Dear Umbra,

Please help; my friend Kathryn Schulz, Grist’s managing editor, is sick of hearing about my guilt. I own an SUV. In my defense, I got it almost six years ago, when I was moving to the mountains and needed a big car with four-wheel drive to support my rugged, transient lifestyle, and it’s a littler model, not a Navigator. Life is funny, though, because now I live in New York, and the only thing I use my SUV for is commuting from my home in northern Manhattan to my job in Westchester. (My job, not just the commute, requires that I have a car.) With popular vilification adding to my own guilt about owning it, plus its mediocre mileage, I’ve been thinking about swapping it for a hybrid. Except that it’s all paid for, insured in a low-cost way that would end if I got something new, and I’m worried about its resale value. What should I do?

New York, N.Y.

Dearest Janet,

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How tragic, to live in New York City and drive to work. That’s just wrong. A new job seems in order.

Barring that, since my editor has already browbeaten you, we’ll assume all driving alternatives are impossible, including mass transit and carpooling. Good: We can skip over the preaching section and get to the interesting part — how to actually make the change from the car you have to the car you should have. Your guilt is not going to subside, because your vehicle is not growing more efficient. You gotta get rid of it.

Jeep trick.

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I think math is the answer. Do a little number-crunching and you’ll know the cost of owning, or dumping, your own personal polluto-mobile. Let’s say you have a 1997 Jeep Cherokee getting 20 to 25 miles per gallon, maybe 17 in the city. A hybrid would about double your mileage, thereby halving your gas bill. If you’ve got the typical American’s half-hour commute, you’re probably filling up twice a week at $20 a pop, so that’s $160 a month to drive to work. Theoretically you could save $80 a month in gas. On the insurance front, we need more information. Call several insurers, who may give you very different bids. The killer will be the car payments on a 2002 Toyota Prius; we’re looking at $250 a month minimum.

Let’s put this in the form of a word problem. Janet has an evil, evil SUV that gets half the gas mileage of a Toyota Prius. She would save $80 per month if she bought the new car, but her insurance would increase by $X and the car payments would be $Y. She would be willing to pay an additional $Z per month to ease her environmental burden and cease being the target of cruel badgering by the likes of Grist Managing Editor Kathryn Schulz. Should Janet sell her SUV and buy the Prius? (Hint: Is X + Y – 80 less than Z?)

And while we’re at it with the word problems, why did I say a 2002 Prius? Because you shouldn’t buy a new car. New objects require that new materials be mined and forged and new toxins be spewn about. Old objects don’t, and the bonus with old cars in particular is that someone else has already paid for the sheer newness. You’re getting the good years, and you didn’t take the hit to your wallet. By purchasing a used car, you’ll effectively put thousands of dollars in your pocket. A 2004 Prius costs more than $20,000; a 2002 with 30,000 miles is $14,500 in the Blue Book. Also, older cars are generally cheaper to insure than new ones.

And in case the bottom line isn’t sufficient motivation, I have two final inspirational thoughts: First, SUVs are quite dangerous, both for occupants and for non-occupants; and second, it is the duty of the conscientious affluent to lead the way in environmental consumership.