​Students often ask me: how did climate history – the study of the past impacts of climate change on human affairs – come to be? I usually give the origin story that’s often told in our field: the one that sweeps through the speculation of ancient and early modern philosophers before arriving in the early twentieth century with the emergence of tree ring science and the theories of geographer Ellsworth Huntington. Huntington’s ideas perpetuated a racist “climatic determinism,” I say, but his imprecise evidence for historical climate changes meant that few historians took his claims seriously. Then, in the 1960s and 70s, the likes of Hubert Lamb, Emmanuel Le Roy Ladurie, and Christian Pfister developed new means of interpreting textual evidence for past climate, and used these methods to advance relatively modest claims for the impact of climate change on history. Their care and precision gave rise to climate history as it exists today – though the field did not attain true respectability until recently, when growing concerns about global warming encouraged many historians to reappraise the past.
 
It’s a compelling story, and true in many respects. Yet it has a problem. Crack open Huntington’s publications, and it’s immediately obvious that there’s an uncomfortable similarity between them and many of the most popular publications in climate history today. Like Huntington, most climate historians write single-authored manuscripts. Like Huntington, many learn the jargon and basic concepts of other fields – such as paleoclimatology – before concluding that this knowledge allows them to identify significant anomalies or trends in past climate. Like Huntington, modern climate historians have assumed that societies were homogenous entities, with some more “vulnerable” to climatic disruption than others. They routinely focus on the rise and fall of societies, typically by focusing on the “fatal synergy” of famines, epidemics, and wars.
 
Such narratives have been influential, and the best of them have helped transform how historians understand the causes of historical change. It is under the scrutiny of climate historians – and many other scholars who consider past environments – that the historical agency or “actancy” of the natural world has gradually come to light. Few historians would now argue that humans created their own history, irrespective of natural forces. Climate historians have also shown that the “archives of nature” – materials in the natural world that register past changes – can be as useful for historical scholarship as the texts, ruins, or oral histories that constitute the “archives of society.” And like other scholars of past climate change, historians have offered fresh perspectives on the challenges of the future: perspectives that may reveal what we should most fear on a rapidly warming Earth. 
 
Yet precisely because climate history has become an influential and dynamic field within the historical discipline, it is time to consider how it might be improved. Among other avenues for improvement, it is time to imagine how the field might transcend some of Huntington’s assumptions. It is time to consider how it could be better integrated within the broader scholarship of climate change, and thereby how historical perspectives might genuinely contribute to the creation of policies for the future. And it is time to ask whether the stories climate historians have been telling – those narratives of societal disaster – really represent the most accurate or useful way of understanding the past.

​I started thinking about that question while working on The Frigid Golden Age, a book that grew out of my doctoral dissertation. When I began my PhD at York University, I assumed my dissertation would confirm that the Dutch Republic, the precursor state to the present-day Netherlands, shared in those fatal synergies that climate historians had linked to the Little Ice Age. After a few months under Richard Hoffmann's tutelage, I learned that a group of scholars had digitized logbooks written by sailors aboard Dutch ships. I realized that those logbooks would allow me to start my research before I could travel to the Netherlands.
 
Working with logbooks encouraged me to look beyond the famines and political disasters that had dominated scholarship on the Little Ice Age. Rather than searching for the climatic causes of disasters, I started thinking about the influence of climate change on daily life (aboard ships). It dawned on me that I could no longer rely on existing reconstructions of temperature or precipitation, which have less relevance for marine histories. I needed to learn more about atmospheric and oceanic circulation, which meant that I had to begin to understand the mechanics by which the climate system actually operates. I had to consider how circulation patterns manifested at small scales in time and place, so I had to think carefully about what it meant when one line of evidence (or “proxy”) – my logbooks, for example – contradicted another. Gradually, I learned to abandon my earlier assumptions, and to reimagine modest climate changes – such as those of the Little Ice Age – as subtle and often counterintuitive influences on human affairs.
 
It didn’t surprise me when, shortly before I finished my PhD, a landmark book in climate history lumped the Dutch in among other examples of societies that shared in the crises of the Little Ice Age. By then I was framing the Republic as an “exception” to these crises, a unique case in which the impact of climate change was more ambiguous than it was elsewhere. Now, I started to wonder: was the Republic really as big of an exception as I had thought? Or were the crises of the Little Ice Age less universally felt than historians had assumed? Had climate historians systematically ignored stories of resilience and adaption?
 
It was a question with significant political implications. By the time I arrived at Georgetown University in 2015, “Doomism” – the idea that humanity will inevitably collapse in the face of climate change – was just beginning to take off. In popular articles and books it relies primarily on two things: a misreading of climate science (occasionally with a heathy dose of skepticism for “experts” and the IPCC), and an accurate reading of climate history as a field. Past societies have crumbled with just a little climate change, Doomists conclude – why will we be any different?
 
At around the time I published The Frigid Golden Age in 2018, I noticed that more of my students were beginning to echo Doomist talking points. I worried, because in my view Doomism is not only scientifically inaccurate, but also disempowering. If collapse is inevitable, why take action? It seemed perverse that the idea would gain momentum precisely as young, diverse climate activists were at last raising the profile of climate change as an urgent political issue. It seemed that now was the time to return to the question that had bothered me as a graduate student.

So it was that I applied for a little grant from the Georgetown Environment Initiative (GEI), a university-wide initiative that connects and supports faculty working on environmental issues. I asked the GEI for funds to host workshops that would bring together scholars who had begun to study the resilience of past communities to climate change. Through discussions at those workshops, I hoped to draft an article that would highlight many such examples – and perhaps systematically analyze them to find common strategies for adaptation. The goal would be submission to a major scientific journal: precisely the kind of journal that had helped to popularize the idea that societies had repeatedly collapsed in the face of climate change.
 
I soon realized that the workshops would have to connect scholars in many different disciplines, not just history. A striking series of articles was just then beginning to call for “consilience” in climate history: the creation of truly interdisciplinary teams wherein sources and methods would be shared to unlock new, intensely local histories of climate change. My experiences as the token historian on scientific teams that had developed their projects long before asking me to join had by then caused me to doubt the utility of working on research groups. Yet the new concept of consilience - and conversations with my new colleague Timothy Newfield - convinced me that there was much to be gained if scholars in many disciplines worked together to develop a project from the ground up.
 
Eventually I learned that the GEI would award me enough money to host one big workshop at Georgetown. That was exciting! Arrangements were made, and before long Kevin Anchukaitis, Martin Bauch, Katrin Kleemann, Qing Pei, and Elena Xoplaki joined Georgetown historians Jakob Burnham, Kathryn de Luna, Tim Newfield, and me in Washington, DC. After a fruitful day of discussion, my colleagues suggested a change of focus. Why not consider how climate history as a field could be improved by telling more complex stories about the past? It was a compelling idea, but I added a wrinkle. What if those more complex stories were also often stories about resilience? To me, complexity and resilience could be two sides of the same coin.

We decided to focus our work on periods of climatic cooling in the Common Era – the last two millennia – and accordingly I began to refer to our project as “Little Ice Age Lessons.” Then we settled on a basic work plan. I would draft a long critique of most existing scholarship in our field. Meanwhile, our paleoclimatologists would collaborate on a cutting-edge summary of both the controversial Late Antique Little Ice Age, a period of at least regional cooling that began in the sixth century CE, and the better-known Little Ice Age of (arguably) the fourteenth to nineteenth centuries.

It had dawned on me while writing The Frigid Golden Age that many climate historians took climate reconstructions at face value, especially badly dated reconstructions, and used them to advance claims that no paleoclimatologist would feel comfortable making. One recent, popular book, for example, claims that the Little Ice Age cooled global temperatures by about two degrees Celsius; that's off by around an order of magnitude. False claims about climate changes lead to erroneous assumptions about the impact of those changes on history, and dangerous narratives about the risks of present-day warming. With our study, we hoped to model how to use - and not use - paleoclimatic reconstructions. 
 
I would work with one paleoclimatologist in particular – Kevin Anchukaitis of the University of Arizona – to reappraise a statistical school of climate history that quantifies social changes in order to find correlation, and therefore causation, between climatic and human histories. By applying superposed epoch analysis – a powerful statistical method that can accommodate lag between stimulus and response – to global commodity databases, we hoped to identify correlations that statistically-minded climate historians had missed, or else interrogate correlations that they had already made.
 
Finally, our historians and archaeologists would contribute qualitative case studies that would each reveal how a population had been resilient or adaptive in the face of climate change. I hoped that these case studies would address my criticisms of our field, partly by relying on the cutting-edge reconstructions our paleoclimatologists would provide. While our initial group would have plenty of case studies to share, I immediately reached out to solicit more and more diverse examples of resilience, primarily from those parts of the world that Little Ice Age historians had most frequently linked to disaster. In the coming months, Fred Carnegy, Jianxin Cui, Heli Huhtamaa, Adam Izdebski, George Hambrecht, and Natale Zappia joined our team.
 
Kevin soon became an indispensable partner. As the months went by, we exchanged countless messages on just about every concern I could come up with, most of which initially dealt with how to identify and interpret regional paleoclimatic reconstructions. After I found and began to interpret commodity price databases from across Europe and Asia, we began our statistical analysis. I was surprisingly unsurprised when we uncovered no decadal correlations between temperature or precipitation trends and the price of key staple crops across China, India, the Holy Roman Empire, France, Italy, or the Dutch Republic. In fact, we found no correlations even between annual temperatures and prices. We did find that precipitation anomalies correlated with price increases, but only during a small number of extreme years.

​These results, I thought, could be really important. Hundreds, perhaps thousands of publications in climate history all assume a relatively direct link between climatic trends, grain yields, and food prices. In fact, many studies conclude that it is from this basic relationship between climate change and the cost of food that all the economic, social, political, and cultural impacts of climate change follow, past or present. Had we found compelling statistical evidence that connections between climatic and human histories were subtler and more complicated in the Common Era than previously assumed? 
 
Maybe not. Kevin worried that we were falling into precisely the tendency that we hoped to criticize in our article: the temptation to reach grand conclusions on the basis of flimsy correlations. Heli Huhtamaa, who authored some of the most important scholarship that links climate change to harvest yields, soon explained that our price data did not necessarily reflect changes in yields - and that our price databases were far from comprehensive. Adam Izdebski consulted economic historian Piotr Guzowski, who pointed out that the gradual process of market integration in the early modern centuries may have blunted the impact of harvest failures (we would later stress this integration as a source of resilience). At the same time, I conferred with climate modeler Naresh Neupane, who asked insightful questions about our statistical methods. 
 
I also consulted leading climate historian Sam White for his perspective. He argued that in order to reach persuasive conclusions, we needed to develop or adopt a model for the impact of climate change on agriculture. Only then could we understand what our price series and correlations – or lack thereof – were telling us. I had mixed feelings – shouldn’t our impact model flow from our data, rather than the reverse? – yet I asked Georgetown PhD student Emma Moesswilde to join our team by sorting through just about every model ever developed by climate historians. As I suspected she would, Emma concluded that most assumed a relatively direct link between temperature, precipitation, harvest yields, and staple crop prices. 
 
