Anthropogenic Earth system change: The problem of attribution

The Anthropocene Working Group’s (AWG) recent search for a geological marker of the Anthropocene has focused mostly on the “Great Acceleration” after the Second World War. There has been much debate, however, about an “Early Anthropocene.” Such pre-twentieth-century markers for a lower boundary of the Anthropocene have been advocated for, mostly from outside the circles of the AWG, by both geologists and scientists from other disciplines. Proposed candidates include the supposedly human-caused megafaunal extinction in the Middle and Late Pleistocene, between 50,000 and 10,000 years BP; the invention and spread of agriculture; and the emergence of global trade networks in the wake of European expansion into the Americas beginning in the sixteenth century. Until 2011, the leading atmospheric chemist Paul Crutzen, who first proposed the Anthropocene, and a number of his coauthors still preferred dating this boundary to the beginning of the Industrial Revolution in England, around 1780.11S. K. Lewis and M. Maslin, “Defining the Anthropocene,” Nature, vol. 519 (2015): pp. 171–80. For the industrial dating proposal, see, for example, W. Steffen, P. J. Crutzen, and J. R. McNeill, “The Anthropocene: Are Humans Now Overwhelming the Great Forces of Nature?,” AMBIO: A Journal of the Human Environment, vol. 36 (2007): pp. 614–21.

None of these proposals really seem to work well from the point of view of stratigraphy. Pre-twentieth-century dating alternatives are either difficult to detect globally in sediments or not unambiguously attributable to human influence.22See, for example, J. Zalasiewicz et al., “Colonization of the Americas, ‘Little Ice Age’ Climate, and Bomb-Produced Carbon: Their Role in Defining the Anthropocene,” Anthropocene Review, vol. 2, (2015): pp. 117–27. This is one reason why the marker for the beginning of the Anthropocene cannot be based on human environmental influence and its earliest possible dating. The evidence for a lower boundary marker of the Anthropocene has to come from stratigraphy, which relates to Earth history, but not—at least not necessarily—to human history. This means that anthropogenic environmental influence comes into consideration only if relatable to fundamental changes in the Earth system as manifest in the sedimentary record.

And yet, the line between Earth history and human history cannot be drawn so unambiguously in the case of the Anthropocene. To name our current era the Anthropocene is justifiable only if a fundamental Earth-historical rupture, proven by stratigraphic methods, can be shown to be causally linked to human impact on the Earth system. This requires an answer to the question of what defines an impact as “human.” In other words, assessments of stratigraphic evidence cannot ignore the Anthropos of the Anthropocene. The problem of attribution needs to be addressed. When we claim a potential marker for the Anthropocene is “anthropogenic,” we imply that we have solved that problem.

Interesting as it might be to approach the problem of attribution from the broader perspectives of philosophy or anthropology, I propose a more pragmatic approach. My argument starts from the following assumption: understanding “humanity” as a geophysical force requires an assessment of the capacity of human agency to cause significant change in the Earth system. Material exchanges between humans and the Earth system are key to this assessment, and they comprise the cumulative effect of human agency at any point in time since humans have been present on Earth. Quantifying the cumulative effect of human agency requires identifying key multipliers. One obvious multiplier is population. However, it is common wisdom in social ecology as well as in environmental history that ecological footprints vary so significantly—particularly in the economically and socially unequal world we live in today—that other factors need to be added to the equation.

The character of human agency varies between societies, in time as well as geographically. It depends on behaviors, socioeconomic organization, cultural habits, technology, and, last but not least, access to natural resources. Social metabolic regimes have proven an excellent approach to assessing these differences and model material exchanges between the anthroposphere and (the rest of) the Earth system quantitatively.33An excellent example is M. Fischer-Kowalski, F. Krausmann, and I. Pallua, “A Sociometabolic Reading of the Anthropocene: Modes of Subsistence, Population Size and Human Impact on Earth,” Anthropocene Review, vol. 1 (2014): p. 833. However, these studies do not consider Earth system feedbacks and, therefore, fail to model coupled human-Earth system dynamics. New approaches in the area of coupled social and Earth system tipping are currently being tested, but they are at an early stage of development. It is doubtful that human-Earth modeling will progress quickly enough to have any influence on the AWG’s work before it makes its conclusion and proposes a formal anthropogenic marker for the Anthropocene’s lower boundary. For the time being, assessing the cumulative effects of collective human action on the Earth system will continue to require more pragmatic and less ambitious approaches.

