Was the Himalayan orogen a climatically significant coupled source and sink for atmospheric CO2 during the Cenozoic?

The hypothesis that the Himalayan orogen was a climatically significant coupled source and sink for atmospheric CO2 during the Cenozoic is evaluated in light of the timing, duration and CO2 fluxes associated with Himalayan metamorphism and chemical weathering. We suggest that diachronous Eohimalayan metamorphism occurred over a ∼20 m.y. time span (Middle Eocene to Early Oligocene) with total metamorphic CO2 production of ∼4–10×1018 mol. Because this is much greater than the amount of carbon stored in the atmosphere and oceans, and because uplift and accelerated erosion began at least ∼5 m.y. after the peak of metamorphism, we conclude that it is implausible that CO2 produced by metamorphism in the Himalayan orogen was consumed millions of years later by erosion-enhanced weathering in this orogen. Assuming a global climate/silicate-weathering feedback, we estimate that metamorphic CO2 degassing from the Himalayan orogen would have produced a warming of <0.5°C, and enhanced weathering in this orogen would have produced a cooling of <0.2°C; thus, direct climate effects of this degassing and weathering were likely to have been minor.