For over a year, we at Smithsonian.com have been telling crucial stories on the front lines of global change. We've showcased the good, the bad and the ugly; solutions, casualties, and key scientific and technological advancements in an effort to illustrate the scope and consequences of this critical time in our planet's history. Today we know that much of these changes owe to humans, whose activities have transformed—and continue to transform—the fundamental nature of Earth's climate, natural resources, and biological diversity on an unprecedented scale.
This profound influence has led many scientists to assert that we have entered a new chapter in Earth’s geologic history: the Anthropocene, which translates roughly into “the age of humans.” Popularized by Nobel Laureate and noted atmospheric chemist Paul Crutzen in the early 2000s, the concept has since become a mainstay of the scientific and popular lexicon. But just how profound has humanity's contribution been? For how long has this been happening, and what steps can we take to address it?
In the past century and a half, some of the brightest philosophical and scientific minds have applied themselves to answering these questions. We reached out to key researchers and experts across the Smithsonian Institution to give their take on a few of the seminal research papers that have shaped our understanding of this new chapter in Earth's history. Here, we present them as a brief annotated guide. Taken together, they show the arc of how we came to understand the extent and nature of the Anthropocene—and how much we have still left to learn.
Air | Water | Earth | Biodiversity
Author: Svante Arrhenius
Publication: Philosophical Magazine and Journal of Science
Why you should read it: Greenhouse warming linked to increasing heat and a changing atmosphere was discovered by Svante Arrhenius, the 1903 Nobel Laureate in chemistry. Arrhenius made his discovery using data from researches on the temperature of the moon and on solar heat by Samuel P. Langley, who would later become Secretary of the Smithsonian and founder of the Smithsonian Astrophysical Observatory. Though Arrhenius doesn't explicitly suggest in this paper that the burning of fossil fuels will cause global warming, he does highlight them as a significant source of carbon dioxide.
Author: T.C. Chamberlin
Publication: Journal of Geology
Why you should read it: At the turn of the 19th century, few scientists were thinking about how mankind had altered the chemical composition of the atmosphere. But in 1897, one lone researcher proposed that we should be thinking about it. American geologist T.C. Chamberlin called for a closer examination of the Earth's atmosphere, which he called "the most active of all geologic agencies." However, Chamberlin noted, "it has received the least careful study from geologists. Its very activity destroys its relics almost as soon as form and gives them peculiar evanescence." That's poetry — and prophecy.
Author: Charles Fabry and Henri Buisson
Publication: Journal de Physique Théorique et Appliquée
Why you should read it: Most people know that the ozone layer has a hole. They may not know that the discovery of human-induced depletion of the stratospheric ozone layer linked to ultraviolet radiation exposure—in other words, the formation of the ozone hole—is a story that unfolds in a fascinating and complex manner. First came the discovery of the Earth's stratospheric ozone layer, credited to French physicists Charles Fabry and Henri Buisson and this paper they published in 1913.
Authors: C. Lorius et al
Why you should read it: C. Lorius and colleagues probed Antarctic ice cores going back 150,000 years to show the rise and fall of glacial and interglacial episodes throughout Earth’s history. Their analysis did not have high enough resolution to show the drastic rise in temperature and CO2 emissions during the last 100 years; however, it did establish background patterns that would prove crucial for understanding the significance of those recent changes. Their work documents a clear 40,000-year cycle in Earth’s climate—marking one of the earliest studies showing evidence for global climate change leading up to and during the rise of modern humans.
Authors: J. R. Petit et al
Why you should read it: Fourteen years after Lorius et al, a group of international researchers extended ice core data from the Volstok station in East Antarctica by more than 250,000 years. The resulting 420,000-year climate record supported those earlier findings, but also provided greater context for understanding the rate of temperature and CO2 variation that we see today. J.R. Petit and colleagues estimated past atmospheric conditions by measuring concentrations of CO2 and methane trapped in ice bubbles, using them to “confirm the strong correlation between atmospheric greenhouse-gas concentrations and Antarctic temperature.” Their findings showed that today’s human-induced climate change is occurring at an unprecedented rate in Earth’s history.
