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Original authors: Jan Zalasiewicz, Julia Adeney Thomas, Colin N. Waters, Simon Turner & Martin J. Head
Although geologists have not accepted the term 'Anthropocene epoch', the concept of a profound mid-20th century shift in the Earth remains significant in the physical and social sciences, humanities, and policy.
The concept of the 'Anthropocene' aims to represent the immense impact humanity has had on Earth. Source: Bob Krist/Getty
On March 5, 2024, the International Commission on Stratigraphy (ICS), the body responsible for defining geological units, announced that it had rejected a proposal to formally adopt the 'Anthropocene' as a geological epoch, intended to reflect humanity's overwhelming impact on Earth. The ICS's Subcommission on Quaternary Stratigraphy (SQS) initiated this process by forming the Anthropocene Working Group (AWG) in 2009, of which we are representatives. The AWG's purpose was to clarify whether there was sufficient evidence to formally adopt the Anthropocene, a process that included identifying a precise starting point within a specific geological layer (stratum).
This rejection sparked much debate, with strong opinions expressed by both sides. However, over the past decade, the term Anthropocene has been widely adopted to describe, analyze, and explain the transformed environment in which humanity now lives.
Currently, different groups use this term in four main ways. First, the concept originated within the Earth System Science community, which, along with related scientific disciplines, uses it to model, assess, and warn about the impacts of human activities, including the transgression of environmental 'planetary boundaries'[1]. Second, scholars in the humanities and social sciences use it to understand how human impacts have ultimately overridden many powerful natural forces, and what implications this has for history, philosophy, politics, economics, society, and culture[2]. Third, the Anthropocene has inspired much work in museums and the arts. Fourth, the public, policymakers, urban planners, and others use this concept to understand human-induced changes to climate and the biosphere, which are necessary for developing and implementing management, mitigation, and adaptation policies[1].
Since the formal geological definition of the 'Anthropocene' has been put on hold (at least for now), we explore how the concept can best be understood and used, taking into account these broad groups. From both specialized and general usage, what is the fundamental meaning of the Anthropocene?
Geological Origins
The Anthropocene was first proposed by atmospheric chemist Paul Crutzen in 2000 at a meeting of the International Geosphere-Biosphere Programme (IGBP) committee, a forum dedicated to discussing global change. Crutzen intended it to represent a new geological epoch consistent with the committee's goals[3]. Its purpose was not merely to signify an Earth transformed by humans. Geologically, significant anthropogenic impacts can be traced back to the Holocene — the post-glacial geological epoch we still live in — and the preceding Pleistocene. Typical Holocene conditions included relatively stable atmospheric and oceanic chemistry and climate (especially temperature), and relatively stable sea levels for about 7000 years. Crutzen proposed that "the Anthropocene represents a shift in the Earth system from these conditions towards an irreversible, still evolving state, for which the name Holocene is no longer appropriate."
A remarkably similar pattern in various environmental markers (e.g., concentrations of different greenhouse gases) attests to a sudden transition, akin to changing from horizontal to vertical on the Holocene axes. Crutzen initially believed that the deviation from Holocene conditions began with the onset of the Industrial Revolution and increased coal burning in Europe in the late 18th century[4], although when he made this argument, IGBP data did not extend that far back. With more data, the mid-20th century beginning became clearer[4], linking to the concept of the 'Great Acceleration' — the rapid post-World War II increase in many socio-economic drivers and Earth system responses.
This transition has been detailed extensively[6-8]. Its main features include: changes in atmospheric chemical composition; global warming; now irreversible glacial melt and sea level rise; accelerated erosion and sedimentation; proliferation of industrial products, many made from artificial materials like plastics; biosphere changes via species invasions, domestication, and extinctions; and the rapid development of human-engineered technological systems forming a globally interconnected 'technosphere'[9].
Proposed Context
This preliminary research advanced the work of identifying the start of the Anthropocene, specifically determining its onset within a geological reference layer known as a Global Stratotype Section and Point (GSSP, often called a 'golden spike'). From 2020 to 2023, 12 research teams proposed candidate GSSPs and other reference sections in 8 different geological environments across five continents.
