Yet the USGS glibly claims that Gerlach's estimate includes both subaerial and submarine volcanoes in roughly equal amounts.
Given the more than 3 million volcanoes worldwide indicated by the work of Hillier & Watts (2007), one might be prone to wonder about the statistical significance of Gerlach's seven subaerial volcanoes and three hydrothermal vent sites.
Furthermore, the discovery of a surprising number of submarine volcanoes highlights the underestimation of global volcanism and provides a loose basis for an estimate that may partly explain ocean acidification and rising atmospheric carbon dioxide levels observed last century, as well as shedding much needed light on intensified polar spring melts.
Based on this brief literature survey, we may conclude that volcanic CO is exclusively anthropogenic.
If we neglect to ask how the greenhouse effect of various gases is quantified in terms of real, measurable thermodynamic properties, the idea of anthropogenic global warming may well survive long enough for us to ask how the carbon budget establishes that observed increases in CO is one of the lightest volatiles (materials of relatively low melting point), found in the mantle (Wilson, 1989).
The fluid nature of the aesthenosphere, or upper mantle of the earth, ensures that lighter volatiles are fractionated, buoyed towards the surface, and either extruded or outgassed into the atmosphere via volcanoes and faults.
Volatiles, such as CO is the second most abundantly emitted volcanic gas next to steam.