People often ask me, “Is your family still car-less?”

I myself am still car-less, but the family has changed. Amy and I have separated, undone our vows, and revised our coupledom into a parenting partnership. The divorce paperwork is underway.

Don’t worry: I’m not going to regale you with the emotional tale. This isn’t that kind of blog.

Instead, I’m going to do what the Daily Score does best: wonk out. In this case, about the carbon footprint of divorce. (No kidding.)

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    • Although the human implications of divorce are constant topics of discussion, divorce’s consequences for sustainability are rarely considered. That may not be surprising: Who could think about carbon budgets at such a time? (Not me, at first. But months have passed.) Still, the impacts of divorce on resource consumption are interesting.

    Sharing a home among more people conserves natural resources, for space and water heating, cooling, lighting, refrigeration, building materials, land, and all the tonnages of consumer goods that furnish our abodes.

    Eunice Yu and Jianguo Liu of Michigan State University recently published a study quantifying the global impacts of divorce on resource consumption. Among their findings were that square footage of home per resident as much as doubles after divorce, while energy and water use per person jumps by about half. Consequently:

    Divorced households in the U.S. could have saved more than 38 million rooms, 73 billion kilowatt-hours of electricity, and 627 billion gallons of water in 2005 alone if their resource-use efficiency had been comparable to married households.

    Thirty-eight million rooms!

    So far, my own experience mostly aligns with those norms. Eight years ago, I bought a modest house with Amy. Once we remodeled it, it accommodated our family of five. Since the separation in early January, however, it’s at half occupancy: me plus (in alternate weeks) my two highschool-age children plus (during semester breaks from college) my eldest.

    My household’s population dropped by half. Consumption of energy has dropped, too, but not by half. Comparing the resource use at my house before our separation (during the first half of last year) with resource use after separation (during the first half of this year), I find: per-person use of natural gas has increased by 36 percent (from 0.5 to 0.7 therms per day). Similarly, per-person electricity use rose 30 percent (from 3.2 to 4.1 kilowatt-hours per day).

    Repeat: I’m not saying that my total gas or electric bills went up. They went down. They just didn’t fall by half, like occupancy did. The reason is that, whether there is one person in the house or five, it takes a certain amount of energy to keep the water in the tank hot, the air in the rooms warm, and the ice cream in the freezer cold. In fact, my per-person bumps in gas and electric consumption were below the 50-percent norm that Yu and Liu documented.

    I beat the norm in water use and driving, too. My tap water use has fallen by half, in direct proportion to household population. We used 40 gallons per person per day before the separation; we use the same since. Meanwhile, our driving tally fell by more than half: before separating, the family used Flexcars to cover 2 miles per person per day; since separating, my half of the family racks up 1 mile per person per day. (Partly, that’s a reflection of my extreme attachment to my bike. But it also doesn’t reflect the 1,500 miles we drove in late August on our vacation in BC’s West Kootenays—not a car-less vacation.)

    Overall, our per-capita carbon footprint (shown below) more than doubled in the first half of this year, compared to the first half of last. Again: that’s per person, not total.

    Carbon footprint of divorce

    Because I beat the norm in power and natural gas use and slashed driving, this spike is probably temporary. The growth was all in air travel: I flew my kids to Ecotopia on the Hudson for a blow-out Spring Break—an adventure together to make some new, happy memories in our changed family. But the general point is still there: divorce boosts resource consumption.

    I’m definitely not saying people should stay married for the climate’s sake. In fact, Yu and Liu’s study may miss a point as large as it hits. The resource implications of divorce are all about the benefits of larger households, not just divorce. A slow if dominant trend for decades in prosperous places like Cascadia has been shrinking household size, and the causes are several. Compared with previous generations, we not only divorce more, we also move away from home at younger ages, stay single longer, have fewer children, and live longer. (On the other hand, we’re quicker to shack up, which conserves resources just as effectively as a marriage license.)

    Housing size hasn’t kept pace with household size, with the result that floorspace per person has grown. Rising affluence has also played a role, of course.

    This line of reasoning raises some wonkish questions for me:

    1. Have we designed buildings and zoning codes to be flexible enough to accommodate shifting family structures? For example, I’ve got room in my house now to install a rental apartment—a “granny flat”—but doing so would be illegal. At the same time, for reasons I don’t understand, my city offers few apartments or condominiums that can accommodate a dad and up to three kids. It’s all one- and two-bedroom units.
    • Are we making co-housing—organized sharing on a large scale—as easy as it should be, in our zoning and building codes, and insurance regulations?
    • Are we encouraging extended-family households to form? My brother and his wife share a house not only with their children but also with her parents. That’s a living arrangement that could be as relevant to our carbon-constrained future as it was to our dollar-constrained past.