To answer the actual question, if the global population of any species is increasing by a steady 1.5 percent per year, then the doubling time is about 70/rate or 69.3/1.5 or 46.2 years or a bit less than a half century.

Now I can talk science, no opinions, so everyone who would rather believe than know can surf on. Confirming one’s bias feels so much better.

The belief that fertility rates will continue to decline is a firmly held belief by many, but merely that. As Steven Pinker likes to point out, the steady reduction in scarcity over the last few centuries have favored the better angels of our nature. If you believe that as we become ever more enlightened (now), that the 21st century will be characterized by ever more abundance and lower poverty rates (per UN mandate), and less conflict, then fertility rates may continue to decline. Or not.

The ‘demographic transition’ is not a theory, just a phrase used to note that with increasing consumption (and pollution and complexity…), fertility rates in evermore complex modern techno-industrial societies decreases for some reason. Is it due to pollution (e.g. phthalates) causing ever reducing sperm count in males and loss of fertility in woman? Looks like this could become a significant driver, but isn’t yet.

Is declining fertility rates due to overdensity living over multiple generations, as happened to John B. Calhoun’s rats (and mice) of NIMH? Why would only humans not experience a ‘behavioral sink’ effect over 8–12 generations of living in urban abundance? Could increasing stress cause reduced fertility in humans as it does in other social species?

Or perhaps, with the glaring exception of Israel, educating and empowering women to serve industrial society by pursuing short-term self-interests (as liberated wage-slaves to corporations, NGOs, governments, and businesses such as higher education) is the cause? I don’t know. And you don’t either.

I mentioned Israel, which is in the ‘news’ again, but that is a distraction. The news (information) the media will mostly ignore is that in areas of high religious conflict, regardless of how educated and empowered the ever so modern women are, futility rates remain high. Sometimes it takes religion.

In ultra-modern and empowered Jerusalem, Jewish women, with similar ‘rights’ and economic opportunities as Jewish women in the US and Britain and where birth control is readily available, Jewish women average 4.27 children each. The Jewish population in Jerusalem will double in (70/4.27) a bit over 16 years.

In Israel as a whole, Jewish women average 3.09 children each compared to 1.5 in the US and Britain. Women (who may self-identify as Palestinian) in relatively conflict-prone Gaza average 3.64 births (average age of population is 18 with over 5,000 people per sq-km—global average is 45 persons per sq km, India is over 320 persons per sq km, so doubling the population of Gaza in 19 years to 10,000 per sq km could affect the level of conflict, especially if resources such as food become scarce). In the more peaceful West Bank area the birth rate is 3.07 per woman, so it will take nearly 23 years to double the population.

As Yasser Arafat noted, when Palestinian women averaged 8 children (1960–65), ‘The womb of the Arab woman is my strongest weapon’. In 37 years, the population of Israel as a whole will double it things keep on. From 1989 to present, the population had doubled, but the economy grew faster. If the economy doesn't more than double by 2058, expect more conflict. Perhaps the better angels of our nature will take a well deserved nap (just guessing, so ignore rhetorical offerings).

For peace in the world, we need to maintain at least the current 3.4 percent economic growth rate to double production and consumption in 20 years, as we have been. And then what? Do it again and again?

As we are now causing over a thousand fold increase in the rate of species extinction, we will be well on the path to causing a ten thousand fold increase by the end of this century as we will ‘need’ to keep growing the economy, doubling it every couple of decades to avoid scarcity induced conflict. All nations need to pass laws to prevent limits to growth. Sorry, just an opinion, ignore all primate prattle. Listen to Nature instead.