Meanwhile, our case studies were beginning to flow in. I had established a hands-on workflow, with a constant pace of reminder emails and shared Google folders and files. I was incredibly fortunate to work with brilliant and motivated colleagues who collectively met our deadlines, despite many other commitments and pressures. By the summer of 2019, I had nearly every case study that would enter our article. Now it was a process of shortening each case study from several pages to about a paragraph each . . . then finding connections between them, organizing them according to those connections, and interrogating them using our cutting-edge climate reconstructions. The weeks dragged by. I hazily remember working long hours late into the night or in the wee hours of the morning, while my newborn son refused to sleep.

​If integrating our case studies was difficult, I found it surprisingly easy to criticize our field. Climate historians, I argued, had often misused climate reconstructions, and many uncritically followed methods that ended up perpetuating a series of cognitive biases. While climate history was multidisciplinary, it was not yet sufficiently interdisciplinary, meaning that it was still unusual for scholars in a truly diverse range of disciplines to work together. The upshot was that many publications were unconvincing either because they misjudged evidence, ignored causal mechanics, did not attempt to bridge different scales of analysis, or did not pay sufficient attention to uncertainty.
 
By the fall, it was clear to me that something exciting might be taking shape. When Kevin joined us at Georgetown for a few days, he suggested that we might consider submitting to Nature, the world’s most influential journal. I found the idea tremendously exciting, if daunting. While still a young child I’d dreamed of publishing in Nature, inspired perhaps by tales told by a much-older brother who was then pursuing a doctorate in neuroscience. Now I thought of the influence our publication could have if Nature would publish it – and of career-altering ramifications for our graduate student co-authors in particular. I also thought about what it might do not only for the field of climate history (and relatedly, environmental history) but also more broadly for the transdisciplinary reach and prestige of qualitative, social science and humanistic scholarship. 
 
When fall turned to winter, I submitted a synopsis of our article to ​Nature, and early in the next year I was delighted (and frankly surprised) to receive an encouraging response. Our editor, Michael White, suggested that he would be interested in a complete article – but only if we considered including a research framework that would allow climate historians to address our criticisms. It was a crucial intervention. Kevin and I had worried that the part of our article that dealt with reconstructions and criticisms was becoming increasingly distinct from our statistical and qualitative interpretations of history. Yet a framework could allow us to convincingly bridge these halves.  
 
Michael asked whether we wished to submit a Nature Review, a format that would give us a bit more space and much more latitude to adopt our own structure. Yet space was still at a premium, and with our article so packed for content we decided that our statistical analysis had to go. This was a painful choice for me. While several co-authors remained skeptical, I considered it to be important, if incomplete, and I wonder whether to pursue its early conclusions in a future publication. Commodity prices do not tell us directly how climate anomalies influenced agriculture, yet to me the lack of statistically significant correlations between those anomalies and prices could still reveal something important about the impact of (modest) climate change on human history.
 
By the spring, COVID-19 had reached all of our institutions, and we all grappled with a depressing new reality. As we transitioned to online teaching and those of us with children struggled with the absence of school or daycare, the pace of work slowed. It slowed, too, because I found the work more challenging than ever before. A key part of our process now involved interrogating our case studies more rigorously than before, and we soon found that many of those studies – including my own – suffered from precisely the problems we were attempting to identify and criticize. At first, this really troubled me. I sent question after annoying question to our co-authors, each of which, I’m sure, required extraordinary effort to answer. Not for the last time was I grateful for selecting such a remarkable team. While some scholars might have been affronted by my questions, all the answers I received were thoughtful and constructive.
 
After a while, it dawned on me that this process of revision and interrogation could be an important part of the new research framework we hoped to advance – and a critical advantage of a consilient approach to climate history. We decided to be entirely upfront about the process, and in turn about how we were able to overcome the shortcomings that are all but inevitable in single-authored scholarship. We hoped that this expression of humility, as we saw it, would encourage other scholars to pursue the same approach.

​By early summer we had a complete draft. We now collaboratively undertook rounds of painstaking revisions to a Google Doc. As the weeks went by, we sharpened our arguments, excised unnecessary diversions, and crafted case studies that, we thought, convincingly considered causation and uncertainties. Everyone took part, and by the fall we were ready to submit.
 
It was only when we received our peer reviews and Michael’s comments that I began to really believe that we might actually be able to publish in Nature. Still, our reviews did raise some criticisms that we needed to address. Using Lucidchart I created detailed tables, for example, that allowed us to visualize how we had interrogated each of our case studies, and a recent environmental history PhD and cartographer, Geoffrey Wallace, designed a crystal clear map to help readers interpret those tables.
 
One big issue occupied me for nearly a week. A reviewer pointed out that we did not have a detailed definition of resilience, and wondered whether we even needed that term. Indeed “resilience” has become a loaded word in climate scholarship and discourse - and this requires a short digression. In 1973, ecologist Crawford Stanley Holling first imagined resilience as a capacity for ecosystems to “absorb change and disturbance” while maintaining the same essential characteristics. In a matter of years, scholars of natural hazards and climate change impacts appropriated and then modified the concept for their own purposes. Today, it is ubiquitous in the study of present and projected relationships between climate change and human affairs.

Yet what it means exactly has not always been clear. Older definitions of the concept in climate-related fields privileged “bouncing back” in the wake of disaster, and were eventually criticized for assuming that all social change should be viewed negatively. Newer definitions can encompass change of such magnitude that all possible human responses to environmental disturbance could be classified as resilient – including collapse.
 
The concept of resilience is also controversial for political reasons. Critics argue that a focus on resilience can carry with it the assumption that disasters are inevitable, and that it therefore normalizes and naturalizes the sources of vulnerability in populations. It can serve neoliberal ends, critics point out, by displacing the responsibility for avoiding disaster from governments to individuals. Since vulnerability is often the creation of unjust political and economic structures, the concept of resilience can obscure and thus support problematic power relations. Critics point out that normative uses of the concept can be used to denounce and “other” supposedly inferior – and typically non-western – ways of coping with disaster.
 
Still, we decided that resilience was a term worth using. Only it and “adaptation” are terms that provide immediately recognizable and therefore accessible means of conceptualizing interactions between human communities and climate change that are different from, and often more complex than, those that can be characterized as disastrous. We decided that recent scholarship had moved beyond using the concept narrowly; in fact the IPCC now incorporates active adaptation within its understanding of resilience. We concluded that if we were careful to precisely define how we were using the term, and if we emphasized how resilience for some had come at the expense of others, then our use of resilience could allow us to more directly communicate to the general public – and to the policymaking community.
 
In revisions it also became clear to us that many scholars who are not historians remain unfamiliar with the term “Climate History,” and associate it narrowly with the historical discipline. What we needed was a new term that, in the wake of our article, would unite scholars in every discipline that considered the social impacts of past climate change – and thereby encourage precisely the kind of consilient collaboration we call for. The term would need to communicate that this field was not another genre of the historical discipline - like environmental history - and it would need to stress our shared focus on the impacts of climate change on society. After we’d bounced around a number of options that seemed to privilege one discipline over another, Adam suggested “History of Climate and Society,” or HCS. We all agreed: this was a term that could work. 
 
Our article improved dramatically owing to the constructive suggestions of our editor and reviewers. Soon after we submitted our revisions, we learned to our delight that we’d been accepted for publication. Thanks to Adam, and with the support of press offices at Georgetown and the Max Planck Institute for the Science of Human History, we immediately started to plan a major effort to communicate our findings to the press, in at least five different languages.

To some extent, this article is part of that effort, and I hope it expresses some of the key findings of an article that, we hope, will also be accessible to the general public. Yet climate historians – or rather, HCS scholars – are the most important audience for this piece. I hope it illuminates, first, what it's actually like to work in consilient teams that aim to publish in major scientific journals. Working in such teams will be foreign to many historians in particular, and it reminded me a great deal of what it's been like to establish, then direct, both this resource and the Climate History Network. It is a managerial task not so different from running a small company or NGO, and it exposed for me how, in interdisciplinary scholarship, the service and research components of academic life easily blend together.
 
Most importantly, I hope this article communicates some of the benefits of working on a thoroughly interdisciplinary, consilient team. On many occasions my co-authors raised a point I wouldn’t have considered, corrected an argument I had intended to make, or warned me against using data that would have led us astray. Through discussions with our brilliant team, I learned far more while developing this project than I have while crafting any single-authored article. Teamwork was not always easy, and it was extraordinarily time consuming. Not all academic departments in every discipline will fully recognize its value. Yet I’m convinced that it is usually the best way to approach HCS projects. And now it gives me a tremendous feeling of satisfaction to know what our team accomplished together.
 
Beyond these questions of process and method, it’s worth asking where HCS studies stand today. Certainly our article did not disprove that climate changes have had disastrous impacts on past societies – let alone that global warming has had, and will have, calamitous consequences for us. Archaeologists moreover have long considered the resilience of past populations, and some of our conclusions will not surprise many of them. Yet we hope that HCS scholars in all disciplines will now pay more attention to the diversity of past responses to climate change, including but no longer limited to those that were catastrophic. 
 
We also hope that our article will both discourage Doomist fears and inspire renewed urgency for present-day efforts at climate change adaptation. According to the Fourth National Climate Assessment, in the United States “few [adaptation] measures have been implemented and, those that have, appear to be incremental changes.” The story is similar elsewhere. Our study shows that the societies that survived and thrived amid the climatic pressures of the past were able to adapt to new environmental realities. Yet we also find that adaptation for some social groups could exacerbate the vulnerability of other groups to climate change.

Our study therefore provides a wakeup call for policymakers. Not only is it critical for policymakers to quickly implement ambitious adaptation programs, but a key element of adaptation has to be reducing socioeconomic inequality. Adaptation, in other words, has to include efforts at environmental and social justice. ​That is, perhaps, the most important Little Ice Age lesson of all. 

​The Little Ice Age (LIA), a climatic phase that overlapped with the late-medieval and early modern periods, increasingly interests historians - academic and popular alike. Recently, they have tied the LIA to the outbreak of wars, famines, economic depressions and overall troublesome times. Not only a handful of climate historians are using the term anymore. These days, perhaps due to the overall increasing climate awareness, the period pops up in history-related print media, teaching, online blogs, and – of course – in academic research, among other places. As the LIA is the last distinctive climatic regime before the contemporary anthropogenic climate change, it can provide important analogues to better understand climate-society relationships on various temporal scales – from the direct consequences of short-term extreme events to multi-centennial dynamics of climate resilience.
 
The term "Little Ice Age" was presumably introduced by François E. Matthes in 1939 when he chronicled the advance and retreat of glacier over the past 4000 years across the present-day United States [1]. Since the late 20th century, hundreds (if not thousands) of paleoclimate reconstructions and models have shed further light on the LIA, and the term has been widely accepted to indicate multi-centennial cooler phase occurring in the Northern Hemisphere during the second millennium CE. However, there the agreement over the universal characteristics of the LIA ends.
 
