Ever wonder why there was a Little Ice Age or a Medieval Warm Period? Or why global temperatures increased slightly in the late 20th Century? On March 8 a preprint of Nicola Scafetta’s new paper entitled “Multi-scale Harmonic Model for Solar and Climate Cyclical Variation Throughout the Holocene Based on Jupiter-Saturn Tidal Frequencies Plus the 11-year Solar Dynamo Cycle” appeared with a sophisticated answer to all these questions. The abstract reads in part as follows:
A simplified harmonic constituent model based on the above two planetary tidal frequencies and on the exact dates of Jupiter and Saturn planetary tidal phases, plus a theoretically deduced 10.87-year central cycle reveals complex quasi-periodic interference/beat patterns. The major beat periods occur at about 115, 61 and 130 years, plus a quasi-millennial large beat cycle around 983 years. We show that equivalent synchronized cycles are found in cosmogenic records used to reconstruct solar activity and in proxy climate records throughout the Holocene (last 12,000 years) up to now. The quasi-secular beat oscillations hindcast reasonably well the known prolonged periods of low solar activity during the last millennium such as the Oort, Wolf, Sporer, Maunder and Dalton minima, as well as the 17 115-year long oscillations found in a detailed temperature reconstruction of the Northern Hemisphere covering the last 2000 years. The millennial three-frequency beat cycle hindcasts equivalent solar and climate cycles for 12,000 years. Finally, the harmonic model herein proposed reconstructs the prolonged solar minima that occurred during 1900– 1920 and 1960–1980 and the secular solar maxima around 1870–1890, 1940–1950 and 1995–2005 and a secular upward trending during the 20th century: this modulated trending agrees well with some solar proxy model, with the ACRIM TSI satellite composite and with the global surface temperature modulation since 1850…. Finally, the model predicts that during low solar activity periods, the solar cycle length tends to be longer, as some researchers have claimed.
In brief, Earth’s climate can be explained by solar cycles of 983, 115, 61, and 130 years. Scafetta’s hindcast is spectacular. Scafetta’s paper represents the most sophisticated effort that I know of to explain Earth’s climatic changes in terms of observationally-based science. Unlike AGW-based climatology it actually contributes to our understanding of this important topic, and in my view represents the beginning of the Copernican revolution in climate science that I recently advocated.