Glacial Cycles and Carbon Dioxide
Andrew McC. Hogg1
1 Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia
The earth's climate over the last million years is punctuated by a 100,000 year cycle of ice ages and warm interglacials. Air temperature over Antarctica, as determined from ice core data, goes through four glacial cycles in the past 430,000 years (see Fig. 1a; reproduced from Petit et al. 1999). At the end of each glaciation temperature increases rapidly, as does CO2, producing a sawtooth pattern.
The role of CO2 in the glacial cycle has been the source of much misinformation in recent public debate on climate change, largely because there is no scientific consensus on the mechanism controlling glacial cycles. Here I propose a simple model which predicts the evolution of global temperature and carbon dioxide over the glacial-interglacial cycle. In this model, CO2 acts to amplify, but not trigger, the glacial cycle. Deglaciation is triggered by variation in the earth's orbit; thus, temperature rises lead CO2 increases at the end of glaciation, but it is the feedback between these two quantities that drives the abrupt warming during the transition from glacial to interglacial periods (shown in Fig. 1b).
Figure 1. (a) Observed records of Antarctic temperature and CO2 over the last 400,000 years. (b) Modelled insolation, global temperature and CO2.
Hogg, A. McC. (2007). Glacial Cycles and Carbon Dioxide: A conceptual model. Geophys. Res. Lett., In Press.