Even a brief reading of the scientific literature on the topic reveals that there are remarkably differing views on the magnitude of the temperature depression, the spatial extent, as well as the onset and termination of the LIA. Within the discipline of history, economic historians Morgan Kelly and Cormac Ó Gráda authored perhaps the best-known publication that highlights the uncertainties related to the magnitude and dating of the event [2]. They have also used change-point analysis to argue that there is no evidence for any statistically significant change in the mean or variance of European temperatures that could be associated with an onset of the LIA [3]. Furthermore, a recent scientific study demonstrated that is it impossible to assign globally coherent dates for the coldest phases of the LIA [4].

Considering the uncertainties related to its periodization, is it appropriate for historians to keep on using the term LIA? In this article, I will argue that it is. However, this requires us to have some basic knowledge about the materials and methods used to detect past climate variability, as well as an understanding of the dynamical drivers of the LIA. My aim here is not to analyse systematically all available climate reconstruction data in relation to the LIA. Instead, I will explain what requirements reconstructions must meet to detect climatic change with statistical analysis, and then present a couple relevant examples. Neither will I revisit earlier criticisms of the LIA concept [2], as these have been addressed elsewhere by historians and scientists [5, 6].
 
Above all, I hope to reveal why the science of the LIA gives us such a complex image of the period and why this is – in fact – not at all a serious problem for historians.  
 
 
Detecting the onset of the LIA
 
Scientists started to measure weather with instruments only in the 18th and 19th centuries. For periods further back in time, we can reconstruct past climate variability from climate proxies. Proxies are indirect climate data, materials which have been influenced by climate of the time when they were laid or written down, formed, or grown. Proxies are found either in the “archives of nature,” like in tree rings, ice layers or sediment varves, or in the “archives of societies.” For example, administrative sources, chronicles and private diaries may contain descriptions of weather and records of climate-sensitive activities, like harvest onset or river ice break-up dates. The later archive type, the written documents, holds climatic and meteorological information particularly relevant to human history [7].
 
The PAGES (Past Global Changes, an international association that bridges paleoclimatologists across the globe) 2k Consortium reconstructions indicate that mean temperatures in the Arctic, Europe and Asia were colder in the 13th and 14th centuries CE than in the previous centuries [8]. These multidecadal cooler anomalies may mark the possible onset period of the LIA (Figure 1a). Likewise, numerous individual climate proxy records show in increasing numbers signs of cooling temperatures from the 1300s and 1400s onwards across the Northern Hemisphere (Figure 1b). Thus, if we aim to identify LIA cooling statistically in individual temperature reconstruction data, our time-series should reach beyond the 13th century. This wide temporal scale, however, poses a challenge: where can we find data that goes back so far?

​From written sources, climate variability is commonly reconstructed with one of the two standard methods: with the calibration-verification procedure or with the index approach [10, 11]. Calibration-verification procedure first translates time-series of climate-sensitive information (like harvest dates from written sources) into meteorological units (such as degrees Celsius) by calibrating the historical data to overlapping period of measured meteorological data. This statistical relationship is then verified with an independent period of overlapping meteorological data [10]. The index approach, on the other hand, first analyses historical climatic information qualitatively and then gives an ordinal-scale value for each datapoint, e.g. from -3 indicating extremely cold to +3 extremely warm [10]. The former method is better suited to detect so-called low-frequency variability (slow and gradual changes like the LIA), whereas the latter identifies primarily year-to-year variability (see Figure 2). For Europe, for example, there is no documentary-based temperature series which would cover the whole last millennium and which would be reconstructed with the calibration-verification procedure. This is because the climate data from European antique and medieval sources are too diverse and inconsistent to use this method to transform the materials into reconstructions [10].
 
Therefore, the reconstructions that extend prior 1500 CE are usually compiled with the index method. Unfortunately, climate reconstructions made from documentary data with this method are not well-suited to detect the LIA change, as these are known to poorly indicate low-frequency variability [10]. At first sight, one exception to the absence of calibration-verification reconstructions extending further back in time appears to be the Netherlands winter and summer temperature reconstruction by A. F. V. van Engelen and others [12]. However, these reconstructions also pose a challenge if we wish to statistically identify change happening over the 13th or 14th centuries because even visual inspection of the series reveal that the early section of the reconstruction appears to be based on ordinal indices. For example, the summer temperature series vary between only seven values before the 14th century (Figure 2). Even these reconstructions are therefore not well-suited to reveal the onset of the LIA, as there is a danger that change detectable with statistical analysis would indicate the change in the reconstruction materials and methods used, not the change in temperatures.

​Because of the lack of adequate document-based climate reconstructions covering the whole past millennium, the onset of the LIA needs to be detected from reconstructions compiled using natural proxy data. Yet, these reconstructions give markedly varying periodisation for the LIA. This is partly because different climate proxies, such as tree-ring width or isotopic concentrations in ice-core data, have different “response windows.” This means that different data from different locations are sensitive to different meteorological parameters (such as temperature or precipitation) over different timescales (from months to decades). Raw proxy data therefore portray a rather heterogeneous image of temperature variability over the past 1000 years (Figure 1b). Furthermore, non-climatic factors also influence the measured proxies, and sometimes it is difficult to distinguish heterogeneity that registers climate and weather from heterogeneity that simply reflects noise. Because proxy data are sensitive to past climate variability only in certain locations over certain seasons, and with imperfect accuracy, we have just a partial view of what has happened to climate prior to systematic meteorological measurements began.
 
However, the differing response windows of different proxy data do not entirely explain our heterogeneous image of the LIA, as reconstructions made from same material type can be in interannual to multidecadal disagreement over past temperature variability. For example, when detecting change from mean warm season temperatures in northern Eurasia, three tree-ring density-based reconstructions suggest different dates for the onset of the LIA (Figure 3).

​Still, most temperature reconstructions from the Northern Hemisphere identify a significant change to cooler mean temperatures, as in the examples presented in Figure 3. All indicate that the change to cooler climate took place well before the 1500s. Thus, the lack of detectable LIA change in previous analyses [3] may simply reflect the relative brevity of the time-series used.

The main trigger of the LIA?
 
The heterogenous spatiotemporal characteristics of the LIA can be primarily explained by the probable trigger of the climatic phase: volcanic aerosol forcing [17]. Large volcanic eruptions can inject sulphur compounds far into the stratosphere, where they are oxidized and become aerosols that absorb and scatter incoming solar radiation. The stratosphere warms but less radiation reaches the ground, cooling Earth’s surface. Many paleoscientists attribute multi-decadal temperature variability prior to anthropogenic warming – including the onset of the coldest phases of the LIA - to volcanic aerosol forcing [17, 18].
 
One common criticism of the LIA as a concept is that current climate change is not comparable to the LIA. Indeed, the LIA and anthropogenic warming are not comparable climatic phases in terms of the extent or magnitude of the change, partly due to the different drivers of these changes. Whereas the LIA was to a great degree triggered by volcanic forcing, the current climatic change is caused by rising atmospheric greenhouse gas concentrations (Figure 4). The climatic impact of these two forcing mechanisms differs considerably, so that while the onset of the LIA varies between reconstructions, the shift to a warmer climate is identifiable in a rather small temporal window (1900s–1920s, see Figure 3a) [19]. Furthermore, whereas long-term variations in temperature differ considerably prior to industrialization, all climate reconstructions presented here indicate similar long-term trends over the past 150 years (Figure 4).

Moreover, volcanic aerosol forcing has both direct and indirect impacts on Earth’s climate. Its direct impacts refer to the mechanisms described above. Its indirect impacts are still not fully understood, but these likely contribute to the spatiotemporal heterogeneity of its climatic impacts. First, the eruption-related cooling is not globally uniform as, for example, oceans cool slower than land. Second, feedback mechanisms can prolong and intensify eruption-related cooling in some areas.

One such feedback mechanism is called ice-albedo feedback. Whereas open waters and dark forests absorb a lot of solar radiation and so warm Earth’s surface, white ice and snow reflect far more incoming solar radiation back into space, cooling the surface. During periods of increased volcanic forcing, the extent and duration of Earth's ice and snow area likely enlarged and prolonged because the cooler conditions, which further lowered temperatures. These feedbacks probably sustained locally and regionally cool surface temperatures long after the impact of volcanic aerosol forcing during the LIA [17].

Third, volcanic forcing alters stratospheric circulation as the direct radiative impacts enhance the Earth’s north-south temperature gradient. This can, for example, strengthen westerly winds. Consequently, northernmost Europe can experience winter warming following strong tropical volcanic eruptions, as westerly winds bring temperate and moist marine air masses to the area [23]. Lastly, some of the indirect effects might influence the main modes of climate variability, such as the summer monsoon circulation, El Niño-Southern Oscillation or the Atlantic Multidecadal Oscillation, which can further increase the spatiotemporal differences of the climate effects of volcanic aerosol forcing [24].
 
In summary, because the climate effects of volcanic forcing are spatially and temporally variable, the onset and the coldest phases of the LIA do not have a readily discernible global pattern. Furthermore, because of its indirect dynamical effects volcanic aerosol forcing can differently influence summer and winter season temperatures. This explains why reconstructions which have varying response windows and sensitivity to climate variability might identify the LIA period rather differently.
 
Due to heterogeneity of the LIA, there was no “typical” LIA climate. Historians should therefore study climate during the period using regional reconstructions relevant to their study area and research questions. In some regions, the LIA was characterised by cool temperatures, in other places by increased year-to-year weather variability. However, climate is, by definition, the long-term average of weather. Commonly, the reference period is at least 30 years. Thus, calculating multidecadal central tendencies from reconstruction data (as well as paying attention to variance and minimum and maximum values) is necessary when defining past climatic regimes. Extreme years cannot be excluded from these calculations. Consequently, drawing attention to possible outliers (i.e. extraordinary cold years) does not lead us to exaggerate the coldness of average LIA conditions, although this has been suggested by some historians. Short-term climate anomalies are part of the prevailing climate.
 
 
The LIA without Periodization
 
This article argues that it is impossible to define universal dates for the onset, termination, characteristics, or coldest phases of the LIA. Instead, these seem to vary depending the region and season in question. But is this a problem for us historians?
 
All historians are familiar with troublesome definitions for historical “periods” – with problematic “periodizations.” For instance, it is impossible to set a common date for the onset of the early modern period. Yet the term is widely accepted and used. Historians are comfortable defining the period depending on the region in question: for some regions a dynastic change marks the onset, whereas the Protestant Reformation or the discovery of Americas might be more appropriate for others. Moreover, the main characteristics of the early modern period vary. In some places the period is marked with a decline of serfdom, for example, whereas in others with an increase. We should accept that, similarly, the periodization and characteristics of the LIA varied from region to region.  
 
The climate variability of the Earth over the past millennium is still an unsolved puzzle. Paleoclimate research resembles other fields that investigate the past, such as the discipline of history. The science of the LIA is not – nor never will be – “done”. Just as each new historical study widens our understanding on the human past, each new reconstruction, simulation and paleoclimate research paper widens our understanding of past climatic changes. There are still many open questions considering the role of volcanic forcing in triggering and sustaining the LIA. Moreover, the possible effects of solar forcing need to be further explored. Therefore, it is essential that historians who are interested in past climates follow the progress of paleoclimatology [25].
 
