by Carl Haub, senior demographer, Population Reference Bureau
I’ve seen many occasions where writers have stated that a particular population is growing “exponentially.” That term seems to have evolved to mean “fast.” The exponential rate—as opposed to percentage increase—is the one usually used to measure population growth. So let’s take a look at what it really means and, honestly, I’m definitely not being picky here. Exponential growth simply means that something, be it money in the bank or the population of Egypt, grows continuously. Compounding continuously is another way of saying it.
But it doesn’t mean fast. The confusion probably comes from many articles written decades ago that developing country populations were increasing at a fast pace and exponential growth was often used to describe it. What writers probably had in mind was doubling. They pointed out that, should a country with 20 million population double in, say, 25 years to 40 million, the next time it doubles it will obviously grow by 40 million, not 20 million. Here again we see the process of compounding. In reality, all population growth—fast or slow, or even decline—is exponential since that’s how population change is usually expressed.
For example, Nigeria’s population is growing at about 2.6 percent per year. If maintained, that rate would cause the country’s population to double in size every 27 years. The population of Russia is growing at 0.1 percent per year. At that rate, Russia’s population would take 693 years to double. Hungary’s population is declining by -0.3 percent per year. All three of those rates are exponential.