The best clothing for a hotter environment is a tad counterintuitive, because it's less comfortable in the short term... you want full sleeves, full pants or a long skirt/kilt/toga/whatever (I'm reasonably certain that if heat waves continue cranking it up, these are going to become a unisex thing, whatever we're gonna call them...). You want everything loose so there's room for evaporation to happen (it's your body's natural swamp cooler), you want large openings everywhere so the air can ventilate, and you want lighter colors that reflect. You'll also want to cover your head, preferably withsomething wide (and/or includes the little neck covering flap deal) that creates a lot of shade, but it's currently more common in deserts to see less shade producing scarves/wraps.
You'll feel hotter in the immediate, and overdressed, but you'll overall be absorbing less energy from direct sunlight, and that means a more stable amount of body heat overall, and less risk of things like cancer.
I wear loose t-shirts, jeans, and a wide boonie/fishing hat. Less overall clothing is better, but more coverage is also better. Gotta find that balance is all.
TL:DR, the clothes most people associate with the Middle East... clothes that are worn by people who've dealt with a hotter climate for millennia. The white robe looking getup is what's gonna work best in a hotter climate.
