Technical Note: Characterising and comparing different palaeoclimates with dynamical systems theory

Numerical climate simulations produce vast amounts of high-resolution data. This poses new challenges to the palaeoclimate community – and indeed to the broader climate community – in how to efficiently process and interpret model output. The palaeoclimate community also faces the additional challenge of having to characterise and compare a much broader range of climates than encountered in other subfields of climate science. Here we propose an analysis framework, grounded in dynamical systems theory, which may contribute to overcome these challenges. The framework enables to characterise the dynamics of a given climate through a small number of metrics. These may be applied to individual climate variables or to diagnose the coupling between different variables. To illustrate its applicability, we analyse three numerical simulations of mid-Holocene climates over North Africa, under different boundary conditions. We find that the three simulations produce climate systems with different dynamical properties, which are reflected in the dynamical systems metrics. We conclude that the dynamical systems framework holds significant potential for analysing palaeoclimate simulations. At the same time, an appraisal of the framework's limitations suggests that it should be viewed as a complement to more conventional analyses, rather than as a wholesale substitute.

Reconstructing Middle and Late Holocene Paleoclimates of the Eastern Arctic and Greenland

The eastern Arctic and Greenland are characterized by diverse paleoclimatic histories. A range of biological, geochemical, and geophysical indicators preserved in ice cores, lake, and ocean sediments, landscape features, or boreholes can be applied to reconstructing Holocene climates over the period of human occupation. Soon after humans arrived in the eastern Arctic around 4800 cal B.P., regional temperatures began to decline. While the proxy records show a strong regional signal, this period of Neoglacial cooling has considerable local variability related to degree of continentality, sea ice conditions and elevation. Much later, the effect of the Medieval Warm Period (AD 850-1360) on the Thule migration appears to have been overstated. Because of the considerable spatiotemporal variability in available paleoclimate reconstructions from the eastern Arctic, data from multiple sites must be integrated, and for archaeological applications, regional syntheses need to be considered alongside highly local reconstructions.