We’re in a climate emergency. This isn’t just rhetorical hyperbole, but a statement backed by more than 13,000 scientists. Even the venerable publication Scientific American agreed to adopt the term earlier this year. Canada is particularly culpable for this crisis because of its petro-state status and hyper-consumerism. 

My research deals with the transborder history and politics of Canada-U.S. water and energy issues, lately involving climate change. But it is in my teaching role that I spend the most time addressing the climate emergency since I’m in an environmental and sustainability studies department (which has a climate change minor). This includes an introductory course that features a major climate change component, as well as senior courses such as the seminar I’m teaching this fall that concentrates on my campus’s carbon emissions. 

True, I have the advantage of teaching in an environment-focused setting that looks as much at the present and the future as the past. But all historians, regardless of experience in environmental history or history of science, can bring the climate emergency into their classroom. What I would like to do in this post is to suggest some areas, based on my teaching experiences and reading of recent literature, where climate change could be injected into Canadian history survey courses.
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During the pandemic, I’ve read a wide range of new popular books about the climate crisis – from the technocratic solutions of Bill Gates to the Green New Deal advocacy of Kate Aronoff. Within those public-facing books, I noticed four key debates – or spectrums since they don’t have to be either-or questions – about tackling climate. These are illustrated below, with the ‘X’ marking where I land within each:

I could write a whole post about why I fall where I do. But that isn’t the point here. Instead, I’m going to offer strategies for infusing lectures, discussions, and assignments with aspects of those four debates. Probably the most obvious way to do that is enhance the emphasis on natural resources. Climate change, as well as our other big ecological problems, are tightly linked to how we use and consume resources. 

The most relevant type of resource when it comes to greenhouse gases is energy. Canadians have long been amongst the most profligate people in the history of the globe in terms of energy consumption (only some of which can be explained by Canada’s widely dispersed population and cold climate). Canada has also been a global production leader in several different energy forms, with hydroelectricity and oil likely the most well-known (though we could count uranium as well because of its role in nuclear power). 
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To incorporate energy history, university instructors could go several routes, such as peppering it into lectures throughout the term, or create an entire section or module. It just so happens that the major energy eras and transitions line up pretty well with major periods of Canadian history extending deep back into the premodern period: animal/human muscle, wood, coal, hydro, fossil fuels, etc. Truthfully, energy could be the organizing principle for an entire survey course (and this book would make a great text).

The development of energy is intrinsically tied to common classroom themes in Canadian political history: federalism (disputes over provincial rights to harvest hydropower and fossil fuels); regional identity (Ontario Hydro, Hydro-Québec, and BC Hydro; the prairies and oil; coal on the east coast; etc.); Canada-U.S. relations (electricity, fossil fuel, and uranium exports). Many major topics that normally come up anyway, from the railways to free trade, are inherently about energy and environment, providing segues to wrestle with climate change and Canada’s contribution and response to it. 
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Hydroelectric dams, fossil fuels, and pipelines have long wreaked havoc on First Nations communities. The history of energy developments therefore also dovetails with Canada’s history of settler and extractive colonialism. And discussions about reconciliation can relate to contemporary calls for a just transition away from fossil fuels. Tying in with the systemic vs. individual debate, other aspects of the history of social movements and human rights in Canada could be an entrée for grappling with climate change. 

Sticking with the systemic angle, another existing theme in the Canadian curriculum where climate change could clearly piggyback is the role of the state. The history of capitalism is yet another prevalent theme that can be merged with exploring climate change. The tension between government regulation and intervention versus the free market is already apparent in Canadian history and lends itself to talking about capitalism as the solution or the cause.   

For those addressing the history of technology, Canada has been at the forefront of a number of technological changes dealing with the extraction and burning of energy, from the world’s biggest hydropower stations a century ago to the tar sands today. Technology is why we have cheap energy. Cheap energy is a sine qua non of “modern” Canadian lifestyles, the reason why consumer products are (relative to their true cost) inexpensive and available. And cheap energy is a major reason, maybe the main reason, we have climate change. 

The extraction and production of energy – e.g., coal miners and oil roughnecks – connects with important themes in labour and class history, while the ways energy is consumed – such as household work or petro-masculinity – can be combined with themes in social and gender history. And how has cheap energy and the attendant assumptions of abundance practically and conceptually shaped modern Canadian society and Canadian identity?

