Evaluating the Anthropocene: is there something useful about a geological epoch of humans?

Braje, Todd J.

Introduction

In just 15 years, the term 'Anthropocene', proposed by Crutzen and Stoermer (2000) to describe a new geological era of our own making, has entered the collective consciousness of the public and scientific communities. Popular news, magazines and other media outlets have proclaimed the age of humans'; and scientists have adopted the 'Anthropocene' to denote a range of human impacts on the environment, with little consensus on precisely what the term means and when the Anthropocene began. Its widespread employment hinges on its usefulness as a rallying cry for collective action on anthropogenic climate change and the (largely) undeniable evidence that humans have destabilised the Earth system.

A loosely defined Anthropocene, centred on an ideological and political call for environmental action, seems to be in line with its intellectual roots. Since at least the mid to late nineteenth century, scholars and environmentalists have recognised the transformative effects of humans, called for responsible environmental stewardship (Marsh 1864) and proposed the dawn of a human age with terms such as the anthropozoic era (see Crutzen 2002: 23) and the noosphere (Vernadsky 1924: 342; Steffen et al. 2011: 844; see Hamilton & Grinevald 2015 for an alternative view). It was not until chemist Paul Crutzen and biologist Eugene Stoermer (Crutzen & Stoermer 2000; Crutzen 2002) offered an AD 1783 starting date (James Watt's invention of the steam engine and the start of the Industrial Revolution) for the age of humans and implicated anthropogenic methane (CH4) and carbon dioxide (C[O.sub.2]) emissions that the term came into use as an epoch-scale (or erascale) designation. In 2008, a discussion paper by a national stratigraphic commission determined that the Anthropocene has some geological merit and should be examined for formal designation, and considered as a potential subdivision of the Geological Time Scale (GTS; Zalasiewicz et al. 2008). Shortly after this, an invitation was extended from the Quaternary Subcommission of the International Commission of Stratigraphy (ICS) to form the Anthropocene Working Group (AWG). The AWG, consisting mostly of geoscientists, is tasked with evaluating whether a new geological time unit (included as part of the International Chronostratigraphic Chart) is warranted and, if so, when the Anthropocene began.

As our world population swells to 7.2 billion, C[O.sub.2], C[H.sub.4] and [N.sub.2]O accumulate in atmospheric records (Crutzen & Steffen 2003); anthropogenic clearance of land surface continues (Ellis 2011; Ellis et al. 2013); species extinctions and biodiversity declines accelerate (Barnosky et al. 2011); our world's oceans are transformed by overfishing, acidification and pollution (Jackson et al. 2001); spikes in human-made radionuclides from atomic detonations are identified (Hancock et al. 2014); and much more. It is untenable to argue that we are not living in the age of humans, and at a time when the Earth's natural systems are being heavily influenced by anthropogenic forces. Even more sobering is the prospect that the most dramatic and significant anthropogenic changes may still lie ahead, and that we are only on the proverbial doorstep of the age of humans (Wolff 2014). The AWG, then, must determine "whether the Anthropocene is geologically justifiable, whether its formalization is useful, and how it might be characterized and defined" (Zalasiewicz et al. 2013: 197).

A variety of boundary markers and chronostratigraphic units have been proposed for the Anthropocene (e.g. Crutzen 2002; Ruddiman 2003, 2013; Steffen et al. 2007, 2015; Zalasiewicz et al. 2008, 2015; Lewis & Maslin 2015), following the classical stratigraphic criteria of fossils, geochemical signatures and other hard rock standards. For the first time, however, geoscientists must think about the implications of the GTS beyond 'hard rock science'. It may be tempting or even comforting to consign Anthropocene debates that stray into socio-political arenas as a different type of Anthropocene (e.g. one that is sociological or anthropological). This creates an artificial and unrealistic divide between science and social issues. The tools of hard rock science cannot and should not free us from considering the wider social and political implications of our nomenclature, especially when designating geological time that hinges on humans. Never before has the designation of geological time been positioned to play such an important role in wider academic and public discourse. While there are certainly a number of strong opponents, my reading of the literature suggests that the Anthropocene is poised to become part of the formal geological lexicon (Zalasiewicz et al. 2011; Waters et al. 2014), either as an epoch equivalent to the Holocene, or as an age that is a subset of the Holocene. Either way, much of the conversation has turned away from whether an Anthropocene designation is useful to debates over when the Anthropocene began (for summaries, see Braje 2015; Zalasiewicz et al. 2015).

