IT BEGAN with the gift of a vintage rabbit fur coat. Not for me; for my friend. Really, my friend. Who was faced with a modern-day fashion dilemma. For most of her life, she had been opposed to fur on the grounds that it was cruel, unnecessary, gauche.

But this coat was so adorable . . . and so thin . . . and so warm. And it was vintage. Which means that, when you think about it, the rabbits were already gone.

And when you compared her fur to the alternatives - the fleece sweatshirts that don’t biodegrade, the “vegan leather’’ jackets made from PVC - the winner of the do-good outerwear derby wasn’t entirely clear.

As the Copenhagen climate talks draw to a close, it’s worth noting how much our culture has come to value the merits of green - both because people truly care about the Earth, and because caring about the Earth has grown so chic. But the actual rules of green living are surprisingly hard to navigate, not least of all when it comes to choosing clothes.

Do you want to save the animals or the planet at large? Do you focus on your outfit’s origins, or its afterlife? Do you submit to the harsh realities of the food chain? Or do you fret about the death of cows and bunnies while the planet weeps over your petroleum-based pleather?

The decline of the anti-fur stigma shows just how complex the rules have become. Jo Paoletti, an American studies professor at the University of Maryland, recalls that she once gave away a vintage fur cape because too many people glared at her at parties.

But over the last decade, many fashion houses have begun to embrace fur again. Onetime PETA models Naomi Campbell and Cindy Crawford have fronted ad campaigns for high-end furriers. Bravo’s Rachel Zoe wears luscious fur vests in public with no apparent guilt. And when my friend started asking around about her coat, she found a lot of people who weren’t appalled by rabbit pelts. Someone told her that Canadians wear fur because it’s warmer than any alternative. Someone else pointed out that people eat rabbit, so why not use all of the rabbit?

These days, the fur industry seems especially emboldened. The Fur Council of Canada has launched an ad campaign declaring that “Fur is Green’’ - in the sense that trappers kill animals who might have overpopulated forests, and that fur breaks down in landfills, unlike performance fleece. The council also takes pains to claim that trappers and farmers treat animals humanely, a byproduct of shame for which animal-rights activists deserve some credit.

But PETA has devolved into self-parody of late, chastising the president for swatting a fly, putting too many naked models in lettuce bikinis, acting overzealous with red paint. When a furrier from Brookline died last month, his obituary ran after his funeral service had taken place, presumably to stave off protesters who had vandalized his store. It’s easier to sympathize with his family than with any friend of the minks.

When it comes to fashion, it seems, everyone has to decide how and when to be cruel, where to stake her own spot on the fur-to-leather-to-meat-to-clean-air continuum. Paoletti points out that, however “natural’’ fur may be, the fur-production process still takes a big environmental toll. But then “greenwashing’’ is rampant in the fashion world today, she says: Fabric made from bamboo is marketed as earth-friendly, but it’s chemically identical to rayon, and manufactured in a way that’s decidedly bad for the planet.

Besides, Paoletti notes, you can make a bigger impact with your laundry habits than with any piece of clothing you buy - and you can also help the Earth by buying fewer clothes in general. In that context, vintage fur could either be the world’s biggest cop-out or a brilliant solution, a way to embrace recycling and luxury at once.

Paoletti isn’t passing judgment, though she wishes my friend could wear a button on her rabbit coat that says, “It’s vintage!’’ Style still has a lot to do with what other people think. But my friend figures that if anyone looks sideways at her coat, she’ll simply tell them it’s a fake.