Over some 60 million years, Homo sapiens has evolved into the dominant animal on the planet, acquiring binocular vision, upright posture, large brains, and — most importantly — language with syntax and that complex store of non-genetic information we call culture. However, in the last several centuries we’ve increasingly been using our relatively newly acquired power, especially our culturally evolved technologies, to deplete the natural capital of Earth — in particular its deep, rich agricultural soils, its groundwater stored during ice ages, and its biodiversity — as if there were no tomorrow.

The point, all too often ignored, is that this trend is being driven in large part by a combination of population growth and increasing per capita consumption, and it cannot be long continued without risking a collapse of our now-global civilization. Too many people — and especially too many politicians and business executives — are under the delusion that such a disastrous end to the modern human enterprise can be avoided by technological fixes that will allow the population and the economy to grow forever. But if we fail to bring population growth and over-consumption under control — the number of people on Earth is expected to grow from 6.5 billion today to 9 billion by the second half of the 21st century — then we will inhabit a planet where life becomes increasingly untenable because of two looming crises: global heating, and the degradation of the natural systems on which we all depend.

Our species’ negative impact on our own life-support systems can be approximated by the equation I=PAT. In that equation, the size of the population (P) is multiplied by the average affluence or consumption per individual (A), and that in turn is multiplied by some measure of the technology (T) that services and drives the consumption. Thus commuting in automobiles powered by subsidized fossil fuels on proliferating freeways creates a much greater T factor than commuting on bikes using simple paths or working at home on a computer network. The product of P, A, and T is Impact (I), a rough estimate of how much humanity is degrading the ecosystem services it depends upon.

The equation is not rocket science. Two billion people, all else being equal, put more greenhouse gases into the atmosphere than one billion people. Two billion rich people disrupt the climate more than two billion poor people. Three hundred million Americans consume more petroleum than 1.3 billion Chinese. And driving an SUV is using a far more environmentally malign transportation technology than riding mass transit.

The technological dimensions of our predicament — such as the need for alternatives to fossil fuel energy — are frequently discussed if too little acted upon. Judging from media reports and the statements of politicians, environmental problems, to the degree they are recognized, can be solved by minor changes in technologies and recycling (T). Switching to ultra-light, fuel-efficient cars will obviously give some short-term advantage, but as population and consumption grow, they will pour still more carbon dioxide (and vaporized rubber) into the atmosphere and require more natural areas to be buried under concrete. More recycling will help, but many of our society’s potentially most dangerous effluents (such as hormone-mimicking chemicals) cannot practically be recycled. There is no technological change we can make that will permit growth in either human numbers or material affluence to continue to expand. In the face of this, the neglect of the intertwined issues of population and consumption is stunning.

Many past human societies have collapsed under the weight of overpopulation and environmental neglect, but today the civilization in peril is global. The population factor in what appears to be a looming catastrophe is even greater than most people suppose. Each person added today to the population on average causes more damage to humanity’s critical life-support systems than did the previous addition — everything else being equal. The reason is simple: Homo sapiens became the dominant animal by being smart. Farmers didn’t settle first on poor soils where water was scarce, but rather in rich river valleys. That’s where most cities developed, where rich soils are now being paved over for roads and suburbs, and where water supplies are being polluted or overexploited.

As a result, to support additional people it is necessary to move to ever poorer lands, drill wells deeper, or tap increasingly remote sources to obtain water — and then spend more energy to transport that water ever greater distances to farm fields, homes, and factories. Our distant ancestors could pick up nearly pure copper on Earth’s surface when they started to use metals; now people must use vast amounts of energy to mine and smelt gigantic amounts of copper ore of ever poorer quality, some in concentrations of less than one percent. The same can be said for other important metals. And petroleum can no longer be found easily on or near the surface, but must be gleaned from wells drilled a mile or more deep, often in inaccessible localities, such as under continental shelves beneath the sea. All of the paving, drilling, fertilizer manufacturing, pumping, smelting, and transporting needed to provide for the consumption of burgeoning numbers of people produces greenhouse gases and thus tightens the connection between population and climate disruption.

