I don't understand the evidence for either volcanic aerosol cooling or subsequent CO2 increase-based warming moving across the globe as they describe, "the annual timing of the regime shift appeared to have moved regionally around the world from west to east, starting with South America in 1984, North America (1985), North Atlantic (1986), Europe (1987), and Asia (1988)". CO2 mixes globally faster than that, to my knowledge.

Granted that "association" doesn't claim causation, what are the proposed mechanisms for this grab bag of changes? How does the CO2 from one eruption outweigh all other ongoing greenhouse gases, causing "a sudden growth in land and ocean carbon sinks"?

Yes one event can trigger regime change at a bifurcation point. But this litany, for me, conjures images of looking for correlations everywhere, and only reporting those that fit a preconceived hypothesis.

Perhaps reading more details of these unforeseen compounding effects in the original paper would answer my questions.