Students are frequently interested in studying the differences between Canada and the United States. Canada’s social safety net and collectivism are often held up as distinctive from American individualism and privatization. But that may be the narcissism of small differences relative to the historic exploitation of natural resources, per capita levels of consumption, and greenhouse gas emissions; on those scores, to the rest of the globe the U.S. and Canada look pretty identical. When it comes time to teach about Canadian international history, for all the claims about Canada’s middle power or peacekeeper proclivities, it is in the realm of fossil fuels and climate change that Canada might actually be a superpower (but the bad kind). 

Another pedagogical approach is to look at past adaptations to a changing climate. That is, the climate has shifted in the past, and peoples living in the territory now called Canada had to figure out ways to cope. If you’re teaching the pre-Confederation survey, the Little Ice Age (roughly the 16th to the 18th centuries) caused changes to food acquisition and agriculture strategies, which in turn had social, political, and military knock-on effects. Resilience emerges as a theme to interlink cultural responses to climate change in the past and present. For those doing post-Confederation history, many of the climactic shifts we currently recognize were already occurring by the Second World War. The start of the Cold War is one of the candidates for dating the beginning of the Anthropocene, which could serve as an organizing topic or concept (this series will have more on the Anthropocene in future posts). 

What about some specific class exercises and assignments? Try integrating historical sources as indirect proxies for comparing climate from past to present. You might have heard of using ice cores, sediments, or tree rings to infer historic climatic conditions. But the types of records historians are likely more familiar with, such as paintings, diaries, ship or whaling log books, and fur trade fort journals, can also be revealing and double as a unique way to introduce undergrads to the use of primary sources. (A contributor to this series, Dagomar Degroot, has written extensively about the use of various textual records for climate history). 

Artistic representations can show glacial retreat or pollution levels, for example. Or, given the prominence of the fur trade in Canada’s history, using fort journals to compare past temperatures and change of seasons with the present could be an instructive way to expose students to both climate history and primary sources.

There are places online where some of those types of information are already organized for easy integration into your curriculum. For the pre-Confederation period, check out Canada’s Year Without a Summer. The titular year in question is 1816; the Tambora volcano erupted the previous year in Indonesia, leading to subsequent cold weather in early eastern Canada. This website was created by Alan MacEachern and Michael O’Hagan with course instructors in mind: it offers more than 120 sources, as well as guidance for how teachers could incorporate these into class. For the post-Confederation period, try Environment Canada’s National Climate Data and Information Archive which has (digital) reams of historical climate data. A professor could create an exercise or assignment, for example, in which students pick a location – such as their hometown or their university – and compare past and present weather/climate conditions. 

This is not an exhaustive list of ideas, but some easy ways to get started. Given the reality and urgency of the climate crisis, and its relevance to the lives and concerns of students, it is something all introductory history courses need to address. 

Daniel Macfarlane is an Associate Professor in the Institute of the Environment and Sustainability at Western Michigan University, co-editor of The Otter-La loutre, and a member of the executive board of NiCHE, Network in Canadian History & Environment.

​Historians have always concerned themselves as much with the present as the past. Some do so explicitly, their work guided by a conscious desire to provide context for a matter of present concern. Others do so implicitly. They may study the past because it makes them curious, but that curiosity is inevitably shaped by their day-to-day lives. One way or another, history as a discipline is the outcome of the history historians must live through.  
 
Today no challenge seems more daunting than the climate crisis. Earth’s average temperature has warmed by over one degree Celsius since the nineteenth century, and it is likely – though not inevitable – that much more warming is on its way. Global temperature changes of this magnitude, with this speed, profoundly alter both the local likelihood and severity of extreme weather. Human-caused heating will reverberate through the Earth for millennia – by slowly melting ice sheets and raising sea levels, for example.
 
Our lives and livelihoods will be – in many cases, are already – shaped by this crisis. No surprise, then, that ever more historians now think urgently and seriously about the implications of climate change for their scholarship. Forecasts of the warmer future are still dominated by economics and climate science, but few now deny that scholars of the past – including historians – can offer unique perspectives on how we entered this crisis, where it might be taking us, and how we can avoid its greatest dangers.  
 
