alt Hacker NewsOutside air temperature isn't an issue. It's not like people drop dead the moment it hits 40. The problem is that after a few days of that everything is heated up through and you have no place to escape it. That's new and hasn't been happening before.
But "somewhat longer heatwave" isn't as scary sounding as "HOTTEST EVER RECORDED TEMPERATURE IN $LOCALE!!!!!!" which is why all the scaremongers keep screaming the latter.