Ha, yes, Terraforming. Or, how our planet is so fucked up that we've made it a common topic of entertainment the idea that we would make another to live on.
"Terraforming to replace Earth" is an idea that pops up (Firefly; maybe Aria) but there's tons of SF where Earth is fine but terraforming is simply part of expanding into The Space Frontier; building orbital habitats may be in addition or an alternative (for authors who think terraforming is too unrealistic.)
Many, if not most (or all even), locations we see in Aria are created in the image of places on Earth which might not exist in the series in their current form or were lost completely. Not even speaking of the setting of Neo-Venezia itself, that one could not be more on the nose.
Earth seems to be a messy place but at least chugging along and Aqua's short history is full of sacrifice and tragedy. Not so much a case of terraforming to replace Earth than preserving and recreating the beauty of Earth that's been lost with a heavy dose of romantization added to it (and if I want to be cynical about it, made into quite the appealing tourist attraction). I don't know how deeply the anime covers these darker bits the manga hints at, I only watched a little of it.
Now I want to re-read it
