Atmospheric Lifetime of Fossil Fuel Carbon Dioxide

TLDR

CO₂ released by fossil‑fuel combustion equilibrates among atmospheric, oceanic, and terrestrial reservoirs over a few centuries, yet a substantial fraction remains airborne, awaiting slow weathering and CaCO₃ deposition, and conventional lifetime metrics that ignore this long tail underestimate anthropogenic warming. The authors review past literature on fossil‑fuel CO₂ atmospheric lifetime and present initial results from a model intercomparison project. Models show that 20–35 % of fossil‑fuel CO₂ remains in the atmosphere after ocean equilibration (2–20 centuries), and CaCO₃ neutralization further reduces the airborne fraction on 3–7 kyr timescales.

Abstract

CO 2 released from combustion of fossil fuels equilibrates among the various carbon reservoirs of the atmosphere, the ocean, and the terrestrial biosphere on timescales of a few centuries. However, a sizeable fraction of the CO 2 remains in the atmosphere, awaiting a return to the solid earth by much slower weathering processes and deposition of CaCO 3 . Common measures of the atmospheric lifetime of CO 2 , including the e-folding time scale, disregard the long tail. Its neglect in the calculation of global warming potentials leads many to underestimate the longevity of anthropogenic global warming. Here, we review the past literature on the atmospheric lifetime of fossil fuel CO 2 and its impact on climate, and we present initial results from a model intercomparison project on this topic. The models agree that 20–35% of the CO 2 remains in the atmosphere after equilibration with the ocean (2–20 centuries). Neutralization by CaCO 3 draws the airborne fraction down further on timescales of 3 to 7 kyr.