The LIA sets certain boundaries in late medieval or early modern history. Needless to say, weather events (which usually are the triggers of human calamities) may or may not be typical for prevailing climatic conditions. For example, in the case of famines in LIA Europe, LIA conditions shortened the length and cooled down the temperatures of the growing season. This made the agricultural production and related food systems more vulnerable to disturbances than they were during warmer climatic phases, especially on the northern margins of agriculture. These disturbances can include weather events like frosts destroying the harvest, violent conflicts damaging grain yields, or entitlement failures due to hoarding of food stuff. Thus, the LIA, or any past period in history, cannot be imagined as the sole cause of past events, like famines. Instead, it gives an environmental context to these events in history.
 
Of course, the term “Little Ice Age” is not perfect. It is, for example, not correct in a geophysical sense, as it took place during an interglacial period. However, the term is short, handy, and already widely used. It is practical in science communication, such as interdisciplinary research, teaching, and public outreach. As long as we remember the heterogenous characteristics of the period, by acknowledging the Little Ice Age and exploring its possible entanglements with the human past, we might get further insights into complex climate-society relationships. These can provide perspectives on both sides of the relationship: the agency of climate in human history and the agency of humans in adapting to changing climate and coping with extreme events. Such insights have arguably never been more important than at present, in the context of ongoing anthropogenic climate change and its rising toll on our societies.
 
 
References and notes:
​
[1] Matthes, F. E. (1939). Report of committee on glaciers, April 1939. Eos, Transactions American Geophysical Union, 20(4), 518-523.
[2] Kelly, M., & Ó Gráda, C. (2013). The waning of the Little Ice Age: climate change in early modern Europe. Journal of Interdisciplinary History, 44(3), 301-325.
[3] Kelly, M., & Gráda, C. Ó. (2014). Change points and temporal dependence in reconstructions of annual temperature: did Europe experience a little Ice Age? The Annals of Applied Statistics, 8(3), 1372-1394.
[4] Neukom, R., Steiger, N., Gómez-Navarro, J. J., Wang, J., & Werner, J. P. (2019). No evidence for globally coherent warm and cold periods over the preindustrial Common Era. Nature, 571(7766), 550-554.
[5] White, S. (2013). The real little ice age. Journal of Interdisciplinary History, 44(3), 327-352.
[6] Büntgen, U., & Hellmann, L. (2013). The Little Ice Age in scientific perspective: cold spells and caveats. Journal of Interdisciplinary History, 44(3), 353-368.
[7] Brönnimann, S., Pfister, C. & White, S. (2018). Archives of Nature and Archives of Societies. In White, S., Pfister, C., & Mauelshagen, F. (eds.), The Palgrave Handbook of Climate History. Palgrave Macmillan, London, 27-36.
[8] The PAGES (Past Global Changes) Consortium (2013). Continental-scale temperature variability during the past two millennia. Nature Geoscience, 6(5), 339-346.
[9] Charpentier Ljungqvist, F., Krusic, P. J., Brattström, G., & Sundqvist, H. S. (2012). Northern Hemisphere temperature patterns in the last 12 centuries. Climate of the Past, 8, 227-249. Note that some of the data locations on the map has been moved slightly to illustrate all the proxy material, also the overlapping ones.
[10] Pfister, C., Camenisch, C., & Dobrovolný, P. (2018). Analysis and Interpretation: Temperature and Precipitation Indices. In White, S., Pfister, C., & Mauelshagen, F. (eds.), The Palgrave Handbook of Climate History. Palgrave Macmillan, London, 115-129.
[11] Dobrovolný, P. (2018). Analysis and Interpretation: Calibration-Verification. In White, S., Pfister, C., & Mauelshagen, F. (eds.), The Palgrave Handbook of Climate History. Palgrave Macmillan, London, 107-113.
[12] Van Engelen, A. F., Buisman, J., & IJnsen, F. (2001). A millennium of weather, winds and water in the low countries. In History and Climate. Springer, Boston, MA, 101-124. The time-series downloaded from the KNLM Climate Explorer.
[13] Matskovsky, V. V., & Helama, S. (2014). Testing long-term summer temperature reconstruction based on maximum density chronologies obtained by reanalysis of tree-ring data sets from northernmost Sweden and Finland. Climate of the Past, 10(4), 1473-1487; Helama, S., Vartiainen, M., Holopainen, J., Mäkelä, H. M., Kolström, T., & Meriläinen, J. (2014). A palaeotemperature record for the Finnish Lakeland based on microdensitometric variations in tree rings. Geochronometria, 41(3), 265-277; Schneider, L., Smerdon, J. E., Büntgen, U., Wilson, R. J., Myglan, V. S., Kirdyanov, A. V., & Esper, J. (2015). Revising midlatitude summer temperatures back to AD 600 based on a wood density network. Geophysical Research Letters, 42(11), 4556-4562. The Polar Urals reconstruction data has been downloaded from a dataset provided by Wilson, R., Anchukaitis, K., Briffa, K. R., Büntgen, U., Cook, E., D'arrigo, R., ... & Hegerl, G. (2016). Last millennium northern hemisphere summer temperatures from tree rings: Part I: The long term context. Quaternary Science Reviews, 134, 1-18.
[14] Analysis was performed with the R changepoint package (2.2.2) as implemented by Killick, R., & Eckley, I. (2014). changepoint: An R package for changepoint analysis. Journal of Statistical Software, 58(3), 1-19.
[15] Analysis was performed with the R bcp package (4.0.3) as implemented by Erdman, C., & Emerson, J. W. (2007). bcp: an R package for performing a Bayesian analysis of change point problems. Journal of Statistical Software, 23(3), 1-13.
[16] Warm season: June–August for the Northern Fennoscandia and Polar Urals, and April–September for the South Finland reconstructions. Correlation analysis performed with the Climate Explorer using the HadCRUT4/HadSST4 filled-in T2m/SST field data (Cowtan, K., & Way, R. G. (2014). Coverage bias in the HadCRUT4 temperature series and its impact on recent temperature trends. Quarterly Journal of the Royal Meteorological Society, 140(683), 1935-1944).
[17] Miller, G. H., Geirsdóttir, Á., Zhong, Y., Larsen, D. J., Otto‐Bliesner, B. L., Holland, M. M., ... & Anderson, C. (2012). Abrupt onset of the Little Ice Age triggered by volcanism and sustained by sea‐ice/ocean feedbacks. Geophysical Research Letters, 39(2).
[18] Neukom, R., Barboza, L. A., Erb, M. P., Shi, F., Emile-Geay, J., Evans, M. N., ... & Schurer, A. (2019). Consistent multi-decadal variability in global temperature reconstructions and simulations over the Common Era. Nature geoscience, 12(8), 643-649.
[19] In addition, perhaps the early (pre-1950s) warming might be attributable also to some degree to the lack of volcanic aerosol forcing. Note also that depending on the reconstruction materials and methods, plausibly also better proxy sample replication or overlapping instrumental data may contribute to the similarity of temperature trends over the past 150 years.
[20] Sigl, M., Winstrup, M., McConnell, J. R., Welten, K. C., Plunkett, G., Ludlow, F., ... & Fischer, H. (2015). Timing and climate forcing of volcanic eruptions for the past 2,500 years. Nature, 523(7562), 543.
[21] Ballantyne, A. P., Alden, C. B., Miller, J. B., Tans, P. P., & White, J. W. C. (2012). Increase in observed net carbon dioxide uptake by land and oceans during the past 50 years. Nature, 488(7409), 70. Time-series downloaded from the KNLM Climate Explorer.
[22] CRUTEM (4.6) T2m anomalies averaged over 20-70E and 60-70N, https://www.metoffice.gov.uk/hadobs/crutem4/; Time-series downloaded from the KNLM Climate Explorer.
[23] Fischer, E. M., Luterbacher, J., Zorita, E., Tett, S. F. B., Casty, C., & Wanner, H. (2007). European climate response to tropical volcanic eruptions over the last half millennium. Geophysical research letters, 34(5).
[24] Good summary of the climatic effects of volcanic aerosol forcing can be found, for example, in Brönnimann, S. (2015). Climatic changes since 1700, Springer, Cham (especially pp. 123–135).
[25] Consequently, it is noteworthy to mention that although the LIA cooling is currently attributed to volcanic forcing, our understanding for the drivers of the period may advance in the future. Likewise, the Southern Hemispheric extent of the cool period may improve with new proxy data available.
 
Special thanks to Dagomar Degroot and Fredrik Charpentier Ljungqvist for the inspiring discussions and comments which helped shape this text.

In article after article, academics, policy analysts, and journalists have told a similar story: climate change, by melting Arctic ice, is unlocking resources that could soon trigger war in the far north. They argue that the race to extract the vast reservoirs of oil and natural gas that lie under the vanishing ice – up to a quarter of the world’s undiscovered fossil fuel reserves, by some estimates – will likely provoke hostilities between Russia, the United States, and other nations with claims to the bonanza. The overall failure of early drilling efforts in the Arctic, it seems, is of little consequence.
 
These claims add a new twist to a vast and growing body of scholarship that links climate change to conflict. Academics working in this area often begin their work by showing that past climate changes reduced – rather than increased – the regional availability of some crucial resource, such as water, or grain, or fish spawning grounds. They then use diverse methods to trace the destabilizing social and political consequences of these resource shortages. Environmental historians, for example, have argued that falling temperatures and changing precipitation patterns in the seventeenth century led to poor grain harvests and famines that provoked rebellions in diverse societies the world over. More controversially, scholars in many disciplines have linked human-caused global warming to droughts that encouraged migration and ultimately conflict in twentieth-century sub-Saharan Africa. Far less attention has been directed at the ways in which more abundant resources might incite violence either within or between states.
 
In fact, those who make claims about the inevitably more violent nature of the future Arctic have rarely thought to consider the history of climate change and conflict in the far north. Yet violence in the Arctic has long coincided with volcanic eruptions and fluctuations in solar activity that altered regional temperatures and in turn the availability of crucial resources. In the early seventeenth century, for example, the Arctic cooled sharply and then warmed slightly just as Europeans discovered, hunted, and fought over bowhead whales off Spitsbergen, the largest island of the Svalbard archipelago. Oil, bones, and baleen from bowheads became crucial resources for the economies of England and the Dutch Republic.

​Diverse manifestations of climate change in the Arctic and Europe influenced how easy bowhead whales were to hunt, the profits that could be fetched by their oil, the proximity of whalers to one another, and the ability of whalers to reach the far north. Skirmishes within and between whaling companies operating from rival European nations reveal that climate change can affect both the causes and the conduct of conflict in diverse ways, even in environments it transforms on a vast scale. There is nothing inevitable or simple about the ways in which climate change influences human decisions and actions. 

​This history would be hard to investigate without new climate reconstructions compiled by scholars in many different disciplines, using many different sources. In 2014, researchers drew from natural and textual sources to create a sweeping new reconstruction of average Arctic air surface temperatures over the past 2,000 years. It confirms that the Arctic was overall very cold in the seventeenth century, but also that it warmed slightly towards the middle and end of the century. Temperatures in the Arctic therefore roughly mirrored those elsewhere in the Northern Hemisphere during the chilliest century of the “Little Ice Age,” a cooler climatic regime that endured for roughly six centuries. The extent and distribution of sea ice in the Arctic – the most important environmental condition that whalers coped with – would have responded to even subtle changes in average annual temperatures.
 