A recent publication by members of the AWG suggests that in early 2016 they will submit their findings to the ICS and recommend an Anthropocene with a mid-twentieth-century starting date, perhaps at AD 1945 (Zalasiewicz et al. 2015). This time period has been termed the 'Great Acceleration' (Steffen et al. 2007) and is characterised by exploding human population, massive increases in carbon dioxide, the intensification of agriculture, rapid globalisation and associated anthropogenic environmental transformations. Zalasiewicz et al. (2015) present a sound argument that such a division makes practical sense and that, as with any global transition, study of the driving forces is required across the stratigraphic time boundary, regardless of its placement. The Great Acceleration and AD 1945, then, offer a 'globally synchronous' and commonly understood' boundary marker (Zalasiewicz et al. 2015).

As an archaeologist specialising in the long-term dialectical relationship between humans and their environments, I believe that the challenges and disadvantages of designating a postindustrial Anthropocene as part of the GTS outweigh its usefulness, and the formalisation of a mid-twentieth-century Anthropocene may actually do more harm than good. We will lose much of the public and academic debate that has been stirred by investigating the longterm and accelerating influence of humans on the planet, and introduce a set of potentially harmful assumptions. Here, I present two major challenges to defining an Anthropocene as part of the GTS, and, if the Anthropocene is to be codified, the best option from my archaeological perspective.

A question of origins and scale

The question of when the Anthropocene began has been an especially prickly one, with very little agreement among the academic community. Some have argued for a specific biotic, atmospheric or stratigraphic marker, while others view the Anthropocene as a long-term process that played out over thousands of years. The challenge is that the Anthropocene is a uniquely human age, created by the ongoing actions of humans, and we can only speculate on the Anthropocene future that awaits us. As such, we lack the temporal distance that has always helped to evaluate boundary markers for geological time units and to identify appropriate Global Stratigraphic Section and Points (GSSP), so-called 'golden spikes (Zalasiewicz et al. 2008: 4), or Global Standard Stratigraphic Ages (GSSA). The AWG recognises this challenge and argues that even an arbitrary numerical age for the Anthropocene offers a practical solution and can provide continuity and agreement in our terminology (Zalasiewicz et al. 2008: 7). Zalasiewicz et al. (2015) argue that a GSSA of AD 1945, then, is a simple and direct marker of the Anthropocene that is based both on a historical event (the first detonation of an atom bomb at Alamogordo, New Mexico, on 16 July 1945) and a chemostratigraphic signal (the subsequent radiogenic fallout) (for other options, see Waters et al. 2015).

Many anthropologists, archaeologists and other scientists, on the other hand, argue that the Anthropocene did not begin either at the dawn of the Industrial Revolution or during the Great Acceleration. This seems to be, unfortunately, one of the few points of agreement among many of these scholars. The proposed start dates for a pre-industrial Revolution Anthropocene range broadly, from 50 000 to less than 500 years ago. Braje and Erlandson (2013a), for example, argue that the initial colonisation of continental landmasses by anatomically modern humans, beginning about 50 000 years ago, helped trigger the extinction of terrestrial megafauna and was the first step in a wave of anthropogenic extinctions that reshaped Earth ecosystems. Doughty et al. (2010) reach a similar conclusion after identifying a spike in birch pollen in Siberia, Alaska and the Yukon at c. 13 800 BC, due largely to natural climatic warming and reduced herbivory from anthropogenic mammoth extinctions. Smith and Zeder (2013) argue that the worldwide domestication of plants and animals between 11 000 and 9000 years ago, and the large-scale human ecosystem engineering that followed, should mark the Anthropocene. Under these scenarios, our current geological epoch, the Holocene, would be in jeopardy and potentially lost from the GTS.

Others are in favour of maintaining the Holocene, but for subdividing it into a smaller geological time unit to make way for the Anthropocene. Erlandson (2013) points to the worldwide appearance of coastal and riverine shell midden soils between 10 000 and 8000 years ago as one possible marker, a notion generally consistent with Edgeworth's (2013) anthropogenic pedospheres formed during the Neolithic. Certini and Scalenghe (2011) point to Anthrosols, but suggest around 2000 years ago as the time when intensive and repeated human activities such as ploughing, fertilisation and artefact deposition became a globally visible boundary marker. An Anthropocene marker tied to European colonialism somewhere between AD 1400 and the early 1800s also has been proposed, using the dramatic declines in plant and animal biodiversity (Lightfoot et al. 2013), or the millions of Native American deaths from Old World diseases, warfare and enslavement, which resulted in atmospheric shifts in C[O.sub.2], as a proxy (Lewis & Maslin 2015).

