It seems that in middle age Europe, burning women as witches gained currency largely because it was extremely cold. Record cold destroyed crops. People looked for someone to blame. Witches came in handy.

Emily Oster, a doctoral student of economics in Harvard, crunched weather data of years 1520 to 1770 and showed that there is a correlation between sharp drops in temperature and burning witches. Her study was published in the Winter issue of 'The Journal of Economic Perspectives' and is available through her website.

This story in NYT magazine might be easier going.