Ice Sheets and the Anthropocene

Ice could play a role in identifying and defining the Anthropocene. The recurrence of northern hemisphere glaciation and the stability of the Greenland Ice Sheet are both potentially vulnerable to human impact on the environment. However, only a very long hiatus in either would be unusual in the context of the Quaternary Period, requiring the definition of a geological boundary. Human influence can clearly be discerned in several ice-core measurements. These include a sharp boundary in radioactivity due to atmospheric nuclear testing; increases, unprecedented at least in the Holocene, in Greenland concentrations of sulphate, nitrate and metals such as lead; the appearance in ice-core air bubbles of previously undetectable compounds such as SF6; and the rise, unprecedented in the last 800 ka, in concentrations of carbon dioxide and methane. Some combination of these changes could be used by future generations to clearly identify the onset of a new epoch defined at a particular calendar date. However, it is not yet clear what the character of the fully developed Anthropocene will be, and it might be wise to let future generations decide, with hindsight, when the Anthropocene started, acknowledging only that we are in the transition towards it. Gold Open Access: This article is published under the terms of the CC-BY 3.0 license. Lifeless planets evolve in response to changing energy levels from their Sun, bombardment by material from space, and internal geological forces. Many aspects of the Earth, however, have long been influenced by the appearance of new forms of life. For example, the emergence of cyanobacteria led to the formation of an oxygen-rich atmosphere over 2 billion years ago, while the emergence of land plants significantly altered the Earth’s albedo. Individual species can dominate local habitats, and significantly change their appearance. However, in the recent past, a single species (Homo sapiens) has begun to alter major aspects of the Earth system at a global scale. Perhaps the most obvious manifestation of this occurs in the carbon cycle, where increased concentrations of carbon dioxide (CO2), well beyond the natural range, are due to anthropogenic emissions. These increases are expected to lead to global-scale climate change and acidification of the ocean, with effects lasting for thousands of years. In this and a number of other aspects of the Earth system, human activity is now a force that is stronger than geological activity, and one that overwhelms the buffering abilities of natural systems. It has therefore been proposed that we are now in a new period of time, coined the ‘Anthropocene’, in which humans have become a controlling influence of the Earth system (Crutzen 2002; Steffen et al. 2011). This is an interesting concept for describing the extent of human influence on the environment, and therefore for emphasizing the extent of human responsibility for managing that environment. However, it has now been taken further, with some authors proposing that the Anthropocene should be formally recognized as a geological epoch (Zalasiewicz et al. 2008, 2011), on a level with the Holocene and Pleistocene that precede it. Such an idea has to be considered from the viewpoint of a geologist viewing sequences thousands or millions of years in the future. Would they be able to recognize that defining characteristics of the preceding epochs had been definitively replaced by new ones in which anthropogenic forces dominated? What would they characterize as the features of the new epoch? What date would they assign as the start of the new epoch, and what feature would they want to use to delineate that start? One difficulty in answering these questions is that, in contrast to all other geological time periods, we do not yet know what the Anthropocene will look like. CO2 concentrations have so far risen from about 280 ppmv in pre-industrial times to just under 400 ppmv in 2013. Under current trends, they could easily rise to between 500 and 1000 ppmv. Climate change is under way, and although global mean temperature remains within the bounds already seen during the Holocene (Marcott et al. 2013), this is unlikely to be the case later this century. The Greenland and Antarctic Ice Sheets have not yet created large changes in landscape or sea level, but some projections suggest they might in the next few centuries. From: Waters, C. N., Zalasiewicz, J. A., Williams, M., Ellis, M. A. & Snelling, A. M. (eds) 2014. A Stratigraphical Basis for the Anthropocene. Geological Society, London, Special Publications, 395, 255–263. First published online November 25, 2013, http://dx.doi.org/10.1144/SP395.10 # The Authors 2014. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics at British Geological Survey on January 19, 2015 http://sp.lyellcollection.org/ Downloaded from