First, that the concept of repeated cycles of forcing–responses driven by long-term climate changes and separated by periods of quasi-equilibrium is now known to be false (Phillips, 2009 and Phillips, 2011). Second, that the present dynamics of Earth surface systems cannot be used uncritically to deduce processes, patterns and products of past system
dynamics; in other words that ‘the present is [not] the key to the past’. In more detail, the monitoring of different contemporary Earth surface systems IWR-1 chemical structure in different physical and climatic settings shows that generalisations of the behaviour of such systems and assumptions of forcing–response relationships cannot be made. These systems’ properties, which are incompatible with the ‘strong’ Principle of Uniformitarianism, include: • Earth surface systems do not exist at steady state or in equilibrium with respect to the combination of external forcings that drive system behaviour. Studies have shown that the workings of Earth systems under ongoing climate change (global warming) and direct human activity in combination are increasingly exhibiting Venetoclax datasheet these systems attributes, listed above (Rockström et al., 2009). Earth systems are now operating in ways that are substantially different to how they are believed to have operated in
previous geologic time periods, irrespective of how such systems are or have been measured (e.g., Edwards et al., 2007). Earth systems modelling (e.g., Phillips, 2003, Phillips, HAS1 2009, Phillips, 2010 and Von Elverfeldt and Glade, 2011) has shown that single equilibrium states are rarely achieved and that many systems appear to have multiple or non-equilibrium states (Renwick, 1992). Moreover, nonlinear feedbacks result in both complex system behaviour and unpredictable outcomes as a result of forcing (Murray et al., 2009 and Keiler, 2011). As a result of this greater knowledge of systems behaviour, Earth systems as viewed today have greater
dissimilarity to those that were initially considered by Lyell and others. The Principle of Uniformitarianism derived from those early studies has thus lost its relevance to Earth system processes viewed today and in light of the Anthropocene. Predictability in the context of Earth systems refers to the degree to which the dynamics (or workings) of a system can be forecast into the future based on our understanding of its previous behaviour. This process is dependent on defining both the present state of the system and the outcome of a measurement, which refers to how systems are monitored in order to identify changes in system state. The Principle of Uniformitarianism implies that, by analogy and comparison with the processes that represent the behaviour of present systems, the behaviour of past systems can be evaluated and – by inference – predicted.