The point about humidity has already been made. I was astonished at how comfortable 115 degrees was in Phoenix. I went on a hike, no problem... Except that I carried a huge water bottle and the bottle ran out in an hour, so there's that.
In humid places, however, sweating is almost useless and you can suffer in mere 90F heat.
The other important point is that somehow folks in Singapore manage to survive, but in Singapore there's never any winter. I once heard a physiologist remark that humans can adjust to a wide range of temperatures, but it takes a few days for the body to reprogram itself for freezing ambient temperatures after spending months in roasting ambient temperatures. That's why the first few days of cold weather in the fall and winter feel really cold and everyone dons parkas, but when spring rolls around the exact same weather feels really warm and everyone puts on their shorts.
So maybe if I set out to live without A/C I'd get more used to it after a while. But the first few days are a killer, and at some point one just gets sick of being listless and warm and starts subconsciously looking for excuses to visit nice air-conditioned buildings.
it takes a few days for the body to reprogram itself for freezing ambient temperatures after spending months in roasting ambient temperatures
I noticed this empirically with myself whenever I traveled from California to Sweden in the winter. Coming to Sweden, I'd be cold all the time for the first couple of days, and then back in CA, I'd have hot flashes for a few days there. Nice to know that I wasn't imagining things. :)
I always assumed the heat-capacity of my bones took much longer to change temperature than the muscles and flesh of my body, but once it does, it lasts longer too.
The problem for most of us in the US is that we can't control how much they refrigerate moste public places. We keep our home ~80F(it makes going outside in south Texas much more comfortable), but that makes my office very uncomfortable at 74F.
You are making an assumption that the Middle East is nothing but a dry desert; the forecast for tomorrow afternoon in Jeddah, Saudi Arabia is 101 degrees with a 29% humidity.
Humidity's usually a bigger problem that the actual temperature. 100 degrees in drier parts of the southern US doesn't feel anywhere near as bad as 85 degrees in rainy towns up north.
It is approximately human body temperature. By design it should be slightly less, Farady intended 100 degrees to be the human body temperature but obviously suffered a light fever the day he took the measurment, so these days the human body has 96 degrees. 0 degrees Fahrenheit is defined to be the coldest it could conceivably ever be on the outside in winter, according to Faradays intuition when he decided that this is the coldest day ever. I don't know if he caught the fever during that measurement.
Fahrenheit. (It doesn't seem to be true that he intended 100 degrees to be human body temperature. It's possible that he specifically wanted the difference between body temperature and freezing point to be (a power of 2) degrees.)
Farenheit's "body temperature" was the axillary (armpit) temperature, and he set it to 96 degrees (on average) when creating his scale. And yes, your supposition about the divisibility of key numbers is right.
The difference that humidity makes cannot be overstated. When it's hot but not humid, sitting in the shade makes a big difference. When it's hot and humid, sitting in the shade just means its not as bright.
Stay out of the sun, sweat a little, you'll be fine. Arabs have it much worse.