The common thread to all these proposals (and the many more that are beyond the scope of this manuscript, but see Braje 2015 for a more thorough coverage), including the post-industrial Revolution starting dates for the Anthropocene, is that they tend to be heavily influenced by the research agendas of their authors. This speaks to the very real challenges of defining a 'human age', 'human domination' and identifying the appropriate Anthropocene indicators and thresholds we should consult. That is, when did we cross the critical tipping point in anthropogenic biotic, stratigraphic or atmospheric changes in entering the Anthropocene? The Anthropocene boundary debate shifts discussions from macro to micro scales, from geological time over billions, millions and thousands of years to human time at centurial, decadal or annual scales. The AWG recognises these challenges and that the customary rules of geological taxonomy were never intended to fall within recorded human history. Zalasiewicz et al. (2011: 837) argue that the Anthropocene, in a similar way to the Holocene, can be designated out of practicality, rather than strict adherence to geological taxonomy. The result, however, has seen conflicts in the field of stratigraphy and a highly politicised debate, with some scientists questioning whether the Anthropocene is a 'pop culture' phenomenon or of serious geological concern (Autin & Holbrook 2012).

(Deep) history matters

A number of mostly social scientists have raised concerns over the Anthropocene and its potentially damaging inherent messages. The primary thrust of these may be that by designating an age of humans, we are therefore suggesting that all humans are equally to blame for our current and growing environmental crises. This neglects underlying issues of power, wealth and global social injustice, and the fact that those most responsible for creating the Anthropocene (wealthy, industrialised nation-states) will be the least susceptible to the potentially damaging consequences (Malm & Hornborg 2014). The Anthropocene naturalises' anthropogenic impacts to all humankind, and fails to recognise that anthropogenic climate change and environmental impacts will differentially affect the poor and under-privileged, and those living in marginalised or vulnerable places (and generally those least responsible for its creation).

Another related critique is that the Anthropocene takes a doggedly anthrocentric view of the world (past, present and future), and rather than exploring the causes of our ecological crises, separates humans from the natural world, placing us on a par with Earth's geological forces (Crist 2013; Visconti 2014). As part of a very Western view, nature, then, serves the good of humanity, and the Anthropocene becomes a time for technological and cultural triumph over our environmental crises. If post-industrial technological innovations propelled us into the Anthropocene, the logical way forward is to develop technologies that will help geo-engineer our future and make human domination sustainable. This is part of the so-called 'good Anthropocene' movement that encourages us to scale up rather than scaling back to fix the environmental challenges we face (Ellis 2011). Such a view takes us far afield from the foremost practical advantage of an Anthropocene designation--to raise awareness about the growing human footprint on earth and to rally efforts to "guide society toward environmentally sustainable management" (Crutzen 2002: 23)--and leaves us on very shaky ethical ground.

The underlying issue is that the Anthropocene, especially one determined by geo-scientists to have begun at AD 1945, neglects perhaps its most important elements: human history and the socio-cultural processes that created the age of humans (Malm & Hornborg 2014). This constructs a potentially fatalist mindset where we are "indirectly advised" that we now live in the human age and must suffer the consequences accordingly (Crist 2007: 55). In the Anthropocene, nature is dead and humans are in charge. Lost is the fact that human decision-making over millennia resulted in the creation of the Anthropocene; it is not simply an inevitable consequence of the human condition. A nuanced understanding of the modern world and our place in it as humans (and by extension the Anthropocene concept itself) requires deep historical perspectives on the intertwined cultural values and biological processes that created the present (Solli et al. 2011). A central component to both understanding and addressing the Anthropocene is tracking the deep historical processes that created the human age. The lessons of history and deep historical data are critical for modern efforts to restore and protect natural systems, and for building sustainable systems that will function in the future (e.g. Hobbs et al. 2011; Szabo & Hedl 2011). We need to be careful that the Anthropocene concept includes the message that just as human decision-making ushered in the human age, it will be human decision-making over the next millennia that can build a more sustainable fixture and restore a more natural world.

Do we need an Anthropocene?

