Period of Debate

Erle Ellis, Mark Maslin, Nicole Boivin and Andrew Bauer, “Involve social scientists in defining the Anthropocene,” Nature 540 (December 2016), 192–193

Jan Zalasiewicz, Colin Waters and Martin J. Head, “Anthropocene: its stratigraphic basis,” Nature 541 (January 2017), 289

Karen L. Bacon and Graeme T. Swindles, “Could a potential Anthropocene mass extinction define a new geological period?” Anthropocene Review 3:3 (2016), 208–17

Philip L. Gibbard and John Lewin, “Partitioning the Quaternary,” Quaternary Science Reviews 151 (2016), 127–39

Last week’s paper is the most systematic recent contribution to the debate about the Anthropocene’s stratigraphic formalization. Here’s a round-up of a few others.

Ellis, Maslin, Boivin and Bauer’s short polemic in Nature swerves between misunderstanding and something rather like paranoia. The misunderstanding lies in their belief that the Anthropocene epoch in its stratigraphic sense is supposed to begin with the beginning of “human influence” on the planet. As Maslin and Erle put it in an amplifying article in The Conversation, they’re under the impression that the Anthropocene Working Group have decided “to declare the start of human transformation of Earth in the 1950s.”

That’s wholly mistaken, as anyone who’s read any of the AWG’s papers (and regular readers of this blog) will know. The base of the Anthropocene is meant to correspond to a change in the rock record that distinguishes the present state of things from the way things were in the (also very human-influenced) Holocene epoch. The beginning of “human influence” has nothing to do with it.

Ellis et al. think that the formalization of the Anthropocene would “divide Earth’s story into two parts: one in which humans are a geological superpower—an epoch called the Anthropocene—and the other encompassing all that came before.” As a matter of actual numerical fact, adding this further epoch would mean that geologists had divided Earth’s story since the Cambrian explosion (the last 541 million years) into thirty-nine parts instead of thirty-eight.

The paranoia creeps in from the opening sentence: “Three dozen academics are planning to rewrite Earth’s history.” What the AWG are planning to do is to submit a proposal to a scientific sub-commission that might vote to forward it to a scientific commission that might in turn vote to pass it on to a scientific union for ratification. The procedure that’s being envisaged for reforming the Geologic Time Scale could hardly be more cautious, or carried out more in public view. But Ellis et al. strike a monitory tone:

The formalization of the Anthropocene must be more transparent and have wider input and assessment. The criteria for assessing the sciences of the new epoch need to be published and peer reviewed, rather than agreed in private meetings.

I don’t know what they mean by calling for published criteria for “assessing the sciences of the new epoch”: I suppose just criteria for “assessing the new epoch.” In which case, the good news is that the International Stratigraphic Guide (the standard “guide to stratigraphic classification, terminology, and procedure”) can be downloaded here. An entire discipline within geology is devoted to thinking about the criteria about which Ellis et al. are concerned, and the AWG’s publications make constant reference to them. It’s very hard to credit the claim that the rules are being made up in “private meetings.”

But here’s the really strange thing. The Nature article implies—and the Conversation article implies more heavily—that there’s something unseemly, if not downright suspicious, about how the AWG excludes critical voices from its membership. “We teamed up with colleagues to challenge the Anthropocene Working Group’s view of the world,” Maslin and Ellis say. The AWG must “open its decision-making processes to review.” One could read both articles—and, most notably, Erle Ellis’s disclosure statement appended to the latter—without realising that the members of the AWG and the signatories of last week’s paper by the AWG include, well, Erle Ellis.

Zalasiewicz, Waters and Head’s letter in the next month’s issue of Nature is a brief, patient explanation that “the ‘anthropogenic’ epoch of Ellis et al. is different” to “the geological Anthropocene.”