After numerous discussions and formal votes, the AWG selected the horizontal plane separating summer and autumn sediment layers in Canada's Crawford Lake in 1952. The autumn layer is characterized by a significant rise in plutonium isotopes, coinciding with the first atmospheric hydrogen bomb tests[10]. This signal is clearly visible in many proposed locations (see 'Consistent Boundary'). Crawford Lake was chosen because it has undisturbed, seasonally deposited sediment layers that preserve an accurate, continuous temporal record, are easily accessible for future research, and are located within a protected area. The annually resolved plutonium data are supported by fly ash, nitrogen isotopes, and biomarkers. To provide a specific date and time, the same time as the first atmospheric hydrogen bomb explosion (known as Ivy Mike) was chosen: 7:15 local time on November 1, 1952 (19:15 GMT on October 31), at Enewetak Atoll in the Marshall Islands, Pacific Ocean.
Source: Reference 7
Through numerous stratigraphic signals, these strata can be precisely correlated worldwide[6], in some places to the nearest year, allowing for systematic quantitative comparisons of processes before and after the time boundary represented by these sediments. This proposal was submitted by the working group to the SQS on October 31, 2023.
Scope of the Anthropocene
The idea of defining the Anthropocene on a geological timescale was to provide a precise reference for the integrated study of the many phenomena mentioned above, placing contemporary changes within a deep-time context. However, it is the present-day, experienced, and observed phenomena, extending beyond the scope of geology, that have sparked wider interest in the Anthropocene: this is a perfectly reasonable interest, as the original guiding concept of the Anthropocene addressed Earth's habitability conditions.
During the 'Anthropocene' period, Earth's surface environment has undergone enormous changes compared to most of the Holocene: Earth is now hotter, more polluted, and more biologically degraded. These negative trends will intensify and extend beyond the Holocene envelope[1]. Some of these changes will persist long-term (e.g., climate change), and some are irreversible (e.g., extinctions). They have already put pressure on political institutions, legal frameworks, and economic relationships, all intended to protect and give meaning to human communities.
The first hydrogen bomb, codenamed 'Ivy Mike', exploded in 1952, marking the proposed beginning of the Anthropocene. Source: Bettmann/Getty.
When discussing the Anthropocene in these broader contexts, precise definitions of year, day, and hour are often less relevant. We also note that slight changes to the formal boundaries of earlier geological time units do not usually lead to a change in their fundamental understanding. For example, in 2008, another SQS working group changed the definition of the Holocene from 10,000 radiocarbon years Before Present to a formally stratigraphically defined 11,700 years Before Present (2000 CE) [11], but this did not alter its basic definition as the most recent post-glacial interglacial period.
The definition of the Quaternary also deserves consideration. This unit, including the Pleistocene and Holocene, was established in 2009, beginning about 2.6 million years ago, using a pre-existing GSSP and a major reversal of Earth's magnetic field for practical purposes. In reality, the intensification of Northern Hemisphere glaciation began slightly earlier, around 2.7 million years ago, but this did not change the general meaning of this period as an 'ice age'[12]. Other similar examples can be found in earlier periods. It is not precise concepts that control the concept of geological time units, but rather the fundamental characteristics of the periods they encompass. Nevertheless, adding clarity to these boundaries makes geological time units more consistently useful.
We argue in this article that understanding the 'Anthropocene' as the result of Earth-wide transformations in the mid-20th century remains useful across disciplines. This period is closely linked to the 'Great Acceleration' (a term coined by American historian John McNeill) and its synonyms (such as the 'post-war economic boom' and 'Japanese economic miracle' between 1946-1990, and 'Les Trente Glorieuses' describing France's continuous economic growth from 1945-1975). Many indicators describing human impact, including greenhouse gas emissions, metal and mineral production, meat consumption, and plastic use, began to show strong upward trends in the mid-last century (see 'Turning Point').
The concept of the 'Anthropocene' aims to represent the immense impact humanity has had on Earth. Source: Bob Krist/Getty
From a historian's perspective, the post-war period was characterized by profound changes in social values in many parts of the world, including the widespread dissemination and popularization of socialism, communism, liberal democracy, social welfare programs, and women's education. These changes stemmed from the growth of industry-wide globalization of industry, trade, and commerce. Nations from different blocs, despite vying for power, still led these transformations through national and international institutions. Shortly after the end of World War II, institutions such as the International Monetary Fund, the World Bank, and the predecessor to the World Trade Organization were established through international agreements. Technological advancements also led to agricultural food production, driving high global population growth rates [2,13].