Authors: Stacy L. Small-Lorenz, Leah A. Culp, T. Brandt Ryder, Tom C. Will, and Peter P. Marra
Publication: Nature Climate Change
Why you should read it: Knowing how climate change will change modern landscapes is crucial for guiding conservation policy. But so is gauging the impact on individual species, which can play a key role in their respective ecosystems. Here, researchers at the at the Smithsonian Conservation Biology Institute’s Migratory Bird Center and colleagues argue that current climate predictions fail to take into account these species-level impacts, citing predictions that one in 10 species will go extinct by 2100 due to manmade climate change. In particular, they point out threats to long-distance migratory species—like monarch butterflies or the American Redstart—whose lives stretch across continents and ecosystems.
Authors: J. Hansen et al
Publication: Atmospheric Chemistry and Physics
Why you should read it: What difference could a puny 2 °C make? A whole lot, it turns out. In this paper, published through the European Geosciences Union, Hansen et al draw on climate simulations, paleoclimate data and modern observations to infer that continued high fossil fuel emissions will impact the ocean in several ways, from rising sea levels to increasingly powerful storms. The result is a detailed, ocean-centric examination of global warming above preindustrial levels, highlighting effects missed in Intergovernmental Panel on Climate Change reports.
Author: A.J. Haagen-Smit
Publication: Industrial and Engineering Chemistry
Why you should read it: Modern Los Angeles residents may prefer not to know what's in the air they breathe, but that air has a fascinating story to tell. Our understanding of air pollution and the atmospheric consequences of anthropogenic activities starts with Arie Jan Haagen-Smit, the father of air pollution control, who produced this landmark paper on the effects of large quantities of hydrocarbons and nitrogen oxides released into the atmosphere in L.A. in the 1950s.
Author: Jack C. Pales amd Charles D. Keeling
Publication: Journal of Geophysical Research
Why you should read it: Though the earlier work of Svante Arrhenius had suggested the possibility of global warming, the idea that warming was likely happening was first strongly suggested in research led by Charles D. Keeling. Keeling did his research at Mauna Loa, Hawaii, where the now famous “Keeling curve” was first introduced. The “Keeling curve” is a graph that plots the ongoing change in concentration of carbon dioxide in Earth's atmosphere beginning in 1958, and is credited as drawing the world’s attention to the issue.
Author: Paul J. Crutzen
Publication: Quarterly Journal of the Royal Meteorological Society
Why you should read it: If the discovery of Earth’s stratospheric ozone layer came in 1913, anthropogenic influences on the ozone only became known later. Paul Crutzen first noted the influence of nitrogen oxides on stratospheric ozone in 1970.
Authors: Michael B. McElroy and John C. McConnell
Publication: Journal of Atmospheric Sciences
Why you should read it: Once the detrimental effect of nitrogen oxides on the ozone was established, researchers grew concerned about supersonic aircraft. Specifically, they sought to investigate the ozone impact of proposed fleets of supersonic transports flying sufficiently high with sufficiently hot exhausts to cause considerable damage to the ozone layer. This paper estimates the effects of a fleet of 500 planes cruising for an average of 7 hours a day, concluding that "these aircraft may catalytically affect atmospheric ozone."
Author: M.J. Molina and F.S. Rowland
Why you should read it: In the unfolding narrative of anthropogenic activities effecting the Earth’s atmosphere, and specifically the human-induced depletion of the ozone layer, it was the discovery that the chlorofluorocarbons (CFCs, a class of non-toxic chemicals whose physical properties can be wonderfully tailored for practical uses, are non-toxic, and were thus thought to be completely benign) are in fact photolyzed in the stratosphere that led to the discovery of drastic ozone destruction.
