Having just heard from a dear friend of mine in Tasmania, I learn to my chagrin that I will not be Climate Change Refugee #1 - there are already folk buying farms south of Hobart wherein to wait out the onrushing climatic apocalypse...
Seriously, while I hope that any change in climate will prove minor, my recent reading does tend to make me consider the "what if" scenario. I assume that if things ever do become dire, Australians will all have to move south to Tasmania, tho' 20.6 million trying to fit into a State currently holding 0.5 million would certainly make the place rather fuller.
(Note that Sri Lanka has a population of 21.1 million in an area only slightly larger than Tasmania. And they still have room enough to play cricket.)
Oh well, there's always New Zealand, comfortably off with only 4.1 million Kiwis, Pakeha and Maori, at present: even if every Pacific Islander moved in, they'd still have only 7 million or so in a landmass around about four times the size of Tas.