One of the frequent means used to drive public policy is the extrapolation of current trends, any current trend, far into the future, showing that it leads to dire consequences, and demanding immediate action to avoid the horrible fate that awaits us if we don’t “do something” right. this. instant.
However, it’s worth taking a look at such predictions and examining what happens to them in the real world.
Consider, for instance, the population growth predicted by Thomas Malthus. One of the bits of “data” he used was Benjamin Franklin’s offhand assertion that the population of the US had doubled over the course of 20 years and would do so again over the next 20. Population doubling every 20 years. Exponential growth. Catastrophe! Well, there were several problems with that. First off, Franklin’s numbers (and others about British population that also went into Malthus’ work) were not exactly the most accurate measures. Additionally, the population growth was highly dependent on the conditions at the time. Great Britain was going through the Industrial Revolution and becoming a major trading economy, leading to a major increase in prosperity. The United States was rapidly growing. And if those trends had continued? Well, the population of the US was just under 4 million according to the 1790 census. Doubling every twenty years would have given the United States a population today of more than eight billion, more than the entire World’s population is now. Similar extrapolation of the population growth rate of Great Britain will produce similar nonsense figures.
Clearly, the growth rates did not continue unabated. The United States has not grown to a multi-billion population and avoided that without repeated widespread famines, without plagues rivaling the Black Death (five or six such plagues would have been required to knock back our population from that predicted from such a growth to what it actually is), or widespread slaughter in war.
Indeed, any such prediction based on extrapolating a trend from then to now would produce equally ludicrous results.
Yet people continue to blindly extrapolate trends into the future and call it “science.” This mindless extrapolation, carried to ludicrous extremes, is used to predict dire consequences unless we “do something” right now.
As one example, the surface area of the Earth is 510 trillion square meters. If we allow 1/2 square meter per person for “standing room only” at a population growth rate of 2% per year and using current population figures (more on that another time), we’d reach that in about 600 years. Oh oh! To Americans that seems a long time but it’s a hundred years less than the last eastern Crusade which still causes such heartburn in the middle East.
Of course, it’s not going to happen. Those trends are not going to continue any more than Franklin’s described trend in US population and Malthus’ predicted trend in British population continued. Demands to “do something” based on those predictions are not science. They’re politics wearing the flayed skin of science while demanding the respect due the edifice it slew in the face of ideology.