Quaternary QUEST: Regulation of atmospheric carbon dioxide on glacial-interglacial timescales and its coupling to climate change

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The climate of the last million years is characterized by regular oscillations between cold glacial and warm interglacial states, thought to be paced by variations in the Earth's orbit around the sun. Sources of ancient climate data, such as marine and lake sediments and air trapped in polar ice cores reveal a remarkable behaviour; the climate behaves as a system of interlinked parts, changing in a complex but ordered way, in a sequence which recurs, with variations, like the themes in a symphony. The individual parts making up this composition are affected by changes in the physical circulation of the atmosphere and ocean, the coverage of vegetation, ice sheets and sea ice, the marine biota, concentrations of carbon dioxide, methane, dust, and precipitation around the world. This behaviour suggests that the system is predictable, but that it is sensitively dependent on conditions and history. If we are ever to understand this complex system we must synthesise our knowledge from the data sources with understanding of how the Earth system works. Accordingly, a consortium of UK scientists will compile syntheses of ancient records from ice cores and sediments, improve the synchronization of these records one with another, and use that information to improve and test Earth System models (principally the 'GENIE' model, designed to simulate the diverse components of the climate system over time scales up to a million years). In particular, we will focus on the still unresolved problem of why atmospheric carbon dioxide changed so regularly with the climate cycles. We will also study how this change interacts with the other components of the Earth system. Until we have such understanding of the past, we are unlikely to have great confidence in our predictions of how Earth's climate will change in the future as we subject it the substantial assaults of human-induced change due to increasing carbon dioxide and other greenhouse gases.