What is the Anthropocene?
Since the atmospheric chemist and Nobel Prize winner Paul Crutzen first mooted it in 2000, a variety of Earth scientists have been arguing that the Anthropocene should be added to the Geological Time Scale. This official scale, determined by the International Commission on Stratigraphy, divides the Earth’s 4.5-billion-year history into eons, eras, periods, epochs and ages, with each division of diminishing length and geological significance. After gathering a multitude of evidence from a range of sources, the Commission’s Anthropocene Working Group will advise on whether the Anthropocene should be officially deemed the successor to the Holocene. The Holocene is the epoch that began at the end of the last Ice Age some 12,000 years ago, and which stabilised 10,000 years ago at a global temperature that, with small variations, persisted until humans began changing the global climate measurably. A formal decision on whether a new epoch has begun is expected in 2016 or 2017.
The Anthropocene’s starting date is a matter of debate. Crutzen and his co-authors initially nominated the beginning of the industrial revolution at the end of the eighteenth century (Crutzen 2002
; Steffen et al. 2011
). Others have suggested it began with the development agriculture some 7,000 or 8,000 years ago (Ruddiman 2003
), although the evidence suggests human impact was not enough to destabilise the Earth system until humans began burning fossil fuels in large quantities. More recently, opinion seems to be converging on the date of 1945, the onset of the ‘Great Acceleration’ whose impact on the Earth system is unambiguous (Zalasiewicz et al. 2014
). That year is also the one in which a layer of radionuclides was spread over the Earth’s surface, a layer that will act like a flashing light for geologists of the future. Some Earth scientists argue that the human-induced changes to the Earth system are so great and enduring that, rather than entering a new epoch
(a relatively minor stratigraphic division), the Earth is now entering a new geological era
, the Anthropozoic, which succeeds the Cenozoic that arose with the Cretaceous extinction event 65 million years ago (Langmuir and Broecker 2012
The concept of the Anthropocene has been developed and explored by various disciplines, including atmospheric chemistry, climatology, oceanography and geology. More recently, it has been further elaborated in an interdisciplinary dialogue with historians and social scientists (Hornborg and Crumley 2006
; Steffen et al. 2011). Interest beyond the natural sciences is burgeoning because it represents a ground-breaking attempt to think together Earth processes, life, human enterprise and time into a totalising framework. We suggest that it entails three definitional dimensions and two powerful and compelling claims that call for new thinking in the social sciences and humanities.
A first definition of the Anthropocene proposes a new interval in geological
history. Stratigraphers – geologists who study rock strata – have a centuries-old epistemic culture based on specific, narrow but stringent kinds of evidence to delimit geological intervals (Rudwick 2005
). To separate two intervals they usually attribute more value to oceanic sediment series for their consistency and continuity of records. It is in such series that they try to detect major geological turning points ascertained by lithological, palaeontological and isotopic evidence. If the evidence is sufficient, a Global Boundary Stratotype Section and Point, or golden spike, is placed in the record to delimit a new interval. According to this stratigraphic definition, the Anthropocene is, to date, only a potential geological epoch, not yet officially validated. As geologists need to take time to agree on hard evidence, and this hard evidence will have to be found in sediments and rocks, official validation may take some years or decades.
A second definition of the Anthropocene arises out of Earth system science, a domain that assembles a wide array of disciplinary expertise (climatology, global ecology, geochemistry, atmospheric chemistry, oceanography, geology and more) around a shared complex systems perspective on the Earth (Steffen et al. 2005
). This Earth system approach, fueled by the dramatic increase in data on the different ‘spheres’ of the Earth (lithosphere, hydrosphere, cryosphere, biosphere and atmosphere) allowed by Earth monitoring programs, takes a broader view of changes to the Earth than geology traditionally has. This concept of the Anthropocene grows from an interdisciplinary ‘Earth system science’ perspective that views the Earth as a total entity, stretching from its core to the upper atmosphere, in an unceasing state of flux driven by energy and material cycles. Although ‘geological’ in its broadest sense, it does not seek evidence only in rock strata. With this wider lens, Earth system science claims that the Earth as a system is experiencing a shift, leaving behind its Holocene state, characterised by several millennia of exceptionally stable temperatures and sea levels, to enter a new Anthropocene state with far-reaching impacts. In this definition, as noted by Jan Zalasiewicz, chair of the Anthropocene Working Group, ‘the Anthropocene is not about being able to detect human influence in stratigraphy, but reflects a change in the Earth system’ (Zalasiewicz 2014
). The words to focus on here are ‘Earth system’, for to grasp his meaning requires a new way of thinking.
