Tuesday, May 21, 2019

Getting to Sustainable Population

Various experts have studied the issue of the ultimate Sustainable Human Population.  Clearly, by measure of any resource use or waste production impact, present global society is way past that, even with 80% of the global population being relatively limited compared with the rest due to economic factors.  Estimates have been in the 500 million to 1 billion persons range.

Hardly anyone seriously considers what kind of non-violent planned population reduction could achieve these levels, in order to stave off about 20 or more impending resource-use related crises.

But that's why I am here, to think the unthinkable.

I see immediately that population change rates are unfathomably difficult to estimate, initally because everthing one is interested in is not a simple thing, but a set of things, such as the set of all living people, which is people of different ages, sexes, reproduction past present and future, and lifespan, all differing per person.

So in this initial exploration, I'll just brush that all away.  This is highly simplified.  And I'm just making it up, because I find other explorations to be far too complex to deal with for my "population reduction" purposes.

I'll say this is the year 2020 and there are 8 billion people, though those are not quite true.

I'll say everyone is 20, and has a lifespan of 60, and all give birth at 20.

Under these assumptions, see what happens if the population is Replacement Rate, or two children per couple with no allowance for remarriage.

In the starting year, 2020, 8 billion more people are born, bringing the total to 16 billion.  In 2040, 8 billion more are born, and none have died yet.  In 2060, 8 billion more are born, and none have died yet.  In 2080, 8 billion more, but then the first 8 billion have died.  So the assumptions yield a condition where population finally reaches a true plateau after 3 generations, and that plateau is 4x the starting population.

I'll have to make the assumptions slightly unrealistic to account for the fact that this is an extreme simplification.

The starting population is everyone 30, gives birth at 30, and lives to 60.

Under that set of assumptions, we do actually have stasis at a "replacement rate" of two children per couple...after the first generation offspring doubles the present population.  In the real world, replacement rate does also yield something close to this, an initially growing population.  So these are more useful ficticious assumptions, despite seeming farther from the actual mark themselves.

What happens if the birthrate falls to 1/2 of replacement rate, on mean average 1.0 children per couple with no remarriage allowance?

2020  8 billion + 4 billion offspring
2050  4 billion offspring + 2 billion grand offspring
2080  2 billion grand offspring + 1 billion great grand offspring
2110  1 billion great grand offspring + 0.5 billion great great grand offspring

So, with these radical assumptions, we could almost get to sustainable rate by 2100 with a "1 child per couple" average.

In the real world, it might take significantly fewer than 1 child per couple on average, maybe 0.5, but I'm quite impressed with how much was achieved with only that "small sacrifice", wheras even the supposed "replacement rate" still represents short term growth before stabilization at higher than present levels.

No comments:

Post a Comment