a)

Despite critical fluctuations that have been suggested by Scheffer et al. to often occurring before a transition, it is difficult by a web search for "critical fluctuations as precursor" to find established examples. However, Olthof et al. suggest "critical fluctuations as an early-warning signal for sudden gains and losses in patients receiving psychotherapy for mood disorders" [Clinical Psychological Science 8(1) 2020. First published 24.09.2019] that the mechanism may be clinically relevant.

b)

There seems to be no indication that, for example, earthquakes are preceded by fluctuations. Nor does the appearance of a new infectious virus with the ensuing pandemic seem to be foreseeable from fluctuations.