- Nicola Scafetta
- Dipartimento di Scienze della Terra, dell’ambiente e delle risorse
- Università degli Studi di Napoli Federico II, Napoli
Solar activity and climate change are characterized by specific oscillations. The most relevant ones are known in the literature as the cycles of Bray–Hallstatt (2100–2500 year), Eddy (800–1200 year), Suess–de Vries (200–250 year), Jose (155–185 year), Gleissberg (80–100 year), the 55–65 year cluster, the 40–50 year cluster plus bidecadal and decadal oscillations, and others.
Herein I review some of my publications on this topic and show that these oscillations emerge from a specific set of planetary harmonics – the orbital invariant inequalities – produced by the Jovian planets (Jupiter, Saturn, Uranus, and Neptune) and other basic astronomical frequencies related to the soli-lunar tides and orbital period of the planets. The result suggests that both solar activity and climatic changes are modulated by harmonic planetary forcings. Since these same harmonics are also found in the climate system, they can be used, in first approximation, to model and forecast climate change.
As an example, I briefly comment and update a semi-empirical model for climate change proposed 8 years ago by the author (Scafetta, Earth-Science Reviews 126, 321, 2013), which uses some of the above astronomically determined oscillations in addition to volcanic and anthropogenic components. The proposed model’s result continues to surpass the performance of the CMIP5 models used by the IPCC, in particular after 2000, in reconstructing the global surface temperature record.
When the 11-year solar cycle was discovered, Wolf (1859) well understood the physical problem that this discovery posed and hypothesized that it could emerge from a planetary influence by Venus, Earth, Jupiter, and Saturn. The idea was that some type of periodic forcing linked to the orbital motion of the planets (for example, gravitational tides) could synchronize the internal dynamics of the Sun by causing it to vary harmoniously at specific frequencies. The 11-year solar cycle is today known in the scientific literature as the Schwabe sunspot cycle.
The theory has always been taken with a certain skepticism because the distance of the planets from our star is so great that the gravitational tides induced by them on the surface of the Sun are tiny. They are, in fact, so small – that is, of the order of a millimeter or smaller – to be considered entirely negligible: see, for example, the discussion in Scafetta (2012a). However, so far nobody has been able to explain in an alternative way why solar activity oscillates with a cycle of around 11 years.
In fact, the most modern theories on the solar dynamo assure us that the solar activity should oscillate, but they do not tell us that it must oscillate with the observed period and phase (Tobias, 2002). These models are appropriately calibrated to obtain something that vaguely resembles reality (Jiang et al., 2007). Their inability to predict the main cycle observed in solar activity is also recognized by the same critics of an astronomical influence on the Sun (cf.: de Jager and Versteegh, 2005). Therefore, what is causing the Sun to oscillate with a period, although variable, around 11 years remains a great mystery.
In the last 50 years, many improvements have been made, and our knowledge about solar activity has significantly increased. It has been discovered, for example, that the 11-year solar cycle is only one of the most evident and macroscopic solar cycles.
In fact, it is a variable cycle, as mentioned. Longer and shorter solar activity oscillations have also been observed. For example, the 11-year solar cycle almost disappeared during the great solar minimum of Maunder from 1645 to 1715; period during which the climate on Earth cooled significantly by experiencing a Little Ice Age (Eddy, 1976). Other grand solar minima were observed during the Dalton minimum (1790-1830), around 1900-1920, and another one is expected between 2020-2040 (Scafetta, 2012b). This pattern makes an oscillation of about 115 years (cf: Scafetta, 2012b; Scafetta, 2014).
In fact, several studies have determined that, in addition to the Schwabe’s 11-year sunspot cycle and its associated 22-year Hale magnetic cycle, solar activity is characterized by several longer oscillations. These are now known in the scientific literature as the cycles of Bray – Hallstatt (2100–2500 years), Eddy (800–1200 years), Suess – de Vries (200–250 years), Jose (155–185 years), from Gleissberg (80–100 years), the 55–65-year cycles and others: see the numerous citations in Scafetta (2020). Identical fluctuations are also observed in climate records, suggesting a close link between solar variability and climate.
These results, of course, have made this research not only fascinating from an astrophysical point of view, but also very useful because it can be used to develop models able to predict climate changes: see, for example, the analyzes proposed in Neff et al. (2001), Kerr (2001), Ogurtsov et al. (2002), Steinhilber et al. (2012) and other studies including those proposed by Scafetta and collegues.
Therefore, understanding solar dynamics has become increasingly important. Due to the inability of traditional solar models to explain the observed solar activity changes, in the last twenty years several works have appeared for re-proposing and modernizing Wolf’s 1859 idea of a link between solar variability and planetary motions, which still today appears to be the only one capable of explaining solar oscillations.
Experimental evidence of a planetary influence on solar activity ranges from the discovery that various solar flares and other phenomena of a certain intensity occurred during specific planetary alignments (Hung, 2007; Bertolucci et al., 2017; Morner et al. 2015), to the observation that there is a certain spectral coherence between solar records and the functions deduced from the orbital motions of the planets of the solar systems. One of these commonly used functions is the motion of the sun relative to the center of mass of the solar system, which must, however, be understood as a proxy for conveniently determining the natural gravitational oscillations characterizing the solar system (Fairbridge and Shirley, 1987; Abreu et al., 2012; Scafetta and Willson, 2013; Scafetta et al., 2016; and others).
One of the author’s latest work (Scafetta, 2020) identifies theoretically a set of planetary harmonics which appear to be responsible for the observations. These derive from the synodal cycles of the great jovian planets (Jupiter, Saturn, Uranus and Neptune) and their combinations or mutual beats. The main physical characteristic of these harmonics is that they are invariant with respect to any rotating reference system such as the sun and the heliosphere. This property is necessary to activate the synchronization processes between weak external harmonic forcings and an oscillating dynamic system, as initially discovered by Huygens in the 17th century who was impressed by the mutual synchronization of two pendulums attached to the same wall which after a while began to oscillate in the same way (Strogatz, 2009). For these properties, these planetary oscillations have been labeled “orbital invariant inequalities”.
Section 1 summarizes the orbital invariant inequality model proposed Scafetta (2020). The result is purely theoretical and can be obtained only by using the well-known orbital periods of the four Jovian planets: Jupiter, T1 = 11.86 year; Saturn, T2 = 29.46 year; Uranus, T3 = 84.01 year; and Neptune, T4 = 164.79 yr. The model prediction is then compared versus the empirical results by Neff et al. (2001), McCracken et al. (2013) and Scafetta et al. (2016). This model reconstructs the main long solar cycles.
Section 2 briefly discusses additional spectral coherence evidences linking planetary motions to climatic oscillations observed in the global surface temperature record at the decadal and multidecadal scales. Details regarding the material and methods yielding these results are found in Scafetta (2010, 2012a-d, 2013; 2014; 2016 2018; 2021a).
Section 3 updates the graphs published in Scafetta (2013) that compare the performance of the CMIP5 climate models adopted by the Intergovernmental Panel on Climate Change (IPCC) in 2013 versus a semi-empirical model that uses some of the identifies astronomical-coherent climate oscillations to reconstruct the natural variability of the climate system. The semi-empirical model also contains volcano and anthropogenic signatures evaluated as discussed in the above publication.
Finally, the conclusion section summarizes the results and briefly comments on them. Extended comments are found in the original papers.