Can a collapse of global civilization be avoided?

Apocalyptic news are always in high demand, especially when transiting into a new year. So, after surviving the end of the Maya calender, and just before entering the year of the Snake, a new variation on an old song caught my eye: Paul and Anne Ehrlich just published an article in Proc. B, asking “Can a collapse of global civilization be avoided?”

Can we predict collapse, and is it likely?

I don’t want to make this a post about the limits of predictability – suffice to say, I believe that some reservations are in order when reading this kind of predictions considering 1) our long cultural track record of apocalyptic fascination and failed doomsday predictions in general, and more specifically 2) a history of wrong and partly over-pessimistic predictions when it comes to the stability of modern civilization, including those of the Ehrlichs. Incidentally, I believe that, regarding stability, we can learn as much from Eastern Island as we can from an Ebola outbreak – if you overshoot your capacity, and your resource grows slower than you, you might go extinct. However, is humanity an Ebola virus, or rather a common flu? I’d say we simply don’t know (yet).

Controlling population growth

Predictability aside, however, by resurrecting an old mantra of theirs, the authors raise a point that maybe does deserve some more debate. From the paper:

Too many studies asking ‘how can we possibly feed 9.6 billion people by 2050?’ should also be asking ‘how can we humanely lower birth rates far enough to reduce that number to 8.6?’ To our minds, the fundamental cure, reducing the scale of the human enterprise (including the size of the population) to keep its aggregate consumption within the carrying capacity of Earth [121], is obvious but too much neglected or denied.

I think it’s true that, after a phase of much attention, the larger field of environmental science as well as the global political debate has accepted population growth pretty much as given, and subsequently shifted all attention towards concentrating on economic growth and resource intensity of the economy as the main issue that environmental policy needs to address (maybe in a somewhat similar way as the climate debate has shift from preventing climate change towards mitigation and adaptation). Resource use is the ultimate cause of environmental problems, but the increasing demand for resources is driven at least in parts by the global demography, where emerging countries such as China, India and Brazil have not only strongly increased their own consumption, but are also providing the working force for much of the consumption in the industrialized nations. Controlling population growth would therefore make a great difference for many environmental problems.

What is the “optimal” population size

But which is the right population size? The Ehrlich’s have it easy – if you buy the collapse story, it’s no question that you need to control right now, because a higher population size now leads inevitably to many deaths and a lower population size later. As Gretchen Daily pointed out in an article together with the Ehrlichs in 1995, one can constrain the question of the optimal population size to the range between the minimal viable population size the global human carrying capacity. Daily et al. estimated those to 500 for the MVP, and lower than 5.5 billion for the carrying capacity. I find that number highly unlikely – this is not to say that I think a high population size, with corresponding environmental problems, is desirable, however, it seems to me that the theoretical carrying capacity of the earth must be considerably higher, assuming we use all our available resources optimally (no war, good medicine, no waste of food, no meat), and for other species than humans only as far as it is necessary for our long term survival (consider that we are currently able to feed 7 billion with an extremely inefficient distribution and diet). How high? I have not the faintest idea. The amount of energy received from the sun seems to pose a fundamental upper limit, below which a lot depends on technology, as the historic population development shows. A Science paper from Joel E. Cohen shows historical estimates to range between 1 and 1000 billion – sounds about right to me 😉


Anyway, maybe the more important question here is not about the maximum, but about the optimal, i.e. the desirable population size. Daily at all are not afraid to give a number:

the optimum number of people to exist simultaneously lies in the vicinity of 1.5 to 2 billion people. That number, if achieved reasonably soon, would also likely permit the maximum number of Homo sapiens to live a good life over the long run.

It seems pretty obvious that there is a vast uncertainty on this number, not only because it relies on uncertain assumptions about how a world of 1.5 billion people looks like as opposed to a world of 3.5 billion, particularly when considering the uncertainty of technology, but also because of the applied preferences, which are not necessarily shared by all. I’m thinking, for example, about the old debated of average vs. total utilitarianism. Still, uncertainty is no excuse for making no decisions at all, and when asked I would also say that, with our current technology, our planet seems to be rather on the crowded side … so, it might well be preferable for environmental sciences to look a bit more at population growth, which, after all, can be influenced with pretty simple and uncontroversial measures such as education, economic opportunities, basic human rights (for women) and political stability, rather than wearing itself off with optimally organizing economic growth and resource consumption.

