You should be able to do the math on this one, with some qualitative adjustments. And you have to define "green" of course. Google "define green" to see just how much disagreement there really is - even among green folks. Look at a transcript from one of the ecology conferences to see how little quant is involved in deciding what's important.

And you really should include safety. GM said at one point that a new car (say 2000) was 1000-lbs heavier than it would have to be because of the safety equipment. Yeah, GM has a bias. But it's still likely to be heavier & so takes more fuel to move. But human life is important and injuries have an impact on the environment - medical equipment, chemical waste, etc.

I keep or help keep several 240s on the road. They didn't qualify as clunkers during the 2008 government program. 22-26 MPG isn't very good these days. The emissions are probably high relative to mid-2000s cars. I don't drive much.

Would I be a better carbon citizen if I traded the 240 on a new car? I have trouble believing that the environment would be better served by my adding a car to the driving pool. But, again, it would take a lot of math.

Net though, I don't kid myself by believing that I'm doing the world an environmental favor in my 240. I drive it because it's cheap & reliable; and it can be banged up and not look too trashy.

For the record, I think I'm contributing more by not spending $100s each Xmas at Wal-Mart et al for things that people will discard in a few months. 1/2 of some retail sales are between Thanksgiving & Xmas. I'd probably look there, at the clothing industry worldwide, and at America's pathetic public transport systems before I worried about folks driving around in 240s.

And, same as you, I'm staying inside in the OH snow.
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240s: 2 drivers and some parts cars