As this series reveals, historians grapple with climate change in increasingly diverse ways, and here it is again useful to draw a distinction between implicit and explicit approaches. In a sense, just about every kind of history has relevance to the present crisis, because climate affects every aspect of the human experience. Climate change alters the environments that sustain and shape our lives, shifting the basic conditions that channel our actions and thoughts. The climate crisis is therefore as much about the transformation of the planet as it is about the reshaping of human relationships. Any history that deals with those relationships – all history, by definition – implicitly tells us something about climate change and its social consequences. If you are a historian, your work is about global warming. 
 
The editors of this series, however, asked me to describe how scholars of the past explicitly engage with the climate crisis. Arguably, the most influential and numerous publications have originated in both the history of science and the related fields of climate history and historical climatology. A quick and necessarily incomplete overview of just these two kinds of scholarship reveals the value and diversity of historical approaches to climate change.  
 
Historians of science initially concentrated on how global warming was discovered and understood by scientists with increasing certainty. While it is simplistic to conclude that scientists “knew” about global warming for many decades, or even over a century – as is often stated in popular media and occasionally in scholarship – historians of science nevertheless revealed the deep roots of today’s scientific understanding of global warming. Led by Naomi Oreskes, they also found that serious debate among climate scientists over the existence of human-caused global warming ended in the 1990s, or perhaps even earlier. Although a majority of the public doesn’t know it, just about every climate scientists understands that humans are today responsible for the rapid heating of the planet.
 
Confirming the scientific consensus on global warming led some historians of science to argue that fossil fuel companies and far-right scientists cynically promoted climate denial in order to serve their regressive political or economic interests. This was – and remains – perhaps the most influential and politically potent argument proposed by historians about the climate crisis. Climate scientists, in this narrative, bravely announced their inconvenient truths but could not overcome the falsehoods propagated by their more media-savvy antagonists.
 
Nevertheless, other historians soon pointed out that climate science has long involved more than the apolitical discovery and communication of truth. Historians of science revealed for example how models and simulations came to dominate climate science – rather than other ways of knowing – and argued that climate scientists themselves failed to choose communications strategies that could mobilize grassroots, local action.
 
Historians have long traced the emergence of ideas about climate from antiquity through the present. Recently, historians of science have revealed that the climate ideas most view as characteristically modern in fact have deep roots. They have shown, for example, that legends of ancient climate changes caused by human sin or shortsightedness helped influence the development of early modern science, and – with new practices in forestry and agriculture –
contributed to the emergence of what we might now call sustainability thinking.
 
Climate historians and historical climatologists take an entirely different approach to the climate crisis. Historians active in historical climatology search for human records – usually documents – that either describe past weather or activities that must have been strongly influenced by weather. By finding enough of these records – by scouring what they call the “archives of society” – historical climatologists uncover how climate changed over decades or even centuries. Working with those who uncover evidence for past weather in the “archives of nature” – tree rings, ice cores, or lakebed sediments, for example – they can develop remarkably precise “reconstructions” that reveal the existence of substantial climatic fluctuations even before the onset of today’s extreme warming.
 
The antecedents of this work date back to the nineteenth century, but it was really only in the 1970s that Christian Pfister and other pioneers proposed ranking qualitative accounts of weather on simple ordinal scales. These scales allowed for the closer integration of the archives of society with the archives of nature, especially in Europe, but historical climatologists studying different parts of the world continued to use distinct methods for quantifying historical evidence. Only now are they working towards developing a common approach.
 
In any case, reconstructions permit histories of human responses to past climate changes. While these climate changes have been relatively modest in global scale – the Little Ice Age, the most studied period of preindustrial climate change, only cooled the Earth by several tenths of a degree Celsius between the fifteenth and eighteenth centuries – some were nevertheless sufficient to dramatically alter local environments. Archaeologists, economists, geneticists, geographers, linguists, literary scholars, and paleoscientists have all used distinct methods and sources to uncover how these alterations shaped the history of human populations.
 
Yet few disciplines have contributed more to this scholarship – recently coined the “History of Climate and Society” – than history. Historians have in recent years increasingly avoided making simple connections between climate changes, harvest failures, and demographic disasters: a chain of events that scholars of past climate have long emphasized. New climate histories instead uncover wellsprings of both vulnerability and resilience within communities, and they increasingly consider the full range of possible relationships between climate change and human history across the entire world and into the twentieth century.
 
