In the mid-17th century in the Swiss Alps, the inhabitants of Les Bois feared destruction by an unusual enemy: a glacier. The immense sheet of ice was slowly advancing through mountain passes to their village. In those days no one suspected that the danger was at least partly connected with the sun¿specifically, with a curious absence of dark splotches on its shiny surface 93 million miles away. Instead they assumed what any devout European peasant of those days would have assumed, namely, that God was angry and punishing humanity for its sins. The bishop of Geneva took action: he led 300 locals to the village and blessed the glacier. Some years afterward a warming trend forced it into retreat.

The Les Bois incident was one of the odder episodes of the so-called Little Ice Age, a prolonged cold snap that lasted many decades and possibly more than five centuries (experts disagree). Nowadays scientists are paying growing attention to the Little Ice Age for two reasons. First, it might shed light on subtle links between solar activity and terrestrial climate; curiously, sunspots largely disappeared between 1645 and 1705. Scientists have debated for years whether the sunspot drought caused terrestrial cooling¿and if so, why. If the Little Ice Age really lasted between 1300 and 1850 (as some scientists believe), then the cooling must have had several causes other than a transient lapse in solar activity.

This article was originally published with the title A Case Study for Global Warming.

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