Spörer Minimum

The Spörer Minimum was a period of low solar activity which lasted from about 1420 to 1570 (some say 1450 to 1550). It occurred before sunspots had been directly observed, and was discovered instead by analysis of the proportion of carbon-14 in tree rings, which is strongly correlated with solar activity. It is named for the German astronomer Gustav Spörer.

Like the subsequent Maunder Minimum, the Spörer Minimum coincided with a time when Earth's climate was colder than average. This correlation has generated hypotheses that low solar activity produces cooler than average global temperatures, though a specific mechanism by which solar activity results in climate change has not been established.

Wilfried Schröder published a table of observed aurora borealis during the Spörer Minimum which showed that the solar cycle was active (see: Wilfried Schröder, Annals Geophys. 1994)

For details on solar activity see: solar variation.

The elimination of Viking settlements in the 1200s and the "Little Ice Age" in the 1600s argues for a 400 year cycle for the Maunder minimum. The Sporer Minimum is connected to this data. As such it has an impact on the present arguments regarding "Global Warming". (More correctly called the "Greenhouse Effect".) Supporters and opponents of the "Global Warming" argument need to consider this effect as it shows that data taken over a few decades has little relavence when one considers a cycle that has a 400 year (or more) period.