Together, historians of science and climate historians have done much more than add a little climate to historians’ understanding of the past. Histories of climate science help uncover why governments and corporations have not responded quickly or adequately to the climate crisis. They also reveal how the crisis might be communicated more effectively, or how more diverse ways of knowing could be incorporated within climate science. They show us why we should nevertheless believe the forecasts of climate science – and how we can best act on that belief.
 
Historical climatology helps reveal the baselines against which human emissions are changing Earth’s climate today, and helps uncover the likely response of local environments to global warming. Climate historians can suggest what strategies may succeed or fail when climates change, and add complexity to forecasts of the future that too often assume simple social responses to shifting environmental conditions. Many tell stories about the influence of climate on human affairs that capture public attention more vividly than frightening statistics ever could.
 
Yet both climate history and historical climatology also demonstrate the fundamental discontinuity between climates present and past. The speed, magnitude, and cause of present-day warming simply has no parallel in the history of human civilization. History is a guide to climate action, but it also warns us that to a large extent we are in uncharted waters.

​Ten years ago, when I started this website, my message was something like: believe me, history helps us understand global warming! I could not have imagined that, in just ten years, climate change would be widely recognized as a serious subject for historical study – or that historians such as Ruth Morgan would earn a seat in a working group of the Intergovernmental Panel on Climate Change. In some ways, the sea change in the historical discipline has mirrored a broader transformation in social attitudes towards climate change: a transformation driven in part by the courage of young activists, but also by the growing severity of the climate crisis. Climate scholarship in history is now more numerous and more diverse – in its topics and authorship – than it ever has been, a shift that also echoes developments in climate activism. 
 
I expect these trends to continue. When future historians write about our time, you can be sure that climate change will play a central role in the story. As we live through that history, our scholarship will be climate scholarship – whether we see it that way or not.

​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. 

Memory is one of the most powerful parts of the human psyche. It can help us make sense of the world around us, but it can also cloud our vision. Over long timeframes, memory can actually become embedded into a culture in ways that are difficult to comprehend. One of the complex effects of this sort of cultural memory may be the development of a culture of resilience in the face of extreme climatic events. Long-term environmental memories might help a community respond to otherwise destructive climate changes in a way that allows them to survive, recover, and sometimes even thrive. Given the increasing impact of extreme weather events due to anthropogenic climate change, it is uniquely important right now to understand how memory can contribute to creating a more resilient culture.

In order to make sense of the connections between memory, culture, and climate, this article considers how memory might have played a role in the interpretation of extreme weather events in Qing dynasty China (1644–1912). A look at Qing dynasty records suggests that long-term environmental memory could indeed help cultivate a culture of resiliency, while at the same time skewing how accurate the perception of a disaster is. More than anything, this look into the potential roles of memory provides a new perspective with which to think about our current interpretation of environmental changes and cultural capacity for adaptation.

Researchers generally agree that we actively use our memory when processing our surroundings, including weather.[1] Imagine you live in a town that has faced extreme flooding in recent years. When you experience a heavy rain, you will probably remember the floods. However, the exact way that we use memory to interpret the environment may not be so simple as providing the background with which we think about weather or climate change. In her work on biological control programs, scholar Karen Middleton describes a feedback loop by which present events reshape how the past is remembered at the same time as the interpretation of past events shapes the understanding of present conditions.[2] So just as memories of a disastrous flood would affect how villagers interpret a heavy rain in their present, if they are not currently experiencing flooding it could influence their memories of that past disaster. In our hypothetical water-logged village, perhaps the current rains are locally just as strong as the rains during a past flood. Yet because those rains are not accompanied by a flood, villagers might mistakenly remember the first flood as having more extreme rains.

