In the past, this list has discussed the risk of sunburn and skin cancer
among paleo-dieters.  The following excerpt from an issue of "Northern
Perspectives" (http://www.carc.org/pubs/v25no1/voices.htm) may be of
interest:

<<Hudson Strait Inuit describe the sun as having a strong burning effect on
human skin, and it has burnt the faces of Belcher Islands hunters, a
phenomenon considered very unusual.  Between 1990 and 1993, the sun's heat
seemed to change; when a white, misty  haze in the higher atmosphere
screened the sun, both northwestern Hudson Bay and Hudson Strait Inuit
observed that insects and vegetation did not thrive and the sun was less
effective in melting the snow and ice.>>

Admittedly, I don't know exactly what these hunters ate (for example, Cree
hunters usually consume flour, sugar, and coffee, in addition to their more
traditional foods).  But it is impossible to deny that the atmosphere, at
least in the far north, has changed dramatically.

Cheers,
-- Aaron Wieland