Yet these very big trends do not tell us exactly how climate change transformed environments around Svalbard. Local temperature trends do not always precisely mirror regional or global developments, and anyway the distribution and extent of Arctic sea ice registers more than just the warmth or chilliness of the lower atmosphere. Ice core and model simulation data both suggest that air surface temperatures around Svalbard were quite cool in the early seventeenth century and somewhat warmer in the middle of the century, at least in summer. Lakebed sediments, by contrast, suggest that glaciers across Svalbard actually retreated beginning in around 1600 owing to changes in precipitation, not temperature, which may have reduced the local frequency of storms that can break up sea ice. Moreover, sea surface temperatures – which also influence sea ice – were quite warm off the west coast of Spitsbergen, the largest island of the Svalbard archipelago, for much of the seventeenth century, although they were very cold off the northern coast.

​Overall, it seems safe to conclude that, in the summer, temperatures around Svalbard roughly mirrored those of the broader Arctic in the seventeenth century. Warmer currents may have brought more nutrients to the region and probably reduced the extent of local sea ice, although a reduction in storm frequency would have preserved the ice that was there. In any case, most Arctic sea ice melts in the summer before reaching its minimum annual extent in the fall, which means that summer weather and currents had the greatest impact on the extent of ice in the Arctic north of Europe. Because sea ice retreated from Svalbard in the summer, it was also the crucial season for whaling.
 
If the local consequences of global climate changes can be counterintuitive – that warming current off Spitsbergen, for example – so too can human responses. One might assume that climatic cooling would have dissuaded explorers, fishers, and whalers from entering the Arctic. Instead, European sailors found and then started exploiting the environments on and around Svalbard in the late sixteenth and early seventeenth centuries, just as volcanic eruptions led to arguably the coldest point of the Little Ice Age in the Northern Hemisphere. In previous work, I have shown that climate changes in this period interacted with local environments to leave just enough sea ice in the Arctic north of Europe to redirect expeditions in search of an elusive “Northern Passage” to Asia. Dutch and English sailors struggling to find a way through the ice ended up discovering Spitsbergen and the many bowhead whales off its western coast. Bowheads are relatively docile, float on the surface when killed, and have very thick blubber that can be turned into oil. Beginning in 1611, they started attracting Dutch, English, and Basque whalers.
 
Other scholars have argued that cooling in the early seventeenth century led bowhead whales to congregate along more extensive sea ice near Spitsbergen, which made them easier to hunt for whalers. By contrast, whales dispersed as sea ice retreated in the warmer middle of the seventeenth century, which made them harder to hunt. There does seem to be a statistically significant correlation between ice core reconstructions and model simulations of summer temperatures around Spitsbergen on the one hand, and the annual whale catch on the other. Iñupiat whalers consulted by our own Bathsheba Demuth, however, report that bowheads in the Berring Sea are not social enough to gather in huge groups. Perhaps bowhead culture was different in the Atlantic corner of the Arctic when whale populations were much higher than they are today. 

The apparent correlation between surface air temperatures and the whale catch around Spitsbergen provides our first point of entry into relationships between climate change and conflict in the far north. From the first years of whaling around Spitsbergen, two companies – the Dutch Northern Company, and the English Muscovy Company – emerged as the leading players in the Arctic whaling industry. The governments of England and the Dutch Republic had granted these companies monopolies on whaling operations, but they were resented by merchants and mariners who preferred to operate independently. After around 1625, as bowhead whales dispersed amid warming temperatures, competition between Dutch whalers devolved into piracy. Many conflicts involved whalers who sailed either for the Northern Company or for themselves, although even some Company whalers hid the best hunting grounds from one another. In these circumstances, the governing body of the Dutch Republic rescinded the monopoly of the Northern Company in 1642.
 
From the beginning, competition between English whalers assumed an even more brutal character. The Muscovy Company took an uncompromising stance towards English interlopers, who responded in turn. In 1626, for example, whalers aboard independently-owned vessels destroyed the Company’s station at Horn Sound, Spitsbergen, after they had been harassed by Company ships. Not surprisingly, petitions submitted to the English Standing Council for Trade in 1652 reveal that small groups of English merchants also sought to overturn the monopoly of the Muscovy Company. Individual merchants insisted that the Company could not adequately “fish” the territories over which it held a monopoly. The Company responded that whalers in the employ of those merchants had interfered with the activities of its sailors and stolen whales they had killed. 

Warming temperatures that reduced the extent of pack ice and encouraged whales to disperse may well have encouraged competition and conflict between whalers belonging to the same nationality. Bizarrely, the whaling industry also responded to fluctuations in the supply of rape, linseed and hemp oils, which were less smelly substitutes to whale oil for fueling lamps or manufacturing soap, leather, or wax. Temperature and precipitation extremes that reduced the supply of vegetable oils naturally also increased the price of whale oils in the Dutch and English economies, and thereby the profitability of whaling. In the context of the Little Ice Age, the 1630s in particular were relatively warm across the Northern Hemisphere. The trusty Allen-Unger commodity database tells us that the price of linseed oil in Augsburg, for example, dropped sharply as average annual temperatures increased. Even the price of lamp oil – which would have also registered the price of whale oil – fell modestly in the same period. Could whalers in the 1630s and 1640s have vied with monopolistic companies just climate change both reduced the supply of their resource and increased its profitability? 

​We can sketch these relationships by mixing and matching different statistics from natural and textual archives. Detailed qualitative accounts written by whalers, however, reveal that climate influenced conflict in more complicated ways during the first decade of the Svalbard whaling industry. In that decade, whalers from several European nations – most importantly England and the Dutch Republic – employed experienced Basque whalers to kill bowhead whales, strip their blubber, and boil the blubber on the coast. Whalers would deploy boats from a mothership to kill small groups of whales. They would then establish temporary settlements on the coast to turn the blubber into oil that could be loaded into barrels and returned to the ship.
 
These techniques forced whalers from different nations to rove along the coast of Spitsbergen, which made it likely that they would encounter one another. Initially, the Muscovy Company falsely claimed that English explorers had found Spitsbergen, which meant that it alone had the right to hunt for whales off the island. The Dutch – who had actually discovered the island – insisted that whalers from all European nations should be allowed to fish off its coast. In 1613, a Dutch expedition under Willem van Muyden, the legendary “First Whaleman” of the Republic, reached Spitsbergen in late May and found the coast blocked by ice. After only two weeks, the retreating ice let his whalers enter a bay roughly halfway down the island, but a better-armed English fleet quickly spotted them. In subsequent weeks, the English harassed the Dutch whalers and stole much of their equipment and whale commodities. Yet the Dutch returned with naval escorts in 1614. After the English seized a Dutch ship in 1617, the Dutch arrived with overwhelming force in 1618 and killed several English whalers. 

The worst skirmishes between Dutch and English whalers raged in years that were relatively warm across the Arctic and probably around Svalbard, despite the generally cooler climate of the early seventeenth century. In cold years, sea ice could have kept whalers working for different companies from lingering on the coast, where tensions simmered and eventually erupted into bloodshed. In any case, the Muscovy Company and the Northern Company eventually agreed to occupy different parts of Spitsbergen. The Dutch would claim the northwestern tip, where they established the major, fortified settlement of Smeerenburg: “blubber town.” The English, meanwhile, took the rest. The Dutch eventually benefited from being closer to the edge of the summer pack ice, where there were more whales to hunt.
 
Hostilities between the English and the Dutch in the volatile first decades of the Svalbard whaling industry convinced the Northern Company to keep a skeleton crew at Smeerenburg and nearby Jan Mayen island during the winter. If they could survive, they would keep Company infrastructure safe from springtime raids and provide valuable information about the region’s winter weather. In 1633/34, two groups of Dutch whalers overwintered at Smeerenburg and Jan Mayen. Regional summer temperatures may have been warming at the time, but winter temperatures across the Arctic were cooling, and 1633/34 was particularly cold. The Smeerenburg group survived the frigid temperatures and killed enough caribou and Arctic foxes to hold off scurvy. The Jan Mayen whalers endured until the spring, but they could not catch enough game to survive the ravages of scurvy. In 1634/35, the Northern Company tried again. This time, both groups died from scurvy, and the Smeerenburg whalers did not even make it to winter. Violent competition between whaling companies – plausibly influenced by warming summers – exposed whalers to a quirk in the climatic trends of the Little Ice Age in the Arctic: the big difference between summer and winter temperatures, relative to long-term averages.

Climate change also influenced hostilities between whalers by altering how easily they could reach the “battlefield” around Spitsbergen. In 1615, a year of typical chilliness during the Little Ice Age, the author of a Dutch whaling logbook reported that sea ice on June 7th blocked the crew’s progress towards Svalbard. The crew spotted a bowhead whale three days later, but ice kept them from pursuing. That evening, a storm rose just as they found themselves surrounded by sea ice. They tried to anchor themselves to an iceberg, but it shattered and would have destroyed their ship “had God not saved us.” The few surviving logbooks written by Dutch whalers also record trouble with ice in the warmer 1630s, yet it surely would have been harder to reach Svalbard and compete with English whalers in the first decade of the Arctic whaling industry.

​Beginning in 1652, the Dutch Republic and England also embarked on hostilities in the North Sea region that would endure, with interruptions, until the Dutch invasion that launched the Glorious Revolution of 1688. During the three Anglo-Dutch Wars that raged in these decades, English and Dutch ordinance kept whalers from sailing to the Arctic or constructing new ships and equipment for the whaling industry. Sailors who might have served aboard whaling ships were urgently needed to crew the warships of the English and Dutch fleets. Many whalers also served as privateers, raiding merchant ships and convoys and then surrendering a share of the profits to their governments. Any whalers who set sail for the Arctic risked losing everything if discovered.
 
As I have written elsewhere, a cooling climate in the second half of the seventeenth century profoundly influenced naval hostilities between the English and Dutch fleets. By altering the frequency of easterly and westerly winds in the North Sea, it helped the English claim victory in the First Anglo-Dutch War but aided the Dutch in the Second and Third Anglo-Dutch Wars, as well as the Glorious Revolution. It probably shortened the First Anglo-Dutch War (1652-54) but lengthened the third war (1672-74). That, in turn, would mean that the manifestations of global climate change in the North Sea affected the opportunities for whalers to engage in hostilities in the Arctic. 

After 1650, the character of hostilities between Arctic whalers changed dramatically. Cooling summer temperatures brought thick ice into the harbors of Spitsbergen, while the depletion of the bowhead whale population may have worsened the prospects of whaling near land. Whalers had to hunt further and further from the shore, and started processing their whales at sea. They abandoned settlements along the coast of Spitsbergen, which soon fell into ruin. Violence between whalers now took place exclusively at sea. The evidence is spotty, but privateers seem to have hunted whalers in the final decades of the seventeenth century. In 1692, Henry Greenhill, commissioner of the English navy at Plymouth, reported that two “Greenland Prizes” – whaling vessels captured off Spitsbergen – had been brought into harbor. Since England had allied with the Dutch Republic against France, these ships were probably French in origin.
 