There is also some evidence that memory can contribute to long-term integration of climate awareness into human societies. Archaeologist Toby Pillat has offered the idea that daily interactions with weather can create cultural norms that dictate how future people might interact with their climate.[3] The cultural norms that Pillat refers to may even develop into a culture of resiliency, as described by environmental historian Adam Sundberg in his work on the infamous Christmas Flood of 1717. Sundberg describes a process of “disaster-induced learning,” in which repeated incidents of disaster lead to long-term “cultures of coping,” a gradualist theory that he reports as currently trending in the field of disaster history.[4]

Occasionally, this sort of cultural learning about climate may take the form of a clearer understanding of weather events over time. For example, environmental historian Dagomar Degroot found that “the human consequences of the Little Ice Age…prompted Dutch citizens to think comparatively and accurately about weather across long timeframes.”[5] Yet long-term environmental learning may also lead to a skewed perception of climatic events due to increased societal preparedness. In his study of lower Austrian floods in 1572-3, scholar Christian Rohr makes the argument that “due to the preparedness of the population, most of the floods were not perceived as disasters.”[6] While in some cases, memory might lead to more accurate interpretations of climate, in others its concrete effects in establishing adaptive cultures may have the opposite impact – which in turn could influence the long-term understanding of climate in a society.

So how might memory have played a role in Qing dynasty cultural understandings of, and responses to, climate change? To answer this question, we will look at the North China Plain (NCP). The NCP is defined here as the modern-day provinces of Beijing, Tianjin, Hebei, Shandong, Henan, Anhui, and Jiangsu. Such a wide definition of the area is useful in that it allows for more data, and therefore clearer identification of patterns; it is reasonable, in that precipitation extremes across the NCP are fairly standard.
 
The Qing dynasty was not only a time of distinct dynastic change in China, but it was also a part of an era of occasionally global climate change that is often termed the Little Ice Age (LIA). The LIA is generally understood to be a period of cooling that in many places reached its coldest phase between the fifteenth and eighteenth centuries.[7] While there was a broad global trend of cooling, the LIA had different effects across different areas over variable time scales. In China, the LIA can be split into three stages: a cool, dry early period, a warm, dry middle period, and a wet, cold late period.[8] These changes are thought to be related to changes in both East Asian Summer Monsoons (EASM), and the El Niño-Southern Oscillation (ENSO) cycle. [9] The NCP in particular experiences highly variable precipitation patterns due to the strong effect of the EASM in the region. [10] Across the Qing dynasty, the region suffered many environmental disasters, including extreme floods and droughts.

During the Qing dynasty, gazetteers called fangzhi 方志 were systematically written every day. Official chronicles were mandated by the government; many more local gazetteers were kept by various scholars or officials, and organized by government historians over the course of the Qing dynasty. These primary source texts contain detailed information about the weather. Because they were written systematically, whether or not a chronicle mentions a disaster, like the floods and droughts we will examine here, is more likely to be a result of the recorder’s interpretation of the weather than, for example, the recorder’s desire or freedom to write. Therefore, a comparison of how often a disaster was documented with the actual occurrence of extreme events can be used as a way to guess at the role of memory and culture in the interpretation of weather. The recently published Reconstructed East Asian Climate Historical Encoded Series (REACHES) database uses the fangzhi to create data points that represent weather events, allowing us to build a timeline for how often a drought or flood disaster was recorded throughout the Qing dynasty.

In order to create a timeline for when droughts and floods actually occurred during the Qing dynasty in the NCP, we can look at the reconstruction of extreme weather events from the work of a team of Chinese geographers led by Zheng Jingyun. Zheng and his co-authors have used a wide range of primary text sources, then verified the information in them with weather measurements compiled using scientific instruments. They also used statistical analysis to account for the fact that the number of textual sources increases over time, due to the higher likelihood that more recent records could be preserved. While it would be ideal to have more scientific data to create our timeline, such as information from tree rings or pollen records, the reality is that most climate history for this region and time relies on historic archives, probably due to the abundance of primary source texts from China.

The methods used by Zheng and his team make their results some of the best currently available, and most useful for this comparison. They look specifically at extreme droughts and floods, which they define as periods lasting more than three years that have an amount of rain more than one and half times greater or lower than about the average precipitation level. The fact that they look at both severity and time scale means that when they note the occurrence of disaster, there should theoretically be fangzhi records for that disaster from across the NCP.

