The heck is “heat index”

A heat index is not an actual temperature reading. This is disingenuous and people whom don't want to believe in things like climate change will latch on to and discredit people for things like this.

Thanks, but the point is it needs to be the main link in the posting

More like "image posted without a link to the source to verify it"

I know. There's also this:

https://en.wikipedia.org/wiki/Wet-bulb_temperature

But mentioning the actual temperature is less misleading.

With a dry air you can support more than 70º (eg in a Sauna), but with high air humidity, which evite the evaporation cooling by your sweat, even 50ºC result lethal in a short time,

Over 90C dry, 50C wet, 10-15 minutes. Longer/hotter if you take dips in cold water to cool down or if you're Finnish. They sometimes go over 100C, they're used to it.

Is hot but Washington Post article says the temperature in recent weeks has got as high as 51C and all time max is 54C. Where are you getting 58C from?

Choking off that straight would absolutely grind to a halt the economic engines of every asian major power faster than they could find a solution to exporting the hundreds of millions barrels a day though that hostile environment.