by Stan Cox

The financial industry is suffering convulsions because it gave too many people too big an answer to the question, "How much house can I afford?" But in looking over the mess left by the popped housing bubble, another question comes to mind, one of much greater consequence in the long run: "How much house can the planet afford?"

Since 1990, construction of supersized homes of 3,000 square feet or more has doubled, to 24 percent of new homes. Combine that with the shrinking size of the American family, and the result is that average floor space per person has grown by three times since 1950.

As the heavy-breathing real estate market reached its zenith, square-footage mania spread from the suburbs into cities, mutating into a doubly wasteful disease: teardown fever. Normal-sized, sound, comfortable houses were demolished to free up urban lots for the biggest, flashiest structures that could be squeezed in.

For homebuyers with more money than time, the big bust is no problem. The Wall Street Journal reports that luxury-home builders in places like Greenwich, Conn., and Aspen, Colo., are hiring armies of construction workers to complete 10,000-square-foot projects in about half the typical time.

Whether they're targeting the tastelessness of mass-produced McMansions bulked up on low-interest steroids or the ostentation of real mansions in enclaves of the rich, critics of the oversized-house trend usually focus on aesthetics. Monumental bad taste is indeed fascinating. But far more serious is the lasting environmental damage these incredible hulks do.

The manufacture and transportation of concrete to build a typical 3,000-square-foot house generate greenhouse gases amounting to 47 tons of carbon dioxide. And laid end to end, the pieces of lumber to make that house would stretch for more than four miles.

Wood, unlike concrete, gets some credit for being a "renewable" resource. The lumber and construction industries point out that they are taking greenhouse carbon out of the atmosphere and locking it into wood-frame houses. But that ignores the ecological effect of wrecking complex forest ecosystems to feed industrial wood production.

And in addition to requiring greater quantities of wood, concrete, plastics and copper, large houses have more volume to heat and cool, and more room for appliances and gadgets. Over a 50-year lifetime, a standard house pumps out greenhouse emissions amounting to 30 to 40 times the weight of the carbon that's socked away in its frame.

The bigger the house, the bigger the emissions. Based on University of Michigan figures, a typical 3,000-square-footer will emit as much carbon dioxide as would three -- count 'em, three -- 16-miles-per-gallon SUVs driven the national vehicle average of 12,000 miles per year over 50 years.

Energy consumption is being addressed in a limited way by eco-friendly construction. But a 2005 analysis in the Journal of Industrial Ecology concluded that a 3,000-square-foot, super-efficient house consumes 50 percent more energy than does a 1,500-square-foot house built only to mediocre energy standards.

Building new, resource-tight houses without curbing their size could make matters worse. Taking monthly energy savings into account, buyers will see that they can afford a bigger mortgage payment -- and more square footage -- with an efficient house.

The long-term effect of titanic houses parallels that of SUVs and pickup trucks. Sales of the biggest and least efficient vehicles might be ebbing, but those that have accumulated over the past decade will be out there by the millions, belching pollutants, for years to come.

And American families will be living in, heating, cooling and powering their current fleet of SUVs without wheels not for years, but for decades.

The economy will eventually shake off its post-bubble hangover and move on to new crises. The bigger challenge will be cutting carbon emissions deeply enough to avert catastrophic climate change. To meet that goal, one thing we will have to do is yank excessive square footage out from the tangle of current housing problems and declare it a luxury whose ecological costs we can no longer afford.

Stan Cox is a plant breeder at the Land Institute in Salina, Kan., and author of "Sick Planet: Corporate Food and Medicine," a book to be released later this month. He wrote this essay for the institute's Prairie Writers Circle. Reach him at t.stan@cox.net.