Too much sun causes melanoma, a skin cancer that can be fatal if left untreated. In fact, Mazda has begun slapping warning labels reminding owners to use sunblock on the windshields of its MX-5 convertible as well as its cars, SUVs, and minivans equipped with a sunroof. If the Mazda Kabura Concept that debuted at the 2006 North American International Auto Show were to make it into production, it wouldn’t get that warning label, because it’s got a fixed glass roof over the front seats through which no UV rays can penetrate.