Our overcrowded planet: a failure of family planning

To be fair, the demographers themselves acknowledge that projections are really at best educated guesses based on past and present human data. John Wilmoth, the UN Population Division's director, told the Associated Press that "there is a great deal of uncertainty about population trends." The impact of potentially devastating epidemics - already the world sees more than five new infectious diseases each year, according to a study by parasitologist Peter Daszak and colleagues - is just one such unknown. Nonetheless, pundits, press, and public assume that demographic experts are confidently and competently predicting the future of human population. And this future presupposes that no level of human presence on the planet will ever undermine its capacity to support human life.

So the projections present us with the optimistic presumption that in 2100 human life expectancy worldwide will average 82 years, up from 70 today - despite growing resource scarcity and temperature increases likely to have blasted through the 2-degrees-Celsius ceiling that climate scientists and governments have agreed is dangerous to exceed. Nigeria's population is projected to quintuple from 184 million today to 914 million in 2100. The country's development is already hobbled by violent conflict, government corruption, untreated waste, and rampant oil spills - not to mention an inequitable economic reliance on oil that is unlikely to keep gushing at current rates for 87 more years. It's difficult to imagine Nigeria heading toward 1 billion human beings as the country's less-than-abundant natural assets of renewable fresh water and arable land shrink by roughly 80 percent on a per-capita basis.

Egypt and Ethiopia are rattling sabers even today over their common dependence on the waters of the Nile as Ethiopia harnesses its flow for hydropower. The countries will see their combined population more than double, from 176 million to 379 million. Jordan is already challenged to share its scarce water supply with an influx of Syrian refugees who have boosted its population of 7.3 million by 500,000. The native Jordanian population alone is projected to grow by that amount in just three years - and by 78 percent by 2100.

People in all these countries are innovative and resourceful. No doubt technological advances we can't possibly imagine today will contribute to health and long life. Maybe we'll soon make real progress in addressing climate change and water scarcity. But all those who believe that such large populations are likely to be living in these countries - with 82-year life expectancies no less - at the end of this environmentally challenged century, please raise your hands. The rest of us need to start taking the rights and potential of women, the importance of sex for its own sake, and the impact of human numbers on the environment a lot more seriously than we do today.