Author: J.C. Farman, B.G. Gardiner, and J.D. Shanklin
Why you should read it: A team from the British Antarctic Survey made the dramatic discovery of the ozone hole. In this seminal paper published in 1985 they outline their ground-based measurements which show rapid, deep declines in stratospheric O3 during Austral spring starting in the 1970s.
Authors: Richard S. Stolarski, Peter Bloomfield, Richard D. McPeters and Jay R. Herman
Publication: Geophysical Research Letters
Why you should read it: The British Antarctic Survey team’s discovery of the ozone hole was confirmed by NASA measurements from the Nimbus 7 satellite. The satellite also mapped the extent of the depletion, finding that it corresponded to the Antarctic polar vortex. Global ozone, including the Antarctic ozone hole, has been mapped from satellites continuously since. Today, the use of CFCs (the main cause of ozone-damaging halogens) has now been largely stopped and the stratosphere, including the ozone hole, is slowly recovering.
Authors: D.W. Dockery, C.A. Pope, X. Xu, J.D. Spengler, J.H. Ware, M.E. Fay, B.G. Ferris, Jr., and F.E. Speizer
Publication: New England Journal of Medicine
Why you should read it: The direct effects of air pollution on human health are detailed in the classic study from the New England Journal of Medicine, which reported “significant effects of air pollution on mortality even when we controlled for sex, age, smoking status, education level, and occupational exposure to dust, gases, and fumes. The compatibility of the effects of air pollution on mortality in this study with those observed in population-based cross-sectional studies and daily time-series studies provides further evidence for the conclusion that exposure to air pollution contributes to excess mortality.”
Author: Daniel Pauly
Publication: Trends in Ecology & Evolution
Why you should read it: Here, Pauly puts his finger on a previously unrecognized but fundamental cognitive blind spot. He writes: “The ‘shifting baseline syndrome’ .... has arisen because each generation of fisheries scientists accepts as a baseline the stock size and species composition that occurred at the beginning of their careers, and uses this to evaluate changes. When the next generation starts its career, the stocks have further declined, but it is the stocks at that time that serve as a new baseline. The result obviously is a gradual shift of the baseline, a gradual accommodation of the creeping disappearance of resource species, and inappropriate reference points for evaluating economic losses resulting from overfishing, or for identifying targets for rehabilitation measures.”
Authors: J. B., Jackson, et al.
Why you should read it: This study alerted the world to the pervasive global alteration of coastal environments by fishing that began with small aboriginal populations and has accelerated with industrial factory ships. Although other publications sounded the alarm earlier, the sheer breadth and volume of evidence marshaled here—from archeological shell middens to ship logs from John’s Smith’s voyage into the Chesapeake through the latest molecular biology—profoundly changed our collective understanding of the state of the ocean in the Anthropocene.
Author: Roger LeB. Hooke
Why you should read it: Humans have transformed far more than climate. Published the same year as the term “Anthropocene” was proposed, this paper focuses on the ways that human societies have physically reshaped the land through agriculture, mining and development throughout history. “We have now become arguably the premier geomorphic agent sculpting the landscape,” the authors propose. Their historical summary reads as a warning for us to be more aware of our dramatic impact, especially as human populations and earth-moving activities increase exponentially around the globe.
Author: Paul Crutzen
Why you should read it: In the OG article proposing and defining the term “the Anthropocene,” Nobel laureate and Dutch atmospheric chemist Paul Crutzen further developed the assertion he and Eugen Stoermer made in the 2000 International Geosphere-Biosphere Programme’s Global Change newsletter. Crutzen argues that the Holocene, the warm period of the past 10,000 to 12,000 years, doesn’t cut it anymore. “It seems appropriate to assign the term ‘Anthropocene’ to the present, in many ways human-dominated, geological epoch,” he muses, cataloging the vast impacts of industry, livestock, agriculture, deforestation and water use since the 18th century. “A daunting task lies ahead for scientists and engineers to guide society towards environmentally sustainable management during the era of the Anthropocene,” he adds—a conclusion that still rings true today.