For researchers in anthropology, political theory, international law, and ethics, questions began to emerge about the impact of human power beginning to dominate biological networks and inorganic processes during this period. Across the world, people are grappling with an altered Earth system, with different cultures experiencing, understanding, and responding according to their own worldviews. The expansion of technological fields providing energy, food, housing, and clothing for a growing population was accompanied by an increase in global inequality, with very minimal real income growth for the poorest populations. Neoclassical economics and its assumptions about infinite growth capacity have also been challenged by the recognition of an increasingly unstable Earth system and a finite Earth.
Some have proposed an earlier start date for the Anthropocene, but we believe these criteria fail to highlight the fundamental changes of the mid-20th century, which can be measured by broad-scale indicators. Other suggestions include the 'Orbis spike' around 1610, corresponding to a decrease in atmospheric carbon dioxide concentration of about 10 ppm[14]. This decrease is attributed to population decline, reduced cultivated land, and forest regrowth following the mass deaths of indigenous Americans after European colonizers arrived in the Americas. However, compared to the 140 ppm increase in carbon dioxide over the past two centuries, this decrease was very small and short-lived, and the increasing trend will continue. Stratigraphic signals related to the 'Columbian Exchange' of species (e.g., the presence of maize pollen) in the Americas and Europe occurred at different locations and times over several centuries. They do not show the kind of sudden, fundamental global transformation comparable to what was seen in the mid-20th century.
Plastic products and other waste have greatly increased since the 1950s. Source: Jason Swain/Getty
Similar objections could be raised against other boundaries based on stratigraphic signals, for example, evidence of lead smelting around 3000 years ago found in European peat bogs and Greenland ice layers[15]. Some have proposed extending the 'Anthropocene' concept further back, to include 'Anthropocene events' at least 50,000 years ago — a definition covering the Parthenon in ancient Greece, the Great Wall of China, Greek pyramids, early deforestation, Mesolithic arrowheads, and even the extinction of large animals in the late Pleistocene[16].
A formal geological definition would strengthen the recognition of the significant Earth changes in the mid-20th century. But even treating it as a quasi-formal boundary reflects reality[17,18] and encourages clear communication across all disciplines where the term 'Anthropocene' is used to encapsulate profound environmental change. Over time, different interpretations of significant impacts caused by all human activities, if all labeled 'Anthropocene', could cause unnecessary confusion.
What is the Anthropocene? What is it not?
Beyond discussing when the Anthropocene is most useful to begin, it has also been interpreted in many ways by various disciplines. In our still highly siloed academic environment, questions often reflect increasingly divergent views and a diminishing common understanding. These differences should be explored and, where necessary, challenged.
Does the Anthropocene disregard socio-political inequality? In coining and using the term 'Anthropocene', some critics argued that Earth system scientists and geologists indiscriminately assigned responsibility to all humanity, rather than to those who heavily over-consumed resources — and who were primarily causing (and continue to cause) the Earth's state change.
This misunderstanding arises because the goals and processes of physical science in the Anthropocene differ from those of the humanities and social sciences. Physics here primarily focuses on measuring and describing the responses caused by today's overwhelming human impact on Earth. Researchers typically do not concern themselves with assigning responsibility to specific groups or particular social, economic, and political systems — although since the concept was proposed, it has been noted that responsibility for anthropogenic change is highly uneven, and some studies[5] have incorporated these connections. Physical science also rarely explores the consequent social, economic, and political responses, or the values behind people's desires and hopes.
Thus, in Anthropocene research, there is a division of labor or lineage of disciplinary work. Physicists study Earth's response to human impact during the Anthropocene, while scholars in the social sciences and humanities study the humans and societies behind these impacts. For most scholars in the humanities and social sciences, inequality is central to the socio-political analysis of the Anthropocene. These approaches are not opposed; the Anthropocene, as understood here, provides a framework that points towards complementarity and interdisciplinarity.
