I seem to post stuff like this fairly frequently in space travel-related stories, so I thought I'd just write it all up here. Summary - Yes, it would probably be a nice thing to have a truly self-sufficient human civilization on another planet so that we are insulated against any catastrophe that might happen to the Earth, but such a colony is basically not possible to create now.
If you're going to be self-sufficient and a backup against the Earth being wiped out, then you must be able to manufacture everything your colony needs in your colony. No country on Earth currently does this now. If one of the continent-spanning countries like the US or China or the EU as a whole suddenly had to exist with no trade at all with any other country, then it would probably be tough for a while, but they could do it. Your colony would have to have a comparable size and level of economic activity for it to be possible.
Let's take IC fabs as an example. If your colony will depend on computers in any way, then you'll have to have one. A huge operation, incredibly expensive even on Earth, demanding lots of specialized personnel. Can you imagine building one on another planet right now? How about building several of them, and having the materials and knowledge base to build more if needed? And that's just one of the highly complex manufacturing facilities you'll need. Steel foundries, aluminum, other metals, casting, forging, pressing, something with hydrocarbons for making plastics, something like concrete, stuff for growing plants and raising animals, thousands of other things that I haven't thought of yet. You would need to move a major country's worth of people, expertise, and capital to your colony planet. You can't just rough it and go without on a planet with no atmosphere.
Right now, we're at the level of moving one robot about the size of a car to Mars. We've got a hell of a long way to go before we can think about setting up even a dinky just-because-we-can colony with a few dozen people that is dependent on the Earth for critical supplies, much less anything that can hope to survive the loss of the Earth. I believe that we'll get there eventually, but it's not something that's even remotely on the horizon right now.
Another way to put it - there is no imaginable catastrophe that could make the Earth less habitable than, say, Mars already is. If we have the technology and the will to set up a real colony there, then we also have the technology and the will to survive whatever might happen to the Earth, and for a lot less expense.
And we haven't even gotten to the type of government and lifestyle that such a colony would need. If you're going to be hard up against the lower size limits, then anything like first-world freedom is probably impossible. If there aren't enough resources to support much of a non-productive population, then anyone too old or disabled to do useful work would have to be sent back to Earth or killed. Reproduction would have to be tightly controlled - too many or too few children at any time could be a disaster, if it either would raise the population beyond what the infrastructure could support, or would not lead to enough workers to maintain the infrastructure or preserve key knowledge. You'd probably need a policy like every woman must bear exactly 2 children before she turns 25, and no more, ever. Education and careers too - you don't want to be a welder, say? Too bad, the colony must have a welder and you've been chosen. Get to work, or else. Getting out of all of that would either require a much larger colony or frequent trade with Earth. But there's not much point in creating an in-case-of-emergency colony that depends on trade with Earth to maintain its lifestyle, so you'd have to go with size.
All of the Global Warming threads these days seem to instantly generate over a thousand comments, which kinda kills my inclination to post my own point of view, so I'll just post it here instead. Why should anybody care about what I think about it? I figure I'm a smarter than average person, and though I don't have much particular background in climate science, I know a bit about general engineering, what it takes to power the world.
My summary of the actual science on it is that I'm not really sure whether it's happening and manmade or not, but I really hope that it isn't, because if it is, I'm pretty sure that we're screwed. Based on all of the numbers I've seen from the AGW people, I think that our chances of reducing CO2 emmisions by a large enough amount soon enough to make a difference are basically zero. If those guys are right, then reducing the rate of increase isn't going to do anything. We'd need genuine reductions in overall global output of over 10% a year, every year without fail, and we'd need that to start like yesterday.
The root of the problem is the total world population, which has grown massively in the last 200 years or so, to the point that there are now over 7 Billion of us. Keeping those 7 billion people fed decently and relatively healthy requires lots and lots of energy, because generating that much food requires mechanized farming, including mechanized production of fertilizers and transportation of them to actual farms, plus transportation of the products to cities and livestock stockyards, etc. Basically, you have to keep the modern economy, based on relatively cheap energy and transporation, active for all of those people to remain fed. There ain't enough land for them to all be subsistence farmers working with hand tools, because it isn't efficient enough. Even smallish cities can't feed everyone with only food produced less than 50 miles away or whatever it is that environmentally-conscious are trying to do now. Don't mistake what a handful of wealthy hippie-types do because they feel like it for a viable solution for how to feed the whole country. Not to mention all of the other requirements for keeping lots of people alive, like good water and sewer systems, requiring lots of industrial technology, and readily available healthcare, including drugs, which also requires lots of instustrial technology and highly educated people too. Speaking of which, such changes in how the population of the world is fed would undo most of the economic changes in the last few hundred years, eliminating probably something like 90% of the high-tech jobs and economy because everybody would have to spend most of their time figuring out how to grow their own food. Also creating a permanant class structure where most of the population is farmers and a only relative handful can afford to do other things.
What all of that means is that a massive reduction in worldwide energy usage is just not possible. Combine every war and genocide in the 20th century and you get something like a few hundred million dead. The world population is over 7 billion now, and the sustainable population using low-energy food production techniques is probably closer to 1 billion. Do the math, it'll be ugly. The only question would be which few billion people would die, and how.
