Solar cycle length and 20th century Northern Hemisphere warming: Revisited

Abstract

It has been suggested that the length of the solar cycle (SCL) is related to solar forcing of global climate change [Friis-Christensen and Lassen, 1991]. Although no physical mechanism had been proposed, the relation seemed to be supported by interesting correlations with several paleoclimate records and, separately, with the 20th century Northern Hemisphere instrumental record. Actually, what has been correlated is the quasi-sinusoidal Gleissberg cycle which is slightly greater in the 18th century than in the 20th century. Using the pre-industrial record as a boundary condition, the SCL-temperature correlation corresponds to an estimated 25% of global warming to 1980 and 15% to 1997.