<p>Understanding the processes controlling the fate of carbon dioxide in deep saline aquifers is critical for safe large-scale carbon storage. We describe an experimental model for the dissolution of capillary-trapped carbon dioxide. Our experiment involves a two-layer porous medium: the upper layer contains glass beads, saturated salt solution and salt powder, which is an analogue of the capillary-trapped carbon dioxide, while the lower layer contains glass beads and unsaturated solution. Convective fingers develop as fluid is exchanged between the layers. The rising fingers are arrested once they dissolve sufficient salt to become saturated, while the descending fingers gradually increase the salinity of the lower layer fluid. We develop a model of the finger motion and the non-linear dissolution process, which agrees with the experiments. We predict that a 1–10 m-thick layer of capillary-trapped carbon dioxide will dissolve into a region of aquifer water 30–100 m deep, in time scales of 10–1000 years.</p>