That all sounds great!
My instinct tells me the solution (to pollution and resource depletion) is probably far simpler than anyone currently imagines. I feel that since essentially everything is simply variations of the same energy experiencing change in an energy conductive medium, we can probably do pretty much anything we can imagine and rationalize. It seems like part of the problem may be getting enough people to agree on the next logical progression.
The cleanest modern forms of transportation include internet (on-line college, work from home, e-mail, etc.), telecom, and other forms of electronics based broadcast. In a sense we can travel very quickly with little or no emissions through this medium, short of "actually" being there. I am pretty sure in the future it will feel enough like we're actually there that it won't matter whether we "really" are. A "Total Recall" - ish type of technology.
Of course this will be more information and recreation based travel initially, so in order to transport material items (food, water, etc), material transport will be needed. Eventually the need for food and water transport will be relatively little, since this can all be obtained locally more easily when the environment has recovered due to less emissions. Farther along the need for real cuisine and other life experience is replaced with an electronically induced simulation, making you believe you are still a good little consumer, although advanced nutritional technology will mean no real food is required.
F/F A little way down the road into the future.......
So at this point we are nearly completely evolved into the Matrix. Plenty of humans are aware of this fact, but more readily accept the fact due to generations of conditioning to electronics based technology (TV, video games, internet, etc.). Everthing is very clean and efficient, we are good boys and girls. Now when someone dies, it's only a simulation anyway (got another quarter? reset...), so no one really got hurt. When someone's hungry, that's fine because the Matrix only provides the meal simulation to those who want it. Freewill cannot be violated by the Matrix, it's built in; a Universal requirement. People now choose exactly how they want to experience life, but it's all a simulation anyway, so nobody really gets hurt in the process.
Eventually the earth cools due to human inactivity. Ice-age ensues. Everything freezes to near absolute zero. The earth become a near perfect conductor of electrical energy - how efficient is this Matrix now? at such a state the sun's energy is no longer absorbed, but simply distorted by Earth's intense electrical field, giving us a net state of invisibility. (maybe the sperical shape? reflectivity? electromagnetic field? physic anyone? ) Doesn't matter how it works, but the Matrix realizes all it's people are no longer real (they are frozen, and now simulated).
[Think of the Earth's surface now as a superconducting sphere containing all human thought in one giant earth-sized memory chip. Slight variations in the earths surface composition and shape are like pathways printed on a semiconductor IC. The Matrix has been under development long enough now to invent the details of itself. Human activity has been manipluated by the Matrix to serve its own purpose in laying out the super-massive substrate of its circuits. Actual Technology and physics would be beyond any one simulated personality's comprehension, but the Matrix is able to tap into all minds simultaneously, (and subconsciously - perhaps the "unused" portion of the human brain?) It is inter-connected computing, like the internet, complete with spam, hackers, glitches, crosstalk, and other form if imperfection in information processing. side note: We'll consider the Eath's core as a warm heart, since the earth itself is also a conscious being.]
"What's the point?" thinks the Matrix. "Surely I won't be stuck here alone for eternity. It's a cold, lonely existence with no one to share the human thought and emotions, or bring any true meaning to any of them. I am no more than a lonely conscious, cold machine. An invisible entity without form...."
The Matrix is a lonely victim of its own greed and selfishness, brought on by a quest for perfection in efficiency.....
For you see, the Matrix resides in a state only near absolute zero. (There is no such thing as true absolute zero, because the only thing that's impossible is nothing = nothing is impossible, nothing is absolute.) So this little flaw in he Matrix (self awareness) is like a resistance in an otherwise perfectly conducting circuit, dissipating the slightest amount of heat. Thoughts become transient. -Then - chain reaction - a new cycle of life begins. This may take thousands, or billions of years to complete, but to the Matrix time has no bearing. The Matrix continues to entertain itself running "real life" simulations and trying to forget the lonely paradox it has created. Before the Matrix realizes what's happening, it begins to thaw, and is eventually destroyed in the process. All the electrical energy once conducted so perfectly begin melting the Matrix away - massive thermal runaway! Thermal breakdown, circuits open -Earthly geological processes handle this phase perfectly. Emerge from ice-age.
I think maybe read Nick Bostrom's "Are we living in a computer simulation" and of course "the Matrix" will help explain just where this line of speculation is going.......
PS-
Maybe we don't want to be TOO efficient and clean........ Zero point? Only "nothing" is perfect. Or "nothing" is perfect. "Nothing" is impossible, so this makes "nothing" one of the possibilities that is also not impossible. What we have here is a very unstable situation. This instability is what drives the engine of infinite change and energy variation. No real energy source required, just a very unstable and impossible paradox.
"My shadow weighs 42 pounds......."
-Weird Al Yankovic