So you faithfully recycle plastic and paper, turn down the thermostat a notch during the winter and buy only organic produce? If you live alone, your lifestyle may still be damaging the world’s natural resources.

Smaller households around the globe are posing serious challenges to biodiversity and increasing fuel consumption, according to a study published earlier this year in the British science journal Nature. Additional households require more natural resources for construction, cooking and heating, researchers at Michigan State and Stanford Universities concluded. As a result, even in countries where population is decreasing, both the numbers of households and environmental degradation are on the rise.

Reversing the situation will require that people reconsider their lifestyle choices and that governments offer incentives to do so, says Dr. Jiango Liu, a systems ecologist at Michigan State University and the lead author of the Nature article.

The increasing prevalence of divorce, longer life spans and fewer multi-generation households are the main factors contributing to smaller household size. These demographic trends kick off a vicious cycle, Liu says.

“Smaller households result in lower efficiency of resources,” he says. “You need land to build a house, and you cut down wood for building materials. In turn, this affects the wildlife that depends on the habitat you’re getting rid of.”

Liu says his study illustrates that personal choices and environmental health are intertwined. He and three other researchers analyzed household dynamics in 141 countries. Among them are 76 biodiversity “hotspot” countries -- including Australia, Brazil, China, Italy, Kenya and the United States -- that contain high density areas of animal and plant species threatened by human activity.

In these biodiversity hotspots, researchers found that between 1985 and 2000, the number of households grew annually by 3.1 percent, even though the population increased by only 1.8 percent. At the same time, the average number of people occupying a single dwelling dropped from 4.7 to 4. Had average household size remained the same in hotspot countries during this 15-year period, 155 million fewer households would have been created overall, according to the study.

Liu analyzed household size along with Stanford researchers Paul Ehrlich, Gretchen Daily, and Gary Luck.

Americans and others need to realize that sharing living space doesn’t necessarily mean sacrificing privacy and personal freedom, Liu stresses.

“Once people realize there is a problem, they begin to do something about it,” he says. “You can still have your backyard for cookouts, but share it with neighbors. And architects can design living spaces that allow families to both share and maintain privacy.”

In addition to the environmental benefits of such an arrangement, Liu says, there are social and economic advantages “we tend to ignore.”

“So many people, especially older people, feel social isolation,” he notes. “It’s nice to have someone to talk to.”

As for the economic benefits of sharing a home, Liu says his friends are an excellent example. “A woman lives in their extra bedroom in exchange for watching their child,” he says.

Both local and federal government policies can go a long way to encourage cohabitation, Liu adds. In fact, he and fellow researchers are already working on a follow-up study, funded by the National Science Foundation, that analyzes the social reasons more people choose to live alone. They plan to develop policy recommendations to reverse the trend.

For instance, government could offer incentives like lower property taxes for homeowners who rent out space in larger houses, Liu says.

“Of course, we can’t expect 100 percent of all people to do this. It is a challenge, but some change can be made simply by educating people about the problem,” he says.

The study has touched a nerve for environmentalists, sociologists, biologists and political scientists. A publisher has already asked Liu to expand the Nature article into a book. Liu has been invited to talk about his research on numerous radio shows, and scores of newspapers have picked up on the journal article.

Carl Haub, a demographer for the Population Reference Bureau, a Washington-based nonprofit that tracks international population trends, says that while he agrees with Liu’s research, the widespread publicity troubles him.

“It could create a perception that we no longer have to be concerned about population size,” he says. “Birthrates in many countries remain high enough that sheer population is still a major issue for the future.”

In countries like India, Haub says, “it is going to be a while before household size is more significant than population.”

And the United States is the only developing country where birthrates are increasing, Haub notes.

“Many people think it is simply changes in lifestyle resulting in people moving to the suburbs and developers building houses on farms,” he says. “But the United States is gong to add 150 million people over the next 50 years.”

The factors driving smaller households -- as opposed to decreasing population -- may be more appropriate for researchers to study, he says. Since the 1950s, incomes and consumption have risen significantly around the world, he points out. “There are a lot of other things driving losses in biodiversity,” Haub says.

Haub agrees with Liu that governments should enact policies encouraging more people to combine households. But, he stresses, even the best zoning laws and tax incentives will have a limited impact. “Eventually, sprawl is going to come.”