The simple answer is, we're running out of easily extractable oil, hence the high oil prices, and, in part, the teetering world economy. But rather than formulate a new direction, we're digging ourselves - literally and otherwise - into an ever-deeper hole. The oil sands are a sad symbol of the cycle of the decline we are facing without a sustainable energy policy.

The rub, as I discovered on a recent trip, is that it takes almost as much energy to free the oil from the sand as you get out in usable petroleum. So why are we spending billions, and pumping tons more greenhouse gases into the atmosphere?

Not many people have heard of the oil sands of Alberta. It's a bleak stretch of pine forest and tundra in northern Canada roughly the size of the UK - but just below the surface are almost double the oil reserves of Saudi Arabia, in the form of tar-like deposits. You will be hearing a lot more about the oil sands because by 2012, 20% of the U.S.'s oil petroleum supply will come from America's friendly neighbor.

So what to do? To give you an idea of the scale of investment in the oil sands: $20 billion has already been spent, and there's $100 billion more over the next few years. That could buy an awful lot of Toyota Priuses and energy-saving light bulbs.

Of course, it's not the oil company's fault that so much money is being squandered on the oil sands. They are following a business model which has been remarkably uccessful over the past hundred years, and which has enriched us all. And neither is it the individual's fault, as the oil companies sometimes like to claim (along the lines that, "We're only supplying what the consumer demands").

What's needed is some old-fashioned government leadership to recalibrate the basis of the world economy. The European Union has made some strides in creating a cap'n'trade scheme which penalizes polluters and rewards alternative energy and efficiency. In the UK, green issues have become a barometer of parties' progressiveness, with both the left and right vying to out-green the other. But the same can hardly be said of political debate in the U.S. Which of the candidates is prepared to put a post-carbon economy at the center of their manifesto? Who's taking the time to explain what that might mean for America? (Other than Gore, of course!)

Just imagine what could be done with US$100 billion to invest in our underfunded green industries. Imagine spending the trillion or so dollars that has gone on the Iraq war on a different kind of energy security. Now that's beginning to sound like that John Lennon song.