Antarctic air bubbles and the long-term ice core record of CO2 and other greenhouse gases

Abstract Nature has been continuously sampling the atmosphere at the surface of Antarctica throughout the ages. Atmospheric gases trapped in Antarctic ice provide the most direct record of changes in greenhouse gas levels during the past 800,000 years. The best-documented and reliable trace-gas records are for CO2 and CH4, and Antarctic ice is the key player in recording past atmospheric CO2. They are archives of the past and a window to the present and future of the interplay between greenhouse gases and climate. We discuss the pioneering work of glaciologists measuring CO2 in the air extracted from Antarctic ice, which confirmed Arrhenius’ prediction about the role of atmospheric carbon dioxide in ice age climate. We detail here how the ice core record has been progressively extended to four and then to eight glacial-interglacial cycles (i.e., over the last 800,000 years). The Antarctic ice record highlights the tight coupling of atmospheric CO2 and Antarctic climate on the timescales of glacial-interglacial cycles for the entire 800,000-year interval. This close linkage suggests that glacial-interglacial variations of CO2 explain a large fraction of glacial-interglacial climate changes observed in the Antarctic ice record, which is consistent with modeling results. We present more recent works showing a near synchronous phasing between Antarctic temperature and CO2 during the last deglaciation and pinpointing the important role of oceanic circulation in both heat transport and CO2 outgassing. We also briefly explore the prospect for investigating Antarctic ice older than 1 million years to document what is often called the enigma of the Mid-Pleistocene Transition around 1 million years ago.