Do you believe in global warming? Do you think the sustainability concept is undervalued, valid, or taken too far?
I believe there is global climate change. I don't like "global warming" as a term because it implies everywhere getting warmer. Climate change simply means that you can't rely on your prior experience as to what kind of weather to expect. This is a better description because "global warming" in the sense of the average global temperature going up is more likely to be noticeable as greater extremes of weather all over. I think the latter -- severe heat waves in Moscow, etc. -- is something much more to be concerned with than slow ocean rise, though slow ocean rise will be a Royal Pain in the Rear for all coastal cities if it goes beyond a few inches.
I'm not sure why the heck sustainability is being shoved in with the prior question; the two are fairly disjoint. Climate change, if it's mainly anthropogenic, is being driven not by people worrying about sustainability but people ramping up their industrial levels in conditions that make sustainability a moot point.
Sustainability isn't really a question. The energy available on Earth can sustain a vastly higher-power civilization than we currently have, with vastly higher populations. We're just not using it very well.
Fossil fuels like oil and gas aren't really energy SOURCES. They're energy CARRIERS. We really need to think about them in that context. We don't have to give up driving cars and such, we just need to build the energy sources so that we can MANUFACTURE the fuel rather than just dig it up or drill it out. Liquid fuels like gasoline are actually excellent energy carriers in terms of energy density, and while they're not SAFE, we have many, many years of experience transporting them, huge infrastructure devoted to its distribution and storage, and plenty of experience dealing with the dangers of those materials. No particular reason, therefore, to not continue to use them. Just manufacture them from raw materials rather than using all of the stored solar energy from the dinosaur age, so to speak. The cost would be, naturally, determined by the energy source and how expensive it was for you to use that energy to produce the fuel. Nuclear power would seem the most practical for the moderate term, with large solar plants as another possibility depending on how cheap you could get your solar conversion to be (including maintenance).