Recognizing the length of time it took the global ecosystem to recover to the precrash baseline depends on assumptions that were explored in the sensitivity tests. What I regard as the most reasonable input parameters result in the data illustrated in Fig. 12.5. That scenario includes domestic livestock, humans, and wild species as megafauna biomass and leads to two important observations.

First, the buildup of human-associated megafauna biomass, even in the absence of the extinct megafauna, took ≈9,700 years to reach precrash levels. That indicates that recovering from global ecosystem shifts takes much longer than the shift itself. Even the sensitivity test that gives the fastest recovery time (unreasonably using large carnivore density equations for all species) requires 8,000 years to reach precrash megafauna biomass. The lesson is that if another threshold causes changes as dramatic as the QME, Earth’s recovery will be far in the future, and not something the next few generations would see.

Second, the point at which biomass recovery is reached is very close to the beginning of the Industrial Revolution (Fig. 12.5) or at most 700 years before that (the sensitivity test noted above). This suggests that humans were unable to exceed the normal, precrash, solar-energy-limited

FIGURE 12.5 Semilog plot of the sum of human and non-human wild megafauna (dots) and the sum of human, wild, and domestic megafauna (triangles connected by line). Light gray bar indicates the timing of the YD-Holocene climatic event that led into the current interglacial. See Methods for parameters used.