Uncertainties and Key Open Questions in the Geological Carbon Cycle

Abstract:

The geological carbon cycle determines the long term distribution of CO₂ between the mantle, crust and atmosphere, and therefore controls the concentration of CO₂ in the Earth’s atmosphere. Records of CO₂ concentrations and temperature for the last 600,000 years indicate a relative stability in atmospheric CO₂ concentrations, reflecting a balance between CO₂ input to the atmosphere from volcanism and metamorphism, and output via silicate weathering. The absolute rates of these global fluxes contributes to controlling the lifetime of CO₂ in the atmosphere. It is therefore extremely relevant and important to quantify the rate of the geological cycle for CO₂, as this will contribute to the timescale of recovery from a change in policy on anthropogenic CO₂ emissions.

Here we review the state of the art in our knowledge of Earth’s geological CO₂ output, and highlight causes of large underestimates, largely due to methodological errors in measurement of CO₂ flux. We produce a new, corrected estimate and use this to estimate a CO₂ lifetime which is significantly shorter than previously thought.