Abrupt transitions in past climates: How reliable are they and what do they mean?

Early evidence of abrupt transitions in Camp Century and Dye 3 Greenland ice cores (Dansgaard et al. 1982) has recently been reinforced by the identification of additional abrupt transitions in the NGRIP ice core (Rasmussen et al. 2014). These additional events correspond to changes of either short duration or amplitude of d¹⁸O that visual or statistical inspections do not necessarily validate. Abrupt transitions have been described for marine (Bond et al. 1992) and continental (Wang et al. 2001) records as well, and they provide a broader spatial perspective. Finally, abrupt transitions have also been documented over much deeper timescales (Zachos et al., 2001, Hodell & Channel, 2016, Westerhold et al. 2020). In spite of the variable time resolution of all these records, the abrupt transitions seem to reflect the individual impact of external forcing, of internal climate variability, or a combination of the two on Earth’s climate system. To illustrate this, we have analyzed 4 reference datasets with timescales ranging from one glacial cycle — i.e., the last 130,000 years — to the last 70 Ma. We show patterns that repeat within a single glacial cycle and seem to be related to internal variability, along with patterns associated with longer time periods and possibly related to external forcing; such forcing may arise from changes in either Earth’s orbit or its dynamics. This study is supported by the H2020-funded Tipping Points in the Earth System (TiPES) project.