Sunspots are temporary phenomena on the surface of the Sun (the photosphere) that appear visibly as dark spots compared to surrounding regions. They are caused by intense magnetic activity, which inhibits convection, forming areas of reduced sun-surface temperature.
The solar cycle, or the solar magnetic activity cycle, is approximately an 11-year periodic solar variation (changing the level of irradiation experienced on Earth) which drives variations in space weather and to some degree weather on the ground and possibly climate change.
Correlations between the solar magnetic activity, (reflected in the sunspot frequency) and climate parameters on Earth have led some scientists to hypotheses that sunspot activity may be subtly linked to the Earth's weather. Suggestive correlations between solar activity, global temperature, and rainfall have been observed, and analysis of tree-ring data spanning centuries seems to show the presence of an 11–13 year cycle.
There is also geological evidence that the solar cycle may have been affecting terrestrial weather since Precambrian times. However, all these data have been disputed on statistical grounds, and there presently no consensus among scientists as to whether sunspots actually affect the earth's weather or not, or if so, how.
Europeans commenced observations of sunspots in the early 1600’s and continuous daily observations were started at the Zurich Observatory in 1849.
Early records of sunspots indicate that the Sun went through a period of inactivity in the late 17th century. Very few sunspots were seen on the Sun from about 1645 to 1715. This period of solar inactivity also corresponds to a climatic period called the "Little Ice Age" when rivers that are normally ice-free froze and snow fields remained year-round at lower altitudes. There is evidence that the Sun has had similar periods of inactivity in the more distant past. The connection between solar activity and terrestrial climate is an area of on-going research.
(2) Long-term Variations in Solar Activity and their Apparent Effect on the
Earth's Climate K.Lassen, Danish Meteorological Institute. Copenhagen