QUICK, NOW. What’s worse: a punch in the nose or a poke in the eye? An ugly divorce or a year in the slammer? Deep drilling in the Gulf of Mexico or tar-sands mining in Alberta?

Federal Environment Minister Jim Prentice has an opinion on the latter. In a statement reported shortly after the Deepwater Horizon exploded, killing 11 people and gushing oil into the Gulf, he said that the environmental risks associated with Alberta’s tar-sands operations are “probably less than the kind of risks associated with offshore drilling.”

Mr. Prentice’s conclusion is debatable, but he may not be wrong. It is not easy to weigh wrecking Gulf of Mexico ecosystems and livelihoods against speeding up climate change and writing off an area of boreal forest and muskeg the size of Greece. We might wish he had observed that neither is acceptable.

Both, however, are what we have. Tar sands and inhospitable drilling locations are the leading substitutes for “conventional” land-based oil supplies that are no longer sufficient to meet demand. If and when these unconventional oil options run low and become too costly, we will find other substitutes.

Or so the standard thinking goes.

The prevailing theory of human material progress is that economic motives and human ingenuity will save us when shortages loom. Increasing scarcity of valued goods will increase prices, leading to more investment in innovative alternatives. The bright and avaricious will then figure out how to replace the disappearing tuna, the cut-over forest and the exhausted mine. They will find ways to exploit a substitute fish, a more distant forest, a less accessible ore body. If necessary, they will construct substitutes for fish, trees and minerals to deliver the desired services.

It’s a riff on the old belief that “necessity is the mother of invention,” supplemented by the economic driver of profit seeking.

Within a certain range of applications and implications, the substitution theory works reasonably well. It at least roughly fits the stories of coal replacing depleted firewood, petroleum replacing whale oil, synthetics replacing natural rubber. And tar sands and deepwater drilling replacing conventional crude.

Sometimes substitutions are cheerful – safer, cheaper, more broadly accessible, more efficient and less ecologically damaging. Think of solar water heaters, libraries, vaccination, streetcars, weather stripping, condoms and the ingeniously simple Canadian water pumps that now serve many poor villagers around the world.

But such results are not automatic. Many big scarcities get little attention because the victims have little money. Big Pharma has little incentive to find new drugs to fight the diseases of the poor. And many substitutions don’t address any real scarcity. Some, such as substitutions of video games for street hockey or sugary pop for tap water, undermine more than they serve, though they all add to our planetary load.

Meanwhile, the risks grow. Because the original resources were the easiest to exploit, finding substitutes tends to require more ambition, deeper invasion and larger-scale hazards. Substitution gets us genetic engineering, nuclear reactors, ocean draggers and unconventional oil.

Most fundamentally, for many crucial but increasingly scarce goods, there is no potentially satisfactory substitute. We have no viable replacements for climate stability or generosity or biodiversity. We have no backup planet.

The absence of an automatic mechanism for beneficial substitution is an inconvenience, but not a disaster. There’s no great mystery about the basic qualities of a decent world, or the criteria for distinguishing cheerful substitutions from regrettable ones. And finding actually desirable substitutions for depleting activities is a worthy collective challenge with grand opportunities for creative innovation.

For Mr. Prentice, the challenge is to find substitutes for conventional oil that are less ambitious, invasive and risky – the energy equivalents of libraries, hand pumps and condoms.

University of Waterloo professor and the magazine’s long-time editor, Robert Gibson chairs Alternatives’ editorial board and writes our back-page column: What’s the Big Idea. He reads every word of every issue and can be thanked for the best – and the poopiest – article titles. Substitution gets us genetic engineering, nuclear reactors, ocean draggers and unconventional oil. 

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