I keep hearing about how Sydney needs sustainable growth and how this means we need to build high density housing in urban infill sites close to existing facilities. Since those people really take their sustainability seriously, I thought we should really look longer term than just the 25 year NSW Metropolitan Plans and gaze 100 years into the future.
According to the UN predictions, world population will max out at about 11 billion in 100 years, up from 7 billion now. I suppose world population growth has to slow down and nearly stop at some point, it's just not sustainable. Other predictions put the percentage of people to be living in urban areas to get to about 80%, up from the current level of 50%. Putting these two predictions together, we can guess that Sydney will need to house 2.5 times its current population 100 years from now.
Now the most sustainable thing would be to even out this growth as much as possible. I'm not sure what happens after the 100 years. I guess the construction industry can sustainably recycle decrepit buildings and focus on upgrading the existing housing stock. Therefore a constant annual growth rate of about 1% will do the trick because (1+0.01)^100=2.7 times larger which is more than enough.
Further, I guess in the long term, it would be sustainable to share the burden of growth equally between density growth and total area growth. In other words, in 100 years Sydney would be 60% larger in area and 60% denser. (1.6^2=2.56 again more than enough.) On a per annum basis, we need 0.5% density growth and 0.5% area growth. For greenfield areas, you need to match the average density of the rest of Sydney, which probably means a bit smaller than your quarter acre block. For already populated areas, the growth is 0.5% annually, achieved through increased density.
But hang on! The City of Sydney LGA population is growing at 3% annually. That's unsustainable! We have to slow down rapidly to 0.5%! Better knock back nearly all of those projects currently on the table.
Therein lies the problem. If we are really and truly committed to sustainability, we have to sustain unsustainability itself. Good old fashioned unsustainability should be heritage listed and preserved for future generations to learn from our folly. There really is no alternative but to sustain the current system - business as usual.
[Postscript: At first, I used 100 year UN predictions and urbanisation levels to predict Sydney population only half seriously, but then discovered the City of Sydney's own population predictions up to 2036 levelling out to 1% growth per annum which is exactly the same as what I came up with. See http://forecast.id.com.au/sydney ]