Authors: Jan Zalasiewicz, Mark Williams, Will Steffen, Paul Crutzen
Publication: Science & Technology
Why you should read it: “The notion that humankind has changed the world is not new,” the authors write. Yet until now, man’s impacts have largely been dwarfed by dramatic natural events like volcanic eruptions, meteor strikes and retreating oceans. This primer by European and Australian researchers chronicles the birth and evolution of the Anthropocene concept, as well as the obstacles it still has to overcome to gain mainstream acceptance. The paper starts by examining the scale of human-caused environmental change—a vanishingly brief blip within the context of geological time. Ultimately, the authors propose an Anthropocene Working Group composed of scientists across diverse fields to address the challenges of this “geologically unique and in many ways novel” era.
Authors: Whitney J. Autin, John M. Holbrook
Publication: GSA Today
Why you should read it: By 2012, the term “Anthropocene” had gone mainstream. Many environmentalists cheered it on, arguing that the idea encouraged popular awareness of mankind’s impact and encouraged a more sustainable use of resources. Yet scientifically, the idea of the Anthropocene was still a bit premature. “As practicing stratigraphers, we are taken aback by the claim that scientists currently have sufficient evidence to define a distinctive and lasting imprint of our existence in the geologic record,” the authors of this paper admonish. While the term “provides eye-catching jargon” and holds “a distinct allure,” they continue, “elevating terms that may become iconic in pop culture is not in itself sufficient evidence to amend formal stratigraphic practice.”
Authors: P.L. Corcoran et al
Publication: GSA Today
Why you should read it: Manmade plastics are “astonishingly abundant in oceans, seas, and lakes, where they accumulate at or near the water surface, on lake and ocean bottoms, and along shorelines." Here, Corcoran et al report that melted plastics can also be solidified into sedimentary rock, forming a new kind of rock layer for future geologists to find. This paper provides some the most compelling visual evidence that the Earth is incorporating human-made pollution and products into its surface. “This anthropogenically influenced material has great potential to form a marker horizon of human pollution, signaling the occurrence of the informal Anthropocene epoch,” the authors conclude.
Authors: Simon Lewis and Mark Maslin
Why you should read it: Humans have dramatically transformed the planet in a vanishingly brief amount of time. With this in mind, two British researchers review the case for formally codifying a new geological epoch. Separating out the Anthropocene from the Holocene would require identifying a global marker—recorded in the stratigraphic material of the Earth—that demonstrates a shift. Their conclusion: “The evidence suggests that of the various proposed dates two do appear to conform to the criteria to mark the beginning of the Anthropocene: 1610 and 1964. The formal establishment of an Anthropocene Epoch would mark a fundamental change in the relationship between humans and the Earth system.”
Authors: Todd J. Braje
Publication: Journal of Archaeological Research
Why you should read it: Some archeologists believe the Anthropocene “severs the necessary relationship between modernity and history.” A wide-ranging synthesis of archaeological thinking on the Anthropocene, this paper identifies the various start dates and criteria put forward for defining the onset of this new epoch. Braje examines rigorous geological criteria to find that the current proposed start date—around 1800, the start of the Industrial Revolution—fails the test. He also considers the role of the Anthropocene in the public discourse, and how it blends the ideas of nature and culture, in an effort to decode and contextualize how we should think of this new era.
Author: Paul Voosen
Why you should read it: Published in Science in August 2016, this short paper details the plans of the Anthropocene Working Group to get the Anthropocene formally recognized as an official span of geologic time by the International Commission on Stratigraphy (ICS). As part of the ICS approval process, the working group must provide evidence that human-caused tracers will persist in the rock record once sediments and soils turn to rock. A useful paper, it highlights the current state of this discussion and some of the controversy surrounding it.
Author: John Carey
Publication: Proceedings of the National Academy of Sciences of the United States of America
Why you should read it: This brief, accessible piece by science writer John Carey lays out the argument that sweeping manmade changes to the environment have ushered in a new geological epoch defined by human influence. Carey takes readers to a key 2000 Mexico City meeting, in which “soaring levels of carbon dioxide in the atmosphere” led one frustrated Earth sciences researcher to reconsider the convention of referring to the present day as the Holocene, the geologic period that began with the retreat of the ice sheets 11,700 years ago. Instead, he offered up a new term: the Anthropocene.
