Jan Zalasiewicz: ‘The Anthropocene has altered the Earth’s history.’

In the First Person

António Guerreiro

The ‘Anthropocene event’ has put geology and a few geologists centre stage, but conflicts arose within this scientific realm that sometimes had little to do with science. The geologist and palaeontologist Jan Zalasiewicz, emeritus professor at the University of Leicester, interviewed here, is a well‑known scientist. Responding to the decision made by a subcommission of the International Union of Geological Sciences, he made the point that, based on current research, there is undisputable scientific evidence that supports the concept that the Earth has entered a new geological epoch. The atmospheric chemist and Nobel laureate Paul Crutzen called this epoch the ‘Anthropocene’.

Jan Zalasiewicz is a renowned geologist and palaeontologist, emeritus professor at the University of Leicester. The history of Earth’s environments (surface and subsurface) spanning half a billion years is his main interest. His scientific insights are presented in books such as The Earth After Us: What Legacy Will Humans Leave in the Rocks? (2008) and The Planet in a Pebble: A Journey into Earth’s Deep History (2010). For some time, he has focussed on the Anthropocene concept, both on a scientific and on an institutional level. In 2008, as Chair of the Stratigraphy Commission of the Geological Society of London, he led the results of a year-long research exercise to a journal of the world’s largest geological association, the Geological Society of America. This was published as a question, prompting a debate that would not stop growing: ‘Are we now living in the Anthropocene?’

In the beginning of March of this year, Jan Zalasiewicz became well-known beyond the narrow circle of his scientific milieu when he publicly contested a vote organised by members of the Subcommission on Quaternary Stratigraphy (SQS), which is part of the International Commission on Stratigraphy, the body that supervises the Geological Time Scale. The events that led to this highly publicised protest are well-known and made headlines all over the world. The Anthropocene Working Group had spent more than a decade analysing the question of whether we have entered a new geological epoch marked by the irreversible action of humankind on the fundamental systems of our planet. After gathering abundant scientific evidence, they wrote a proposal that recommended official recognition of the Anthropocene concept. Most of the members of the SQS then rejected, with little discussion, this proposal to officially declare the Anthropocene as a new epoch of geological time. Jan Zalasiewicz formally protested the voting process, noting how the official Statutes of the International Commission on Stratigraphy had been violated in the process. He stated that this rejection vote should be annulled, considering the manner in which it was obtained. For the public what remained was this strange news: that the Anthropocene concept, which has entered everyday language and is legitimised by a vast bibliography, had been rejected by a group of scientists who had the power to make it official.

In this interview, Jan Zalasiewicz speaks about this incident and its consequences. At the same time, he makes clear that despite not being an official designation, the Anthropocene represents the reality of the colossal challenge faced by humanity today.

Leonardo da Vinci, A ravine, 1482–1485 © Photo: Scala, Florence / Royal Collection Trust, London

ANTÓNIO GUERREIRO In March, the International Union of Geological Sciences (IUGS) rejected a proposal that had been discussed for more than a decade: the official declaration, by the scientific institution that has the power to do so, that we are in a new geological epoch called the Anthropocene because it is caused by human action on the entire system of our planet. What were the arguments used to justify this rejection by 12 members of the IUGS subcommission involved? (Only 4 members voted in favour.)

JAN ZALASIEWICZ The rejection of the proposal to make the Anthropocene a formal epoch of the Geological Time Scale, via voting of members of the Subcommission on Quaternary Stratigraphy (SQS: part of the International Commission on Stratigraphy (ICS), which oversees the Geological Time Scale, which is itself in turn part of the IUGS), was accompanied by no commentary on, or specific responses to, the Anthropocene Working Group’s (AWG’s) lengthy (191 pages) and detailed proposal, itself largely a synthesis of many preceding studies by the AWG and others. Thus, no formal arguments were presented in response to the arguments and supporting evidence provided in the formal proposal, and no specific commentary or rejoinder to it accompanied the announcement of the vote: only the voting record was provided. The rejection – as announced via a New York Times article and based on comments by ICS and IUGS executive members in that and other articles – was based on more general objections that might be called philosophical, or ideological, that have been rehearsed (and responded to) almost from the beginning of the AWG’s analysis. Thus for many geologists, the Anthropocene is simply too short (just one human lifetime!), too much of a simplification of human history, and too political (in a discipline that has prided itself on dealing with a planet’s deep history, and not with its current travails). All these objections can be responded to. Thus, the Anthropocene is brief – but it has already irrevocably altered the course of Earth’s history, and this changing of planetary course will be changing the nature of the fossil record far into the future (even once humans have gone). It also represents Earth history, not human history – and the change here, as measured by, say, rises in greenhouse gas levels and their consequences, are both striking and geologically abrupt. And it is demonstrably real, and demonstrably already affects human lives, and so we must deal with its effects and consequences: the political implications are inescapable.

