The one easy option, voluntary restraint, isn't even on the table, not that I noticed. So what makes you think that's so likely, what about our current priorities and behaviours makes you so optimistic? Where is the economic incentive to solve the problem? Sure, it means more long-term life and profit, but having even 1% less quarterly profit so that in 1000 years some other company can exist at all is not exactly how we do things around here. Instead companies invested in fossil fuels are happily funding "global warming skeptics".
That proverbial man who plants trees knowing he will never sit in their shade is proverbial for a reason.. it's an amazing and heartwarming little saying because it's a contrast to how we generally behave, as individuals as well as organizations and masses. We learn from repeated catastrophe.. sometimes, maybe. But this problem is not one we can have a lot of attempts at solving. Right now we are still moving into the wrong direction, and probably even accelerating.. sure, hitting a wall can make people change their direction, but not if it breaks their neck, so to speak.
I suspect that in turn depends on whether we're able to create 'digital' humans or not.(I'm not weighing in on whether or not we'll be able to, just pointing out that if we can, 'manned' interstellar travel becomes much, much easier.)
