2. Solar Variation

Sunspots are magnetic storms on the sun's surface. Photo courtesy of Wikimedia. 

The amount of energy the sun radiates is variable. Sunspots are magnetic storms on the Sun's surface that increase and decrease over an 11-year cycle. When the number of sunspots is high, solar radiation is also relatively high.

However, there is no known 11-year cycle in climate variabitlity. Why did it turn up on climatologists' radar then?  The Little Ice Age corresponded to a time when there were no sunspots on the sun. Climatologists think that sunspot activity, when combined with other causes, can alter global temperatures.