Whether or not we need the Anthropocene, it is already here. Hoping it will go away because of its inherent flaws, and ignoring it, is probably not realistic. The Anthropocene concept has become deeply entrenched in academic and public discourse, and has, without question, sparked a wide range of interesting and useful debates. It has helped to raise public awareness about environmental issues, stimulated useful discussions across disciplinary boundaries and challenged climate change deniers. That is in keeping with its nineteenth-century intellectual roots and the goals of the environmental philosophers who first proposed an age of humans. It also is in line with Crutzen and Stoermer's (2000) goal of drawing attention to the accelerating modern environmental crises created by humans. The primary objective of the Anthropocene, then, should be continued discussions that move debates towards developing interdisciplinary socio-ecological solutions that address our world's environmental challenges. Rather than continuing to argue over thresholds, golden spikes and boundary markers, we need to focus on finding scientific, political and interdisciplinary solutions to the problems we face.

The question becomes, how do we maintain the Anthropocene's usefulness while limiting its inherent flaws and assumptions? The term is useful for geologists because it reflects a change in the Earth system so distinctive that future geologists, studying flora and fauna, ice cores, atmospheric records, stratigraphic layers and much more, will find clear human signatures. To geologists living a million years from now, it will make little difference whether the Anthropocene began in AD 1800, 10 000 years earlier or is marked by the invention of the steam engine or the first appearance of Neolithic tools. The processes that resulted in planetary shifts are what will be most important. If the Anthropocene is to serve a largely practical purpose, as have other geological epochs (see Zalasiewicz et al. 2011: 837), it should be to frame scientific enquiry focused on the long, complex and dynamic role humans have played in transforming Earth's biosphere (Smith & Zeder 2013: 12). Relegating the underlying processes that resulted in the human domination of Earth to a pre-anthropocene (Steffen et al. 2007) or palaeoanthropocene (Foley et al. 2013) overlooks the deep historical perspectives that are essential for interpreting modern systems and determining what is 'natural' from what is anthropogenic.

The best option I see for designating an Anthopocene is to merge the Holocene and Anthropocene into a single geological unit (see Braje & Erlandson 2013b: 120; Smith & Zeder 2013). The Holocene is just the most recent of a series of interglacial climatic cycles over the last two million years, and its designation has always been tied to humans--it demarcates the interval when many of the surfaces (soils, alluvial deposits, deltas and the like) on which humans currently live were formed (Zalasiewicz et al. 2011: 837). The Anthropocene can continue to be a useful term, as the Holocene/Anthropocene, to denote the growing human impacts on local, regional and global scales that accelerated after the domestication of plants and animals and the adoption of agricultural systems. A Holocene/Anthropocene Epoch forces us to step back and think about the long-term impacts of humans, which have been variable across time and space. This option recognises the deep history of human impacts and offers a clear message to scientists and the public about humanity's role in our growing environmental crises. A Holocene/Anthropocene Epoch makes no claims as to the specific moment when humans began to exert significant control over earth systems. Rather, this transition is viewed as a long-term process that grew out of the dialectical relationship between human cultural, political and economic systems and the natural world. The Holocene/Anthropocene sends the message that we are not destined to live in a strictly anthropogenic world. That is, in fact, impossible. No matter how quickly or how extensively human actions result in the melting of North Atlantic ice, for example, the world's natural systems will respond in kind--perhaps by altering thermohaline circulation and creating potentially devastating consequences for human livelihoods. The natural world survives and continues to operate in conjunction with human actions. The message of the Anthropocene should be that we still have a chance to develop sustainable systems that could reduce the scale and impact of these human activities.

This proposal shifts the focus away from the effects of the Anthropocene to its causes. The conversation turns from flora, fauna, gases and soils to the single most important player in the creation of the Anthropocene--humans and, in particular, human decision-making. Such a strategy should help stimulate interdisciplinary research efforts (DeFries et al. 2012). The Holocene/Anthropocene cannot be understood without collaboration across the sciences and humanities. Physical, biological and social scientists must work together to confront the Holocene/Anthropocene, diagnose the millennia-long causes that resulted in the age of humans and more effectively address environmental challenges across local to global scales.

doi: 10.15184/aqy.2016.32

Acknowledgements

Thanks to San Diego State University for their generous support of this research with a critical-thinking grant. A variety of colleagues have helped shape my thinking about the Anthropocene, and I have greatly benefited from conversations with, and support from, Jon Erlandson, Matthew Lauer, Bruce Smith and Melinda Zeder. Sopagna Eap, Torben Rick and two anonymous reviewers offered extremely helpful comments on earlier drafts of this paper. Thanks to Chris Scarre for inviting me to write this manuscript.

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Received: 10 September 2015; Accepted: 9 November 2015; Revised: 19 November 2015

Todd J. Braje, Department of Anthropology, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182-6040, USA (Email: tbraje@mail.sdsu.edu)