The only way to cut CO2 emissions on the scales required while still maintaining the modern economy and the world population then would be to displace fossil fuels as an energy source. Any good AGW/Environmentalist type will surely go on and on about wind and solar power, and if you're really lucky, they'll bring up even more oddball stuff. The trouble is, I'm not convinced that any of them will be capable of displacing fossil fuels on a large enough scale in the timeframe that we need. The best I've heard is that a couple of small, wealthy European nations have claimed to be at around 15% wind power. I wouldn't mind seeing some numbers behind that, but even if it's 100% legit, it's still nowhere near enough. Looks to me like, at best, wind and solar are too little, too late, and everything else is a joke.
I believe that the only technology capable of actually stopping global warming, meaning meeting our energy needs without releasing lots of CO2 and being ready to go now, is nuclear fission. There's some stuff out there that looks interesting or has some potential, but it has to be ready to go now - if you can't design a 1GW plant today with whatever technology you're looking at, then you're already too late. Fission has its problems and dangers, but it's real, it works, and it's ready to go. If the people in charge of these things really believed the stuff that they're saying about global warming, they'd demand that we spend as much as necessary to start construction on hundreds of GW of new fission capacity yesterday. The actual worst-case scenarios of nuclear accidents still aren't as bad as what they say that global warming will do. Since nobody seems to be doing this, I can only conclude that everybody involved either 1. Doesn't really believe that global warming is happening or will be as bad as they say, meaning that they're lying to all of us either to increase their own personal power or make themselves feel better or 2. Doesn't really understand the issues of generating and using power, and are more concerned with reinforcing their own beliefs and preferences than in researching how to actually solve the problem. Either way, we're being very poorly served by the current global warming political movement - they're using all of their political capital pushing things that they know or should know cannot possibly solve the problem.
My conclusion - if Global Warming is real, then bend over and hold on, because it's going to happen and we aren't going to slow it down.
The thing that most people do wrong when arguing about 9/11 is paying too much attention to the technical details of things. Start talking about construction techniques, steel alloys, flame temps, etc. and you just get bogged down in techno-babble that doesn't convince anyone. An argument based on people and their motives, plans, and actions is much simpler and much more effective proof. To form this argument, ask 3 questions that no troofer will be able to answer meaningfully:
1. Who planned the attacks of 9/11? 2. What did the plotters hope to gain from the attacks? 3. Why did the plotters decide that the attack plan executed on 9/11 was the best way to achieve the goals stated in #2?
Number 3 is the key - it just doesn't make sense for anyone else. The whole attack plan was so risky and out-there that only someone who thought they had nothing to lose and needed to impress lots of people would do it.
Let's say the people behind the attack were some shadowy group of Americans. Within or outside of the Government, whatever. And their goal is to trick the American people into going to war for... some reason or other. The whole reason their group is secretive and shadowy would be that they have a lot to lose if anyone ever figured out who they were and what they were doing.
Let's take a quick look at the nature of the attacks, sticking to high-level stuff. Hijacking planes and flying them into buildings - very risky, lots of people involved any way you do it, lots of ways for it to go wrong. If it was by the book, you'd need a couple dozen people who are fairly smart and willing to perform suicide attacks. Going into the alternates proposed just makes it even more complex and involves more people. Setting demolition charges to do something like that requires a team of experts, and there's only a handful of them in the world. Remote control aircraft involves lots of engineering and testing work, someone to buy and set up the hardware, etc, and you still have to do something with the original planes and the people on them. Using missiles requires people to take them out of inventory, load them, arm them, target them, etc. It just spirals into impossible complexity.
So you're a small group of conspirators that needs to keep themselves and their plans secret while carrying out a false-flag terrorist attack that will drive the US to war. What do you do? A truck bomb requires maybe 3-4 people, a few tens of thousands of dollars, and none of them have to die if it's planned right. A Mumbai-style shooting spree takes like 5-6 people and probably not more then a few thousand dollars in gear. There's tons of other cheap and simple plans that involve minimal people and money and are very low-risk for a well-organized group. But we're supposed to believe that our group of conspirators looked at all of those options and said to themselves that some plan involving rigging up remote control aircraft, firing missiles, rigging up demolition charges, and disappearing multiple aircraft carrying hundreds of people, which would require hundreds, maybe thousands of conspirators, many of which had very specialized skills and very specific jobs, and would cost tens of millions, maybe hundreds of millions of dollars, was a much better idea? Are you guys insane?
In addition to the sheer complexity of the attacks, there's also the implied organization. You can pass off a truck bombing or a shooting as the acts of a handful of nutjobs. That's why that's the kind of attack that Pakistan carries out against India - they don't want to provoke India into a shooting war with them. A complex attack like 9/11 pretty much announces that there is a well-organized group behind it. If you are a group of American conspirators, that's the last thing that you want - ideally, you want nobody to be aware of your existence at all.
An attack like that is carried out by a group that needs to advertise it's existence, to make the other side fear it, to increase it's own prestige, leading to more support, recruits, and money. All stuff that Al-Quada wanted to do, and that no group of American conspirators would ever want to do.
While we're on the subject, I'm also kinda fuzzy on number 2. Exactly how has any group really profited from the wars? Yeah, some companies made money, but if that was the real goal, it would have been a hell of a lot easier to just give that company money straight out of the treasury for some reason or other, which happens all the time to thousands of companies, than to carry out a ridiculously complex false-flag terrorist attack, hope nobody figures it out, and go to war, causing many thousands of American casualties, not to mention foreign solders, insurgents, and civilians, and undego massively complex changes in the international order.
BTW, I'm happy to debate anyone who posts with a username and makes some attempt to address the points I made.