Date: 20 February 2022
Riyadh, Saudi Arabia
Research Director Emeritus
With respect to the current genuine public concern regarding the anthropogenic increase of Green-House gases, intensive research and technology development focus on the capture and underground storage of industrial quantities of CO2 concentrated in emissions from combustion sources. At the global scale, the withdrawal of the CO2 diluted in the atmosphere reliesessentially on natural bio-geological processes. As a complement to the study of the involved factors in the modern terrestrial eco-system, the geological perspective provides the opportunity to investigate these processes and their consequences at different time scales.
During Earth’s history the atmospheric CO2 has been subjected to extensive changes in term of absolute quantity and relative concentration. From ageological perspective, the current anthropogenic-driven alteration of the Earth’s atmosphere actually occurs during a period of low atmospheric CO2(Ice-House). A large part of the remaining time intervals of the Phanerozoic were apparently dominated by Green-House conditions. The latter situation resulting from the high concentration of atmospheric CO2, due to volcanic and metamorphic degassing associated with the long term tectonic activity of Phanerozoic megacycles. The subsequent decrease of atmospheric CO2 at the end of the megacycles is interpreted by a negative feedback involving the CO2 driven silicate weathering which consumes CO2.
Based on the CO2 sourcing(tectonic degassing) and CO2 sinking (sedimentation of carbonates and organic matter), the most popular model depicting the change of atmospheric CO2 during the Phanerozoic are based on the Berner’s GEOCARBSULF approach. The resulting curve which exhibits the long-term change is, to some extent, comforted by the comparison with the estimates of past PCO2 values provided by different indicative proxies.
However, some available data depart from the model and high-resolution series of proxies suggest that high amplitude and high-frequency changes in atmospheric CO2 were occurring at a much lower time scale. Implications include the possibility to better explain short term climatic events such as the Late Ordovician continental-wide glaciation, to reconsider the significance of brutal events of injection of CO2 in the atmosphere as a result of intra-plate volcanism and their environmental responses and geochemical record in oceanic sediments(e.g.the Permo-Trias Siberian traps), to revisit the so-called climatic optima such as the Late Palaeocene and Early Eocene, and the necessity to improve our assessment of the kinetics of the retroaction loops controlling the level of CO2 in the atmosphere.