Long Beach, California—Paul Gilding wants to scare us. He wants to scare us into acting before it's too late. "The Earth is Full. Full of us, full of our stuff. Full of our waste," he said during his TED talk. In financial terms, we live on the Earth like we are spending 50 percent more than we earn.

Gilding has been agitating for sustainability long before most people became aware of the concept, and he has a bleak message for the prospects of the free market. Our economy is not sustainable, and woefully unprepared for hitting the Earth's limits. It's not just a little bit over the limits of sustainability, either—we are way beyond that.

But humanity has a tendency to think it is only getting started. We imagine economic development magnitudes greater than we have now. This is the very same growth we rely on to solve poverty, to make life better. But open-ended growth is simply not possible, Gilding argued. So, instead of counting on this train never stopping, we might be better off assuming it's going to go off the rails. And he used his TED talk to try to drive the idea home.

"The idea that we can smooth these transitions" through economic difficulties so that "9 billion people can live in 2050 a life of abundance and digital downloads," he said, is "dangerously wrong." The system will break down, it will stop working for us, and we're not doing enough to prepare for that. And it's not like we haven't seen it coming. We've had 50 years of warnings from scientific analyses. And, if that weren't enough, we've had economic studies showing us that it would be better for us to not to wait—that it will ultimately be even more profitably for us to act sooner—but we're doing very, very little. Our eyes are still on the short term, whether it's food, water, or waste.

Gilding argued that we have to have our best economic minds, our best entrepreneurs, communicators, and leaders, shift their thinking to one unassailable fact: "We cannot have infinite growth on a finite planet." We need that kind of intellectual backing because people simply do not want to believe this. They have amazing faith in technology, that it will help us solve these problems somehow, someway. Although technology has overcome many once-thought impossible problems, Earth is a finite resource, and technology has never had to overcome the finite nature of the planet we live on. We have to prepare for the end of growth.

"The most important issue we face is how we respond," Gilding notes. "The crisis is now inevitable. The issue is how we react." To be sure, it would be better to react now than latter, in part because we don't know for sure what bubble will pop first. Gilding asked his audience to imagine what happens if the carbon bubble bursts. Nations will battle not just for gasoline, but food and water. Thirty percent unemployment in America could be the norm. It will fundamentally change society. It will fundamentally change how we think of the future.

Yet our national dialogue is fixated on gas prices. Our assumptions about the future presently have little bearing on what will actually happen when the lights go out on the global economy. We are hiding from ourselves.

And this is where Gilding saw the value of fear. The truth is, we should all be afraid. Fear is an appropriate response to danger. If we harness that fear now, we still have time. If we wait until the lights are out, it's going to be nasty. Tapping into fear is important. The fact is, we need to change how we feel, because only that will change how we act. Free market fundamentalists are wrong; we do not have limitless resources, and if growth is the only solution we have to offer to our problems, we will eventually be terribly wrong.

"This could be our finest hour," Gilding concludes. But we must start thinking and planning now for the end of growth. And to do that, we probably need to be afraid of the alternatives.