I think frankly that the problem is not that we can't do it (constructing technology to allow us to survive is one of the things we do best) but that we don't want to do it as a species.
Right now the percentage of us that want to explore the cosmos are in the minority. And really with the eventual coming of extinction level events that are long overdue we shouldn't be. In fact we should be concerned completely as a species. Unfortunately we seem to be more concerned with fouling our own bed to get off this rock.
And it's not as if it's hard really. I mean given the resources the world has we could easily create the following:
Mars "igloo bots" that use the ice at the poles to create radiation safe shelters for the humans who land there.
Mars "diggers" that slowly tunnel into the surface making human safe underground shelters.
A non-human compatible space elevator that does nothing but transport seawater up to a large storage bag. It need not be able to transport anything as large as a human but just be a hose. Anchored in the sea bed all you'd have to do is make sure the intakes stay clear and the bag gets changed out when full. (Yes I know the stresses on the tether would be immense but again we're problem solving beings. We could do this if we actually put more than a minor effort into it.)
Alternatively we don't even need to have the tether reach the ground. We just have to have it reach low enough that something like an automated blimp could reach it. Automated blimp sucks up seawater then transports it to one of three bags in orbit that have intakes within the atmosphere.
Once we've got water into space we have our space shielding for travel. Build a ship in pieces and fill the outer shell with water then off to Mars where the igloos await.
And it need not even exhaust or pollute our resources. The amount of seawater would be minimal. The amount of technical resources would be far less than what we use on any war or conflict on the planet.
We need to stop thinking so small.
Cross-posted from Dreamwidth ( http://nimitzbrood.dreamwidth.org/271296.html ) but feel free to comment here as well.