Multiple Equilibria in the Climate System

Abstract

The most detailed information about past climate states of the last 800,000 years can be retrieved from polar ice cores (Jouzel et al. 2007). One example for the last 90,000 years is presented in Fig. 9.1. The Holocene, the present interglacial, has started after the abrupt end of the last glacial period, 11,650 years ago. The transition from the last ice age to the Holocene, called Termination I, started about 20,000 years ago. An increase in the concentrations of particular isotopes could be detected in Antarctic ice cores. Stable isotopes of the water molecule are a measure for the local temperature. The temperature indicators also show that the climate changed in an abrupt way 25 times in Greenland during the last glacial period. These abrupt warming events, numbered in Fig. 9.1, are now referred to as Dansgaard–Oeschger events (D/O events) in remembrance of the research of the two pioneers in ice core science Willy Dansgaard (1922–2011) and Hans Oeschger (1927–1998) from the University of Copenhagen and the University of Bern.