Geologic methane as a source for post‐glacial CO 2 increases: The Hydrocarbon Pump Hypothesis

This paper evaluates the hypothesis that historical CO 2 levels could have been governed by releases of geologic methane. Methane clathrates and natural gas could have contributed to CO 2 increases at the ends of the last two glacial periods. Computations indicate that oxidation of CH 4 to CO 2 could have rapidly provided enough CO 2 to cause historical CO 2 changes. A simple dynamic model, the hydrocarbon pump, for methane as the source term for changes in CO 2 over the glacial cycles matches several features of the historical record. If methane clathrates were the source of CO 2 , then CO 2 at the interglacial transitions should be depleted in 14 C because of the low 14 C levels in C from this source. Evidence is presented that this is the case. 13 C data are also evaluated. Overall, CH 4 is a credible source for CO 2 , but definitive conclusions await further data.