Is the Anthropocene equivalent to climate change? Recent rapid climate change caused by rising greenhouse gases in the atmosphere poses a clear threat to human societies. Despite efforts to control emissions, over 100 million tons of carbon dioxide are added to the Earth's atmosphere every day. While climate change is currently the most significant force destabilizing the Earth system, the Anthropocene also includes many other physical, chemical, and biological changes, linked to economic, political, social, and technological phenomena worldwide.
Expanding activities like mining have left their mark on Earth. Source: Anton Petrus/Getty
When Crutzen proposed the term in 2000, atmospheric carbon dioxide levels were 'only' about 370 ppm, 85 ppm higher than the pre-industrial maximum concentration. Average global temperatures were about 0.5 °C higher than pre-industrial levels (standardized to the 1850-1900 average), thus still within the range of climatic conditions reached in other periods of the Holocene. In 2000, warming might have been considered just beginning: but the overall changes in the Earth system at that time already supported Crutzen's proposal for a new geological epoch. By 2022, atmospheric carbon dioxide levels approached 420 ppm, and average warming was 1.5 °C higher than pre-industrial levels. Considering the impact of other greenhouse gases (especially methane, nitrogen dioxide, and chlorofluorocarbons), the atmospheric CO2 equivalent reached about 523 ppm in 2022, a level not seen since the mid-Miocene (about 17 million years ago). It is therefore not surprising that Earth as a whole is hotter than at any time in the Holocene. At the same time, biodiversity loss and the increasing homogenization of Earth's once unique biogeographic combinations also constitute another important aspect of the Anthropocene[19]. Climate change is a significant component of the Anthropocene, but it does not define it.
Does the Anthropocene begin concurrently with its causes? The boundaries of geological epochs generally do not begin at the very start of planetary transformation, but rather at well-identifiable and operationally usable points. Many evolving developments, activities, and perspectives ultimately led to the changes in the Earth system in the mid-20th century. These can be traced back to the rise of Homo sapiens, the mastery of fire and complex communication skills, as well as animal domestication, agriculture, urban societies, writing systems, global trade, the steam engine, capitalism, the Haber-Bosch process for fertilizer production, and so on. The causes of the Anthropocene must necessarily predate the beginning of this epoch. By analogy, the formal definition of the Holocene 11,700 years ago marks the end of a long, complex, stepped pattern of warming and glacial retreat leading to sea-level rise, with glacial retreat beginning about 8,000 years ago[10]. Subsequently, the Holocene as an interglacial period was not much different from previous interglacials, providing the physical conditions for civilization to develop, conditions which the Anthropocene is now overturning.
Consensus
The Anthropocene was initially understood by Crutzen as representing not only the impact of humanity on Earth's geological record (he was well aware of the impact of early human activities) but also reflecting how, since widespread industrialization, the physical characteristics of a system had deviated from the long-term relatively stable conditions of the Holocene.
The Anthropocene concept can be anchored to a start in the mid-20th century, coinciding with the 'Great Acceleration' and a fundamental transformation of the Earth's state. Understanding the Anthropocene in this way will avoid the current confusion of the term pointing to different meanings in different contexts. It aligns with what the term initially sought to express and reflects clear, evidence-based geological characteristics[20]. This concept is consistent with the term's use in Earth System Science[21] and broader usage, such as by emerging institutions (e.g., the Anthropocene Research Center at KAIST in Daejeon, Korea, the Anthropocene History Centre of Excellence at the Royal Institute of Technology in Stockholm, and the Max Planck Institute for the Science of Human History in Jena, Germany). It emphasizes the role of geology in addressing issues of societal concern and can also be applied in the social sciences and humanities to discuss significant social upheavals, energy production, and the globalization of trade that have occurred. Policy and international law can also benefit from a clear definition; undoubtedly, in the era we now inhabit, the functioning of Earth has transformed due to overwhelming human impact.
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Originally published in Nature's News & Views section on August 26, 2024, under the title 'The meaning of the Anthropocene: why it matters even without a formal geological definition'.
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Doi: 10.1038/d41586-024-02712-y
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The 'Anthropocene' has been rejected as a formal epoch, but scientists believe Earth underwent a fundamental shift in the mid-20th century. What are your thoughts?
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