I once rode 240km at 40 celsius with humid air through sunny mid day in a hilly route, lightest gear was 39x25 then and there were hills going over 10%. Took 9 liters of liquid as I remember, and still I left home with some 63.5kg and got back with 59.5. I felt like flesh as falling from my bones. Not recommended.

​​​​​Still I commute year round to orchestra rehearsals that end 12:00 and I have a 30min ride with a backpack and a CELLO on my back, including very hot days, and a few times arrived home dizzy, a couple about to black out. I try to get my head under a tap with cold water as soon as I get off the bike in very hot days to avoid that. And thats how much I hate (not) driving in a traffic jam.

I live in Florianopolis, south Brazil, and guys in the north face waaay higher temps, still they ride. Rio is hot year round, and is still far from north.

I think the problem isn't really riding, it's stopping suddenly. Also climbing steep hills is a bad idea as theres no wind. Still I do it, I love climbing!