Carbon capture and geological storage represents a potential means of managing atmospheric carbon dioxide levels.Understanding the role of faults, as either barriers or conduits to the flow of carbon dioxide, is crucial for predicting the
long-term integrity of geological storage sites. Of particular concern is the influence of geochemical reactions on the sealing behaviour of faults and the impact of seismicity and stress regime on fault stability. Here, we examine a 135,000-year palaeorecord of carbon dioxide leakage from a faulted, natural carbon dioxide reservoir in Utah. We assess the isotope and trace-element composition of U–Th-dated carbonate veins, deposited by carbon-dioxide-rich fluids. Temporal changes in vein geochemistry reveal pulses of carbon dioxide injection into the reservoir from deeper formations. Surface leakage rates
increase by several orders of magnitude following these pulses. We show that each pulse occurs around 100–2,000 years after the onset of significant local climatic warming, at glacial to interglacial transitions. We suggest that carbon dioxide leakage rates increase as a result of fracture opening, potentially caused by changes in groundwater hydrology, the intermittent presence of a buoyant gas cap and postglacial crustal unloading of regions surrounding the fault.