When I was a child a summer was considered hot if it was regularly 21 degrees (70 in Fahrenheit then). We'd hear stories of people who lived in hot cities in Southern Europe who had to move out for the whole of July and August because it was a crazily high temperature like 32 degrees (90F).
I can't believe that here in the UK I have actually been looking at rentals in Scotland for next summer, with the same idea in mind....