To the long list of oxymoronic garments produced by our novelty-desperate fashion complex—corduroy culottes! Uggs in Malibu!—now add sleeveless coats. “They look great!” enthused Kasia Steńczyk, 27, a special-events intern at the Brooklyn Academy of Music who owns a whopping ten of ’em. “I just make sure I have a long-sleeved shirt under, or very long gloves. You can have a lot of long cute and diverse gloves with that type of coat.”

What’s the latest thing in fashion these days? Buying stuff that requires you to buy … more stuff. Think iPod accessories, those little clip-on gew-gaws now available for Hermes Birkins, and these baffling arm-exposing coats that appeared on the Marc Jacobs fall ’06 runway and have been spotted everywhere from high-end stores like Opening Ceremony and Miss Sixty to Forever 21, H&M and Club Monaco. “This silhouette is extremely versatile,” said Wichy Hassan, co-founder and creative director of the Sixty Group. “Wear it open for a stylishly casual look on warmer days or zip it up when the temperature drops!”

One can’t help but think the trend has something to do with increasingly erratic winter temperatures. For all the eco-conscious magazine theme issues and organic parties (waitresses in hemp dresses! greentinis!), the fashion industry’s basic response to Al Gore and his sufferin’ polar bears has been: Hey, New Options! Witness the spread in the August Vogue that blithely declared: “As the planet heats up, the jacket is stealing the coat’s thunder. … It’s got every age and sensibility stylishly covered.” We may not be able to un-melt the polar ice caps—but we’ll be damned if we can’t find a style solution in the interim.

“A short-sleeve jacket is a great option for unpredictable weather,” Ms. Hassan said. “The short sleeves remove bulk while simultaneously keeping the body warm, and allow the wearer the opportunity to showcase their outfit.”

Helena Fredriksson, designer of the eponymous label H Fredriksson, who has designed coats with shorter sleeves, called the category “the new in-between piece.”

“The short or no sleeve has felt a bit unpractical previous seasons with cold fall and winters,” she said. “Now in our current times of global warming, they do make more sense.”

And there are aesthetic advantages as well. “The three-quarter sleeve can give a more interesting shape in terms of design, and it’s easier to make sense with a volume three-quarter sleeve than a full length,” Ms. Fredriksson said. “It also gives an opportunity to show longer gloves, which I like, and it gives a less bulky feel when wearing. The short sleeve and no sleeve is not as interesting in terms of sleeve design to me, but I do like the simplicity of it.”

As do, apparently, many young women around the city, who’ve been tootling around on crisp winter days in bundled layers topped off by the abbreviated coats. “Like crotchless panties!” said Jenna Rathe, 22, a marketing associate, adding that (unlike the panties, presumably) they’re “mostly for show; very little function.”

“I have one and I love it!” said Lisa Rondholz, 31, who works in retail operations for the preppy fashion firm Paul Smith and sports an olive wool coat designed by her employer that retailed for $815. “It’s a three-quarter-sleeve swing coat, and although one may think it defeats the purpose of a coat, it really does keep me warm.”

“I love it; however, I bought it for really cheap at a ubiquitous store,” said Saehee Hwang, 30, the director of auction services at Mutualart.com, of the voluminous black number she got from H&M. “I did not want to spend a lot of money for a coat with no full-length arms.”

Of course, the style has its detractors.

“Those coats drive me crazy!” said Julie Gerstein, 29, a writer for OK! magazine. “I saw a woman today in a floor-length sleeveless fur coat. So tacky and wrong on so many levels.”

“It is an urban look,” argued Izzet Ers, the new designer for the London furrier Hockley, currently going gangbusters with the trend. “With fur the garments somehow look lighter and better proportioned.”

He had a suggestion for how to make it work: “Wear a cropped jacket with cropped sleeves with cashmere polo-necks showing longer sleeves!”

Is this a climate change thing? “I don’t think so,” Mr. Ers said. “Saying that, if you are going to a really cold country, one wouldn’t necessarily choose cropped sleeves.”

“I don’t think the trend has anything to do with global warming,” Ms. Hwang agreed. The appeal to her, she said, was that “I thought the shape was very retro.”

More retro even than the 1980’s puffer ski jackets and 1950’s “bracelet-length” coats that preceded it. As early as September 1918, it turns out, The New York Times ran a piece under the headline “Sleeveless Coats Still Liked.”

“Some novelties are appearing in the Fall models, among them the sleeveless coat made of a tan leather such as trench and aviation coats are made of,” the paper declared. “This makes a very smart coat for sports wear and seems in a fair way to become quite a favorite.”