So why is the topic of overpopulation so generally ignored? There are some obvious reasons. Attempts by governments to limit their nation’s population growth are anathema to those on the right who believe the only role for governments in the bedroom is to force women to take unwanted babies to term. Those on the left fear, with some legitimacy, that population control could turn racist or discriminatory in other ways — for example, attempting to reduce the numbers of minorities or the poor. Many fear the specter of more of “them” compared to “us,” and all of us fear loss of liberty and economic decline (since population growth is often claimed necessary for economic health). And there are religious leaders who still try to promote over-reproduction by their flocks, though in much of the world their efforts are largely futile (Catholic countries in Europe tend to be low-birthrate leaders, for example).

But much of the responsibility must go to ignorance, which leads mainstream media, even newspapers like The New York Times, to maintain a pro-natalist stance. For example, the Times had an article on June 29 about a “baby bust” in industrialized countries in which the United States (still growing) was noted as a “sparkling exception.” Beyond the media, great foundations have turned their “population programs” away from encouraging low fertility rates and toward topics like “changing sexual mores” — avoiding discussion of the contribution demographics is making to a possible collapse of civilization.

Silence on the overconsumption (Affluence) factor in the I=PAT equation is more readily explained. Consumption is still viewed as an unalloyed good by many economists, along with business leaders and politicians, who tend to see jacking up consumption as a cure-all for economic ills. Too much unemployment? Encourage people to buy an SUV or a new refrigerator. Perpetual growth is the creed of the cancer cell, but third-rate economists can’t think of anything else. Some leading economists are starting to tackle the issue of overconsumption, but the problem and its cures are tough to analyze. Scientists have yet to develop consumption condoms or morning-after-shopping-spree pills.

And, of course, there are the vexing problems of consumption of people in poor countries. On one hand, a billion or more people have problems of underconsumption. Unless their basic needs are met, they are unlikely to be able to make important contributions to attaining sustainability. On the other hand, there is also the issue of the “new consumers” in developing economies such as China and India, where the wealth of a sizable minority is permitting them to acquire the consumption habits (e.g., eating a lot of meat and driving automobiles) of the rich nations. Consumption regulation is a lot more complex than population regulation, and it is much more difficult to find humane and equitable solutions to the problem.

The dominant animal is wasting its brilliance and its wonderful achievements; civilization’s fate is being determined by decision makers who determinedly look the other way in favor of immediate comfort and profit. Thousands of scientists recently participated in a Millennium Ecosystem Assessment that outlined our current environmental dilemma, but the report’s dire message made very little impact. Absent attention to that message, the fates of Easter Island, the Classic Maya civilization, and Nineveh — all of which collapsed following environmental degradation — await us all.

We believe it is possible to avoid that global denouement. Such mobilization means developing some consensus on goals — perhaps through a global dialogue in which people discuss the human predicament and decide whether they would like to see a maximum number of people living at a minimum standard of living, or perhaps a much lower population size that gives individuals a broad choice of lifestyles. We have suggested a forum for such a dialogue, modeled partly on the Intergovernmental Panel on Climate Change, but with more “bottom up” participation. It is clear that only widespread changes in norms can give humanity a chance of attaining a sustainable and reasonably conflict-free society.

How to achieve such change — involving everything from demographic policies and transformation of planet-wide energy, industrial, and agricultural systems, to North-South and interfaith relationships and military postures — is a gigantic challenge to everyone. Politicians, industrialists, ecologists, social scientists, everyday citizens, and the media must join this debate. Whether it is possible remains to be seen; societies have managed to make major transitions in the recent past, as the civil rights revolution in the United States and the collapse of communism in the Soviet Union clearly demonstrate.

We’ll continue to hope and work for a cultural transformation in how we treat each other and the natural systems we depend upon. We can create a peaceful and sustainable global civilization, but it will require realistic thinking about the problems we face and a new mobilization of political will.

(Por Paul r. ehrlich and anne h. ehrlich, Environment 360, 04/08/2008)