Volcanic CO 2 degassing is considered the primary process that controls the global carbon cycle over geological timescales. However, fluxes of CO 2 from individual volcanoes, in particular those in past activities, have been poorly constrained. One way to estimate the flux is by using the H 2 OCO 2 systematics of melt inclusions, which, according to petrological studies, records fluxing of a deep-derived CO 2 -rich fluid in the deep to shallow-level crustal magmatic systems. Assuming that this fluid fluxing is the process of volcanic CO 2 emission, we quantified the fluxes of CO 2 by combining a fluid transport model with melt inclusion data. We formulated CO 2 fluxing as an advective fluid flow in a basaltic magma column with exchanging volatiles, and applied it to the melt inclusion data from Mount Etna, the type locality of a CO 2 -emitting volcano. The flux of CO 2 was calculated to be 2.4–6.0kt/day, which is consistent with the observed volcanic CO 2 emission rate of 1–10kt/day. We propose that this method potentially provides a means to quantify CO 2 emission rates in past volcanic activities. Because CO 2 fluxing is an open-system process, the estimated CO 2 emission over geological timescales evaluated with this method should give much higher values than evaluations based simply on the volume of the erupted magmas.