latitude & gdp

I was having a hard time getting work done during this week's heat wave in SF. I told the kids that there is a strong correlation between the latitude of a place and its economic development. It seems that the hotter it gets, the slower people do things. Even within specific countries (I am thinking of Italy's Norrth & South, for example) the more "tropical" regions are less "developed". Of course, too much cold is also a problem: not much development in Siberia or Antartica... And, air conditioning might change this over time...