In this spirit, this contribution unfolds a historical argument starting from the controversial Orbis spike hypothesis. Land use change is crucial to this hypothesis. But we must shift focus to the broader context—to what I call the early modern “Agrarian Acceleration.” The point of discussing these preindustrial human-Earth system interactions is to help us understand the character and limits of collective agency in this period. Comparison with twentieth-century global material extractions, in the final part of this paper, shows a regime shift, which is evidence of a metabolic anomaly in human history. This regime shift explains an entirely new potential for collective human agency to impact the Earth system and leave traces in recent sediments.

The case of the Orbis Spike

The Orbis spike hypothesis, first advocated by global change scientist Simon Lewis and geographer Mark Maslin, involves an interesting discussion of parallelism between geological and historical change. In short, the parallel is between the Late Preindustrial CO₂ Minimum (LPI-CO₂Min; ca. 1590–1700) and the Columbian Exchange, which was a key factor in creating a “world system” of socioeconomic, political, and biological networks.44“LPI-CO₂Min” is not yet an established term. This view of an “Early Anthropocene” chronology has also been linked with a fairly popular terminological alternative, the “Capitalocene.”55For example, J. W. Moore, Capitalism in the Web of Life. London: Verso Books, 2015. Closely considering the claims and problems of the Orbis spike hypothesis brings the problem of attribution into clearer focus.

CO₂ and other greenhouse gas levels declined slightly in the second half of the sixteenth century and, for more than a hundred years, stayed below average levels of the previous thousand years to form the LPI-CO₂Min, which coincides with the peak Little Ice Age in the seventeenth century. Law Dome ice provided evidence for an absolute low point in atmospheric CO₂ in 1610 (fig. 1); called the Orbis spike, it was proposed by Lewis and Maslin as a candidate for a preindustrial Global Boundary Stratotype Section and Point (GSSP) for the Anthropocene. This proposal attributes declining CO₂ levels to land-cover changes (reforestation, decline in biomass burning after 1500) following the rapid collapse of Indigenous populations in the Caribbean and Spanish colonial America in the aftermath of European contact from 1492. In other words, global CO₂ levels dropped supposedly due to land use change in the Americas. The most recent study on this subject presents model calculations confirming that population decline in the Americas potentially explains most of the CO₂ variability observable in the ice core record, but alternative explanations favored by other scientists still cannot be ruled out.66A. Koch et al., “Earth System Impacts of the European Arrival and Great Dying in the Americas after 1492,” Quaternary Science Reviews, vol. 207 (2019): pp. 13–36. Some models suggest that Little Ice Age cooling in the second half of the sixteenth and throughout the seventeenth centuries may have increased terrestrial carbon storage.77M. Rubino et al., “Low Atmospheric CO2 Levels during the Little Ice Age Due to Cooling-Induced Terrestrial Uptake,” Nature Geoscience, vol. 9 (2016): pp. 691–94. Other arguments have been brought forward to challenge the Orbis Spike hypothesis: CO₂ variability during the LPI-CO₂Min is well within the range of Holocene CO₂ variability. Moreover, the 1610 low point is only shown in Law Dome ice; it lacks confirmation from other sources. See Zalasiewicz et al., “Colonization of the Americas” and J. Zalasiewicz et al., eds., The Anthropocene as a Geological Time Unit. Cambridge: Cambridge University Press, 2019. In other words, cooling might also have caused the LPI-CO₂Min.

The anthropogenic factor remains controversial, as none of the CO₂ supposedly stored in the regrown forests of post-Columbian America qualifies as anthropogenic the same way as CO₂ released from fossil fuel burning does. The latter is biochemically detectable due to the Suess effect, while the first is not. The very lack of the detectability of anthropogenic impacts on CO₂ variability connected with land use change indicates how much human agency remained embedded in the biosphere prior to industrialization. Human activities were predominantly within the biosphere, and the collective impact on the Earth system at a geological scale was restricted by the limits of human-biosphere interaction.

That said, let us assume for a moment that the LPI-CO₂Min is indeed attributable to land use change in the Americas. In that case, at least two problems remain for assessing the anthropogenic factor in Earth system change. One is the problem of scale of Earth system change; the other relates to the character of human agency in this case.