The history of climate change, whaling, and violence in and around Svalbard during the seventeenth century is above all complicated, filled with surprising twists and turns. Climate change may have occasionally provoked violence, but it probably did so by reducing, rather than increasing, the accessibility of bowhead whales to whalers. More importantly and more certainly, it altered the character of confrontations between whalers in the far north. Moreover, its manifestations thousands of kilometers from the Arctic ended up having important consequences for hostilities in and around Svalbard.

These intricate relationships in the distant past should give us pause as we contemplate the warmer future in the Arctic. Global warming may indeed set the stage for war in the far north, but we have no way of knowing for sure. It is equally likely that climate change will provoke human responses that are hard to guess at present. In this case, we cannot use the past to predict the future, but we can draw on it to ask more insightful questions in the present. 

~Dagomar Degroot

Selected Works Cited: 

Degroot, Dagomar. “Exploring the North in a Changing Climate: The Little Ice Age and the Journals of Henry Hudson, 1607-1611.” Journal of Northern Studies 9:1 (2015): 69-91.
 
Degroot, Dagomar. “Testing the Limits of Climate History: The Quest for a Northeast Passage During the Little Ice Age, 1594-1597.” Journal of Interdisciplinary History XLV:4 (Spring 2015): 459-484.
 
Degroot, Dagomar. “‘Never such weather known in these seas:’ Climatic Fluctuations and the Anglo-Dutch Wars of the Seventeenth Century, 1652–1674.” Environment and History 20.2 (May 2014): 239-273. 

Hacquebord, Louwrens. De Noordse Compagnie (1614-1642): Opkomst, Bloei en Ondergang. Zutphen: Walburg Pers, 2014.

Hacquebord, Louwrens. “The hunting of the Greenland right whale in Svalbard, its interaction with climate and its impact on the marine ecosystem.” Polar Research 18:2 (1999): 375-382.

Hacquebord, Louwrens and Jurjen R. Leinenga. “The ecology of Greenland whale in relation to whaling and climate change in 17th and 18th centuries.” Tijdschrift voor Geschiendenis 107 (1994): 415–438.

Hacquebord, Louwrens, Frits Steenhuisen and Huib Waterbolk. “English and Dutch Whaling Trade and Whaling Stations in Spitsbergen (Svalbard) before 1660.” International Journal of Maritime History 15:2 (2003): 117-134.

Laist, David W. North Atlantic Right Whales: From Hunted Leviathan to Conservation Icon. Washington, DC: Johns Hopkins University Press, 2017.

McKaya, Nicholas P. and Darrell S. Kaufman. "An extended Arctic proxy temperature database for the past 2,000 years." Scientific Data (2014). doi: 10.1038/sdata.2014.26.

In the year 1001 CE, Leif Erikson made landfall in Greenland, and traded with people who “in their purchases preferred red cloth; in exchange they had furs to give.” The Vikings called these people Skraelings. Present-day archeologists and historians call them the Thule. At its height, Thule civilization spread from its origins along the Bering Strait across the Canadian Arctic and into to Greenland. The ancestors of today’s Inuit and Inupiat, the Thule accomplished what Erikson and subsequent generations of Europeans never managed: living in the high Arctic without supplies of food, technology, and fuel from more temperate climates.

The Thule left archeological evidence of a technologically sophisticated, vigorous people. They invented the umiak, an open walrus-hide boat so large that it was sometimes equipped with a sail. These boats, when used alongside small, nimble kayaks, made the Thule formidable marine-mammal hunters. On land, they harnessed dogs to sleds and built homes half-underground, insulated by earth and beamed with whale bones.

People did inhabit the high North American Arctic before the Thule. Their immediate predecessors, called the Dorset by archeologists, were expert carvers, and there are signs of other cultures that date back at least five thousand years. But the Thule appear to have been a particularly robust society, one that inhabited thousands of challenging Arctic miles. Eventually, they even traded with Europeans for metal tools, sending walrus ivory as far abroad as Venice.

In the twentieth century, many archeologists linked the success of the Thule to the climate. In this view, rapid Thule expansion coincided with the Medieval Warm Period in the years between 1000 and 1300. The Thule were expert whalers, especially of bowhead whales. This slow species makes for good prey. Their 100-ton bodies can be fifty percent fat by volume, giving people ample calories to eat and burn through long winters. With the slight increase in temperature during the Medieval Warm Period, the theory went, the range of the bowhead whale expanded across newly ice-free waters. Atlantic and Pacific bowhead populations eventually met in the Arctic Ocean north of Canada, offering an uninterrupted banquet of blubber to hunters.

​The Thule, in this view, were simply whale hunters who followed the migration of their prey in a warming climate. Environmental conditions, not a sophisticated culture, was the key explanation for their success. Emphasizing climate as the cause of migration and social success reduced the achievements of the Thule, essentially, to those of their prey.

However, twenty-first century evidence is changing this account of Thule migration. In 2000, Robert McGhee questioned the validity of the radiocarbon dates that helped establish Thule expansion as an eleventh-century phenomenon. He proposed the 1200s as the earliest date of migration. Then, genetic tests by marine biologists showed that Atlantic and Pacific bowhead whales did not mix their populations during the Medieval Warm Period, meaning that there was a substantial gap in whaling possibilities on the Arctic coast.

Something more complicated than just following the blubber drove the Thule eastward. McGhee speculated that communities moved for iron, which is short supply in the Arctic. Thule hunters learned from the Dorset people of a deposit left by the Cape York meteorite. They colonized huge territories to secure their access to this precious resource from outer space. Other specialists theorized that population pressure, overhunting, or warfare led the Thule to migrate east. 

The ongoing work of Canadian archeologists T. Max Friesen and Charles D. Arnold seems to confirm that we must look beyond simple climatic explanations for the Thule expansion. Working on Beaufort Sea and Amundsen Gulf sites, the pair established that there was no definitive Thule occupation in this part of the western Arctic prior to the thirteenth century. Because any Thule migrants would have had to pass through these points as they moved east, their research indicates that the Thule civilization was only beginning its continental spread around the year 1200, well into the period of warming. The climate may have helped the Thule quickly spread toward Greenland, but the onset of the Medieval Warm Period did not automatically draw people eastward.

Moreover, the work of other archeologists on the Melville Peninsula, along Baffin Bay, indicates that the Mediaeval Warm Period was not always so warm. Some areas of the Arctic saw slight temperature increases, but in general the millennium was cooler than those past. In places, the effects of the so-called Little Ice Age began a century or two before they were evident across the globe, meaning the Thule adapted not to a warmer Arctic, but a colder one. This cooling was more apparent in the west, where the team found fewer Thule sites but also more stability, both in the climate and the record of human occupation. To the east of the Melville Peninsula, where temperatures did warm, the climate was also more variable – adding a new set of complexities to social and economic life. The move into the central Arctic, therefore, reflected forces other than climate.

Beginning in the fifteenth century, Thule culture fragmented, specialized, and emerged eventually as distinct contemporary Inuit and Inupiat groups. The Little Ice Age is often the reason given for the disintegration of Thule civilization in the fifteenth century. Yet, the work by Finkelstein, Ross, and Adams indicates that, while the Thule abandoned some sites due to cooling trends, this did not hold in all cases. Other causes, including increased contact with Europeans and their infectious diseases, might have had more to do with the disintegration in some locations.

Overall, the new vision of the Thule prominence in the Arctic makes their rise shorter, but even more impressive. And if the Thule began their migration only in 1200, it seems unlikely they spread east simply to find iron. This would have required only smaller-scale movements to precise locations. Instead, the Thule developed a thriving, intricate network of settlements across the Arctic. For Friesen and Arnold, this is evidence that the Thule expanded in order to recreate the ideological and economic lives that they had enjoyed in their origins along the Bering Strait. And in just a century they did, not only by inhabiting land from the Bering Strait to Greenland, but through explorations to the northern edges of the continent.

All of this also helps us reinterpret a well-known tale from the Viking exploration of the Arctic. When Leif Erikson’s sister Freydis frightened off a band of Skraelingar in the early eleventh century by striking “her breast with the naked sword” of a fallen Viking, she was likely not fighting the Thule, as scholars have assumed. Perhaps it was the Dorset people that “were frightened, and rushed off in their boats.” The Thule, at least, were likely still a century away from the eastern Canadian coastline. They were not easily daunted either by a shifting climate or by Viking weapons. 

References

Quotes from the Saga of Erik the Red, English translation by J. Sephton, can be found here: http://www.sagadb.org/eiriks_saga_rauda.en

Friesen, T. Max and Charles D. Arnold. “The Timing of the Thule Migration: New Dates from the Western Canadian Arctic,” American Antiquity 73 (2008): 527-538.

Finkelstein, S.A., J.M Ross, and J.K Adams. “Spatiotemporal Variability in Arctic Climates of the Past Millennium: Implications for the Study of Thule Culture on Melville Peninsula, Nunavut,” Arctic Antarctic, and Apline Research 41 (200): 442-454.

McGhee, Robert. “Radio Carbon Dating and the Timing of the Thule Migration,” in Appelit, M. Berglund, J, and Gullov, H.C. eds. Identities and Cultural Contacts in The Arctic: Proceedings from a Conference at the Danish National Museum. Copenhagen (2000): 181-191.

Morrison, David. “The Earliest Thule Migration.” Canadian Journal of Archaeology 22( 1999): 139-156.

 Betts, Matthew, and T. Max Friesen, “Quantifying Hunter-Gatherer Intensification: A Zooarchaeological Case Study form Arctic Canada,” Journal of Anthropological Archaeology 23 (2004): 357-384.

Dyke, Arthur S., James Hooper, and James M. Savelle. “A History of Sea Ice in the Canadian Arctic Archipelago based on Postglacial Remains of the Bowhead Whale (Balaena mysticetus)”, Arctic 49 (1996): 235-255.

Park, Robert W. “The Dorset-Thule Succession Revisited,” in Appelit, M. Berglund, J, and Gullov, H.C. eds. Identities and Cultural Contacts in the Arctic: Proceedings from a Conference at the Danish National Museum. Copenhagen (2000): 192-205. 

​Although it may seem like the sun is one of the few constants in Earth’s climate system, it is not. Our star undergoes both an 11-year cycle of waning and waxing activity, and a much longer seesaw in which “grand solar minima” give way to “grand solar maxima.” During the minima, which set in approximately once per century, solar radiation declines, sunspots vanish, and solar flares are rare. During the maxima, by contrast, the sun crackles with energy, and sunspots riddle its surface. 

The most famous grand solar minimum of all is undoubtedly the Maunder Minimum, which endured from approximately 1645 until 1720. It was named after Edward Maunder, a nineteenth-century astronomer who painstakingly reconstructed European sunspot observations. The Maunder Minimum has become synonymous with the Little Ice Age, a period of climatic cooling that, according to some definitions, endured from around 1300 to 1850, but reached its chilliest point in the seventeenth century.

