We present the first regional map of CO₂ Earth degassing from a large area (most of central and south Italy) derived from the carbon of deep provenance dissolved in the main springs of the region. The investigation shows that a globally significant amount of deeply derived CO₂ (10% of the estimated global CO₂ emitted from subaerial volcanoes) is released by two large areas located in western Italy. The anomalous flux of CO₂ suddenly disappears in the Apennine in correspondence to a narrow band where most of seismicity concentrates. Here, at depth, the gas accumulates in crustal traps generating CO₂ overpressurized reservoirs which induce seismicity.

Volcanoes are the main pathway to the surface for volatiles that are stored within the Earth. Carbon dioxide (CO₂) is of particular interest because of its potential for climate forcing. Understanding the balance of CO₂ that is transferred from the Earth’s surface to the Earth’s interior, hinges on accurate quantification of the long-term emissions of volcanic CO₂ to the atmosphere. Here we present an updated evaluation of the world’s volcanic CO₂ emissions that takes advantage of recent improvements in satellite-based monitoring of sulfur dioxide, the establishment of ground-based networks for semi-continuous CO₂-SO₂ gas sensing and a new approach to estimate key volcanic gas parameters based on magma compositions. Our results reveal a global volcanic CO₂ flux of 51.3 ± 5.7 Tg CO₂/y (11.7 × 10¹¹ mol CO₂/y) for non-eruptive degassing and 1.8 ± 0.9 Tg/y for eruptive degassing during the period from 2005 to 2015. While lower than recent estimates, this global volcanic flux implies that a significant proportion of the surface-derived CO₂ subducted into the Earth’s mantle is either stored below the arc crust, is efficiently consumed by microbial activity before entering the deeper parts of the subduction system, or becomes recycled into the deep mantle to potentially form diamonds.