First, let’s consider the problem of scale. For climatologists (and climate historians like myself), consulting calculations of radiative forcing in order to assess external forcings in the climate system in relation to each other is a standard methodology. This helps put the relative force of lower CO₂ levels during the LPI-CO₂Min into perspective. In the thousand years that preceded the LPI-CO₂Min, atmospheric CO₂ and solar forcing moved within a narrow margin of ± 0.5 Wm^-2, with solar forcing exceeding that of CO₂ by at least an order of magnitude for most of the preindustrial period (fig. 2). Radiative forcing for lower CO₂ levels during the LPI-CO₂Min closes this gap; in this period, greenhouse gas forcing almost equaled solar forcing. This observation is significant from the point of view of historical climatology. But concluding, as Lewis and Maslin did, that the LPI-CO₂Min “resulted, as expected, in global cooling from 1594 to 1677” is out of proportion. Other external—namely solar and volcanic forcing—as well as internal forcing factors were at least equally relevant.88See, for example, H. Wanner et al., “Mid- to Late Holocene Climate Change: An Overview,” Quaternary Science Reviews, vol. 27 (2007): pp. 1,791–1,828; P. D. Jones et al., “High-Resolution Palaeoclimatology of the Last Millennium: A Review of Current Status and Future Prospects,” Holocene, vol. 19 (2009): pp. 3–49; S. Brönnimann et al., “Last Phase of the Little Ice Age Forced by Volcanic Eruptions,” Nature Geoscience, vol. 12 (2019): pp. 650–56. That is to say, radiative forcing related to the LPI-CO₂Min wasn’t at all dominant. And, therefore, even if we could attribute all of these level variations to land use change, we still have no grounds to speak of anthropogenic climate change during the peak of the Little Ice Age. The scale of Earth system change during the LPI-CO₂Min was simply not enough.

Now, the problem of human agency. The generally held view is that pathogens were the dominant force leading to the collapse of Indigenous populations in the Americas.99L. A. Newson, “The Demographic Collapse of Native Peoples of the Americas, 1492–1650,” Proceedings of the British Academy, vol. 81(1993): pp. 247–88. Europeans were the vectors of pathogen expansion. While mostly agreeing with this framework, historians emphasize that the spread of such epidemic diseases is directly linked to colonial violence and conquest. That is to say uncontrolled diseases combined with these circumstances and low immunity among Indigenous populations at the time of first contact with Europeans provided the foundation for the role nonhuman biological agents played in the decimation of Indigenous populations. In addition, reforestation as a consequence of population decline is a case of the biosphere reclaiming space from the expansion of (agrarian) land use in the Americas before the sixteenth century. Arguably, this is a scenario of typical Holocene human-biosphere interaction, with regard both to pathogens and to reforestation. The capacity and variance of human agency, here, continues to follow patterns established by the invention and spread of agriculture in human history. Just like the variability in CO₂ levels, the level of human agency in this case provides no evidence that European arrival in the Americas constitutes a new epoch—neither in human history, nor in Earth history.

There is more to say about reforestation. Advocates of the Orbis spike hypothesis recognize that the declining effect of reforestation on atmospheric CO₂ does indeed reflect the opposite effect of agrarian land use expansion that occurred in the Americas long before the arrival of Europeans. Obviously, their argument gets twisted at this point. And it gets even more twisted with regard to land use change. While the decline of Indigenous populations in the Americas is supposed to have caused the Orbis spike as a consequence of reforestation, advocates of the hypothesis have also argued that European colonialism initiated a new “world system” of global trade before the industrial era, and that this new system of global economic exchange created a “New Pangaea” of ecological exchange. The idea isn’t entirely new. It has, in fact, a long tradition in environmental history. And it is certainly worthy of reconsideration in the context of historical research on the origins of the Anthropocene. However, combining temporary decline in total land use in the Americas after 1492, with its expansion on the global scale in the three centuries preceding early industrialization, requires a discussion of the case of the Americas in the context of the Agrarian Acceleration. I’m introducing a new term, here, for something that isn’t new at all—at least not to global historians, historians of world population, and Earth system modelers. But it deserves wider attention.

The “Agrarian Acceleration” of the Little Ice Age

The demographic disaster of the Americas was an anomaly within the long-term trend of demographic rise. And the dominant global land-use trend in the period of the LPI-CO₂Min is the opposite of what happened in the Americas: the expansion of land use, rather than its decline.

