The cause of glaciations
Blog 20151216 The cause of glaciations
Earth has been subject to warming and cooling periods for the last 2 million years. Glacial-interglacial cycles were first thought to be associated with volcanism. Large eruptions of stratovolcanoes eject tremendous quantities of volcanic ash and sulfuric acid into the jet stream, blocking out the Sun and cooling the globe. For instance, the 1991 eruption of Mount Pinatubo in the Philippines reduced global temperatures by 0.5 oC between 1991 and 1993. The cycles were quite regular, but there was no well-known reason for volcanism to have cyclic behavior.
The emphasis on volcanism waned with the advent of a theory proposed by Milankovitch in 1930. This theory depended on what I call POE (precession, obliquity, and eccentricity), which yielded astronomical cycles of about 20,000, 40,000, and 100,000 years. Precession describes the wobble of Earth’s axis over time. Obliquity is the tilt of Earth’s axis (23.3+2.4o) with respect to the plane of its orbit. Eccentricity describes Earth’s almost, but non-circular orbit around the Sun. The theory had a rough start, but has been increasingly accepted as the mechanism for glacial cycles. Unfortunately, the main problem is that the theory, despite its long history, has not been properly validated, as we show in our most recent paper:
Puetz, Stephen J., Prokoph, Andreas, and Borchardt, Glenn, 2016, Evaluating alternatives to the Milankovitch theory: Journal of Statistical Planning and Inference, v. 170, p. 158–165. [doi:10.1016/j.jspi.2015.10.006], which is already available for download at: http://www.sciencedirect.com/science/article/pii/S0378375815001901
• Orbital tuning removes spectral power from non-Milankovitch frequencies.
• Orbital tuning inhibits testing of alternatives to the Milankovitch theory.
• Reporting bias occurs by publishing positive results while hiding negative results.
• Spectral analysis of orbitally tuned time-series involves circular reasoning.
• Choices about how to orbitally tune records also results in altered cyclicity.
The physical process that causes cycles in Earth’s precession, obliquity, and eccentricity is well established, and researchers have detected and modeled the orbital cycles for millions of years into the past. The Milankovitch theory postulates that Earth’s orbital cycles contribute to similar periodicity in climatic variation — with the periods of the climatic cycles primarily ranging from 19,000 years to 1,200,000 years. Even while support for the Milankovitch Theory remains strong, opposition to the process of tuning sedimentary records to Milankovitch models has become increasingly vocal. Here, we discuss another negative aspect of orbital tuning that has been ignored to this point. Specifically, orbital tuning contributes to a type of negative analytical bias against research aimed at modifying the Milankovitch theory as well as bias against testing alternatives to the Milankovitch theory, such as the Universal cycle model, presented in this work.
In essence, most investigators have been using the theory to test the theory, which normally is a no-no in science. Our analyses of the raw data do not confirm the POE speculations, although many of our UWS cycles, developed from raw data, are close to those of Milankovitch. We don't really know the cause of the cycles either, but think that it has something to do with aether pressures that vary systematically throughout the universe.