​During the Maunder Minimum, temperatures across the Northern Hemisphere declined, relative to twentieth-century averages, by about one degree Celsius. That may not sound like much – especially in a year that is, globally, still more than one degree Celsius hotter than those same averages – but consider: seventeenth-century cooling was sufficient to contribute to a global crisis that destabilized one society after another. As growing seasons shortened, food shortages spread, economies unraveled, and rebellions and revolutions were quick to follow. Cooling was not always the primary cause for contemporary disasters, but it often played an important role in exacerbating them. 

Many people – scholars and journalists included – have therefore assumed that any fall in solar activity must lead to chillier temperatures. When solar modelling recently predicted that a grand solar minimum would set in soon, some took it as evidence of an impending reversal of global warming. I even received an email from a heating appliance company that encouraged me to hawk their products on this website, so our readers could prepare for the cooler climate to come! Of course, the warming influence of anthropogenic greenhouse gases will overwhelm any cooling brought about by declining solar activity. 

In fact, scientists still dispute the extent to which grand solar minima or maxima actually triggered past climate changes. What seems certain is that especially warm and cool periods in the past overlapped with more than just variations in solar activity. Granted, many of the coldest decades of the Little Ice Age coincided with periods of reduced solar activity: the Spörer Minimum, from around 1450 to 1530; the Maunder Minimum, from 1645 to 1720; and the Dalton Minimum, from 1790 to 1820. However, one of the chilliest periods of all – the Grindelwald Fluctuation, from 1560 to 1630 – actually unfolded during a modest rise in solar activity. Volcanic eruptions, it seems, also played an important role in bringing about cooler decades, as did the natural internal variability of the climate system. Both the absence of eruptions and a grand solar maximum likely set the stage for the Medieval Warm Period, which is now more commonly called the Medieval Climate Anomaly.

This gets to the heart of what we actually mean when we use a term like “Maunder Minimum” to refer to a period in Earth’s climate history. Are we talking about a period of low solar activity? Or are we referring to an especially cold climatic regime? Or are we talking about chilly temperatures and the changes in atmospheric circulation that cooling set in motion? In other words: what do we really mean when we say that the Maunder Minimum endured from 1645 to 1720? How does our choice of dates affect our understanding of relationships between climate change and human history in this period?

​To find an answer to these questions, we can start by considering the North Sea region. This area has yielded some of the best documentary sources for climate reconstructions. They allow environmental historians like me to dig into exactly the kinds of weather that grew more common with the onset of the Maunder Minimum. In Dutch documentary evidence, for example, we see a noticeable cooling trend in average seasonal temperatures that begins around 1645. On the surface of things, it seems like declining solar activity and climate change are very strongly correlated.

And yet, other weather patterns seem to change later, one or two decades after the onset of regional cooling. Weather variability from year to year, for example, becomes much more pronounced after around 1660, and that erraticism is often associated with the Maunder Minimum. Severe storms were more frequent only by the 1650s or perhaps the 1660s, and again, such storms are also linked to the Maunder Minimum climate. In the autumn, winter, and spring, easterly winds – a consequence, perhaps, of a switch in the setting of the North Atlantic Oscillation – increased at the expense of westerly winds in the 1660s, not twenty years earlier. 

All of these weather conditions mattered profoundly for the inhabitants of England and the Dutch Republic: maritime societies that depended on waterborne transportation. Rising weather variability made it harder for farmers to adapt to changing climates, but often made it more profitable for Dutch merchants to trade grain. More frequent storms sank all manner of vessels but sometimes quickened journeys, too. Easterly winds gave advantages to Dutch fleets sailing into battle from the Dutch coast, but westerly winds benefitted English armadas. If we define the Maunder Minimum as a climatic regime, not (just) a period of reduced sunspots, and if we care about its human consequences, what should we conclude? Did the Maunder Minimum reach the North Sea region in 1645, or 1660?

​These problems grow deeper when we turn to the rest of the world. Across much of North America, temperature fluctuations in the seventeenth century did not closely mirror those in Europe. There was considerable diversity from one North American region to another. Tree ring data suggests that northern Canada appears to have experienced the cooling of the Maunder Minimum. Western North America also seems to have been relatively chilly in the seventeenth century, although there chillier temperatures probably did not set in during the 1640s.

By contrast, cooling was moderate or even non-existent across the northeastern United States. Chesapeake Bay, for instance, was warm for most of the seventeenth century, and only cooled in the eighteenth century. Glaciers advanced in the Canadian Rockies not in the seventeenth century, but rather during the early eighteenth century. Their expansion was likely caused by an increase in regional precipitation, not a decrease in average temperatures.

Still, the seventeenth century was overall chillier in North America than the preceding or subsequent centuries, and landmark cold seasons affected both shores of the Atlantic. The consequences of such frigid weather could be devastating. The first settlers to Jamestown, Virginia had the misfortune of arriving during some of the chilliest and driest weather of the Little Ice Age in that region. Crop failures contributed to the dreadful mortality rates endured by the colonists, and to the brief abandonment of their settlement in 1610. 

Moreover, many parts of North America do seem to have warmed in the wake of the Maunder Minimum, in the eighteenth century. This too could have profound consequences. In the seventeenth century, settlers to New France had been surprised to discover that their new colony was far colder than Europe at similar latitudes. They concluded that its heavy forest cover was to blame, and with good reason: forests do create cooler, cloudier microclimates. Just as the deforestation of New France started transforming, on a huge scale, the landscape of present-day Quebec, the Maunder Minimum ended. Settlers in New France concluded that they had civilized the climate of their colony, and they used this as part of their attempts to justify their dispossession of indigenous communities. 

Despite eighteenth-century warming in parts of North America, the dates we assign to the Maunder Minimum do look increasingly problematic when we look beyond Europe. If we turn to China, we encounter a similar story. Much of China was actually bitterly cold in the 1630s and early 1640s, before the onset of the Maunder Minimum elsewhere. This, too, had important consequences for Chinese history. Cold weather and precipitation extremes ruined crops on a vast scale, contributing to crushing famines that caused particular distress in overpopulated regions. The ruling Ming Dynasty seemed to have lost the “mandate of heaven,” the divine sanction that, according to Confucian doctrine, kept the weather in check. Deeply corrupt, riven by factional politics, undermined by an obsolete examination system for aspiring bureaucrats, and scornful of martial culture, the regime could adequately address neither widespread starvation, nor the banditry it encouraged.

Climatic cooling caused even more severe deprivations in neighboring, militaristic Manchuria. There, the solution was clear: to invade China and plunder its wealth. The first Manchurian raid broke through the Great Wall in 1629, a warm year in other parts of the Northern Hemisphere. Ultimately, the Manchus capitalized on the struggle between Ming and bandit armies by seizing China and founding the Qing (or "Pure") Dynasty in 1644. 

This entire history of cooling and crisis predates the accepted starting date of the Maunder Minimum. Yet, the fall of the Ming Dynasty unfolded in one relatively small part of present-day China. Average temperatures in that region reached their lowest point in the 1640s. By contrast, average temperatures in the Northeast warmed by the middle of the seventeenth century. Average temperatures in the Northwest also warmed slightly during the mid-seventeenth century, and then cooled during the late Maunder Minimum.

​Smoothed graphs that show fluctuations in average temperature across centuries or millennia give the impression that dating decade-scale warm or cold climatic regimes is an easy matter. Actually, attempts to precisely date the beginning and end of just about any recent climatic regime are sure to set off controversy. This is not only because global climate changes have different manifestations from region to region, but also because climate changes, as we have seen, involve much more than shifts in average annual temperature. Did the Maunder Minimum reach northern Europe, for instance, when average annual temperatures declined, when storminess increased, when annual precipitation rose or fell, or when weather became less predictable?

Historians such as Wolfgang Behringer have argued that, when dating climatic regimes, we should also consider the “subjective factor” of human reactions to weather. For historians, it makes little sense to date historical periods according to wholly natural developments that had little impact on human beings. Maybe historians of the Maunder Minimum should consider not when temperatures started declining, but rather when that decline was, for the first time, deep enough to trigger weather that profoundly altered human lives. When we consider climate changes in this way, we may be more inclined to subjectively date climatic regimes using extreme events, such as especially cold years, or particularly catastrophic storms. Dating climate changes with an eye to human consequences does take historians away from the statistical methods and conclusions pioneered by scientists, but it also draws them closer to the subjects of historical research.

In my work, I do my best to combine all of these definitions, and incorporate many of these complexities. I date climatic regimes by considering their cause – solar, volcanic, or perhaps human – and by working with statisticians who can tell me when a trend becomes significant. However, I also try to consider the many different kinds of weather associated with a climatic shift, and the consequences that extremes in such weather could have for human beings.

As you might expect, this is not always easy. I have long held that the Maunder Minimum, in the North Sea region, began around 1660. Increasingly, I find it easier to begin with the broadly accepted date of 1645, but distinguish between different phases of the Maunder Minimum. An earlier phase marked by cooling might have started in 1645, but a later phase marked by much more than cooling took hold around 1660.

These are messy issues that yield messy answers. Yet we must think deeply about these problems. Not only can such thinking affect how we make sense of the deep past, but it can also provide new perspectives on modern climate change. When did our current climate of anthropogenic warming really start? At what point did it start influencing human history, and where? What can that tell us about our future? These questions can yield insights on everything from the contribution of climate change to present-day conflicts, to the timing of our transition to a thoroughly unprecedented global climate, to the urgency of mitigating greenhouse gas emissions. 

~Dagomar Degroot

Further Reading: 

Behringer, Wolfgang. A Cultural History of Climate. Cambridge: Polity Press, 2010.

Brooke, John. Climate Change and the Course of Global History: A Rough Journey. Cambridge: Cambridge University Press, 2014.

Coates, Colin and Dagomar Degroot, “‘Les bois engendrent les frimas et les gelées:’ comprendre le climat en Nouvelle-France." Revue d'histoire de l'Amérique française 68:3-4 (2015): 197-219.

Dagomar Degroot, “‘Never such weather known in these seas:’ Climatic Fluctuations and the Anglo-Dutch Wars of the Seventeenth Century, 1652–1674.” Environment and History 20.2 (May 2014): 239-273.

​Eddy, John A. “The Maunder Minimum.” Science 192:4245 (1976): 1189-1202. 

Parker, Geoffrey. Global Crisis: War, Climate Change and Catastrophe in the Seventeenth Century. London: Yale University Press, 2013.

White, Sam. “Unpuzzling American Climate: New World Experience and the Foundations of a New Science.” Isis 106:3 (2015): 544-566.

​Ask most people about climate change, and you will soon find that even the relatively informed make two big assumptions. First: the world’s climate was more or less stable until recently, and second: human actions started changing our climate with the advent of industrialization. If you have spent any time reading through this website, you will know that the first assumption is false. For millions of years, changes in Earth’s climate, driven by natural forces, have radically transformed the conditions for life on Earth. Admittedly, the most recent geological epoch – the Holocene – is defined, in part, by its relatively stable climate. Nevertheless, regional and even global climates have still changed quickly, and often dramatically, in ways that influenced societies long before the recent onset of global warming.
 
