Forget the temperature and look at how many weeks before or after Summer Solstice it is (June 21+- a day for here).

Summer Solstice in June is the day the Sun is at it's highest point in the Northern Hemisphere and the most light from the Sun is reaching the earth North of the Equator.

Right now the Sun is as powerful as it is at the end of July, forget the outside temperatures. You think you won't get sunburned if you go out in late July if you are pasty white and don't use sunscreen? You WILL ... just as you will get burned right now too since the sun is producing the same amount of rays hitting the Northern Hemisphere NOW as then.

Why people associate outside temperatures with the risk of Sunburns is beyond me. It doesn't work that way and never has. It has to do with how much SUNLIGHT is reaching the earth, NOT the outside temperature.

(mid winter sunlight with light reflecting off the snow can really burn you, which is why people wear sun screen on their faces when skiing in mid winter)