The third of the new AWG articles is a long review essay with a colossal scope, by Mark Williams and 24 others: “The Anthropocene: a conspicuous stratigraphical signal of anthropogenic changes in production and consumption across the biosphere.” It’s open-access in Earth’s Future.
The title refers to the Anthropocene as a signal, not as an epoch. To think about the current catastrophe as the emergence of a new geological epoch is to credit it with a pretty huge scale: the catastrophe would have to be something unprecedented for thousands, maybe millions, of years. But this article is an invitation to think about the Anthropocene as an even more radical novelty. That’s not (necessarily) as an alternative to the Anthropocene-as-a-new-epoch way of looking at things: many of these 25 authors have been to the fore in proposing the idea of an Anthropocene epoch. But discussions of golden spikes take a back seat here. Maybe, in order to really understand the ecological presence of human modernity, you have to interpret it as something “more fundamental” still.
The paper is an expansion of one that was published just in time for me to draw on it in my increasingly-imminently-forthcoming book. That was “The Anthropocene Biosphere,” also lead-authored by Mark Williams. But there are other, much older antecedents for this paper. In Buffon’s Epochs of Nature (1778), the “Seventh, and Last Epoch” is that in which “the power of Man supplements that of Nature”: for Buffon, the interval marked by human presence was one of the seven grand divisions in the history of the planet. That’s not what Williams and co. argue, but it’s not so far off.
Whereas Buffon’s seven epochs were stages in the physical composition of the earth, however (animals only enter the scene for the final three), Williams et al. are specifically concerned with the biosphere, and with its most absolutely cardinal turning points.
The first in their list is the evolution out of prebiotic chemistry, around 3.8 billion years ago, of sulphur-eating bacteria—beings that were confined to the chemically lively settings of volcanoes and hydrothermal vents. The second is the evolution of oxygenic photosynthesis no later than 2.5bn years ago, which caused the Great Oxygen Catastrophe that sizzled away most forms of anaerobic life and triggered an immense glaciation, but also allowed for the first truly global biosphere. They roll the evolution of eukaryotes, and of multicellular organisms, into that stage of life.
Their third transition is the evolution of metazoans (animals), beginning 800 million years ago and culminating in the Cambrian revolution: complex behaviour and Treptichnus pedum-like burrowing into the sub-sea sediment layer. The fourth is the colonization of land from about 460 million years ago: the spread of life into a realm in which plants rather than animals dominate the biomass.
“Measured against these changing geological-scale patterns, is the human impact on the biosphere significant?” Williams et al.’s answer to their own question is a cautious “yes.” The rise of humans, they think, might—might—count as the latest transition on that grandest of scales. So the six consecutive “worlds” that they envisage are:
- The prebiotic world
- The anaerobic microbial world
- The aerobic microbial world
- The “metazoan world—oceans”
- The “metazoan world—land and oceans”
- The human world
What kind of modern anthropogenic effects could compare to those seen in the four previous transitions on this list? Merely in order for the Anthropocene to count as an “epoch,” the significance of modern-day changes needs to be akin to those of the post-glacial warm-up 12,000 years ago at the birth of the Holocene, or even to the joining of North and South America at Panama three million years ago. Fine. But what might put recent biospheric changes up there on the same level as the original flooding of the atmosphere with oxygen?
Different kinds of evidence are needed, clearly. For instance, compared to work on Anthropocene stratigraphy narrowly defined, the paper generally plays down the significance of modern species relocations. That’s often seen as one of the biggest ways in which recent centuries will leave geological traces in the far future, but shifting even many thousands of species all around the world is hardly on a par with the very evolution of animals as such.
Instead, the Haber-Bosch process is at the heart of Williams et al.’s analysis. They point to climate change, ocean acidification, and species extinctions too. A key source, however, is this paper, and its oft-cited claim that
Humans may have produced the largest impact on the nitrogen cycle since the major pathways of the modern cycle originated some 2.5 billion years ago.
That certainly is grist to their mill. The nitrogen cycle is one of the central cogs of the earth system. The combination of the Haber-Bosch technique to produce reactive nitrogen, and of mining millions of years’ worth of fossil fuels to power that process on a large scale, is a big deal however far back you stand. Williams and co. stress that the new state of the nitrogen cycle has helped radically to expand the sheer magnitude of (parts of) the biosphere: all those cattle, sheep, and pigs add up to maybe a tenfold multiplication in the global biomass of large terrestrial vertebrates. So their central argument is about the human expansion and “appropriation” of Net Primary Production: the increase in the amount of carbon contained in biomass, and the fraction of that carbon that’s used for human ends (between 25% and 38%, they reckon).
