Ice cores provide the only direct way of determining past concentrations of atmospheric CO2. In the absence of artefacts (which is generally the case in Antarctic ice cores), the air extracted from ice gives a direct measure of the CO2 concentration. The ice core record has now been extended back beyond 650,000 years in the past, using the core from Dome C retrieved by the European Project for Ice Coring in Antarctica (EPICA). CO2 rises and falls in very close connection to Antarctic climate throughout this period, between a range of about 180 ppmv in the coldest glacials and 300 ppmv in the warmest interglacials (Siegenthaler et al., Science, 2005). Lower interglacial concentrations match colder interglacial climates in the part of the record before 450,000 years. No long-term trend in the average value is apparent so far. The close CO2-climate connection is consistent with a system in positive feedback, with CO2 acting as one of a number of amplifiers in glacial-interglacial climate change. However, the exact mechanisms controlling the CO2 changes remain uncertain, and a number of candidates in the physical and biogeochemical realm were considered in the EPICA challenge (Wolff et al., Eos, 2005). Modelling and data can to some extent constrain the possibilities, and the Southern Ocean is almost certainly of greatest importance, but the uncertainties mean that the CO2 changes cannot yet be confidently ascribed to any single mechanism or combination of mechanisms.
Helmholtz Research Programs > MARCOPOLI (2004-2008) > MAR2-Palaeo Climate Mechanisms and Variability
Helmholtz Research Programs > MARCOPOLI (2004-2008) > POL-MARCOPOLI
Helmholtz Research Programs > MARCOPOLI (2004-2008) > POL6-Earth climate variability since the Pliocene
Helmholtz Research Programs > MARCOPOLI (2004-2008) > New Themes
Helmholtz Research Programs > MARCOPOLI (2004-2008) > NEW KEYS - New keys to polar climate archives