Salby & Harde 2021 Control of Atmospheric CO2 Part I

Murry Salby1, Hermann Harde2
1Ex Macquarie University, Sydney, Australia 2Helmut-Schmidt-University, Hamburg, Germany.


An in-depth analysis is performed on the record of atmospheric 14CO2, an isotopic tracer of CO2 that was perturbed by nuclear testing. In addition to long-term behavior, we examine short-term changes that have been largely ignored. It pays to look closely. Those changes reveal the under- lying mechanisms responsible for the observed decline of atmospheric 14CO2 and, thereby, for removal of overall CO2. They represent effective absorption that is considerably faster than appears in the average decline of 14CO2, initially and then later in its long-term decline. The average decline of 14CO2 is slowed initially by periodic re-enrichment from the stratosphere, which offsets direct absorption at the Earth’s surface. Eventually, however, its decline is slowed by re-emission of absorbed 14CO2 from the Earth’s surface, which likewise offsets direct absorp- tion. With CO2 absorption revealed by the record of nuclear-perturbed 14C, fundamental princi- ples are then shown to reproduce the observed evolution of 14CO2, on long as well as short time scales. Applying the same considerations to anthropogenic emission of CO2 recovers effective absorption that is an order of magnitude faster than operates on 14CO2. The difference follows from magnified disequilibrium between the atmosphere and the Earth’s surface, a state which, unlike for perturbed 14CO2, is maintained by continuous anthropogenic emission. Supported by fundamental principles, the observed behavior of 14CO2 provides an upper bound on the anthro- pogenic perturbation of atmospheric CO2. It represents only a few percent of the observed in- crease.

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