Building these parallel timelines of documentation and occurrence for both droughts and floods reveals curious correlations and discrepancies. First, the highest numbers of fangzhi records of flood and drought do not always correlate with the frequency and severity of disasters. For example, two of the most extreme events identified by Zheng and his co-authors in the NCP were a decade-long drought that took place from 1634 to 1644, and another calamitous drought from 1719 to 1723.[11] Yet there are several points in our timeline of documentation where the amount of drought records is higher than in those years of especially extreme drought. While the frequency of fangzhi flood documentation lines up a little bit better with the occurrence of extreme floods, there are still moments where we see a higher amount of flood records in years when extreme flooding did not occur.

Disaster records therefore often did not grow more common during, or even immediately after, many of the worst disasters. Usually the quantity of fangzhi records only surged over a decade after a disaster. In fact, years immediately following extreme weather events generally had fewer records of disaster. These patterns may suggest that when a disaster was ongoing, it was harder to keep records like local fangzhi as people struggled to survive and rebuild. They could also indicate that in the short term, the memory of a disaster helped give a more realistic sense of what constituted that sort of event, and led to more accurate reporting. However, over time, this accuracy of memory may have faded, and instead cultural memory could have encouraged a heightened sensitivity towards recording disaster.

Looking more broadly, it seems that there is overall more documentation of disaster earlier in Qing history. For both droughts and floods, moving forward in time there is a moderate trend from more to fewer fangzhi records of either type of extreme event. Moreover, the amount of variation in disaster documentation frequency from year to year appears to be higher earlier in history. There also seems to be a slight trend over time towards more stability in the amount of records of both floods and droughts.

These wide patterns of decreasing records and increasing stability of documentation frequency may suggest more or less long-term accuracy in memory of disaster severity, depending on whether you emphasize periods of extreme events or of non-disaster. This might also point to the development of a culture of resiliency. If the people of the NCP were better equipped to deal with these types of events over time, they might not be so inclined to interpret the weather as a disaster, even in cases when it was as extreme as in previous decades.

It is clear that there is no simple relationship between memory and environmental disasters. It should also be noted that these potential patterns and connections are based on a simple visual comparison of timelines. However, the lack of precision here speaks to the fact that this area holds much potential for future research. In particular, Chinese climate history scholarship thus far has often focused on using statistical significance testing to propose correlative relationships between environmental changes and societal reactions. [12] This sort of quantitative research is an ideal starting point for exploring more nuanced aspects of environmental history. It allows for engagement with unique scholarship, like the ideas about memory explored here, and in this case, offers diverse new perspectives on the possible links between culture and environmental extremes.

This study reveals that memory could be a powerful part of how we respond to environmental changes. At the same time as memory may help develop an adaptive culture, accurate judgement of the seriousness of a disaster might be clouded. As we enter an era of increased extreme weather events, it is important to consider whether our interpretations of disaster are accurate. Moreover, while long-term memory has potentially contributed to climate change resilience in our cultures, our current adaptations may not be enough to deal with the disasters of the future. We might also examine how the gradual nature of the current rise in disaster severity may influence both our cultural adaptations and misunderstandings of memory. As the consequences of anthropogenic climate change become more pronounced, it is crucial that we look to the past for new ideas about the relationship between culture and environment, including the complex effects of memory.

Works Cited:
 
Andrew Salvador Mathews. "Suppressing Fire and Memory: Environmental Degradation and Political Restoration in the Sierra Juárez of Oaxaca, 1887-2001." Environmental History  8:1 (2003): 77-108.
 
Brook, Timothy. The Troubled Empire: China in the Yuan and Ming Dynasties. Cambridge, USA: Harvard University Press, 2010.
 
Cui, Anning, Chunmei Ma, Lin Zhao, Lingyu Tang, and Yulian Jia. "Pollen Records of the Little Ice Age Humidity Flip in the Middle Yangtze River Catchment." Quaternary Science Reviews 193 (2018): 43-53.     
 
Degroot, Dagomar. “Climate Change and Society from the Fifteenth Through the Eighteenth       Centuries.” WIREs Climate Change Advanced Review, 2018.
 
Degroot, Dagomar. The Frigid Golden Age: Climate Change, the Little Ice Age, and the Dutch  Republic, 1560–1720. New York: Cambridge University Press, 2018.    
 
Fang, XiuQi, Xiao, LingBo, and Wei, ZhuDeng. “Social Impacts of the Climatic Shift Around   the Turn of the 19th Century on the North China Plain.” Science China Earth Sciences 56:6 (2013): 1044–58.
 
