Orbital insolation variations, intrinsic climate variability, and Quaternary glaciations

Abstract

Abstract. The relative role of external forcing and of intrinsic variability is a key question of climate variability in general and of our planet's paleoclimatic past in particular. Over the last 100 years since Milankovic's contributions, the importance of orbital forcing has been established for the period covering the last 2.6 Myr and the Quaternary glaciation cycles that took place during that time. A convincing case has also been made for the role of several internal mechanisms that are active on timescales both shorter and longer than the orbital ones. Such mechanisms clearly have a causal role in Dansgaard–Oeschger and Heinrich events, as well as in the mid-Pleistocene transition. We introduce herein a unified framework for the understanding of the orbital forcing's effects on the climate system's internal variability on timescales from thousands to millions of years. This framework relies on the fairly recent theory of non-autonomous and random dynamical systems, and it has so far been successfully applied in the climate sciences for problems like the El Niño–Southern Oscillation, the oceans' wind-driven circulation, and other problems on interannual to interdecadal timescales. Finally, we provide further examples of climate applications and present preliminary results of interest for the Quaternary glaciation cycles in general and the mid-Pleistocene transition in particular.

Theoretical and paleoclimatic evidence for abrupt transitions in the Earth system

“…by the slow increase in overall ice mass on the planet (Ghil and Childress 1987) or by the decrease in atmospheric CO 2 concentration (Saltzman and Maasch 1991). Several hypotheses as to the cause of the MPT are still under discussion (Chalk et al 2017) and a fairly extensive and annotated list is provided in Riechers et al (2021).…”

“…It has been known for six decades that nonlinearities in the dynamics of the Earth's climate system and of its components can in principle lead to abrupt transitions (Stommel 1961, Veronis 1963, Lorenz 1963a. Such jumps in behavior can occur in response to external forcing, even if the latter varies only gradually, and it may also be the result of self-sustained, oscillatory dynamics (Ghil and Childress 1987, Ghil and Lucarini 2020, Riechers et al 2021.…”

“…It was found, however, also in a general circulation model (GCM) (Wetherald and Manabe 1975); and, quite some time later, it became clear that in the Earth's deep past, some 650 million years ago, such a snowball Earth state had indeed occurred, possibly more than once (Hoffman et al 1998, Hoffmann et al 2010. Over the course of the last decades, several abrupt climate transitions have been identified in paleoclimate proxy records, from glacial terminations (Crucifix 2018, Bagniewski et al 2021, Riechers et al 2021 to millennial-scale abrupt shifts during previous glacial intervals (Johnsen et al 1992, Dansgaard et al 1993 and abrupt climate events during the Holocene (Bond et al 2001), such as the desertification of the Sahara and North Atlantic ice rafting events that had profound impacts on the tropical monsoon system and early human civilizations (Gibbons 1993, Stanley et al 2003. Some instances of past abrupt climate transitions of the last 30 kyr and their impacts on different Earth system components have recently been reviewed in Brovkin et al (2021).…”

The PaleoJump database for abrupt transitions in past climates

“…The 1.25–0.65 Ma BP interval in the figure corresponds to the Mid-Pleistocene Transition, characterized by an increase in the amplitude of the glacial–interglacial fluctuations and a shift from a predominantly 40 kyr to a predominantly 100 kyr periodicity; see Reichers et al 185 and references therein. The abrupt transition at 0.35 Ma marks the start of the strongest interglacial of the record, which corresponds to the marine isotope stage (MIS) 9.…”

Review Article: Dynamical Systems, Algebraic Topology, and the Climate Sciences

“…The contributions of "nonlinear dynamics," as dynamical systems theory tended to be referred to by physicists and other non-mathematicians by training, were presented for the first time in a quadrennial report (1987)(1988)(1989)(1990)(1991) of the U.S. geosciences community to the International Union of Geodesy and Geophysics (IUGG) by Ghil et al (1991). The presentation of elementary bifurcations below is for a broad audience and is based on Boers et al (2022). It focuses on multistability and the possible transitions between different regimes of behavior: in Sec.…”