This paper continues the debate sponsored by Science of Climate Change on the root causes of atmospheric CO2 rise during the last century. A little progress has been made in finding common ground, but not very much. A suggestion is made to make the discussion more productive.
Introduction and a Proposal
In an earlier paper (Andrews 2023), three primary points were made:
(1) Data show that land and sea reservoirs have been net sinks, not sources, of carbon from the atmosphere during the Industrial Age.
(2) Mixing of carbon between reservoirs, which happens on a time scale of about one decade, precludes making inferences on the cause of atmospheric carbon increases from the present composition of the atmosphere.
(3) The attempt of (Harde and Salby 2021) to reconcile their model with correctly interpreted radiocarbon data was unsuccessful (despite their claim to the contrary) as it required postulating unrealistically large new sources of 14C.
(Harde 2023a) and (Berry 2023) contested these points, while (Engelbeen 2023) supported and elaborated on the first two. Now (Harde 2023b) in a response to Engelbeen, has agreed that the basic argument in support of point (1) is correct, though he continues to dispute the consequences.