This approach supports the declaration of a new epoch by deploying an array of evidence in addition to stratigraphic evidence, including evidence of anticipated sea-level rise due to anthropogenic warming, large-scale shifting of sediment, rapid rates of species extinction and prevalence around the globe of artificial organic molecules (Zalasiewicz et al. 2012
). The well-known work on ‘planetary boundaries’ dovetails with this approach (Rockström et al. 2009
). A tipping point has been reached beyond which ‘the Earth system is now operating in a no-analogue state’ (Crutzen and Steffen 2003
, 253). Here we are no longer talking about the spread of human influence across ‘the face of the Earth’ (the geographical and ecological approaches that predominated in the twentieth century) but of a shift in the total system (Hamilton and Grinevald 2015
A third definition of the Anthropocene describes an even wider notion of human impact on the planet, including transformations of the landscape, urbanisation, species extinctions, resource extraction and waste dumping, as well as disruption to natural processes such as the nitrogen cycle. This is what James Syvitski (2012)
refers to as ‘the cumulative impact of civilisation’. In this usage the Anthropocene represents a threshold marking a sharp change in the relationship of humans to the natural world. It captures the step-change in the quality of the relationship of the human species to the natural world represented by the ‘impossible’ fact that humans have become a ‘force of nature’ and the reality that human action and Earth dynamics have converged and can no longer be seen as belonging to distinct incommensurable domains.
If the Stratigraphy Commission, with its narrow remit, were to decide there is not yet enough evidence to declare that the Earth has entered a new geological epoch, the term will continue to be used in the second meaning and a fortiori in the third, even broader and looser, sense. The first definition requires evidence from rock strata while the other definitions are based on data and norms of proof from a wider array of scientific disciplines. The first is descriptive and evidentiary, while the other definitions call in addition for further causal and systemic investigations.
Radically new implications for our worldviews
The Anthropocene thesis is also embodied and embedded in various kinds of grand narratives – a mainstream naturalist narrative, a post-nature narrative, an eco-catastrophist narrative and an eco-Marxist narrative – analysed by Christophe Bonneuil in Chapter 2
of this volume. It seems to us that, beyond the three definitions and these diverse narratives, the Anthropocene thesis makes two powerful and compelling claims that need to be addressed by the social sciences and humanities. First, it claims that humans have become a telluric force, changing the functioning of the Earth as much as volcanism, tectonics, the cyclic fluctuations of solar activity or changes in the Earth’s orbital movements around the Sun. Palaeoclimatologists, for instance, estimate that human-induced greenhouse gas emissions may be enough to suppress the glacial cycle for the next 500,000
years (Archer 2009
). Whatever the chosen date for this human hijacking of the Earth’s trajectory, acknowledging the Anthropocene means that natural history and human history, largely taken as independent and incommensurable since the early nineteenth century, must now be thought as one and the same geo-history (Chakrabarty 2009
) – developed further by Dipesh Chakrabarty in Chapter 4
of this volume – with the addition of this new, dominant and willing telluric force. This marks the end of nature as no more than the external backdrop for the drama of human history, and the end of the social-only shackles of modern understanding of society. Modern humanities and social sciences have pictured society as if they were above material and energy cycles and unbound by the Earth’s finiteness and metabolisms. Now they must come back to Earth. Their understandings of economy and markets, of culture and society, of history and political regimes need to be rematerialised. They can no longer be seen only as arrangements, agreements and conflicts among humans. In the Anthropocene, social, cultural and political orders are woven into and co-evolve with techno-natural orders of specific matter and energy flow metabolism at a global level, requiring new concepts and methods in the humanities.