Authors: Jan Willem Erisman, Mark A. Sutton, James Galloway, Zbigniew Klimont, and Wilfried Winiwarter
Publication: Nature Geoscience
Why you should read it: An eye-opening review of the consequences, intended and otherwise, of the chemical breakthrough that led to industrial nitrogen fertilizer production. This was arguably one of the most significant turning points in human history.
Authors: Torben Rick et al.
Why you should read it: This paper spotlights the unique history of California’s Channel Islands, a group of eight islands that lie between 20 and 98 kilometers off the state’s coast. Home to a wealth of biodiversity, the Channel Islands have undergone drastic ecologic changes over the past 20,000 years. The authors, including researchers from the Smithsonian’s National Zoo and the National Museum of Natural History, chronicle the first human occupation of the islands going back 13,000 years as well as the transformative effects of invasive species, overgrazing, drought and soil damage starting in 1800. Taking into account modern impacts of tourism and conservation efforts, they make recommendations for habitat restoration on the islands that would “manag(e) for resilience,” and could have broader implications for restoration on islands globally.
Authors: Robert H. MacArthur and Edward O. Wilson
Why you should read it: This landmark paper is considered by many to contain one of a small number of truly unifying theories in the field of ecology. In it, the authors build a theoretical foundation for understanding biodiversity loss as a result of accelerating habitat transformation in the Anthropocene. Although the paper is academic in nature, it's a worthwhile read: It stimulated a huge amount of research and discussion regarding conservation implications at the time.
Authors: Courtney A. Hofman, Torben C. Rick, Robert C. Fleischer, Jesús E. Maldonado
Publication: Trends in Ecology & Evolution
Why you should read it: To know the future, we must first know the past. Here, researchers from multiple units across the Smithsonian Institution examine the potential impacts of climate change on global biodiversity by looking back in time. Significantly, they examine archaeological and genomic data to understand past human impacts and predict future impacts, bringing genomics into the wider conversation regarding the Anthropocene. Ancient DNA analyses of plants and animals prove especially useful for understanding the past human relationship with the environment.
Authors: Bruce D. Smith and Melinda A. Zeder
Why you should read it: If we ask, “when did humans begin significantly contributing greenhouse gases to the atmosphere?” we might end up placing the start of the Anthropocene at the start of the Industrial Revolution, or around 1800. But researchers at the National Museum of Natural History's Program in Human Ecology and Archaeobiology argue that this is the wrong question. Instead, they say, we should be asking: “When exactly did humans attain dominance of the earth’s environments?” The answer to that question takes us some 10,000 years earlier, to when humans first began domesticating plants and animals to make them “more to their liking” (and better to eat). Talk about paradigm-changing.
Author: Helmuth Trischler
Publication: NTM Journal of the History of Science, Technology and Medicine
Why you should read it: Also published in August 2016, this paper provides a lucid review of the origins of the term “Anthropocene,” including the ongoing scientific debates regarding its adoption and then the wider cultural significance of the concept. Most significantly, Trischler writes, “it blurs established boundaries on many different levels between science and the public as well as between the sciences and the humanities. Equally importantly, it opens up the possibility of freeing ourselves from traditional dichotomies such as ‘nature’ vs. ‘culture’ and redefining the relationship between environment and society as inextricably intertwined."
Authors: William F Laurance et al.
Publication: Conservation Biology
Why you should read it: This paper showed experimentally and definitively how the fragmentation and loss of habitat that is universal in the Anthropocene is leading to extinction. Earlier papers set the theoretical foundation (see MacArthur and Wilson 1963) by showing the clear relationship between species diversity, habitat area, and distance to source, but this one summarized the consequences of that relationship for conservation based on data from a long-term field experiment in the Amazon rain forest.