Karen Bacon and Graeme Swindles make an argument that I’m surprised isn’t made more often. The current crisis looks rather like the early stages of a mass extinction. On a crude but effective measure, a “mass extinction” is when 75% of living species are wiped out. We’re not remotely near that level at the moment, but the extinction rate is high and climbing. It’s a similar story with the rise in global temperature and atmospheric carbon. That’s an observation familiar from books like Elizabeth Kolbert’s Pulitzer-winning The Sixth Extinction. What Bacon and Swindles point out is that Phanerozoic mass extinctions have previously defined the ends of geological periods, if not geological eras, rather than geological epochs (epochs fit inside periods; periods fit inside eras). So it might be too hasty to identify the Anthropocene now as a new epoch:

Perhaps debates over the timing of the Anthropocene boundary would be better focused on considering the likelihood of a new period in the next century rather than a new epoch in the 20th century to define the age of human dominance on the Earth System. In the mid-term future, a new period boundary may completely overwrite the proposed epoch boundary for the Anthropocene. (p. 231)

That’s a reasonable argument for which I have quite a bit of sympathy (though here again we see a glimpse of that red herring about “the age of human dominance”). But it’s an argument to which the AWG responded convincingly in last week’s paper, albeit without citing Bacon and Swindles directly. The AWG’s aim is to represent the geological column as it actually exists right now. It’s not to establish the final and definitive version of the Geologic Time Scale. As they write:

Waiting until fuller effects become clear would be in essence an appeal to the future, a path we are trying to avoid in documenting extant geologic evidence for an Anthropocene epoch. Recently elapsed (and in part irreversible) changes already imprinted on the stratigraphic record provide reasonable evidence that epoch-scale change has now taken place. (p. 218)

Gibbard and Lewin’s paper gives a longer view: it’s about the conceptual organisation of the Quaternary period as a whole, not just the Anthropocene. Philip Gibbard is, like Erle Ellis, a member of the AWG who’s more sceptical than most of the move towards stratigraphic formalization. Unlike Ellis he’s himself a geologist, and he wasn’t one of the 26 members who signed last week’s paper. In fact, “Partitioning the Quaternary” and a couple of other papers he co-authored were among the critiques to which last week’s paper responded

Gibbard and Lewin reflect on how the Quaternary should be partitioned, but also and more interestingly on how one should think about those partitions. The question of how to demarcate the Quaternary and its sub-units can stir up ferocious controversy amongst specialists. But the actual fixing of boundaries is only one part of a continuous process of interpretation. That’s true of any historical interval. When you organise a continuous span of time into sections (“late antiquity,” “the High Middle Ages,” “the boomer era,” or whatever), the dividing lines always come packaged up with attitudes towards those lines that might well matter more than the lines themselves.

Hence Gibbard and Lewin: “Without hierarchical subdivision, stratigraphic history would seem the equivalent of an interminable tsunami with associated surges, waves, ripples and organic flotsam,” but when you make such divisions, “it can be that researchers are guided towards putting everything into pre-defined time boxes that they do not actually fit. Sharp changes may be overemphasized when there are only markers of convenience in continuous trajectories” (pp. 137, 128). It’s not just a question of where you place (for instance) the Holocene–Anthropocene boundary. It’s equally a question of precisely what convenience you think you gain from that “marker of convenience.”

Gibbard and Lewin don’t have an enormous amount to say about the Anthropocene itself in this paper. Other live debates—the relative place of climate and paleontology in partitioning the Quaternary; the nature and status of the puzzling climatic transition in the early to middle Pleistocene—take up more of their time. They’re clearly concerned, though, that fixing the Anthropocene’s stratigraphic base might foster that tendency they describe to “overemphasize” sharp changes within basically continuous processes: to mistake partitions in the Geologic Time Scale for “material essences” instead of “helpful artifice[s]” (p. 137). And they think that Earth System scientists have been pressing the case for a single start date for the Anthropocene, whereas geologists proper have (“ironic[ally]”) been more warily attentive to the temporal complexity of Earth-system responses to anthropogenic forcings.

I’m not sure that last is a fair representation of how the debate has gone so far. But it’s absolutely true that the Anthropocene epoch, like every other geologic time division, is neither more nor less than a  prospectively helpful artifice through which to try to articulate the history of the Earth. The refinement of that artifice, of that craft of conjunction and disjunction, is precisely what’s at issue.

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