The second claim made by the Anthropocene concept and related Earth system science studies is that the human inhabitants of our planet will face, in a time lapse of just a few decades, global environmental shifts of an unprecedented scale and speed, not since the emergence the genus Homo
some 2.5 million years ago and certainly not in the mere 200,000 years that Homo sapiens
have been walking the Earth. For instance, the current intensity of biodiversity loss is unmatched since the fifth mass extinction some 65 million years ago that saw some three-quarters of plant and animal species on Earth, including the dinosaurs, vanish. And a climate 4°C hotter by the end of the twenty-first century – every day seeming more like an optimistic
scenario – has not enveloped Earth for 15 million years. Other parameters – such as human-induced disturbances to the nitrogen and phosphorus cycles, ocean acidification and synthetic chemical pollution – may alone or severally soon reach a tipping point, pushing the Earth – and thus the conditions for life on Earth – into a radically new state (Rockström et al. 2009). So rather than a mere global ecological crisis, the Anthropocene thesis heralds a new geological regime of existence for the Earth and a new human condition. If all humans (and, in particular, the richest 7 per cent to which we the editors belong and who are responsible for half of humanity’s global ecological footprint) were to become totally ‘green’ and all societies adopted ‘strong sustainability’ tomorrow, it might nevertheless take centuries or, more likely, millennia (if at all) to return to Holocene-like conditions. Meanwhile, living in the Anthropocene means living in an atmosphere altered by the 575 billion tonnes of carbon emitted as carbon dioxide by human activities since 1870 (Le Quéré et al. 2014
). It means inhabiting an impoverished and artificialised biosphere in a hotter world increasingly characterised by catastrophic events and new risks, including the possibility of an ice-free planet. It means rising and more acidic seas, an unruly climate and its cortege of new and unequal sufferings. It’s a world where the geographical distribution of population on the planet would
come under great stress. And it is probably a more violent world, in which geopolitics becomes increasingly confrontational (Dyer 2008
). Furthermore, the emergence of the Anthropocene leads naturally to the question of what lies beyond it. Though its starting point is debated, the matter of its end poses fundamental questions: What kind of geological epoch or era will follow the Anthropocene? Will there be a permanent Anthropocene state of the planet with humans steering and engineering the whole Earth system? Is it an epoch in which human activities and the Earth system have reached a new balance, so that humans are no longer the main agents for change? Or is it an epoch in which humans are simply no longer present on the surface of the Earth?
Reinventing a life of dignity for all humans in a finite and disrupted Earth has become the master issue of our time. If we are entering an era beyond the experience of human beings, it is one for which there has been no biological adaptation and no cultural learning or transmission to prepare us for the kind of environmental/geological changes that loom. This constitutes a new human condition. Nothing could call more insistently for new social sciences and humanities research, for the human being who finds itself in this uncertain and radically new age is above all an assemblage of social systems, institutions and representations.
The advent of the Anthropocene challenges some established boundaries between nature and culture, between climate and politics, between natural sciences and the social sciences and humanities. The point here is deeper than a call for interdisciplinarity around hybrid ‘socio-ecological’ objects. The conception of the natural world on which sociology, political science, history, law, economics and philosophy have rested for two centuries – that of an inert standing reserve of resources, an unresponsive external backdrop to the drama of human affairs – is increasingly difficult to defend. And in an epoch in which ‘Gaia’ has been reawakened, the social-only conceptions of autonomy, agency, freedom and reflexivity that have been modernity’s pillars since the nineteenth century are trembling. The idea of the human, of the social contract, of what nature, history, society and politics are all about – in other words, all of the essential ideas on which these disciplines have been constructed – ask to be rethought.