Thus, [they conclude,] it can be argued that the scale of human change to the biosphere with its transformation of terrestrial and marine ecologies, its use of fossil fuels to elevate the energy available to the global ecosystem, its impact on the standing biomass of terrestrial vertebrates, and its displacement of apex predators in both terrestrial and marine foodwebs, is of the magnitude of past major changes in the biosphere [like those in the list above].
What are the implications of that argument? I think that what’s most interesting about this paper is the way in which it draws on two different interpretations of human impact on the biosphere.
First of all, I’m not really taken with the whole notion of calculating the overall level of human appropriation of Net Primary Production. I’m persuaded, instead, by Vaclav Smil’s argument that the concept is subject to so many problems of definition that it ultimately isn’t useful. Smil writes:
Human appropriation of global net primary production is not just a poorly defined measure whose quantification depends on an abstract modelled value and on a concatenation of variables whose values have considerable margins of error. More fundamentally, it is a concept whose unambiguous formulation would be very difficult, whose practical applications are questionable because of some of the necessary underlying assumptions, and whose final ratio reduces many complex processes into a single figure that is hard to interpret.
I think that’s probably true. For reasons that Smil explains in great deal, I don’t think you can really say that humans co-opt 25–38% of the biosphere’s total productivity. But what’s the significance of the supposed new human dominance of NPP, anyway?
On the one hand, you could argue that it constitutes a fifth basic quantitative change in the underlying patterns of energy and carbon flow through the biosphere, “the Earth’s biological-consumption system.” From a dead world to a biosphere clustered around hydrothermal vents, to a worldwide biosphere of photoautotrophs, to a metazoan food web in the seas and seabeds, to a world of animal and plant life both on land and in the oceans… to a world in which humans’ “combined energy use now approaches that available to the entire terrestrial biosphere prior to human intervention.” That fifth transition is akin to the first four. On a disinterested view, a view from nowhere, the size and shape of the biosphere has changed to an extent that happens only very, very rarely. Perhaps.
Alternatively, you could justify this six-part view of earth history by pointing to the special qualities of human beings as a species. Williams et al. emphasise that the Phanerozoic biosphere (worlds 4 and 5 on their list) was characterised by a great diversity of species in which no single one dominated the rest. That’s changed. Just one species is now the top predator both on land and at sea, and at practically every biologically productive latitude and longitude. And, they further emphasise, “only humans use technology to modify Earth’s environment at a global scale.” That’s an observation about causation, rather than about consequences, and in that way it’s in contrast to the stratigraphy-of-the-Anthropocene tradition, which has focused very heavily on the ecological effects of modernity, deliberately bracketing the question of anthropogenic causation during the first stage of its analysis.
I think that probably this second line of argument is the only one that can really substantiate Williams and co.’s overall claim. I think that in order to see the Anthropocene as one of five basic transitions in the history of life, you need to reintroduce a certain measure of human exceptionalism and of progressivism (if not some teleology) into your view of the world.
In other words—and even though Jan Zalasiewicz is the second named author of this paper—I think that the argument made here by Williams and co. fits much more neatly than does most of Zalasiewicz’s recent work into the tradition in the philosophy of history that’s typically cited as ancestral to the idea of the Anthropocene. That’s the tradition that includes Buffon’s Epochs of Nature and runs up to Vladimir Vernadsky and Pierre Teilhard de Chardin. That tradition typically (a) divides the history of the physical world into a single-figure number of stages; (b) makes the final stage the “human” one; and (c) sees the defining feature of that final stage as the evolution of mind, the world’s evolution of self-reflexive consciousness, the progressive “cephalisation” of the biosphere, or some such. This paper, with its emphasis on the birth of technology and on humans’ deliberate pursuit of full-spectrum dominance of the food web, has a good deal in common with that tradition. If you want to argue that “it is reasonable to suggest that the biosphere has made one of the greatest transitions in the history of life and entered a new stage of its evolution” (the last words of the paper), you probably need to point to the unique properties of human intellection in order to make your case.
But in contrast to the three points of the Buffonian tradition, Zalasiewicz’s other recent work has tended to (a) make the Anthropocene just one of many intervals in the history of the earth; (b) reject the idea that it is the “epoch of humans” in any simple sense; and (c) define it by reference to empirical sedimentological traces rather than to causal mechanisms. Those are important differences, and they deserve to be explored much further.
For now, though, that’s it for these three early-2016 papers from the AWG members. They’ve each—the one on stratigraphy, the one on plastics, and this one—taken a long, long blog post to even begin to get to grips with them, and there’s no doubt much more to come (I plan to write here at some point about a recently published report on an AWG conference in Cambridge). The force and excitement of the work being done within the AWG at the moment is just huge.
Coming up next week: some thanks are due.