I've seen several paintings depicting how people dressed in the antebellum South. They seemed to wear heavy, European clothing, such as large dresses. Why is it that the style of clothing seems so out-of-sync with the actual warm climate?

A few things.

Antebellum white southerners were well within the cultural norms of western Europe and the larger western Atlantic world. In fact, the elite among them imagined themselves the example par excellence of western civilization. So in cultural practice, including clothing and fashion, southerners found no cultural need to adopt anything less than what their ancestors and contemporaries used. Their connection of fashion currency and cultural initiative is reflected in their cultural marginalization of black slaves, in part through inadequate clothing rations and contentment in allowing some enslaved people the absolute minimum in covering.

Large parts of the south are rather moderate in weather—no different from New York, Pennsylvania, and Illinois—so we might not expect their clothing conventions to be much different.

Clothing consisted chiefly—depending on time, place, work, class, etc.—of linen, cotton, and wool. Linen and cotton, if worn well, is eminently breathable and wicks away sweat quite rapidly. Woolens (and cotton/wool or linen/wool mixes) are a bit more problematic in humidity (judged by yours truly, who is addicted to air conditioning) but is durable as work clothes (where cotton and linen wear out quickly) and are fabrics that look good in fashionable wear. Who wouldn’t want to express their wealth and aspirations with anything but broadcloth and silk?

I’d advise you not to transpose Godey’s Ladies Book fashion plates onto your vision of white working women in the antebellum south. Most white women, and many free and enslaved black women, used petticoats to create a modest bell shape, but did not flounce around in those ridiculous caged crinoline or hoop skirts on a regular basis. Some observers (Charles Woodmason, for instance, in the late colonial period) noted that lower class women frequently drew up skirts and exposed bare feet—likely to accommodate movement and ventilation (but Woodmason attributed it to lack of morals). But again, like with men’s clothing—women knew how to wear linen, cotton, and wool in ways that enhanced their breathability and cooling qualities.

See, for instance, this image from Hardin Taliaferro’s Fisher’s River Sketches: http://docsouth.unc.edu/nc/taliaferro/hardi215.jpg The artist was probably not making an anthropological record of Surry County, North Carolina residents… but still, Surry County was hardly a fetid swamp.

I suspect you’ll find Europeans in the Caribbean conforming to Atlantic world clothing conventions, and they’re in a far more inhospitable environment.

Sorry I don’t have any academic references on this. I can’t think of any scholarly work on this topic.

I guess my short response, then, is that antebellum southerners didn’t dress any different from anyone else because their climate wasn’t too different, and their cultural aspirations weren’t too different.