Article Progress in Physical Geography 2019, Vol. 43(3) 319–333 ª The Author(s) 2019 A formal Anthropocene is Article reuse guidelines: sagepub.com/journals-permissions compatible with but distinct from DOI: 10.1177/0309133319832607 its diachronous anthropogenic journals.sagepub.com/home/ppg counterparts: A response to W.F. Ruddiman’s ‘three flaws in defining a formal Anthropocene’ Jan Zalasiewicz Peter Haff School of Geography, Geology and the Environment, Duke University, Durham, NC, USA University of Leicester, UK John R McNeill Colin N Waters Georgetown University, Washington, DC, USA School of Geography, Geology and the Environment, Michael Wagreich University of Leicester, UK University of Vienna, Austria Martin J Head Ian J Fairchild Brock University, St Catharines, ON, Canada School of Geography, Earth and Environmental Cle´ment Poirier Sciences, University of Birmingham, UK Morphodynamique Continentale et Coˆtie`re, Daniel D Richter Universite´ de Caen Normandie, France Duke University, Durham, NC, USA Colin P Summerhayes Davor Vidas Scott Polar Research Institute, Cambridge Fridtjof Nansen Institute, Oslo, Norway University, UK Mark Williams Reinhold Leinfelder School of Geography, Geology and the Environment, Freie Universita¨t Berlin, Germany University of Leicester, UK Jacques Grinevald Anthony D Barnosky IHEID, Gene`ve, Switzerland Jasper Ridge Biological Preserve, Stanford University, Will Steffen Stanford, CA, USA The Australian National University, Canberra, Alejandro Cearreta Australia Facultad de Ciencia y Tecnologı´a, Universidad del Jaia Syvitski Paı´s Vasco UPV/EHU, Bilbao, Spain University of Colorado-Boulder Campus, Boulder, CO, USA Corresponding author: Jan Zalasiewicz, School of Geography, Geology and the Environment, University of Leicester, Leicester LE1 7RH, UK. Email: [email protected] 320 Progress in Physical Geography 43(3) Abstract We analyse the ‘three flaws’ to potentially defining a formal Anthropocene geological time unit as advanced by Ruddiman (2018). (1) We recognize a long record of pre-industrial human impacts, but note that these increased in relative magnitude slowly and were strongly time-transgressive by comparison with the extraordinarily rapid, novel and near-globally synchronous changes of post-industrial time. (2) The rules of stratigraphic nomenclature do not ‘reject’ pre-industrial anthropogenic signals – these have long been a key characteristic and distinguishing feature of the Holocene. (3) In contrast to the contention that classical chronostratigraphy is now widely ignored by scientists, it remains vital and widely used in unambiguously defining geological time units and is an indispensable part of the Earth sciences. A mounting body of evidence indicates that the Anthropocene, considered as a precisely defined geological time unit that begins in the mid- 20th century, is sharply distinct from the Holocene. Keywords Anthropocene, Holocene, chronostratigraphy, geological time scale, Earth sciences I Introduction II Anthropogenic impacts long Ruddiman (2018) raises important questions, preceded the mid-20th century, summarized as ‘three flaws’ in the definition the potential boundary level of a formal Anthropocene. His analyses and currently most closely studied by discussion of the Anthropocene concept, espe- the AWG cially as it touches on its interpretation in a chronostratigraphic context, is an important Such impacts have never been in doubt, nor component of the scientific process required questioned by the work of the AWG (e.g. to understand whether the Anthropocene Edgeworth et al., 2015; Zalasiewicz et al., should be added to the International Chronos- 2017, 2019). Pre-industrial anthropogenic tratigraphic Chart and hence the Geological impacts range from the megafaunal extinc- Time Scale. His arguments follow on from tions, starting *50 ka in the Late Pleistocene notable and ground-breaking studies of how (Koch and Barnosky, 2006), to the progressive humanimpactsmayinteractwithlanduseand and eventually widespread deforestation asso- climate (Ruddiman, 2003), and specifically on ciated with agricultural development from near how these interactions may relate to the the beginning of the Holocene, the ever-greater Anthropocene concept (Ruddiman, 2013; Rud- spread and population growth of humans, and diman et al., 2015, 2016). associated fauna (e.g. rats, pigs) and flora (rice, We emphasize here that the task of the wheat, maize, etc.) around the world, and, Anthropocene Working Group (AWG) is not locally, the development and spread of tech- to provide another prism through which to nology and urban centres (Zalasiewicz et al., reinterpret human history and environmental 2019). Indeed, anthropogenically reduced ver- impact, but rather to identify a practical stra- tebrate diversity, a rich archaeological record, tal and time marker as point of reference in and a progressively profound anthropogenic the formal classification of geological time. impact on terrestrial vegetation have long been In this context, we offer the following key features that distinguish the Holocene from responses to the