Civilizations are built on knowledge, population – and energy. They thrive only when a good balance is struck between these three, a balance dependent (like that of a bicycle) on motion, which is to say growth. Human successes are always taken from the past or borrowed from the future: sooner or later the bike runs out of road. The first humans evolved by devouring the great wild beasts that once roamed all parts of the Earth. When they exhausted this primodial energy hoard at the end of the last ice age, they starved; and the humble survivors – our ancestors – became more and more dependent on plants.

Over time, early civilizations arose with the development of systematic agriculture. Through crop breeding, animal husbandry, deforestation and irrigation, they concentrated the energy of soil and seeds into the muscle power of domesticated animals and equally domesticated human beings. Towns, cities, governments and priesthoods rose like pyramids on a broadening agrarian base. Despite booms and busts along the way, humanity grew at an ever-increasing rate, especially after the crops of the Americas (such as maize and potatoes) spread around the world. By some two hundred years ago, human beings had reached the maximum number who could feed themselves by muscle power and pre-industrial machinery. That number was about one billion.

What has allowed us to soar nearly sevenfold since then was not any breakthroughin new food: all our crops are ancient; we have raised yields by tinkering, but we have developed no new staples from scratchsince prehistoric times. The breakthrough was in energy – in finding new ways to use the vast stocks of fossil carbon that Nature had buried under the planet's skin long before the first mammal crawled upon it.

We tend to think of the looming energy crisis in terms of cars, factories, heating and air conditioning, but the first thing to keep in mind is thet fossil fuels are feeding us. We all know that coal and oil drive the tractors, trains, trucks, ships and freezers that grow, store, and move foos from farm to city, nation to nation. But how many are aware that we have literally been eating oil and gas for more than a hundred years? Fossil carbon is a prime ingredient of the artificial fertilizers that have sidestepped the dec line of natural fertility each time crop is taken off a field. A two-century carbon binge has allowed mankind to fill its planet way beyond the natural carrying capacity for feckless, reckless, self-indulgent apes. If we run out of carbon or fail to find good substitutes, we are back to dung and muscle power. Billions will die.

An absolute shortage of fossil energy is still a long way off. But the amount that can be easily, cheaply and above all safely exploited is indeed running low. Because of carbon dioxide's effect on climate, an abundance of carbon fuel – especially in its dirtier forms such as coal and tar sand – is far more dangerous than a dearth. Long before fossil fuel getstruly scarce, its consumption will overthrow the predictable weather patterns on which all farming has relied for the past ten thousand years. In short, the industrial carbon economy has turned out to be what I call a ”progress trap” - a seductive and seemingly benign development which, upon reaching a certain scale, becomes a dead end.

Even if abundant sources of clean energy were to come on stream tomorrow, we would still face problems of overpopulation, overconsumption, soil erosion and the most unequal distribution of wealth and health in history. But, as the essays in this important book explore and document in different ways, a ”carbon shift” - a swift transition to much cleaner energy – is our only hope of escaping the dire consequences of our runaway success.