Sunburn isn't heat burn. Has nothing to do with temperature really.I know I got burnt on my arms & legs in the Snowy high country over Christmas, & I don't here with much higher temps ( not really burnt, just red for a few hours then went a bit darker )
If I'm outside in the winter my face can become just as tanned in the summer. Add in the fact in winter you have the snow reflecting sunlight back up at you, you can be getting twice the amount at one time. Usually just limited to my face though since I'm wearing many, many clothes a lot of the time
Could easily have to do with day length as well. Yeah northern QLD has some harsh sun, but it has shorter days. The sun here, in comparison, might not feel like it's cooking you alive as often, but you can be out in it for hours longer than FNQLD people ever could be. Plus I want to say there's something about refraction of sunlight to reach the farther latitudes that can have a different effect than the more direct angles near the equator.
Probably so many factors we've never even discovered yet.