AG You, who were the head of the Anthropocene Working Group, one of the three working groups of the Subcomission on Quaternary Stratigraphy, pronounced yourself in favour of canonising the Anthropocene. As a geologist, palaeontologist and stratigrapher, what are your scientific reasons in favour of the canonisation of the Anthropocene?

JZ ‘Canonisation’ may not be quite the word I would use, with its quasi-religious resonances, but formalisation would be useful, and should still be sought, though this may take some time, and perhaps will need a new generation of geologists more attuned to the planetary changes currently underway. Simply, the Anthropocene, as identified by Paul Crutzen and analysed geologically by the AWG is real: the Earth System has indisputably departed from the relatively stable conditions that characterised the Holocene; that departure is marked by many distinct and unambiguous signals in recently formed strata, including radionuclides, plastics and many novel chemical compounds, and this means that the Anthropocene may be considered and explored in a geological context; and it has caused an irrevocable and permanent change in the trajectory of Earth history.

Caspar David Friedrich, Gebirgslandschaft mit Regenbogen [Mountain Landscape with Rainbow], 1809–1810 © Photo: Scala, Florence / De Agostini Picture Library / Museum Folkwang, Essen

Caspar David Friedrich, Das Eismeer [The Sea of Ice], 1823–1824 © Photo: Elke Walford / Scala, Florence / bpk, Bildagentur für Kunst, Kultur und Geschichte, Berlin / Hamburger Kunsthalle, Hamburg

"The Anthropocene event should be more correctly known as an Anthropogenic Modification Episode which does not replace an Anthropocene epoch, but could happily co-exist with it as a separate but complementary concept."

AG This decision by the IUGS has practical effects on how governments will face up to the challenges ‘face à Gaia’ (to quote a famous title by Bruno Latour). Are we witnessing a scandalous politicisation of science?

JZ The IUGS decision may have been partly taken to ‘keep politics out of the Geological Time Scale’. But that is now impossible, and indeed it may well have practical effects regarding, for example, policy decisions on issues such as climate change and biodiversity loss, if it helps maintain the (mistaken) impression that the current human-driven Earth System changes are fleeting, trivial and reversable. The IUGS decision has already been welcomed, say, by climate denial websites, and taken as justification of their negation of the scientific evidence of climate change. So it may, as one consequence, make it harder for us all to properly find ourselves ‘face à Gaia’. Bruno Latour was one of the great supporters of the work and findings of the AWG, and we use his memory and inspiration to carry on developing the Anthropocene as a valid de facto concept, even if it is not yet de jure.

AG There are various theses about the date on which the start of the Anthropocene can be established. The ‘Great Acceleration’, starting in the mid-20th century, is one of the dates that is often referred to. Do you also think that this is the most scientifically plausible date? Why is it important to establish a date?

JZ A number of dates have been proposed for the beginning of the Anthropocene, ranging back to 50,000 years or more, with the beginning of human impacts as expressed, for instance, by the use of fire, and by the start of human-caused large mammal extinctions on land. The Anthropocene was not conceptualized to denote all human impacts, though, but to mark a departure from the distinct and relatively stable planetary conditions, of surface chemistry, climate, biosphere and so on, that characterized the Holocene Epoch. This departure came, essentially, after the world became industrialized. Paul Crutzen originally suggested the beginning of the Industrial Revolution as a potential start date for the Anthropocene, and this was also considered by the AWG. But, when examined closely, the changes and the signals left in strata at that time did not provide a clear, effective boundary. The beginning of the rise of atmospheric carbon dioxide above Holocene background levels, for instance, took place in about the mid-19th century, but was almost imperceptibly slow, and so is hard to delineate precisely, while other signals (of industrial pollution, landscape modification etc.) were regional rather than global, and formed at different times in different places, as industrialisation spread across the Earth. With the Great Acceleration of the mid-20th century, though, such signals took a sharp, worldwide upturn, and were joined by many other unique signals (such as artificial radionuclides, plastics etc). The mid-20th century quickly became, and has remained, the optimum level to draw the boundary, and that was agreed by Paul Crutzen himself. It is important to draw a boundary because the Anthropocene is basically a measure of time, and any measure in science should be precise – as should the metre, the kilogram and so on. With a precise, agreed boundary one can systematically measure and compare processes between the Holocene and Anthropocene. For instance, Jaia Syvitski led an AWG study to show, inter alia, that total human energy consumption in the 74 years since 1950 exceeded total human energy consumption throughout all of the preceding 11,600 years of the Holocene. Such comparisons are insightful – but would lose much of their effectiveness and meaning without a stabilized, agreed and systematically used time boundary for the Anthropocene.

[...]