Let's talk about global population for a moment. There's a technotopian view that "Given current trends, it is very possible that the size of the human population will peak this century and then start to decline.". This is an idea that Stewart Brand promotes as does Kevin Kelly as evidenced by their bets on the Long Bets website among others. Typically this goes along with comments like "The growth rate of the human population has already peaked. Today’s population growth rate is one percent per year, down from its high point of 2.1 percent in the 1970s."

Now, the best source of data about global population is probably the UN. Their papers are pretty dry but there's a good summary of their data here. http://www.worldometers.info/world-population/ And also in the UN's executive summary here. http://esa.un.org/unpd/wpp/publications/files/key_findings_wpp_2015.pdf What seems to have happened is that the growth in population was close to an exponential curve up to about 1950. But then it transitioned to a linear growth so that from about 1965 to 2015 the growth in absolute numbers has been pretty constant at 1b every 12-14 years, 80m every year. Now in a linear growth phase, of course the RATE in terms of the percentage of the total is going down. Simple maths. A constant addition is a smaller and smaller proportion of the growing total. However the linear rate is constant. If the growth in population is following a resource constrained logistics curve we would expect an S shape. So that after the linear region we would expect the growth to slow and the total to then plateau out. However looking at the UN forecasts, even the most optimistic has the peak at around 10b in 2080. The median predictions don't top out this century and hit 11.2 billion by 2100. The UN has recently revised (2015) their forecast of 10 billion persons in the year 2056 (six years earlier than previously estimated). If anything the recent historical data and near term (30-40 years) forecasts are for slightly higher than linear growth. This is the data that Hans Rosling uses as the basis of his presentations to the BBC and Davos, although he manages to a positive spin on it. We should be more sceptical.

All of this forces me to say "citation needed" when referring back to statements like "very possible that the size of the human population will peak this century" or "Human population of the world will peak at or below 8 billion in the 2040s and then drop dramatically.". It looks too much like hand waving. So where's the justification for a different outcome from the forecasts of the most well respected source? When should we expect a slow down in the linear growth, because it's still happening.

This seems critical to me because people who seek to find technological answers to our problems tend to argue that Malthus and Erlich were wrong and continued economic growth is possible indefinitely. Continued growth in global population makes this harder and harder to support. It may not be the relatively quick Malthusian disaster produced by exponential growth, but linear growth is ultimately just as bad, it just takes a bit longer before you hit the limits.

Projections and futurists usually take a predictable approach. Take what's happening right now, project the graphs out to 15 years with no real changes in approach. Then push the models to 30 and then to 60 years with some changes that make a certain amount of sense. Now go back to 1970 when Erlich and crew were predicting Malthusian apocalypse. They'd had 40 years or so of accelerating exponential growth in global population and it was currently peaking at 2% pa compound. If that had continued we'd be on 9b now (2016), 12b in 2030 and 18b in 2050. Understandably they couldn't see how the Earth could possibly support that. But given the current situation they were seeing around them at the time, it was reasonable to wonder what would happen.

As it turned out they were writing just as the first demographic transition happened from exponential growth to linear growth. Instead of 2% pa, the system switched to 80m pa. It's now kept that linear growth up for 50 years. So if you were projecting right now, it would be reasonable to expect that linear growth to continue for at least another 15 years, maybe to 30 years out. And you'd be stretching the point to justify it for 60 years. It is possible that we're on the threshold of the next transition from linear growth to zero growth or even falling growth. But right now in 2016 it's hard to see.

So what is underpinning these 3 regimes?

- Exponential growth: Agricultural revolution. Crop science. Industrialisation of agriculture. Cheap nitrogen fertiliser produced with cheap energy. Antibiotics.

- Linear growth: Urbanisation. Falling fertility rates among developed populations. Underdeveloped areas with exponential growth becoming a smaller proportion of the whole. What else?

- Zero and falling growth: Pollution and resource constraints. Food capacity constraints. Ageing menopausal populations. What else?

What have I missed as justifications? And why should the transition happen from linear growth to zero growth? What I don't feel I've got a handle on is why we've had constant linear growth for 50 years and why it should stop. Instead of arguing about the details of which futurist was right or how previous predictions turned out to be absurd, where's the analysis of what was happening then, now and in the 30 year future?

I don't really see how to avoid this. It suggests to me that it's a core, big and difficult problem that won't go away. And it's the one big problem that underpins all the other big problems. If we're not to have those catastrophic failures defined by "SFPD - Systems Fail, People Die", then we have to come up with solutions for supporting 11-12b people within the next 100 years. And we have to do it while in the middle of climate change and resource limitations (eg fossil fuels) becoming major factors. And of course it's worse than it appears because that rising population has increasing expectations of consumerism. Generating increasing amounts of pollution, both as CO2 and as more traditional forms. And using up our resources at an increasing rate.

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[ 28-Mar-16 11:28pm ]