This fact is indicated by well-established estimates of global population during the Little Ice Age. Generally, the Little Ice Age is considered to be a period of heavy pressure on agrarian production almost everywhere, particularly in the cold seventeenth century. It is a common narrative, regaining popularity in historical accounts recently, that the climatic fluctuations of the Little Ice Age caused more frequent harvest failures in many places around the world, often leading to famines, and in their aftermath, higher mortality, a phenomenon that peaked in the seventeenth century.1010See, for example, the seminal work by G. Parker, Global Crisis: War, Climate Change and Catastrophe in the Seventeenth Century. New Haven, CT: Yale University Press, 2013; and also D. Degroot, “Climate Change and Society in the 15th to 18th Centuries,” Wiley Interdisciplinary Reviews: Climate Change, vol. 9 (2018): e518. Crises of increased mortality caused by epidemics—the Black Death in the fourteenth century, cholera in the nineteenth—have also been associated with periods of climatic hardship.1111On the Black Death, see B. M. S. Campbell, The Great Transition. Cambridge: Cambridge University Press, 2016; and on cholera, see G. D. Wood, Tambora: The Eruption that Changed the World. Princeton, NJ: Princeton University Press, 2014.

However, it is in fact misleading to conclude that the Little Ice Age, or what has been called the “crisis of the seventeenth century,” translated into a demographic crisis on the global scale. Historical demography—the study of past human populations—is rather unambiguous about the dominating trend on the centennial to millennial scale, which indicates that populations were in fact growing throughout that period. Estimates for the last thousand years agree that populations went up almost everywhere, and even considerably faster than in previous millennia (fig. 3). Between 1650 and 1850, the number of people living on Earth doubled, due to an average annual growth ratio of roughly 0.4 percent. This is ten times quicker than during the first doubling of world population in the Common Era, which took more than one-and-a-half millennia. Although these estimates are associated with considerable uncertainty, there is little doubt that the general picture they sketch is reliable. From around 1400, we can see population growth accelerate, first slowly, then much more rapidly from the eighteenth century onward.1212A. Maddison, Contours of the World Economy 1–2030 AD. Oxford: Oxford University Press, 2008; M. A Livi-Bacci, Concise History of World Population. Oxford: Wiley Blackwell, 2017.

The nature of accelerated population growth during the Little Ice Age—prior to and around the dawn of early industrialization—was genuinely agrarian. This is why accelerated demographic growth in this period deserves to be called the Agrarian Acceleration (a name, of course, riffing on that of the Great Acceleration, which followed the Second World War). Stunning as the Agrarian Acceleration’s coincidence with the Little Ice Age may be, explaining it doesn’t pose any serious challenge, considering the fact that agrarian expansion continued over millennia from the asynchronous beginnings of agriculture in multiple places around the world. The Little Ice Age put additional pressure on agrarian production, in combination with population growth, thus fostering agrarian expansion (among other adaptations, by means of technological and social innovations) in response to declining yields per hectare per person.1313A. Kander, P. Malanima, and P. Warde, Power to the People: Energy in Europe over the Last Five Centuries. Princeton, NJ: Princeton University Press, 2015; P. Malanima, “Energy Crisis and Growth 1650–1850: The European Deviation in a Comparative Perspective,” Journal of Global History, vol. 1 (2006): pp. 101–21.

This transition is reflected in population-based models of preindustrial land use change, which have proven useful for attributing the source of atmospheric CO₂ to specific regions.1414J. Pongratz et al., “A Reconstruction of Global Agricultural Areas and Land Cover for the Last Millennium,” Global Biogeochemical Cycles, vol. 22 (2008); J. Pongratz et al., “Effects of Anthropogenic Land Cover Change on the Carbon Cycle of the Last Millennium,” Global Biogeochemical Cycles, vol. 23 (2009); J. Pongratz et al., “Radiative Forcing from Anthropogenic Land Cover Change since A.D. 800,” Geophysical Research Letters, vol. 36 (2009); J. Pongratz and K. Caldeira, “Attribution of Atmospheric CO₂ and Temperature Increases to Regions: Importance of Preindustrial Land Use Change,” Environmental Research Letters, vol. 7 (2012): 034001. These models have gained further importance through the latest emission scenarios generated by the Intergovernmental Panel on Climate Change, which suggest that the +1.5–2°C target defined by the Paris Agreement cannot be reached without negative emissions in certain areas of economic activity—land use being one such candidate. In any case, models of preindustrial land use change confirm expectations that the Agrarian Acceleration led to a rise in greenhouse gas emissions (fig. 4).1515Julia Pongratz and Ken Caldeira, “Attribution of atmospheric CO2 and temperature increases to regions: importance of preindustrial land use change,” Environmental Research Letters, vol. 7, no. 3 (2012): Figure 1.

