Discovering Earth's future in its past: Palaeohydrology and global environmental change

Palaeohydrology is the study of various past aspects of the hydrological cycle. It is accomplished by interpreting indices of past hydrological processes. By its focus on the effects of realized processes, palaeohydrology provides a critical scientific complement to studies that idealize hydrological systems in order to predict future change. Future habitability of the planet will surely require the guidance of scientific concepts, but it will also require a basis in the perception of change that compels people to act. Human perception is grounded in the concrete particulars of reality, not in the abstract idealizations of theoretical science. While we scientists may wish otherwise, say for a more enlightened public and political sector, it is pragmatic not to expect such on the short time scale of potential detrimental changes for Earth's habitability to humankind. The greatest repository of scientific knowledge for stimulating human perception is the geological past. This experience of the Earth is the only real evidence of global environmental change available. It can function scientifically as a source of data with which to test models of change, confirming or falsifying theoretical extrapolations to past states (retrodictions). However, its more important role is as a source of discovery. In the geological record the scientist can discover previously unanticipated realizations of hydrological processes that will require new or revised models (hypotheses) for their explanation. It is our challenge as scientists to devote as much effort to exploring this real world of Earth experience as we currently apply to idealizing the abstract world of Earth systems.