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 , 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.