Injecting Climate Modeling into Deep Time Studies: Ideas for Nearly Every Project

Studies of present and future climate change and of the connected issues of energy, pollution, and mineral resources strongly connect the geosciences with society. Global climate models (GCMs) have become an important tool in the study of climate. Their development since the late 1980s has been shaped by two needs: (1) to attribute the rapid rise in global mean temperature in the 20th and 21st centuries to its causes (2) to predict how climate will change in the future, particularly because much of recent climate change is attributed to human activities, as described in the reports of the Intergovernmental Panel on Climate Change (IPCC) (IPCC, 1990, 1996, 2001, 2007, 2014). Modeling contributions to the IPCC have mostly focused on the very recent past and near future of climate (1850–2100) (e.g., Taylor et al., 2012). However, it was soon recognized that models that could simulate a wider range of climates than during the instrumental record might simulate future climate better. Therefore, standardized GCM simulations of the middle Holocene (6 ka) and Last Glacial Maximum (LGM, 21 ka) were undertaken soon after the first IPCC Report in 1990. They are now considered valuable enough to merit an entire chapter in IPCC’s (2007) Report (Joussaume et al., 1998; Crucifix et al., 2005). Geoscientists interested in the deep past, the history of the Earth solely recorded in the rock record (prior to the Pleistocene, 2.588 Ma), have suggested that climate change throughout Earth history is also relevant to the direction of climate today. They propose studying icehouse–greenhouse transitions during Earth’s history and designing standardized global climate model (GCM) experiments to understand them (NRC, 2011). Comparing these experiments with the geological record would (among other things) test the ability of GCMs to simulate the response of climate to large, rapid changes in greenhouse gases (Valdes, 2011; Zeebe, 2011; NRC, 2011). GCM simulations of the Earth’s deep past are nothing new (e.g., Kutzbach and Gallimore, 1989), but, to borrow from medical parlance, they long have been an off-label use. However, there are at least three reasons why observers of deep time (geologists, geochemists, paleobiologists, etc.) should continue to engage with the broader climate science enterprise represented by the IPCC by further integration of observational studies with GCM simulations. First, deep time climate studies relevant to present day climate could open new funding opportunities for the academic sedimentary geology and paleobiology community, which has significantly contracted in recent years in the U.S. (Parrish et al., 2011). Second, many GCMs do not just model the atmosphere but consider the ocean, the land surface, and the cryosphere in their abiotic and (increasingly) biotic characteristics (see Heavens et al., 2013 for an overview). These new capabilities may allow more direct simulation of some aspects of the geological record. Finally, the expanding capabilities of GCMs can pose new technical challenges for modeling deep time climates, which also would merit more ABSTRACT