There are two reasons to use sustainable materials and undertake energy retrofits. One is a cold, hard energy-payback calculation; the other is a warm, fuzzy save-the-planet attitude. Often the payback period is too long, so a lot of homeowners opt out. And to many, the second reason is wishy-washy and completely ignores economic reality.

A recent dinner conversation turned these arguments on their head. I was talking with Eric Zencey, an old friend who for 30 years has been thinking and writing about something called “ecological economics.” This small but growing school of thought would replace modern “infinite planet” economic theory with one that acknowledges that an economy is not a perpetual growth machine.

I’m not an expert, but here’s the gist of it. An economy extracts matter and energy out of the environment and discharges waste matter and energy back into it. Some of these resources — wood, soil nutrients, animal and plant life — are renewable and could be sustainably sourced. Others — coal, gas, oil, copper — are finite and in diminishing supply. The goods and services we create from these resources don’t reflect the true costs of their production, largely because ecological costs are ignored. That underpricing leads to poor economic decisions.

To give a familiar analogy, imagine a remodeler who doesn’t include the cost of his spouse’s labor as bookkeeper. The omission makes overhead seem lower than it really is. As long as the spouse continues to work for free, the system works, but when that labor has to be replaced by hired help, the true cost is revealed. Unless prices go up, the business fails.

The solution for the remodeler is simple: include the cost of a spouse’s labor in overhead. (Include your own labor, too, while you’re at it.) On a much grander scale, there are ecological costs to modern life and commerce that go uncounted. When we build a dam, we lose a trout fishery. When we cut a forest, we lose erosion protection.

At one point, Eric said that whether all costs are accounted for or not, a lot of us try to act as if they were. And it struck me that those warm and fuzzy customers who want to save the planet are doing exactly that. So are those who, with every piece of paper they recycle, acknowledge the value of the tree. They can’t always articulate it, but their behavior signals that they have already started to create a new economy.

The fact that someday the oil will run out should inform today’s decisions about how and what and where we build. Before it runs out, we need to use less fossil energy to keep warm and get from place to place, and more to build a post-petroleum economy.

Right now, solar-energy looks pretty good. The sun isn’t infinite, but it’s close: estimates are that it will keep producing energy for another 5 billion years.

That’s warm and fuzzy enough for me.

—Sal Alfano, editorial director, REMODELING.

Read two recent articles by Zencey, on the History New Network site and in The New York Times.