By Paul R. Ehrlich and Anne H. Ehrlich

July 14, 2009

No driver of environmental deterioration is more obvious than population growth, and none has been more taboo to talk about – especially in recent decades. Even ecologists have often danced around the topic. Although more than 40 years have passed since we wrote The Population Bomb, the book is still attacked daily on blogs, misquoted and excoriated. On the positive side, however, it has received great honors from the lunatic fringe. It was listed by the Intercollegiate Review as one of the fifty worst books of the 20th century, along with John Rawls’ A Theory of Justice. In Human Events’ list of the “Ten Most Harmful Books of the Nineteenth and Twentieth Centuries,” it came in 11th place (“honorable mention”); even so, it bested Charles Darwin’s The Origin of Species and Silent Spring by Rachel Carson.

Such nonsense over four decades has allowed the role of population growth and related issues (especially patterns of rising consumption) as drivers of some of our most serious problems to be largely ignored. That makes a collapse of civilization now seem ever more likely. Climate disruption alone, tightly tied to overpopulation through such activities as fossil-fuel use and deforestation, could make achieving sustainability impossible.

A possibly even more serious problem is the increasing release of toxic chemicals in support of growing numbers of people, each striving to consume more. The releases are done with essentially no cost-benefit analysis; a potentially dangerous compound that might cure cancer is treated much the same as one that strengthens eyelash glue. While there are nut-case plans for “geoengineering” that might be tried if the climate starts to get away from us, there are no such possibilities if synergisms among toxics begin to kill us or our life-support systems. Especially threatening are endocrine-disrupting contaminants with non-linear dose-response curves – synthetic compounds sometimes more dangerous in tiny rather than large doses.

Then, of course, there’s the decay of the epidemiological environment, intimately tied to the increasing absolute numbers of people and of hungry (and thus immune-compromised) individuals – the latter now at a record more than one billion. More susceptible people pushing into the habitats of animals carrying novel (to us) infectious diseases, larger human populations to maintain those diseases, and ever more rapid transportation systems make nasty pandemics increasingly likely.

The Population Bomb, ironically, was much too optimistic about the future. In 1968, when it was published, carbon dioxide was thought to be the only human-produced greenhouse gas, and some climatologists believed that cooling by other pollutants would overwhelm its effect. As a result, we could only write that exploding human populations were tampering with the energy balance of Earth and that the results globally and locally could be dire. Now we know that increasing flows into the atmosphere of a series of anthropogenic greenhouse gas, a consequence of the near doubling of the human population and the more than tripling of global consumption, have the potential to cause catastrophic climate disruption unless rapidly abated.

In 1968, Sherwood Rowland and Mario Molina had not yet discovered the potential of chlorofluorocarbons to destroy the ozone layer and make life on Earth’s surface impossible. Norman Myers was years from calling world attention to the destruction of tropical rainforests; when The Bomb was written, the possibility that those forests might be destroyed was essentially unknown. Also unknown were the threats of endocrine-disrupting contaminants. The Bomb also should have paid attention to the potential for resource wars. The 1967 Israeli-Arab war, partly over water, and the current Iraq and Afghanistan wars over fossil fuels may be precursors of many more resource wars with similarly intimate overpopulation connections.

There were of course also flaws in The Population Bomb’s analysis of known threats. The first lines of the Prologue (p. 11) proved to be among the most troublesome in the book: “The battle to feed all of humanity is over. In the 1970s the world will undergo famines — hundreds of millions of people are going to starve to death in spite of any crash programs embarked upon now.” We are often asked about the famines The Bomb predicted, as if the last four decades were a period of abundant food for all. Although hunger became less newsworthy as humanity did try to ameliorate the worst famines, they nonetheless were essentially continuous in parts of Africa. Perhaps 300 million people overall have died of hunger and hunger-related diseases since 1968. But the famines were smaller than our reading of the agricultural literature at the time had led us to anticipate. That was largely because of the medium-term success of the “green revolution,” the export of high-yielding grain technology to poor nations. The analysis of the food situation in The Population Bomb was thus wrong in that it underestimated the impact of the green revolution. At the same time, it did correctly recognize that serious ecological risks would accompany the spread of that revolution.

Partly due to the message of The Population Bomb, there has been a highly desirable decline in birthrates in much of the world, but the depressing prospect is that some 2.5 billion people will be added to the population before growth stops and (we hope) a slow decline begins. Those additional people will have a disproportionately negative impact on our life-support systems. Our ancestors naturally farmed the richest soils and used the most accessible resources first. Now significant amounts of those soils have been eroded away or paved over, and farmers are increasingly forced to turn to marginal land to grow food. Instead of extracting rich ores on or near the surface, deeper and much poorer deposits must be mined and refined today, at ever greater environmental cost. Water and petroleum must come from lower quality sources, deeper wells, or the latter often from far beneath the ocean, and must be transported over longer distances. The environmental and resource impacts of future population growth will dwarf those of the past.

In the face of these problems, humanity seems paralyzed on many fronts, but especially in confronting issues of population and consumption. There is a growing movement to initiate a Millennium Assessment of Human Behavior (MAHB) to globally examine and publicly discuss the failures of cultural evolution to direct society towards sustainability. The population bomb is returning to public prominence, but it remains to be seen whether anything effective and humane will be done about it.

Paul Ehrlich is the Bing Professor of Population Studies and President of the Center for Conservation Biology at Stanford University.

Anne Ehrlich is Senior Research Scientist and Policy Coordinator at Stanford’s Center for Conservation Biology.