I'm not sure how easy it is to make good estimates like this, there are so many variables. (Reminder to UE: I would like to see the UK with a stable or gently reducing population but the rest of this post is not about what I want, or even about what is practical, let alone likely, but about what is theoretically possible.)SleeperService wrote: So RC's 80M could be accommodated but likely with a reduced life expectancy brought about by crowding, disease, restricted diet, stress and violence. If you aim for a standard similar to now then I think 45M would be more realistic assuming cities could be supplied from their hinterland. If the aim was quality of life and a high degree of national independence then 25M ...
Much depends on where one draws system boundaries. Let's first say that no population is sustainable if it continues to be reliant on a finite resource such as fossil fuel or if it requires the emission of greenhouse gasses such as those produced by burning fossil fuel. So let's, for the sake of discussion, imagine we've somehow transitioned to a zero-carbon Britain.
Back to system boundaries. Do we draw a line along, say, the M25 and ask whether the system therein contained with it's current population can be sustainable in terms of food and other resources in isolation? Hard to imagine! But what if it were allowed to trade, say with the rest of the British Isles, or with the rest of the World? Then, clearly, yes, it would be sustainable. So a region's sustainable population must be, at least in part, a function of it ability to trade with other regions.
To take an absurd (and horrid) case, could we describe the UK as 'sustainable' if all the world's urban populations were to move to Britain, concreting over our green and pleasant land so it all looked like London, but trading with the rest of the planet's remaining rural population. I think the answer could be 'yes' (though I would have emigrated long before).
The point is, we can't put numbers onto things like regional sustainability without first defining system boundaries.