Forgas, Joseph P., Liz Goldenberg, and Christian Unkelbach. 2009. Can Bad Weather Improve        Your Memory? an Unobtrusive Field Study of Natural Mood Effects on Real-Life    Memory. Vol. 45.
 
Guy, R. Kent. Qing Governors and Their Provinces: the Evolution of Territorial Administration in China, 1644-1796. Seattle: University of Washington Press, 2010.
 
Hall, A. and G. Endfield, “Snow Scenes”: Exploring the Role of Memory and Place in    Commemorating Extreme Winters. Wea. Climate Soc. 8 (2016): 5–19.
 
Hao, Zhixin, Yingzhuo Yu, Quansheng Ge, and Jingyun Zheng. “Reconstruction of High            resolution Climate Data over China from Rainfall and Snowfall Records in the Qing Dynasty.” WIREs: Climate Change 9 (3) (2018): e517.
 
Koselleck, Reinhart. Futures Past: On the Semantics of Historical Time. Cambridge, Mass: MIT      Press, 1985.
 
Kwiatkowski, Teresa, and Alan Holland. "Dark Is the World to Thee: A Historical Perspective      on Environmental Forewarnings." Environment and History 16:4 (2010): 455-82.        
 
Li, S., He, F. & Zhang, X., "A spatially explicit reconstruction of cropland cover in China from 1661 to 1996." Reg Environ Change 16:2 (2016): 417-428.
 
Middleton, Karen. "Renarrating a Biological Invasion: Historical Memory, Local Communities    and Ecologists." Environment and History 18:1 (2012): 61-95.        
 
Pillatt, Toby. “Experiencing Climate: Finding Weather in Eighteenth Century Cumbria.” Journal      of Archaeological Method and Theory 19:4 (December 2012): 564–81.        
 
Rohr, Christian. "Floods of the Upper Danube River and Its Tributaries and Their Impact on        Urban Economies (c. 1350-1600): The Examples of the Towns of Krems/Stein and Wels            (Austria)." Environment and History 19:2 (2013): 133-48.        
 
Rohr, Christian. "Man and Natural Disaster in the Late Middle Ages: The Earthquake in            Carinthia and Northern Italy on 25 January 1348 and Its Perception." Environment and            History 9:2 (2003): 127-49.
 
Shuoben Bi, Shengjie Bi, Changchun Chen, Athanase Nkunzimana, Yanping Li, and Weiting           Wu. “Spatial Characteristics Analysis of Drought Disasters in North China during         the Ming and Qing Dynasties.” Natural Hazards & Earth System Sciences Discussions 2016, 1–13. 
 
Sundberg, Adam. “Claiming the Past: History, Memory, and Innovation Following the  Christmas Flood of 1717.” Environmental History 20:2 (April 2015): 238–61.       
 
Wang, P. K. et al. Construction of the REACHES climate database based on historical         documents of China. Sci. Data. 5:180288.
 
Zheng, J., W. C. Wang, Q. Ge, Z. Man, and P. Zhang, 2006: Precipitation variability and extreme    events in eastern China during the past 1500 years. Terr. Atmos. Ocean. Sci., 17, 579-  592.

Roughly 11,000 years ago, rising sea levels submerged Beringia, the vast land bridge that once connected the Old and New Worlds. Vikings and perhaps Polynesians briefly established a foothold in the Americas, but it was the voyage of Columbus in 1492 that firmly restored the ancient link between the world’s hemispheres. Plants, animals, and pathogens – the microscopic agents of disease – never before seen in the Americas now arrived in the very heart of the western hemisphere. It is commonly said that few organisms spread more quickly, or with more horrific consequences, than the microbes responsible for measles and smallpox. Since the original inhabitants of the Americas had never encountered them before, millions died.
 
The great environmental historian Alfred Crosby first popularized these ideas in 1972. It took over thirty years before a climatologist, William Ruddiman, added a disturbing new wrinkle. What if so many people died so quickly across the Americas that it changed Earth’s climate? Abandoned fields and woodlands, once carefully cultivated, must have been overrun by wild plants that would have drawn huge amounts of carbon dioxide out of the atmosphere. Perhaps that was the cause of a sixteenth-century drop in atmospheric carbon dioxide, which scientists had earlier uncovered by sampling ancient bubbles in polar ice sheets. By weakening the greenhouse effect, the drop might have exacerbated cooling already underway during the “Grindelwald Fluctuation:” an especially frigid stretch of a much older cold period called the “Little Ice Age."

