habitability is finding a more or less exact copy of the Earth and settling down on it to farm, then things are looking kinda bleak. But, if we have the technology to get to Bb, then we have the technology to live and thrive there.
Not on the surface, of course. Not even in a nearby orbit. But even if Bb is uninhabitable, it is still a great source of building material. If we have the technology to get to it, we'll have the technology to mine it, if only by dangling a skyhook down from the L2 point (or from a heliostat) to dredge the magma ocean. Haul the magma up, render it in the terrible light of the star, and ship the refined goods to a higher orbit where the temperature's a bit better. There, we can build habitats--either O'Neill colonies or, if we can harvest enough material, the coronals I describe in my novel Lady of Mazes.
With unlimited energy and (nearly) unlimited building materials, we can construct a thriving civilization around Alpha Centauri B, even if all we have to work with is this one piece of melted rock. (In terms of details, it would be a bootstrapping operation, with an initial small seed of robot miners constructing more or bigger skyhooks, more miners, etc. until exponential growth sets in, by which time it's safe for the human colonists to show up.)
Watts, meanwhile, argues in "Geoengineering and the Evils of Conservation" that geoengineering, or some form of managed human intervention in the environment, is going to be necessary to keep a world already thrown out of balance comfortable for our civilization.
The problem is that as any population varies, so too does its behavior. Mortality curves, reproductive rates, vulnerability to pathogens and predators — a hundred other variables — all change with population density. It’s a complex system, full of cliffs and folds and intertwined curves unwinding across a range of conditions; and when you keep your population from varying, you only acquire data from a very narrow band of that tapestry. But Nature’s a fickle bitch, and sooner or later she’ll kick your population out of that comfort zone despite your best efforts. When that happens you’ll be adrift in a dark, data-free wilderness where anything can happen.
Unless you kick it out there yourself beforehand, to get some idea of what’s waiting for you.
The term is Adaptive Management and back in grad school days my supervisor was one of its early champions. The idea was that you combine “management” with research, that you don’t strive to keep your system stationary year after year. Every now and then you cut your salmon quotas to zero, leave the scaly little buggers completely alone. Other years you hammer the shit out of them. In all cases you take notes— and gradually, over time, you beat back those dark zones, scratch out here there be dragons and scribble Ricker curves and Lotka-Volterra parameter values in their place. You do what Nature would do eventually anyway, only you do it on your own timetable, to a degree of your own choosing.
That’s the trick, of course: because sometimes there are dragons out there, and what if one of them swallows your salmon stock to extinction because you hammered them too hard? It’s a balancing act. You have to tread carefully, weigh risk against opportunity; the techniques used to find that sweet spot are what distinguishes Adaptive Management from just rolling the dice and unleashing a series of shotgun blasts.