In a few months, the California Supreme Court will rule on whether California’s same-sex couples can marry. The Attorney General argues that California’s law favoring heterosexual marriage is based on procreation and tradition, and that domestic partnership is essentially the same as marriage.

Opponents argue that same-sex couples often have children, and that domestic partnership is separate and inherently unequal.

Yet another argument in support of same-sex marriage might be protection of the environment. The state’s two top environmentalists (Gov. Arnold Schwarzenneger and Attorney General Jerry Brown) can certainly agree that promoting marriage and families is better for the environment.

Some letter writers have questioned why single people, especially those who live alone, should have to subsidize married or domestically partnered persons. After all, can’t two live more cheaply than one? Shouldn’t couples be subsidizing couples?

But now there’s proof that married and domestically partnered persons should get some consideration…. It’s because they consume less energy and thus contribute less to global warming.

The National Academy of Science issued a report in late December concluding that married households, per capita, consume less energy than divorced and/or single households. The study compared married households (with at least two or more people) with divorced/single households (with one adult or more). The divorced households use 46 percent more electricity and 56 percent more water than married households.

As for physical space, the study reported that the average divorced/single household in the U.S. offers a sprawling 3.7 rooms per person, while married people and their kin must make do with 2.5 rooms per person. In short, the study concludes that persons who live alone have bigger carbon footprints.

Census figures from 2005 show that 26 percent of Americans live by themselves, which is higher than ever before. In 1970, it was 17 percent.

The reason all of this is important for the Court is that it provides a rational basis as to why the state has an interest in supporting unions and encouraging folks to stay together. These are the considerations a court brings up when addressing an issue. Why shouldn’t the state do all that it can to support people living in environmentally friendly housing units? In fact, if the California government is worried about overcrowding, as population climbs to 40 million, maybe encouraging people to live together without producing children would be better for the environment.

Otherwise, as Meghan Daum wrote recently in The Los Angeles Times, people nowadays may prefer to live alone. Daum suggests that living alone is a choice we’ve all grown entitled to. Some of us need to live in a home built for five because we need at least five rooms just to house our clothes.

Having your own place accrues status points, she says. It’s much better than living indefinitely with your buddies, or your roommate(s) from hell.

She says that a lot of us “still think life is not sustainable without a walk-in closet the size of Gambia.”

I raise all this because California faces a water shortage, our electrical supply is questionable, and we’re likely either going to have gas rationing or those who can afford it will pay more at the pump.

And when this happens, state and city officials may have some interesting laws designed to get us to conserve. Just as the Mayor of San Francisco has proposed a tax on sugary sodas, could there be a “single” tax or a room tax? If there is a way for a city to levy a tax (and get away with it), we’ll be seeing it.

There’s also a certain irony to all this. This past year, we’ve all heard about those horrible mini-dorms near San Diego State University and in Pacific Beach. From an environmental standpoint, those students are using less energy and water than their neighbors.

In fact, it was in 1979 that the California Supreme Court struck down zoning laws that prohibited so called “mini dorms.” The case involved a Santa Barbara woman whose home operated as a “commune.” She rented out rooms to single people, not surprisingly, they were gay or lesbians.

The cities, including San Diego, argued that preserving the “single family” nature of a community was more critical than the association rights of individuals, even though in the ’70s gas rationing and energy conservation were realities. And that’s what led the court to strike down such zoning laws. They were simply irrational, given the needs of the state.