The cause of the MPT- period shift is generally thought to be a change within the Earth System, since the orbital insolation forcing does not change its pattern through the event. Here we propose that the MPT could be a dominant-period relaxation process that is strongly dependent on the initial state of the system and this sensitivity to the initial state is enabled by the orbital forcing.

It was recently suggested that global warming can be explained by the non-anthropogenic factor of seismic activity. If that is the case, it would have profound implications. We have assessed the validity of the claim by using a statistical technique that evaluates the existence of causal connections between variables, finding no evidence for any causal relationship between seismic activity and global warming.

The dynamics of ice sheets is defined by the advection of mass and temperature. Reduced mass influx makes advection timescale to become longer, which is equivalent to a longer system’s memory of its initial conditions. In this case the Milankovitch theory becomes an initial value problem. The dependence of the similarity parameter that governs initial-values sensitivity on poorly defined mass balance makes ice ages to be hardly predictable and disambiguation of paleo-records to be challenging.

Are phenomenological dynamical paleoclimate models physically similar to Nature? We demonstrated that though they may be very accurate in reproducing empirical time series, this is not sufficient to claim physical similarity with Nature until similarity parameters are considered. We suggest that the diagnostics of physical similarity should become a standard procedure before a phenomenological model can be utilized for interpretations of historical records or future predictions.

Phenomenological models may be impressive in reproducing empirical time series but this is not sufficient to claim physical similarity with nature until comparison of similarity parameters is performed. We illustrated such a process of diagnostics of physical similarity by comparing a phenomenological dynamical paleoclimate model with a more physically explicit dynamical model.