Half a world population ago

In 1968, a couple of years after Lunar Orbiter I made the first images of Earth—back when the planet's human population was half what it is today—I gave a talk recommending zero population growth at a meeting of a chapter of the American Association of University Women.

Many of those present had already heard the term zero population growth, and some may have read Stanford University ecologist Paul Ehrlich's bestseller of that year, The Population Bomb, which was among my primary sources of information. The basic idea was that if humans, on average and as a personal commitment, produced just enough offspring to replace themselves (two per couple), then population could remain approximately constant. Zero population growth. Or, as an entry in Wikipedia puts it, "In the long term, zero population growth can be achieved when the birth rate of a population equals the death rate...."

Ehrlich's predictions of worldwide famines between 1970 and 1985 because of overpopulation may have failed in their details, but few informed people today doubt that overpopulation has driven and continues to drive global warming, including unmistakable changes in weather patterns, shrinking polar icecaps, and the rising acidity of oceans (some of the increased carbon dioxide in the atmosphere going into the formation of carbolic acid)—all of which have stark consequences for life on earth.

For along with rising numbers of humans come their rising expectations, which can be summarized briefly as expecting to live like an American. You know, drive an SUV and produce, by Third World standards, an astounding amount of garbage.

I don't know how accurate Erhlich's 1968 prediction was for when the Earth's population would double (I'd have to read his book again to check), but he did expect it to double. He knew how difficult it would be to achieve ZPG, because, to quote Wikipedia again, "a country's population growth is often determined by economic factors, incidence of poverty, natural disasters, disease, etc."

According to the U.S. Census Bureau, here are the Earth's population figures for 1966 and 2008: 3,416,212,203 and 6,677,602,292 (doubling in those 42 years). Its prediction for the next 42 years (2050) is 9,392,797,012. While that would be a growth of less than half the preceding period, remember that the extra people will be hustling to realize their growing expectations...so long as conditions don't worsen to the point where such expectations are impossible to maintain and many will give up hustling in favor of desperately hoping and waiting for an afterlife.