Take, for example, the sixteenth century. Relative to early twentieth-century averages, the decades between 1530 and 1560 were relatively mild in much of the northern hemisphere. Yet, after 1565, average annual temperatures in the northern hemisphere fell to at least one degree Celsius below their early twentieth-century norms. Despite substantial interannual variations, temperatures remained generally cool until the aftermath of a bitterly cold “year without summer,” in 1628. Since the expansion of the glacier near Grindelwald, a Swiss town, was among the clearest signs of a chillier climate, these decades are collectively called the “Grindelwald Fluctuation.” It was one of the coldest periods in a generally cool climatic regime that is today known as the “Little Ice Age.” 

​Volcanic eruptions undoubtedly caused some of the cooling. In 1595, the eruption of Nevado del Ruiz released sulphur aerosols into the atmosphere, scattering sunlight and thereby cooling the planet. Just five years later, Huaynaputina exploded in one of the most powerful volcanic explosions of the past 2,500 years. Major volcanic eruptions following in close proximity to one another can trigger long-term cooling by activating "positive feedbacks" in different parts of Earth’s climate system. In the Arctic, for example, volcanic dust veils lead to chillier temperatures, which can increase the extent of Arctic ice that, through its high albedo, reflects more sunlight into space than the water or land it replaces. That in turn leads to even cooler temperatures, more ice, and so on.
 
However, the onset of the Grindelwald Fluctuation preceded the eruption of Nevado del Ruiz by some thirty years. Clearly, volcanoes were not the only culprits for the colder climate. Some scientists believe that low solar activity also played a role. Yet, although the sun was less active during the Grindelwald Fluctuation than it is today, it will still more active than it was in most other decades of the Little Ice Age.

That leads us to our second assumption: the idea that anthropogenic climate change began with industrialization. Most scholars of past climate change would still agree, but that might be changing. Recently, a growing body of evidence has started to suggest that humanity’s impact on Earth’s climate might be much older. Human depravity, it seems, might have been to blame for the cooling of the sixteenth century.
 
Back in 2003, palaeoclimatologist William Ruddiman proposed that humans were to blame for preindustrial climate change, in a groundbreaking article that shocked the scientific community. Two years later, he thoroughly explained and defended his conclusions in book called Plows, Plagues, and Petroleum: How Humans Took Control of Climate. Ruddiman argued that humanity had slowly but progressively altered Earth’s atmosphere since the widespread adoption of agriculture. Some 8,000 years ago, communities in China, Europe, and India made room for agricultural monocultures by burning away forests. According to Ruddiman, the scale of deforestation was enough to steadily increase the concentration of atmospheric carbon dioxide. Then, from around 5,000 years ago, rice farming and, to a lesser extent, livestock cultivation slowly raised atmospheric methane concentrations. Ruddiman concluded that the cumulative effect of these anthropogenic greenhouse gas emissions was to gradually increase average global temperatures, and perhaps ward off another ice age.
 
Ruddiman also argued that, since the adoption of agriculture, temporary fluctuations in atmospheric carbon dioxide concentrations followed from dramatic changes in human populations. During major disease outbreaks, Ruddiman insisted, populations declined to such an extent that agricultural land went untilled on a vast scale. Woodlands expanded, pulling more carbon dioxide out of the atmosphere than the agricultural crops they replaced, and thereby cooling the planet. When populations recovered, farmers burned down forests and planted their monocultures, warming the Earth. ​

​During the sixteenth century, Spanish soldiers and settlers established a vast empire by waging environmentally destructive wars on the indigenous peoples of central and southern America. They forced many of the survivors into new settlement patterns and gruelling forced labour. They also disrupted indigenous ways of life by appropriating, and often transforming, regional environments. Their animals, plants, and pathogens encountered virgin populations and spread rapidly. Indigenous communities in hot, humid climates were especially vulnerable to outbreaks of Eurasian crowd diseases, which included smallpox, measles, influenza, mumps, diphtheria, typhus, and pulmonary plague. Recent population modelling suggests that the population of the Americas declined from approximately 61 million in 1492 to six million in 1650.
 
By the late sixteenth century, this holocaust was well underway. Land previously colonized by indigenous communities through controlled burning or the planting of agricultural monocultures gradually reverted to woodlands. While all plants inhale carbon dioxide and exhale oxygen, tropical rainforests are much more effective carbon sinks than human crops. In the Americas, reforestation on a vast scale probably lowered atmospheric concentrations of carbon dioxide by 7 to 10 parts per million between 1570 and 1620. Human cruelty may therefore have contributed to the climatic cooling also caused by volcanic eruptions and, maybe, a decline in solar radiation relative to modern or medieval norms.

A growing body of scholarship now provides evidence for these relationships. However, there are many questions that must be answered before we can confidently conclude that depopulation helped trigger the Grindelwald Fluctuation, let alone other episodes of climatic cooling. For instance: did the cooling effect of sixteenth-century reforestation in the Americas overwhelm the warming influence of contemporaneous deforestation in China and India? Were invasive species introduced by Europeans into the Americas incapable of preventing reforestation? Was the pace of depopulation, and in turn reforestation, really so fast and so universal that it could substantially reduce atmospheric carbon dioxide concentrations over the course of a few decades? 
 
It will take a while to answer these questions, but some scholars are already drawing big conclusions. Earlier this year, geographers Simon Lewis and Mark Maslin argued that the cooling set in motion by the depopulation of the Americas could be considered the beginning of the “Anthropocene,” the proposed geological epoch dominated by human transformations of the world’s environment. Dating big changes in geological time is tricky business. The changes must be visible in the global stratigraphic record – that is, in rock layers – and they must be traceable to a specific date. Lewis and Maslin lean on earlier environmental histories of the “Columbian Exchange,” the European transfer of plants, animals, and pathogens between the New and Old Worlds. The impact was a global biotic homogenization that, according to Lewis and Maslin, should be visible in the stratigraphic record. That still leaves them without a specific date, however. They settle on 1610, because that was when atmospheric carbon dioxide levels reached a minimum caused, they say, by European depopulation of the Americas. ​

​There may be one more wrinkle to this sad story. In a forthcoming book, I argue that the Dutch revolt against the Spanish empire was provoked, in part, by high food prices that followed from harvest failures during the chilly onset of the Grindelwald Fluctuation. Then, until the early seventeenth century, the Dutch rebellion benefitted from a chilly climate. Dutch fortifications routinely forced Spanish armies to stay in the field during the frigid winters of the Grindelwald Fluctuation. The effect on Spanish soldiers could be disastrous. It is possible, therefore, that Spanish conquests in one part of the world contributed to climate changes that benefitted a rebellion against Spanish rule in another.
 
If so, the Eighty Years’ War may provide one of the first examples of such a self-defeating climate history of violence. It was certainly not the last. Recently, interdisciplinary researchers have found similar connections at work in the Syrian civil war. In a poorly governed society already destabilized by migrants fleeing the American invasion of Iraq, a severe drought caused, in part, by anthropogenic warming created fertile conditions for rebellion. The countries now at war in Syria and Iraq include those most responsible for the climate change that helped set the conflict in motion. Studying the Grindelwald Fluctuation may provide deep context for these relationships, by rooting them in a long history of violence and environmental transformation. It may also show that both assumptions commonly held about climate change are wrong. 
 
~Dagomar Degroot
 
My thanks to professors John McNeill, Richard Hoffmann, and Sam White for suggesting sources and helping me think through these relationships.
 
Graph Source:

Nussbaumer, Samuel U. and Heinz J. Zumbühl, "The Little Ice Age history of the Glacier des Bossons (Mont Blanc massif, France): a new high-resolution glacier length curve based on historical documents." Climatic Change 111 (2012): 301-334.

On Volcanic Cooling: 

Sigl, Michael, M. Winstrup, J. R. McConnell, K. C. Welten, G. Plunkett, F. Ludlow, U. Büntgen, M. Caffee, et al., “Timing and Climate Forcing of Volcanic Eruptions for the Past 2,500 Years,” Nature 523 (2015): 543–49.

On Anthropogenic Cooling:
 
Dull, Robert A., Richard J. Nevle, William I. Woods, Dennis K. Bird, Shiri Avnery, and William M. Denevan. “The Columbian Encounter and the Little Ice Age: Abrupt Land Use Change, Fire, and Greenhouse Forcing.” Annals of the Association of American Geographers 100 (2010): 755–71. doi:10.1080/00045608.2010.502432.
 
Etheridge, D. M., L. P. Steele, R. L. Langenfelds, R. J. Francey, J.-M. Barnola, and V. I. Morgan. “Natural and Anthropogenic Changes in Atmospheric CO2 over the Last 1000 Years from Air in Antarctic Ice and Firn.” Journal of Geophysical Research: Atmospheres 101, no. D2 (1996): 4115–28. doi:10.1029/95JD03410.
 
Ganopolski, A., R. Winkelmann, and H. J. Schellnhuber. “Critical insolation–CO2 Relation for Diagnosing Past and Future Glacial Inception.” Nature529 (2016): 200–203. doi:10.1038/nature16494.
 
Hunter, Richard, and Andrew Sluyter. “Sixteenth-Century Soil Carbon Sequestration Rates Based on Mexican Land-Grant Documents.” Holocene 25 (2015): 880–85. doi:10.1177/0959683615569323.
 
Kaplan, Jed O. “Holocene Carbon Cycle: Climate or Humans?” Nature Geoscience 8 (2015): 335–36. doi:10.1038/ngeo2432.
 
Lewis, Simon L. and Mark A. Maslin. “Defining the Anthropocene.” Nature 519 (2015): 171-180.
 
Mitchell, Logan, Ed Brook, James E. Lee, Christo Buizert, and Todd Sowers. “Constraints on the Late Holocene Anthropogenic Contribution to the Atmospheric Methane Budget.” Science 342 (2013): 964–66. doi:10.1126/science.1238920.
 
Nevle, R.J., D.K. Bird, W.F. Ruddiman, and R.A. Dull. “Neotropical Human–Landscape Interactions, Fire, and Atmospheric CO2 during European Conquest.” The Holocene 21 (2011): 853–64. doi:10.1177/0959683611404578.
 
Pasteris, Daniel, Joseph R. McConnell, Ross Edwards, Elizabeth Isaksson, and Mary R. Albert. “Acidity Decline in Antarctic Ice Cores during the Little Ice Age Linked to Changes in Atmospheric Nitrate and Sea Salt Concentrations.” Journal of Geophysical Research: Atmospheres 119 (2014): 5640–52. doi:10.1002/2013JD020377.
 
Ruddiman, William. “The Anthropogenic Greenhouse Era Began Thousands of Years Ago.” Climatic Change 61 (2003): 261–93.
 
Ruddiman, William. Plows, Plagues, and Petroleum: How Humans Took Control of Climate. Princeton, NJ: Princeton University Press, 2005.
 
Ruddiman, William, Steve Vavrus, John Kutzbach, and Feng He. “Does Pre-Industrial Warming Double the Anthropogenic Total?” The Anthropocene Review 1 (2014): 147–53. doi:10.1177/2053019614529263.
 
Wang, Z., J. Chappellaz, K. Park, and J.E. Mark. “Large Variations in Southern Hemisphere Biomass Burning During the Last 650 Years.” Science330 (2010): 1663–66.