Wednesday, June 18, 2008

Nine Billion Shades of Malthus

I've read (or read mocked) too much lately about the demographic pressures facing successful people. It seems like a cultural meme these days, with any number of authors sweating about the breeding patterns of the unlettered brown hordes, the perceived crises that threaten everything from economic growth we're all banking on to the integrity of the culture. I don't really understand this stance: isn't reduced fertility a good thing? In an earlier article, I wondered aloud whether there's a managable population ceiling for this fine globe, or whether some horrible Malthusian catastrophe will correct the numbers for us. For the record, I think agricultural independence is a wonderful way to live, and the idea that consumption patterns can approach zero sum, that is, that my habits can directly take food out of someone else's mouth, is deeply unsettling. (All the indirect consequences are bad enough.) Do we really want to get to the point where there's only so much to go around?

In the eighteenth century, Thomas Malthus famously compared the rates of agricultural production to the rates of population growth, and frightened a generation into believing that the people of the world were rapidly hurtling to an overpopulated doom. Obviously, it didn't happen right away, and the refutation to Malthusian population dynamics was the observation that a higher population density also drives innovation, which, as you might imagine, was generated amid the most rapid technological transformation since agriculture, which Malthus, in 1798, was on the old hardscrabble, self-sufficient side of. The truth is that Malthus was wrong about all of his rate laws, but he was also still basically right about everything. The same is also true about the Cornucopians (as those armchair innovators came to be known), who also perceived important demographic trends, but either model still produces ridiculous results when considered in exclusion and extrapolated to infinity.

I'm not given to optimism about this sort of thing. The people who latch onto Cornucopian ideas of population growth remind me too much of the (misnamed) global warming skeptics whose goal seems to be to convince themselves that easy times will continue unabated. Eventually--and I wish I had a better understanding of how eventually--it's going to be limited by the fact that it takes energy to grow people, and once we burn all the stuff in the ground that we can reach, it only falls from the sky so fast. (And despite what professional optimists may believe, tapping into the zero point energy looks a lot farther out than oil will take us.) A human population ceiling may or may not reflect the global energy balance, and as I see it, whether it does is the pressing question facing the species over the next couple hundred years.

Demographic trends are estimated by analyzing fertility rates (how quickly people are born) and mortality rates (how quickly they die). Mixed in with that are better versions of Malthus's ideas about land use, about migration patterns, and other ideas about how better organization and technological growth improve agriculture, and how education and increased per capita income relate to fertility, and some reasonable models about how these things all affect one another. Of course, the end result is still an extrapolation, and there are disagreements about the respective rates of this thing or that thing, but a global picture is emerging, with a reasonabl(y large)e degree of uncertainty. Wolfgang Lutz of the International Institute for Applied Systems Analysis has developed a model that incorporates modern studies of food security, land development and degradation as they pertain to fertility and mortality rates. It's well known that fertility decreases with overall affluence, (or, that is, with food security), but land scarcity and poverty also tend to shrink fertility, despite the story you often hear. (I guess it depends on where you start: in Ethiopia, where he makes a case study, reduced fertility rates are due to both economic growth and remaining poverty conditions. They still haven't dipped below the replacement rate.) These authors also note that migration rates tend to remain relatively slow thanks to resistance to social change, but in their global model, they are obviously important, and will be the primary cause of population growth in the first world (as it is in fact now). Lutz predicts a median estimate of peak global population of about 9.3 billion, in 2070, after which it will decline. The U.N. adopts a number that's a little ower (9.1 billion" in 2050), and Lutz presents estimates ranging from a peak of 14 billion in 2100 at one extreme, to 6.5 billion peaking right now.

The land use model that he employs is broken into geographic bins, and the evolution of the population as a function of the above parameters is borne out per region. Lutz uses "expert surveys" as well as historical data to come up with some of the values of the parameters in his rate laws. That's okay as far as it goes, and he appears to go into acceptable detail in his book (I read a couple of highly redacted chapters on Google Books) even if it makes a letter to Nature look a little cheesy in its absence. I'll note that at the very least, historical rates haven't always varied gently, as the Cornucopians may have observed during the industrial revolution, or as the first world may have observed with the introduction of reliable contraception. Interestingly, he includes the effects of climate change, and it's probably easier to predict how deforestation and development will impact the drier and poorer communities of the world, since it's already impacting those places pretty hard, and they're presumably far enough behind the growth curve that they'll predictably follow hydrological improvements that are already well understood.

I wish he presented resource depletion in greater depth. Presumably it falls under his model of land degradation, but over the next hundred years, we should have a good idea of how finite fossil fuel resources actually are. Peak oil worriers espouse a similar timeline for energy resources as Lutz does for population, and I don't know the extent they're correlated on purpose. The limited supply of global real estate is a lot more obvious. The arable land per capita is approaching the exact area of my tiny lawn, and while I might have a better chance of growing spuds than grass, it'd still be pretty hard to feed the family for 12 months off a piddling quarter acre. Yes, there is land reserved for planting worldwide, and it's engineered to hyper-efficiency, and in the highly-developed countries approaching their population peaks, there remains even a tiny sliver of wilderness and recreational land, all of which is good, sort of, even if it breaks my naturalist heart.

But the prices today are startling, and a correction, if there's one to be made, will take seasons. The Commies at the U.N. are calling for more investment in agriculture worldwide, as well as more international aid. It's probably a redundant plea: the rising prices should encourage investment. As for food aid, the value probably depends on how it's implemented--I'm not sure it's a great idea to shift the food supply even more to subsidized first-world growers, but I'm also pretty certain it's a bad idea to wantonly develop the Amazon or the edges of the Sahara into crappy farmland--but sooner or later investment will mean using the land that we can. Will we go gently over the peak? Will we fight or bargain over the limiting resources? Will prosperity win out over starvation? Lutz's model suggests we may barely get away with it. Here's hoping for the best.

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