points raised in Ruddiman’s the many preceding interglacial phases of the thoughtful analysis. Quaternary Period. Zalasiewicz et al. 321 Consideration of the scale of early human affected those parts of the Earth’s surface occu- impact focuses on the land surface, its associ- pied by agriculture. Hence, the physical, biolo- ated biota, and the environment in which we gical and geochemical signals evident in live. But *70.8% of the Earth’s surface is geological successions are subdued by contrast oceans, and human impact there has in compar- with those associated with the accelerated rates ison been minimal and/or local until the 19th of transformation from the mid-20th century and 20th centuries, except on lowland coastal onwards (e.g. Waters et al., 2016) (Figure 1). areas where human population centres were Ruddiman (2003, 2013) and Ruddiman et al. established early because of abundant and (2016) argue that deforestation accompanying accessible food sources. Even on land, by the increase of farming was a key factor (i) in 1700 CE about half of the global ice-free land halting the slow decline of atmospheric CO2 surface was still wildlands, while ‘used’ anthro- levels at *8 ka BP, when they had reached mes (anthropogenic biomes) covered only *255 ppm (declining from *260 ppm at 11 *11% of the planet’s surface close to the dawn ka BP at the beginning of the Holocene), and of the Industrial Revolution (Ellis et al., 2010). (ii) in slowly raising them to *280 ppm for the During gradual development of agriculture in millennium prior to 1800 CE (Figure 2), thus the Early and Middle Holocene, the area of postponing the onset of renewed glaciation. influence would be yet less. Ruddiman indicates While this scenario is plausible and elegant, it that per-capita land use was greater millennia may well represent an oversimplification of the ago than at 1700 CE. Nevertheless, estimates origin of this slow CO2 rise. For instance, Ciais of annual human population of about 4 million et al. (2013; their Figure 6.5) concluded that the at the start of the Holocene indicate population oceans may have contributed most or all of this increase at *0.04%/yr throughout most of CO2, as they did in the preceding glacial-to- the Holocene to about 1 billion by 1800 CE interglacial transition (e.g. Skinner et al., (Figure 1). Subsequently, population grew to 3 2010). Along the same lines, Studer et al. billion people by 1960 CE and *7.6 billion (2018) noted that nitrogen isotope evidence now, with peak annual growth rate of 2.1% in from the Southern Ocean was consistent with 1971 CE. The vastly greater and more rapid a weakening of the oceanic biological pump increases in human population of the last cen- that stores CO2 in deep water, hence possibly tury, together with greatly increased per capita accounting for much of the Holocene rise in energy expenditure from fossil fuel burning, had atmospheric CO2. Observing that the carbonate commensurately greater impact on landscape ion concentration of deep water had declined modification and cultivation than in earlier over the past 8000 years, Broecker et al. (1999) times. Even if it is accepted that the pre-1950 had already pointed out that this fall was con- changes itemized by Ruddiman ‘have been the sistent with the rise in atmospheric CO2 seen in largest transformations of Earth’s surface in all ice cores, hence attributing the rise in CO2 to of human history’, a point that is arguable given, oceanic rather than terrestrial mechanisms. for example, the growth of the global road net- Broecker and Stocker (2006) subsequently work (Alamgir et al., 2017), damming most of noted that carbon isotopes appeared to rule out the world’s major rivers (Syvitski and Kettner, the possibility of there having been a large 2011) and >60% loss of the world’s wildlife release of terrestrial carbon of the kind (Grooten and Almond, 2018) that have taken required by Ruddiman’s hypothesis. By ana- place since the mid-20th century, compared logy with what happened in the interglacial with recent changes those historic transforma- of Marine Isotope Stage (MIS) 11, Broecker tions were relatively slow to develop and mainly and Stocker concluded that the cause for the 322 Progress in Physical Geography 43(3) (a) PleistoceneHolocene Anthropocene Greenlandian Northgrippian Meghalayan ) –1 1.5 2.0 1.0 (b) 0.5 Population change (% yr change Population ) 0.0 –1 0.15 0.20 0.10 change (% yr change (c) 2 CO 0.05 ) 0.4 0.5 –1 0.00 0.2 change (% yr change 4 CH 0.0 0.1 0.3 –0.1 14 12 1086420 Year BP Figure 1. Average values of relative change to (a) global human population, (b) atmospheric CO2 concen- tration and (c) CH4 concentration since the last 20,000 years. World population data is sourced from https:// ourworldindata.org/world-population-growth (based on Goldewijk et al., 2010). CO2 and CH4 data showing the % change per year are stacked from the low-resolution, long Epica Dome C ice record (Monnin et al., 2004; Loulergue et al., 2008), the high-resolution, short Law Dome record (MacFarling Meure et al., 2006) and recent air samples (Dlugokencky et al., 2018a, 2018b).