Throughout the past century, while greenhouse gas (GHG) abundances have been steadily increasing and influencing Earth’s climate, the Sun has remained relatively bright and quiescent. Solar cycles have been steadily active, with instantaneous sunspot numbers at solar maximum exceeding 100 in every cycle since 1893 (Cycle 13).
The climate warming we have experienced since the beginning of the modern industrial era cannot be attributed to the Sun. However, the recent minimum between Cycles 23 and 24, and NASA predictions of a substantially lower sunspot number at 2013 solar maximum suggest that the Sun’s recent bright and quiescent period may be ending.
Both autocorrelation studies of recent solar cycles and studies of solar analogs in nearby field stars suggest a greater than 40 percent chance of the Sun entering a new Maunder Minimum sometime in the Twenty-First Century.