PHILADELPHIA (MCT) — Forget about staying together for the sake of the kids.

Researchers have a new reason: Do it for the planet.

An analysis of data on domestic relations and resource use in the U.S. and 11 other countries shows that divorce leads to more households — so more land gets built up and more building materials are used.

They concluded that in the U.S. circa 2000, there were about 6 million "extra" households due to divorce.

Worse yet, the households have fewer people in them. So on a per-capita basis, divorced residents consume more goods, use more electricity and water, and thus contribute to the emission of more greenhouse gases than those whose marriages are intact.

Lead researcher Jianguo Liu, a sustainability expert with Michigan State University's Department of Fisheries and Wildlife, wasn't all that surprised by the results, published in Monday's online version of the Proceedings of the National Academy of Sciences.

He and fellow researcher Eunice Yu concluded that in 2005, in the United States alone, divorced households could have saved 38 million rooms, 73 billion kilowatt-hours of electricity and 627 billion gallons of water if their "resource-use efficiency" had been comparable to that of married households.

At its most basic level, the efficiency math comes down to this: If you use energy to light a lamp and heat a room, are two people in it, or one?

It's a new twist on the notion that love conquers all: Can it also help fight global warming?

"Even those people who care dearly about the environment are not aware of the environmental impacts of divorce," said Liu.

To be sure, when Rabbi Margot Stein of Lower Merion, Pa., got divorced 12 years ago, "I was not thinking about the impact on the planet."

She was thinking about the impact on her children and, to a lesser extent, she drolly noted, "the wear and tear on my car" because she was going to be driving the children to their father's new home in New Jersey every other weekend.

Now, with the passage of years and a growing eco-awareness in society, Stein and her new husband have two hybrid cars. But the children's father has moved to California, so they fly to visit a couple times a year. Talk about carbon emissions.

Likewise, Orly Zeewy, a brand name consultant from Wynnewood, Pa., said when she and her husband split, the fate of the planet was the least of her worries.

"It's such a heavy-duty issue. When it happens, you don't think about the environment at all."

But now, she can see the point, and not just related to the per-capita use of resources.

Her children, now 10 and 13, also have two of just about everything, from clothing to toys. "You're basically setting up two households for the kids, so that they feel they live there."

These days, her youngest is learning to play the piano on an electric keyboard. Zeewy said she plans to buy him a piano, and when she does, the keyboard will go to her former husband's house.

Stuff "can get multiplied pretty quickly," she said.

Liu said his study is important because, with the number of divorces rising, the number of households is rising. It's even outpacing population growth itself.

In a 2003 study published in the journal Nature, he found that in some places, in the period from 1985 and 2000, households increased by 3.1 percent, while population only rose by 1.8 percent.

The divergence is expected to widen over the next 15 years, he said.