[irdc]

A wet bulb event occurs when the combined temperature and humidity (the so called "wet bulb temperature") exceeds the limits of human physiology, causing humans to overheat and perish even in the absence of any activity beyond basal metabolism.

I'm not sure it'd look like the "bodies in the street" image GP likes to call up, but yes, a prolonged wet bulb event would result in mass casualties.

[truculent]

Earnest question: what makes you doubt the depiction? Trust in infrastructure or institutions?

[irdc]

The widespread availability of air conditioning plus the fact that we've had such events before on rare occasions (see https://en.wikipedia.org/wiki/Wet-bulb_temperature#Highest_r...) and we didn't see bodies piled up in the street back then.

[RetroTechie]

True.. so far.

All that's needed is an intersection of high-humidity heat wave + densely populated area + extended power outage.

And/or too few buildings that have A/C or other places to escape the heat like swimming pools, metro tunnels or whatever.

Probably more likely to occur in less-developed areas like India or Africa. But regardless, could happen in many places. Just a few degrees might be the difference between 1000s or 100k+ deaths.