October 20, 2008

Was Malthus right to forecast starvation?

No. As a practical matter I think we're going to have a hard time juggling all of our resource crunches (especially energy), but I think we should be clear on what the theoretical problems are, and are not.

The most important refutation of Malthus is on the population side: world population as a whole has clearly stopped growing exponentially (or geometrically, if you like), due to the demographic transition (it's roughly arithmetic at the moment). This is a key point: in many ways, growth is generally self-limited, and follows a logistic (or sigmoid curve), generally referred to as an S-curve. For instance, US car sales peaked about 35 years ago, and the US has a clear over-supply of vehicles, due to increasing vehicle longevity.

In fact, in most of the world population growth is on a long-term negative path, due to fertility rates well below replacement, including Western Europe, China, and the US (excluding immigration). Russia, Eastern Europe, Japan and Italy are starting to show absolute declines in population. This is detailed at the UN site below, where we see that the growth rate was as high as 2.19% back in 1963. The total population peak is currently expected to be at about 9 billion around 2075 and population is expected to drop after that.

See especially Figure 3, page 6: http://www.un.org/esa/population/publications/longrange2/WorldPop2300final.pdf

Let's explore a couple of key concepts: the difference between arithmetic and exponential growth, and the difference between high fertility and "bottom line" growth.

Consider the following series of numbers: 10, 11, 12, 13, 14. There is growth of 7.7% at the end, but this is arithmetic growth: the change from number to number is constant, not growing with the base. Malthus assumed exponential growth for population, and arithmetic growth for agriculture. The growth rate of the world's population has been falling for 50 years, from 2.2% (in 1963) to 1.1% (in 2012).http://www.census.gov/population/international/data/idb/worldpoptotal.php . We see the current absolute number is about 78M per year,  and decreasing: exponential growth for population has ended.

Growth varies enormously by country - in Japan, for instance, absolute growth will be negative next year. Italy and Russia will follow soon after. These alone are sufficient to refute Malthus's general rule in a simple, clear fashion.

For many more countries, the fertility rate is below replacement. If every couple has less than about 2.1 children (the definition of the replacement fertility rate), the population is very young, and the death rate is low, there can be a lot of children and "bottom line" growth in the population, but in the long run the population will stabilize and decline, as every generation is smaller than the one before. So, if we clearly have fertility rates below replacement, we clearly have in the long run stable or declining population growth.

Now, are there still parts of the world growing pretty quickly? Sure, but they're in the minority. Just as importantly, the parts of the world that aren't growing clearly refute Malthus's idea that population always grows until it hits a resource limit - he couldn't conceive of voluntary birth control.

Do we still have huge, basic sustainability problems? Sure, but it's important to know that the broad, simple framework that Malthus proposed is just plain wrong.

This kind of logic also applies to energy. Like population, US car sales, and many other examples, energy markets (at least renewable ones, like those for wind and solar electricity - so no, I'm not talking about oil) will naturally mature and flatten out long before we reach theoretical limits.

For far too long we've been talking about a false dichotomy between "infinite exponential growth" and collapse. In fact, with a little luck, growth in resource consumption will gradually come to a stop, while humanity switches it's desire for improvement to what are generally known as "services": health, education, art, etc.


Just for the value of good trivia, let's note that Malthus believed that population growth would continue forever because he believed that contraception was morally wrong, not that it couldn't work.

Further, some argue that Malthus’s argument was principally a class one, designed to rationalize why the poor must remain poor, and why the class relations in nineteenth-century Britain should remain as they were.

His greatest fear was that due to excessive population growth combined with egalitarian notions “the middle classes of society would . . . be blended with the poor.” Indeed, as Malthus acknowledged in An Essay on Population, “The principal argument of this Essay only goes to prove the necessity of a class of proprietors, and a class of labourers.” The workers and the poor through their excessive consumption, abetted by sheer numbers, would eat away the house and home (and the sumptuous dinner tables) of the middle and upper classes.

He made it clear that the real issue was who was to be allowed to join the banquet at the top of society.

Charity simply encouraged early marriage and larger families, he concluded, inspiring an 1834 Poor Law that effectively limited public relief to people toiling in workhouses. Charles Dickens, appalled, rebuffed Malthus with the tale of a flinty miser who had a change of heart. "A Christmas Carol" is still in print.

update: here's comments by "relhager":

There are two relevant points: One, as Nick noted above, is that the UN predicts that the human population will never double again, and will start decreasing during this century. That’s critical.

The second is just as important: Malthus was simply wrong. Or at least half wrong. He was right about population growth (up until now, at least) but very wrong about food production. During the twentieth century, global population increased sixfold, and food production increased sevenfold, thanks to advances in genetics (the Green Revolution) and especially chemical fertilizers (see my recent book on the history of the subject, "The Alchemy of Air," as well as Vaclav Smil’s excellent "Enriching the Earth.").

Yes, we will have big issues handling the population high-water mark (+ another 4 billion or more) before we start going down in numbers, especially because of pollution. No, this does not answer questions about energy resources (making chemical fertilizer currently eats up about 1 percent of all the energy used on earth). But if we ate a reduced-meat, high-vegetable diet, we should be able to avoid the mass starvation predicted by Malthus — forever. www.thinhouse.net


Anonymous said...

I think Malthus did consider birth control - that's what he called "vice."

Nick G said...

True, but he thought it was not something people would use, due to it's immorality, and lack of motivation.

Clearly, people are willing to use it.