We demonstrate that (a) the patterns of the Pleistocene climate history as different as classic reconstructions of Lisiecki and Raymo (2005) and the new one of Clark et al (2025) may both be produced by the same long-memory ice-climate system under different initial conditions or under slightly different millennial forcing, and (b) even single “brief” (on orbital timescales, i.e., a few hundred years) pulse-perturbation of the forcing, consistent with a possible human impact, may fundamentally change the dynamics of the global ice-climate system for hundreds of thousands years, making the time series we have not observed in the past.