At first they did this through geographic expansion, extending their economies — and ecological footprints — onto other continents. More recently they've used exponentially increasing amounts of energy to avoid or soften their encounter with ecological limits. Thus, fossil-fuel-based fertilizer, diesel tractors, and energy-intensive pumping have allowed us to increase our population far beyond the number that a prepetroleum agriculture could support.

Climate change is the result of our violation of a planetary limit — the capacity of the planet to absorb a human effluent without being dramatically changed. If we take a limited view of history, professor Armstrong is right: For nearly half a millennium, European peoples have found ways to sidestep many kinds of limits.

In “The high tech of low carbon” (Page A1, Jan. 23), Robert Armstrong, director of the MIT Energy Initiative, claims that “history says we can invent our way out of” the climate-change crisis. The historical record, as I read it, is not so clear.


A longer view of history attuned to energy use offers little ground for being sanguine about the power of human invention. Physical law tells us that we'll never create energy out of nothing, and that energy return on energy invested, or EROI, is a crucial measure of a civilization's energy harvesting system. History suggests that it's easy to look smart and be inventive on the high-EROI upslope of new energy-harvesting technologies, as was shown by Egypt under the pharaohs, China after the invention of intensive rice cultivation, Rome during its expansion of slave-based wheat farming, and European culture as we began to exploit coal and then, even more dramatically, petroleum.

But today humans have discovered and used more than half of the oil the planet has on offer. Our use of it must eventually decrease, and the longer we postpone that decrease the more dramatic the decrease will be. Far from reassuring us that we can always solve our problems, history tells us that civilizations that experience dramatic declines in their net energy uptake usually develop authoritarian political systems in an effort to stave off collapse, but then crash and disappear anyway.


The challenge we face is difficult. We need to face it squarely, without illusions.

Eric Zencey

Montpelier

The writer is a fellow at the Gund Institute for Ecological Economics at the University of Vermont, and is the author of "The Other Road to Serfdom and the Path to Sustainable Democracy."