Abstract

This chapter is dedicated to the slow dynamics of the climate system, at time scales of 1000 to 1 million years. We focus specifically on the phenomenon of ice ages that has characterised the slow evolution of climate over the Quaternary. Ice ages are a form of variability featuring interactions between different large-scale components and processes in the climate system, including ice sheet, deep-ocean and carbon cycle dynamics. This variability is also at least partly controlled by changes in the seasonal and latitudinal incoming solar radiation associated with the combined effects of changes in Earth's orbit shape, precession of equinoxes, and changes in obliquity. A number of possible mechanisms are reviewed in this chapter. We stress that the nature of the interactions between these slow dynamics and faster modes of variability, such as millennium and centennial modes of variability, are still poorly understood. For example, whether the time sequence of ice ages is robustly determined or not by the astronomical forcing is a matter of debate. These questions need to be addressed with a range of models. We propose to use stochastic parameterisations in the lower-resolution models (focusing on climate time scales) to account for weather and macro-weather dynamics simulated with higher-resolution models. We discuss challenges – including statistical challenges – and possible methods associated with this programme.

The Ice Age Phenomenon

Short Summary of Observational Evidence

Glacial cycles, or ice ages, are a form of climate variability that can be characterised as the succession of interglacial (similar to today) and glacial conditions over time scales of several tens of thousands of years. At the Last Glacial Maximum – 21,000 years ago, henceforth noted 21 ka BP – the sea-level was 120 m lower than today.