if we have to move people in numbers of hundreds of millions etc - in a hurry (like a couple of decades etc - or heaven forbid within a few years)
frankly I've got no idea how one would do it.
if we just think of a city - any city one can think of - say above 1 million - let alone these monsters of 20 million or so
if we think of it - bridges alone, took years to build and were major projects -
ditto highways
airports
rail lines
power networks
internet
god help us - buildings
imagine if we had to move that lot within years - that have taken hundreds of years to develop
it really takes adaptation to an extreme extreme
for a stone age community - say 10 to 30 people - or maybe 100 people max -
it's not a huge deal. They pack their sack and, they walk. They go over ground they've been over before - they find a cave or shelter - and, back to normal.
A mega city??????????? ---------------- now, that's a very different kettle of fish.
And as far as powering the change goes? ----------- well, frankly on that one, I think we'll put in whatever power we can get our hands on that will get on the ground asap. - and I don't think we'll care what it is. Nor, IMO - should we.