Spörer Minimum
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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-13 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. It appears that low solar activity is correlated with cooler than average global temperatures, although the mechanism by which solar activity results in climate change is not yet understood.
For details on solar activity see: solar variation.
