Guest essay by Kirby Schlaht
Nir Joseph Shaviv is an Israeli-American physics professor, carrying out research in the fields of astrophysics and climate science. He is a professor at the Racah Institute of Physics of the Hebrew University of Jerusalem.He is also a member of the Institute for Advanced Study in Princeton.
He is best known for his controversial solar and cosmic-ray hypothesis of climate change. In 2002, Shaviv hypothesized that passages through the Milky Way’s spiral arms appear to have been the cause behind the major ice-age epochs over the past billion years.
In 2014 Shaviv and coworkers published the paper “Is the Solar System’s Galactic Motion Imprinted in the Phanerozoic Climate?in Scientific Reports. Fossil shells, mainly brachiopods with some conodonts and belemnites are proposed as chronometers with a physical mechanism inferred to exists to link the solar system’s vertical motion through the galaxy to the terrestrial climate
The motion of the solar system through the galaxy. The main components (relevant to climate on Earth) are the periodic passages through the galactic spiral arms as it revolves around the galaxy, and the motion of the solar system perpendicular to the galactic plane (the horizontal “wavelength” of that motion is actually longer than portrayed in the cartoon
“A new δ18O Phanerozoic database, based on 24,000 low-Mg calcitic fossil shells, yields a prominent 32 Ma oscillation with a secondary 175 Ma frequency modulation. The periodicities and phases of these oscillations are consistent with parameters postulated for the vertical motion of the solar system across the galactic plane, modulated by the radial epicyclic motion. We propose therefore that the galactic motion left an imprint on the terrestrial climate record. Based on its vertical motion, the effective average galactic density encountered by the solar system … suggests the presence of a disk dark matter component.”
Paper Figure 1: The Gaussian filtered δ18O fossil shell data, separated into four groups
The green line is the low-latitude, blue the mid-latitude, red the high-latitude, and the black line the deep sea subset. The latter three subsets were shifted to minimize the χ2 between them and the low-latitude subset (see Supplementary Materials for details). Note that the low-latitude data show a warming for the past 15 Ma while the three other subsets exhibit cooling. Note also the data gaps around 110 and 210 Ma. The dotted vertical lines denote time intervals used for splicing the different combinations of subsets.
Paper Figure 2: The linearly detrended and high pass filtered ML200 δ18O dataset (in red) for Fourier modes shorter than 49 Ma
The simulated VO motion of the solar system in the galaxy (blue) has a secondary frequency modulation caused by the epicyclic motion of the solar system that generates slightly shorter VO periods around 130 Ma and 300 Ma and longer ones in between. Because the vertical potential changes adiabatically with the epicyclic motion, the vertical amplitude is larger when the period is longer. The shaded region denotes the 95% confidence range for the measured δ18O obtained from the finite number of data points in each bin and the variance in the data.
From the author’s discussion:
“Given the consistency between the vertical and radial oscillations and the paleoclimate data, and the low probability that it could be mimicked by random fluctuations, we conclude with high confidence that the terrestrial temperature has a component which is quadratic in the distance from the galactic plane. Although this can be naturally explained through the cosmic ray climate link, the observations by themselves do not prove it.
In addition, it should be noted that although a galactic driver can naturally explain a stable ~32 Ma cycle, there are terrestrial processes that could drive climate variations on the ~32 Ma time scale as well. The most prominent is probably mantle convection periodically producing plumes that result in large volcanic eruptions/igneous provinces. These eruptions will in turn add aerosols and carbon dioxide to the oceanic-atmospheric system and either cool or warm the climate. The influence of the Earth mantle connection could also drive changes or even reversals in Earth’s magnetic field, which would modulate the atmospheric ionization. The advantage of the proposed galactic forcing over a terrestrial driver is that it will produce a gradual (sinusoidal) fluctuations as found for most of the δ18O record with a relatively steady periodicity, while volcanic forcing will more likely produce random abrupt perturbations followed by gradual relaxations to climate base levels”
Presenter’s note: this is not to defend or refute the authors’ theory but to provide the community with the information – decide for yourselves.