Another points to a post by Duke scientist Bill Chameides, who says that "if white roofs became ubiquitous [worldwide], the extra energy needed for heating in the winter would exceed the energy savings in the summer." An innovative solution:It's true, a white roof doesn't make sense for every climate. I reckon it would work best in a very hot place like Phoenix that requires little or no heating during winter. My village in the Kalahari is actually rather temperate—yesterday it was freezing cold—but given that most people here don't have any heating and most houses are so poorly designed they retain little heat anyways, a white roof is still a decent idea.
A group of recent M.I.T. grads, as reported on the school’s web site, has developed a temperature-sensitive tile — it’s black when temperatures are cold and white when temps are warm. It’s a chameleon roof tile — so adding the Greek word for heat to the English word for the colorful lizard, they named their invention Thermeleon.
House design plays an important factor too. My parents' house back home, high in the Colorado mountains, has enough south glass that during winter it can get past 90 degrees during the afternoon, but it's well-insulated enough that they could probably get away with no night heating even with a white roof. During summer, a roof overhang (and heavy insulation) keeps the sun out so they dispense with cooling too. Not bad, eh?