What is an Emergent Risk?
Emergent risks are the ones that couldn't have been identified in advance — unknowable unknowns arising from complexity, novelty, or a changing environment. You can't list them; you can only build the capacity to absorb them: management reserve, schedule margin, modular designs, and fast detection loops.
That capacity has a name — resilience — and PMBOK 7 pairs it with risk management precisely because registers, however good, only hold what someone could imagine.
Worked example
No 2019 risk register contained "global pandemic closes every site for months." Projects with resilience — management reserve, cross-trained crews, digitized documents, remote-capable workflows — bent; the rest broke. The lesson wasn't "make longer risk lists." It was: budget and design for the risk you cannot name, because it's coming anyway.