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Metamorphic decarbonation in magmatic arcs remains a challenge to impose in models of the geologic carbon cycle. Crustal reservoirs and metamorphic fluxes of carbon vary with depth in the crust, rock types and their stratigraphic succession, and through geologic time. When byproducts of metamorphic decarbonation (e.g., skarns) are exposed at Earth’s surface, they reveal a record of reactive transport of carbon dioxide (CO2). In this paper, we discuss the different modes of metamorphic decarbonation at multiple spatial and temporal scales and exemplify them through roof pendants of the Sierra Nevada batholith. We emphasize the utility of analogue models for metamorphic decarbonation to generate a range of decarbonation fluxes throughout the Cretaceous. Our model predicts that metamorphic CO2 fluxes from continental arcs during the Cretaceous were at least 2 times greater than the present cumulative CO2 flux from volcanoes, agreeing with previous estimates and further suggesting that metamorphic decarbonation was a principal driver of the Cretaceous hothouse climate. We lastly argue that our modeling framework can be used to quantify decarbonation fluxes throughout the Phanerozoic and thereby refine Earth systems models for paleoclimate reconstruction.