Note that "Use less energy" is never going to work in the long run.
It is a critical period (think "war time") delaying strategy at best.
You want to make most of the earth beautiful and pristine? It's easy,
all you have to do, is make everybody on Earth, everybody, at
least as wealthy as Americans are today. And that's going to take
energy, lots and lots of cheap energy. Therefore, see also
technology R&D, and especially space access and development.
(Note that I strongly suspect that world-wide wealth is the
only way a pristine earth is going to happen. That is, other
than mass murder, human species die off, and/or crushingly repressive
Stalinesque regimes - all of which I presume are out of bounds for
rational consideration by all participating here. One more way might
be some bizarro new world-wide "green" religion, but barring mind
control drugs that seems astonishingly unlikely - perhaps less likely
than us all being killed by an asteroid.)
Overpopulation? On the large scale, the only proven method of birth
control is wealth. (Sorry no reference. But there are
historical studies looking back centuries, and good economic arguments
for why the observed results, that as societies get wealthier they
have fewer children, make sense.) See above.
And heh, I've never tried crunching all the numbers myself (although
for what it's worth I was trained as a chemical engineer, so I
probably could if I really had to, and had the time), but my
understanding is it's usually possible to make just about any
manufacturing process clean and non-polluting - it's just a question
of how much energy it's going to take. Often the answer is, "a very
large amount". See cheap energy above.
Btw, Todd, Malte, in particular, I salute you.
Recent reasons for possible optimism:
