ESEX Commentary
The Anthropocene: is there a geomorphological
case?
Antony G. Brown,1
* Stephen Tooth,2
Richard C. Chiverrell,3
James Rose,4
David S. G. Thomas,5
John Wainwright,6
Joanna E. Bullard,7
Varyl R. Thorndycraft,4
Rolf Aalto8
and Peter Downs9
1
Palaeoenvironmental Laboratory University of Southampton (PLUS), Highfields Campus, Southampton, SO17 1BJ, UK
2
Institute of Geography and Earth Sciences, Aberystwyth University, Aberystwyth, SY23 3DB, UK
3
School of Environmental Sciences, Roxby Building, University of Liverpool, Liverpool L69 7ZT, UK
4
Department of Geography, Royal Holloway University of London, Egham, Surrey, TW20 0EX, UK
5
School of Geography and Environment, University of Oxford, Oxford OX1 3QY, UK
6
Department of Geography, Durham University, Science Laboratories, South Road, Durham, DH1 3LE, UK
7
Department of Geography, Loughborough University, Leicestershire, LE12 8PA, UK
8
Geography, College of Life and Environmental Sciences, University of Exeter, EX4 4RJ, UK
9
School of Geography, Earth and Environmental Sciences, University of Plymouth, Portland Square, Drake Circus, Plymouth,
Devon, PL4 8AA, UK
Received 3 August 2012; Revised 29 October 2012; Accepted 1 November 2012
*Correspondence to: Antony G. Brown, Palaeoenvironmental Laboratory University of Southampton (PLUS), Highfields Campus, Southampton, SO17 1BJ, UK.
E-mail: Tony.Brown@soton.ac.uk
ABSTRACT: The ‘Anthropocene’, as used to describe the interval of recent Earth history during which humans have had an ‘overwhelming’
effect on the Earth system, is now being formally considered as a possible new geological Epoch. Such a new geological
time interval (possibly equivalent to the Pleistocene Epoch) requires both theoretical justification as well as empirical evidence preserved
within the geological record. Since the geological record is driven by geomorphological processes that produce terrestrial and
near-shore stratigraphy, geomorphology has to be an integral part of this consideration. For this reason, the British Society for
Geomorphology (BSG) has inaugurated a Fixed Term Working Group to consider this issue and advise the Society on how geomorphologists
can engage with debates over the Anthropocene. This ESEX Commentary sets out the initial case for the formalisation of
the Anthropocene and a priori considerations in the hope that it will stimulate debate amongst, and involvement by, the geomorphological
community in what is a crucial issue for the discipline. The Working Group is now considering the practical aspects of such a
formalization including the relative magnitude problem, the boundary problem and the spatial diachrony of ‘anthropogenic geomorphology’.
Copyright © 2012 John Wiley & Sons, Ltd.
KEYWORDS: human impact; erosion; alluviation; anthropogenic; geomorphology; Holocene; stratigraphy
Just over a decade ago, Paul Crutzen, a Nobel Laureate and
atmospheric chemist, informally coined the term ‘Anthropocene’
to describe the interval of recent Earth history during
which humans have had an ‘overwhelming’ (undefined) effect
on the Earth system (Steffen et al., 2007; Zalasiewicz et al.,
2010) and a stratigraphic argument has been outlined by
Zalasiewicz et al. (2011). This was not an entirely new concept,
with recognition having been given to human impacts in
earlier centuries (Marsh, 1874) and cognate terms proposed
(e.g. ‘Anthropogene’ by Nilsson, 1983). The more formal issue
of whether the Anthropocene represents a new interval of geological
time was aired at an international meeting of the Geological
Society of London (GSL) in May 2011, receiving widespread
media coverage and appearing on the front cover of The Economist
(May 27th
, 2011). The Subcommission on Quaternary Stratigraphy
(SQS), a constituent body of the International Commission
on Stratigraphy (ICS), has inaugurated a working group to consider
the Anthropocene as a formal division of geological time. There
are strong links between the SQS and the Geological Society of
London (GSL), to which the British Society for Geomorphology
(BSG) is affiliated. The BSG represents scientists who, inter alia,
investigate Earth-surface processes operating in the Pleistocene
and Holocene, but to date too few geomorphologists have been
involved in a debate that is being promoted forcefully by
geologists, ecologists, climatologists, and the global climate
change community. Even if the term Anthropocene is not yet
widely used in geomorphology, changes in the rates and patterns
of Earth-surface processes are central to the debate (Church,
2010). Where human activity acts on the Earth’s surface, potentially
this activity changes the rates at which these processes operate
and may produce landforms including sedimentary deposits
that are a consequence of these changed rates. Consequently,
EARTH SURFACE PROCESSES AND LANDFORMS
Earth Surf. Process. Landforms 38, 431–434 (2013)
Copyright © 2012 John Wiley & Sons, Ltd.
Published online 28 January 2013 in Wiley Online Library
(wileyonlinelibrary.com) DOI: 10.1002/esp.3368
the geomorphological community cannot avoid participation in this
debate and should make a significant contribution. This ESEX
Commentary arises from the initiation of the BSG Fixed Term Working
Group on the Anthropocene and is presented in order to stimulate
informed debate within the geomorphological community.
One purpose of this Commentary is to pose the fundamental
question: is such a subdivision of Earth time warranted in
geomorphological terms? In answering the question, we should
not, at least initially, get overly concerned with formal chronological
questions relating to the status and boundaries of
putative stratigraphy. Arguments concerning dominant or overwhelming
human activities relate more to processes and rates
than to stratigraphy, and this perspective lies at the heart of geomorphology.
Rather, the answer lies in whether the rates and
patterns of Earth-surface processes are so different in the time
interval concerned as to make a subdivision valid and meaningful.
This question is clearly methodologically challenging,
and raises epistemological objections along the lines of
‘wouldn’t it be better to consider this in a million years time?’
or ‘how do you identify a new geological interval from within
the interval’? However, given the debate has already gained
momentum, the fundamental question cannot be ignored, and
we should not neglect our responsibilities to science and society
to embed geomorphology in the debate as an essential
requirement for understanding the stratigraphic record from
recent Earth history, and for how this history can be used to
improve environmental management. In river restoration
projects, for instance, there is the vexed issue of whether we
can identify and define the ‘historical range of variability’ –
the spatial and temporal range of river variables such as flow
regime and planform that existed prior to intensive human
alteration (Wohl, 2011) – and adopt this as a desirable management
target. Below, we approach the fundamental question posed
above through two considerations. First, have Earth-surface
process domains (patterns and rates) changed fundamentally
during recent Earth history with rising human population? Second,
if so, will the consequences of these process regime changes be
preserved in the geological record?
For the first consideration, we can use our knowledge of
geomorphological processes and examine the geological
record to assess whether Marine Isotope Stage (MIS) 1 – the
present interglacial that has seen the rapid growth of humanity
– will be significantly different from preceding interglacials in
sedimentological and associated stratigraphic terms. Since the
Earth is also undergoing long-term dynamics related to internal
(endogenic) factors such as plate tectonics and external (exogenic)
astronomical factors, it is logical to start with the most recent
and astronomically comparable interglacial (MIS 5e). In
cool temperate regions, MIS 5e has long been associated with
high biomass production and low-energy fluvial and slope
systems (Rose, 2010), conditions that produced fine grained,
organic-rich river channel fills nested within antecedent coldphase
aggradational sequences. Significant overbank units are
rare, and although this rarity can result from selective erosion,
is fundamentally a consequence of vegetated land surfaces
and stable soils, some of which are preserved as palaeosols.
Within these temperate regions, slope deposits tend to be rare.
By contrast, when considering the present interglacial, the
widespread occurrence of later Holocene thick colluvial and
overbank units in lowland European river valleys was pointed
out by scientists last century (Happ et al., 1940; Natermann,
1941; Shotton, 1978). Globally, these units are clearly diachronous,
as shown by ‘legacy’ valley sediments in North America
(Trimble, 1981; Walter and Merritts, 2008) and parts of the
southern hemisphere (e.g. Australia – Fanning, 1994; Rustomji
and Pietsch, 2007). This occurrence should come as no
surprise: it has long been known, indeed since antiquity (see
Plato’s Critias), that accelerated hillslope erosion has been
caused by many human activities including agriculture (Sauer,
1938), mining (Gilbert, 1877) and urbanization (Wolman and
Schick, 1967), with concomitant accelerated downstream sedimentation
recorded in alluvial basins and floodplains (Trimble,
1981), lakes (Dearing and Jones, 2003) and offshore (Syvitski
et al., 2005). Even if hillslope erosion and downstream sedimentation
is most pronounced in the early phases of disturbance,
and eventually decreases to lower levels (Chiverrell,
2006), these lower levels commonly still exceed background
(pre-human impact) rates. Indeed, in some river systems, there
is growing recognition that the human footprint is now so
pervasive that we cannot hope to restore to pre-human conditions,
even if we can identify and define the historical range
of variability (Brierley and Fryirs, 2005), and that many floodplains
can be regarded as ‘genetically modified’ by human activities
(Lewin, 2013) that started in some cases many centuries
or even millennia ago (Brown, 2008).
Nearly two decades ago, Hooke (1994) provided an early attempt
to quantify continent-wide rates of earth movement by
human activities, arguing that if ploughing was included,
humans now displace a greater mass of rock and soil per year
than all other natural geomorphic agents combined. More
recently, Montgomery (2007) summarized the cultural history
of soil erosion and Haff (2010) has proposed that technological
‘mass-action’ now exceeds that of all land-based geomorphic
systems except rivers. Given the current global human population
(7 billion), such quantified claims for the dominant or overriding
influence of human activities are unsurprising. Even if a
conservative 10 spades of soil (c.100 kg) were moved for every
person each year, total annual human sediment flux would be
c.700 million metric tons, which is greater than the total annual
river sediment flux from Europe. Indeed, sediment ‘accounting’
studies have shown that humans have inadvertently increased
sediment transport in rivers by approximately 300 kg per person
annually (Syvitski et al., 2005). Even with reservoir construction
disrupting a significant proportion of the sediment transferred
from land to ocean, the dominant factor in global ocean clastic
sediment flux is now the direct and indirect effects of human
activity (Wilkinson, 2005).
The second consideration concerns the longer term preservation
potential of this increased flux. Many recent alluvial, lacustrine
and offshore records demonstrate the links between
human-altered earth surface processes and the resulting shortto
medium-term sedimentary products, but we need to engage
in thought experiments to assess whether evidence of human
activities will be preserved in the future long-term geological
record. We can postulate that beyond future glacial limits,
human-induced increases in sediment flux will have driven
geologically rapid aggradation in lower terrains, and continued
accumulation, caused in this case by cold climate physical
processes, will likely bury and ‘fossilize’ the products of recent
human activity, from bones to buildings. Even with reservoir
construction disrupting sediment flux from land to ocean, such
an ‘event’ stratigraphy can be seen extensively within floodplains
(Hoffman et al., 2010; Aalto and Nitrouer, 2012), in many deltas
(Evans, 2012) and on near-shore parts of continental shelves and
could therefore be preserved in marine geological records. This
event stratigraphy also contains a major biological discontinuity,
namely a pulse in species extinction, and the appearance of alien
species and a large biomass of new species, including both
humans and their domesticates. Geobiological combinations also
occur, such as anthropogenic soils (Wilson, 2002; Jablonski,
2004; Certini and Scalenghe, 2011; Zalasiewicz et al., 2011).
From the above discussion, we present two propositions for
consideration. First, there is enough geomorphological
evidence to support the contention that human activities in
432 A. G. BROWN ET AL.
Copyright © 2012 John Wiley & Sons, Ltd. Earth Surf. Process. Landforms, Vol. 38, 431–434 (2013)
the later part of the present interglacial have been the dominant
(but not necessarily overwhelming) drivers in many, but not all,
sediment-flux systems from the scale of individual hillslopes to
large catchments, and as a consequence have recognizably
altered the nature of terrestrial, and parts of the marine, sedimentary
records. Barring unforeseen changes, the impacts of
these ‘forcing’ activities are likely to continue into the future.
Second, the human-induced alterations to terrestrial and
marine sedimentary records are likely to be preserved in the
long-term geological record, at least in some environments.
Neither proposition would deny the importance of nonanthropogenic
(natural) climate change and weather extremes
in influencing geomorphic systems and associated sedimentary
records; along with anthropogenic influences, these factors will
generate difficult future environmental management issues. Likewise,
although this discussion has focused largely on fluvial and
colluvial systems, the role of anthropogenic factors in aeolian,
carbonate and even glacial systems remain crucial avenues for
research. If these two propositions are accepted, then by implication
there is a prima facie geomorphological case for possible
recognition of the existence of the Anthropocene as a time interval
in Earth’s history under which these conditions apply (i.e. the
‘recent’ past, the present and at least the near future).
However, the transition during the present Epoch (Holocene)
to human-dominated geomorphic process regimes is spatially
non-uniform and highly diachronous in global terms (Wainwright
and Thornes, 2004). Indeed, the case can be made that
human activity is certainly not dominant everywhere. In areas
of active mountain building (e.g. New Zealand Alps or the
Andes), tectonically- or rainfall-induced sediment movement
probably outstrips human earth moving. In deserts or desert
margins, natural aeolian sediment movement may exceed human
earth moving and human-enhanced aeolian sedimentary
signatures are likely to be indistinguishable from natural
products. Indeed, the very nature of aeolian transport leads to
dispersion rather than concentration of erosional products. In
frozen terrains (e.g. Antarctica and under ice sheets), natural
processes probably still dominate although the periglacial zone
is of course highly sensitive to the removal of vegetation by human
activity as well as human-induced global climate change.
In all these environments, however, some elements of direct or
indirect human influence can now be found (e.g. alien plants in
Antarctica) and their geomorphic process regimes include
some anthropogenic component, even if only secondary. Even
where human activity is now dominant, the transition to a
human-dominated regime is highly diachronous within the
Holocene. In much of Eurasia, the transition was early but gradual,
starting c. 4 ka, and was driven by agricultural changes. In
parts of Africa, the transition may also have been early (e.g.
Mali – Lespez et al., 2011) but occurred later in most areas
due to agricultural changes in the Iron Age and with European
colonization (Schwartz et al., 1990). In the so-called ‘New
World’, although indigenous peoples had some impact on geomorphic
systems (largely through the use of fire), the dominant
human signal is a feature of the post-colonial era – albeit complicated
in places like South America and New Zealand by
lower population densities, a more fragmentary pattern of agricultural
uptake, and by high, tectonically-driven background
erosion rates. Recognition of diachrony does not fatally diminish
the argument for recognition of an Anthropocene time interval,
as all geological boundaries derived from changes in the
stratigraphic record, except the Pleistocene/Holocene boundary
(Walker et al., 2009), have diachronies in the order of, or
much greater than, 5–10 ka. However, process-based studies
and complexity-theory approaches suggest that diachrony in
human impacts on the landscape is likely to be the rule rather
than the exception (Wainwright and Millington, 2010) and is
an integral component of the Holocene and what marks it apart
from the Pleistocene Epoch. Diachrony does, however, have
implications both for how we demarcate the Anthropocene
and potentially for its formal chronological status (e.g. Era,
Period, Epoch or Stage) and therefore potentially for the duration
and even status of the Holocene. If we decide that recognition
of an Anthropocene time interval is theoretically justified
and hence a lower boundary needs to be defined, one issue
is how to prevent any formalization being constraining and arbitrary
(Gale and Hoare, 2012). Even if the geomorphological
community put forward some preferences for a lower boundary
it would still require some diagnostic criteria by which the level
of human impact on geomorphic systems and sedimentary
records can be gauged and a definition of what constitutes
‘overwhelming’ human forcing? These issues are now being
considered by the BSG Anthropocene Working Group and all
contributions are welcomed (see the BSG website for an online
survey where views can be presented). We need your views on
the above arguments, the positive and negative aspects of
formally recognizing the Anthropocene as a geological time
interval and possible alternative approaches. Whether the
Anthropocene does or does not become a new formal geological
time interval should, at least in part, be a matter of geomorphology
and thus for geomorphologists. Geomorphologists
have long researched the impacts of human societies on earth
surface processes and landform records, without needing the
motivation of creating a new geological time interval.
However, the community must wake up to the debate before
they find themselves inside, outside or straddling a new geological
era (small E), having had their disciplinary framework
shifted under them.
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