These model calculations make the Agrarian Acceleration worthy of further study, as they may help to improve our understanding of the climatic shift from the Little Ice Age to global warming. If Little Ice Age cooling, perhaps in combination with reforestation in the Americas in the first 100 to 150 years after European arrival, triggered the LPI-CO₂Min, then slowly rising atmospheric CO₂ from the seventeenth century onward might indicate an early anthropogenic effect caused by land use change through intensification of agriculture in China, South Asia, and Europe, as well as the rise of cash-crop agriculture in the Americas and other places. It cannot be ruled out that the LPI-CO₂Min helped prevent the climate system from reaching a tipping point in positive feedbacks toward the next ice age. Recent climate model simulations suggest that northern hemisphere ice sheets would very likely have started growing quite rapidly around 1750 if not for the unusually high preindustrial levels of atmospheric CO₂.1616A. Ganopolski, R. Winkelmann, and H. J. Schellnhuber, “Critical Insolation-CO2 Relation for Diagnosing Past and Future Glacial Inception,” Nature, vol. 529 (2016): pp. 200–03.

More research is needed to better understand the transition from preindustrial to industrial patterns of anthropogenic changes in the atmosphere and the effects of the Agrarian Acceleration, which at this point remain a matter of speculation. The current state of research doesn’t allow unambiguous attribution of the rising trend in CO₂ levels during the LPI-CO₂Min to land use change during the Agrarian Acceleration. In any case, ±10 ppm of CO₂ in the atmosphere is well within the range of Holocene variability and far from a dominant forcing factor in the Little Ice Age and the transition to global warming. Hence, even if the source of rising CO₂ in the LPI-CO₂Min was anthropogenic, it is misleading to speak of it in terms of anthropogenic climate change, the way we do today with regard to global warming.

The metabolic anomaly of the twentieth century

Keeping in mind the open questions that remain about anthropogenic influences related to land use change on late preindustrial atmospheric CO₂ levels—and potentially also on the climate system—it is now time to assess human agency from the perspective of metabolic regimes. The Agrarian Acceleration was likely the period of potentially greatest impact regarding land use change on the Earth system in the entire preindustrial period. At least from the point of view of population growth, this conclusion seems plausible enough. Moreover, historical models of social metabolic rates (i.e., the average energy and material input per individual per year) suggest that since 1500 BCE, energy intensity has more or less tripled the impact of population growth.1717Fischer-Kowalski, Krausmann, and Pallua, “A Sociometabolic Reading of the Anthropocene,” p. 833. This tripling is for the entire period from 1500 to the present. However, energy intensity was already increasing during the Agrarian Acceleration due to the expansion of agriculture, while the principal material character of the metabolic regimes operating during this period was not significantly different from earlier periods. That is, the late preindustrial global economic metabolism was still a mixture of various forms of agriculture and foraging (or hunting and gathering). In other words, the dominant form of material exchange between the Earth system and society was biomass. Bioculturally variable and complex as this mixture was, socially organized and technologically supported biomass production and extraction also hint at the limits of human impacts on the Earth system.

This limitation becomes particularly apparent through comparing the preindustrial with the industrial era, which is also reflected in the sedimental record. The AWG has published extensively on Anthropocene chemostratigraphy and the traces that the industrial technosphere has left in the strata.1818J. Zalasiewicz et al., “The Geological Cycle of Plastics and Their Use as a Stratigraphic Indicator of the Anthropocene,” Anthropocene, vol. 13 (2016): pp. 4–17, among other references already mentioned in notes 2 and 7. From the point of view of social-historical ecology, potential mid-twentieth-century markers for the Anthropocene reflect a metabolic anomaly in human history, as well as a new capacity for collective human agency to impact and change the dynamics of the Earth system.1919For more elaborate accounts of the metabolic anomaly, see F. Mauelshagen, “Die große Stoffwechselanomalie,” in Transformationsgesellschaften, ed. M. Christ, B. Sommer, and K. Stumpf. Weimar: Metropolis, , 2019, pp. 17–46; F. Mauelshagen, “The Dirty Metaphysics of Fossil Freedom,” in The Anthropocenic Turn: The Interplay between Disciplinary and Interdisciplinary Responses to a New Age, ed. G. Dürbeck and P. Hüpkes. London: Routledge, 2020, pp. 59–76.

