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Author Posting. © Annual Reviews, 2007. This is the author's version of the work. It is posted here by permission of Annual Reviews for personal use, not for redistribution. The definitive version was published in Annual Review of Environment and Resources 32 (2007): 31-66, doi:10.1146/annurev.energy.32.041706.124700.The global carbon and climate systems are closely intertwined, with biogeochemical processes responding to and driving climate variations. Over a range of geological and historical time-scales, warmer climate conditions are associated with higher atmospheric levels of CO2, an important climate-modulating greenhouse gas. The atmospheric CO2-temperature relationship reflects two dynamics, the planet’s climate sensitivity to a perturbation in atmospheric CO2 and the stability of non-atmospheric carbon reservoirs to evolving climate. Both exhibit non-linear behavior, and coupled carbon-climate interactions have the potential to introduce both stabilizing and destabilizing feedback loops into the Earth System. Here we bring together evidence from a wide range of geological, observational, experimental and modeling studies on the dominant interactions between the carbon cycle and climate. The review is organized by time-scale, spanning interannual to centennial climate variability, Holocene millennial variations and Pleistocene glacial-interglacial cycles, and million year and longer variations over the Precambrian and Phanerozoic. Our focus is on characterizing and, where possible quantifying, the emergent behavior internal to the coupled carbon-climate system as well as the responses of the system to external forcing from tectonics, orbital dynamics, catastrophic events, and anthropogenic fossil fuel emissions. While there are many unresolved uncertainties and complexity in the carbon cycle, one emergent property is clear across time scales: while CO2 can increase in the atmosphere quickly, returning to lower levels through natural processes is much slower, so the consequences of the human perturbation will far outlive the emissions that caused them.S. Doney acknowledges support from the NSF Geosciences Carbon and Water program (NSF ATM-0628582) and the WHOI W. Van Alan Clark Sr. Chair. D. Schimel acknowledges support from the NSF Biocomplexity in the Environment program (NSF EAR-0321918)