5 thoughts on “Can a collapse of global civilization be avoided?

  1. Yes, the Ehrlich’s have drawn apocalyptic scenarios in the past which did not come true. Their recent article I find rather agreeable though. By now we are living at the cost of people in the developing world and at the cost of future generations and I believe that we will not be able to sustain neither the actual population nor an increasing number of people using that much ressources as we do in the developed world on the long run.

    Gretchen was noting in her article that she did a back-of-the-envelope- type of calculation (so, no exact number with exact uncertainties as a modeller like you would like to have) – you might find their number unrealistic but it came with some assumptions: sustainability, viable biodiversity, security of human rights, spatial dispersion, and maybe most importantly it is informed by the actual resource use and behaviour. There are 7 billion people now (not 8, or do I miss something/someone) – but this is far from being sustainable and biodiversity is not what I would call viable nowadays.


    • Hi Jan,

      thanks for the comments – to make a few clarifications:

      1) When I speak about the human carrying capacity, I don’t assume that all aspects of the biosphere (including biodiversity) need to be sustained in the current state, I just refer to the maximum population size that we would be able to maintain for a long time, in a potentially radically different world from the one we live in now – I think this is different than the typical discussion about a “sustainable world” which usually extends also to the sustainability of other aspect than the human population size. And thanks btw., I corrected the typo with the 8 million!

      2) About back-of-the-envelope calculations: I don’t object to this type of calculations, actually, I find them in many cases as reliable and often more useful than a complicated model that comes out with the same uncertainty. I think the fundamental uncertainty in this type of predictions is technology and culture, and this is not modellable. However, also a back-of-the-envelope calculation should point you in the right direction – I guess it comes down to a matter of gut feeling, but my envelope tells me that we could sustain 5.5 billion, alas, potentially at the cost of giving up other things such as biodiversity, eating meat, or being able to hike in the alps without seeing other people

      3) Finally, I’m not diagreeing about the fact that it would probably be desirable to have a smaller population size given our current technology (I think one can have endless discussions about this, however, and how this is going to be achieved and by whom is another question as well)- but I think we can easily come to this conclusion without having to believe in collapse.


      • Hi Florian, thanks for clarifiying these things. I think Gretchen calculated the carrying cappacity based on the actual ressource use and not on an optimal one. Calculating a number based on an a minimal ressource use (no meat, very little transportation) feels to me more like an academic excercise than an achievable scenario. Not that I think doing this is wrong, but that I think doing this implies that it could be possible to achieve it (sacrifying biodiversity seems realistic though). Anyway, the important question is more how a certain population size and behaviour can be achieved and technology will certainly not save us. It rather made things worse as the experience of the last 150 years tells us.


        • Well, to be exact, the paper is based entirely on per capita energy use; its in some sense a discussion about what would happen if we maintain a similar to industrialized resource footprint with 10 billion people or more.

          But exactly these assumptions are in parts what I object to – maybe it’s a matter of definition, but it just doesn’t seem a sensible definition of a carrying capacity to require a per capita resource footprint of today – I assume that you agree that we could easily get rid of a large part of our consumption without posing a direct danger to our life, and I also think we have no reasons to believe that humans wouldn’t do this if things got really nasty. Much easier to change your habits than to get rid of 8 billion people at any rate.

          Regarding technology, I would say that it is clear from looking at the population development in the last 10.000 years that technology has allowed us to feed more people with the same amount of resources: a hunter-gatherer society simply makes less efficient use of their land than an agricultural society. True, in the last century, higher efficiency has been offset by higher consumption and global population growth, but I don’t think that this is necessarily a general rule, population growth in the industrialized nations, for example, has come to a halt despite the fact that resources for further growth would be available. See also in today’s issue of Nature.


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