Compared with the Agrarian Acceleration, the relative importance of biomass declined during the industrial era. Data on global material extraction during the twentieth century provide evidence for the share of biomass falling below 50 percent shortly after 1950 (fig. 5).2020Data used for this graph are from F. Krausmann et al., “From Resource Extraction to Outflows of Wastes and Emissions: The Socioeconomic Metabolism of the Global Economy, 1900–2015,” Global Environmental Change, vol. 52 (2018): pp. 131–40. Since then, raw materials from Earth’s mantle have dominated. They are used primarily for construction, the demand for which has grown not only exponentially but also disproportionately over the course of the twentieth century. Steel production today is as large in one year as it was in the entire first decade after the Second World War, and annual cement production has increased so rapidly that in every single year since the turn of the millennium it has roughly equaled the amount produced during the entire first half of the twentieth century.2121V. Smil, Making the Modern World: Materials and Dematerialization. Chichester, UK: Wiley, 2014.

In the above graphs, the dashed line in the “B” graph can be regarded as the point at which global material extraction transcended the biosphere. This material shift is equally significant for human history as it is for Earth history. The link between these two is material culture(s), which reflect(s) metabolic regimes. A few remarks must suffice here to underline how profound these changes around 1950 were. At this point, the greater share of our constructed material world became increasingly detached from the growth and renewal cycles of biomass, despite continuous absolute growth of biomass extraction over the same period. Biomass-based material cultures are linked to climatically determined growth periods of certain plants and reproductive cycles of certain farm animals, whose annual cycles vary locally. In agrarian societies, most human activities are adapted to these cycles; and the social complexity of these activities is built up through the organization and coordination of repetitive processes and sequences. Industrial societies, on the other hand, have rapidly broken away from the confines of this biospheric organization of time. A new energy regime, new material bases, and the concomitant intrusion of a rapidly expanding technosphere into the old domains of “agrarian time”—as, for example, into the domain of crop production (due to machines) or into the dark of the night (due to electric light)—have deeply transformed society. From a historical perspective, this conclusion can be made solely from the fact that the number of people working in agriculture dropped rapidly in all industrialized nations and has now reached a level that renders agricultural work economically insignificant. Of course, this reality should not obscure the fact that the primary economic sector still secures the biological basis of life (that is, food) for nearly all people on Earth.

From the fact that material culture has become, over the course of the twentieth century, increasingly dependent on the extraction of geological resources, it follows that renewability has become more and more tied to geological material cycles—that is to say, to the long periods of Earth-historical processes needed, for example, to naturally produce coal, crude oil, and gas. Geological time, however, undermines renewability on the human timescale. Degradability of what a society releases back into the environment as waste materials—primarily into the biosphere and hydrosphere (rivers and oceans)—is another game changer in Anthropocene ecology. In both respects, we need to think of sustainability as a problem of temporal scale. For as long as material culture was largely tied to raw materials extracted from both natural and controlled biosphere production, its temporality was closely linked and largely adapted to the renewability and decomposition of biomass. This situation changed fundamentally with the dominance of geologically mined resources, such as fossil fuels and metals.

What these remarks convey is that the potential for anthropogenic Earth system change varies, both quantitatively and qualitatively, with the character of earthly materials accessed by societies, transformed technologically, circulated within these societies, and then released back into the environment. Fundamental differences exist between the anthropogenic Earth system impacts of land use change during the Agrarian Acceleration and the impacts of the Great Acceleration of the twentieth century. In fact, historical differences in the level of collective human action are so significant that the adjective “anthropogenic” cannot be applied to both periods without obscuring the rupture that lies between them.

Franz Mauelshagen’s work as an environmental historian focuses on climate history and the Anthropocene. His recent research is on planetary politics, particularly the role of science-policy cooperation, climate engineering, the history of climatology, and modeling land use change and its earth system impacts.

Please cite as: Mauelshagen, F (2022) Historical Assessment of the “Anthropogenic” Factor. In: Rosol C and Rispoli G (eds) Anthropogenic Markers: Stratigraphy and Context, Anthropocene Curriculum. Berlin: Max Planck Institute for the History of Science. DOI: 10.58049/s1my-qf17