Last month, an extraordinary article by a team of scholars from the University College London captured international headlines by uncovering new evidence for these apparent relationships. The authors calculate that nearly 56 million hectares previously used for food production must have been abandoned in just the century after 1492, when they estimate that epidemics killed 90% of the roughly 60 million people indigenous to the Americas. They conclude that roughly half of the simultaneous dip in atmospheric carbon dioxide cannot be accounted for unless wild plants grew rapidly across these vast territories.
 
On social media, the article went viral at a time when the Trump Administration’s wanton disregard for the lives of Latin American refugees seems matched only by its contempt for climate science. For many, the links between colonial violence and climate change never appeared clearer – or more firmly rooted in the history of white supremacy. Some may wonder whether it is wise to quibble with science that offers urgently-needed perspectives on very real, and very alarming, relationships in our present.
 
Yet bold claims naturally invite questions and criticism, and so it is with this new article. Historians – who were not among the co-authors – may point out that the article relies on dated scholarship to calculate the size of pre-contact populations in the Americas, and the causes for their decline. Newer work has in fact found little evidence for pan-American pandemics before the seventeenth century.

More importantly, the article’s headline-grabbing conclusions depend on a chain of speculative relationships, each with enough uncertainties to call the entire chain into question. For example, some cores exhumed from Antarctic ice sheets appear to reveal a gradual decline in atmospheric carbon dioxide during the sixteenth century, while others apparently show an abrupt fall around 1590. Part of the reason may have to do with local atmospheric variations. Yet the difference cannot be dismissed, since it is hard to imagine how gradual depopulation could have led to an abrupt fall in 1590.
 
To take another example, the article leans on computer models and datasets that estimate the historical expansion of cropland and pasture. Models cited in the article suggest that the area under human cultivation steadily increased from 1500 until 1700: precisely the period when its decline supposedly cooled the Earth. An increase would make sense, considering that the world’s human population likely rose by as many as 100 million people over the course of the sixteenth century. Meanwhile, merchants and governments across Eurasia depleted woodlands to power new industries and arm growing militaries.

In any case, models and datasets may generate tidy numbers and figures, but they are by nature inexact tools for an era when few kept careful or reliable track of cultivated land. Models may differ enormously in their simulations of human land use; one, for example, shows 140 million more hectares of cropland than another for the year 1700. Remember that, according to the new article, the abandonment of just 56 million hectares in the Americas supposedly cooled the planet just a century earlier!

If we can make educated guesses about land use changes across Asia or Europe, we know next to nothing about what might have happened in sixteenth-century Africa. Demographic changes across that vast and diverse continent may well have either amplified or diminished the climatic impact of depopulation in the Americas. And even in the Americas, we cannot easily model the relationship between human populations and land use. Surging populations of animals imported by Europeans, for example, may have chewed through enough plants to hold off advancing forests. Moreover, the early death toll in the Americas was often also especially high in communities at high elevations: where the tropical trees that absorb the most carbon could not go.

In short, we cannot firmly establish that depopulation in the Americas cooled the Earth. For that reason, it is missing the point to think of the new article as either “wrong” or “right;” rather, we should view it as a particularly interesting contribution to an ongoing academic conversation. Journalists in particular should also avoid exaggerating the article’s conclusions. The co-authors never claim, for example, that depopulation “caused” the Little Ice Age, as some headlines announced, nor even the Grindelwald Fluctuation. At most, it worsened cooling already underway during that especially frigid stretch of the Little Ice Age.

For all the enduring questions it provokes, the new article draws welcome attention to the enormity of what it calls the “Great Dying” that accompanied European colonization, which was really more of a “Great Killing” given the deliberate role that many colonizers played in the disaster. It also highlights the momentous environmental changes that accompanied the European conquest. The so-called “Age of Exploration” linked not only the Americas but many previously isolated lands to the Old World, in complex ways that nevertheless reshaped entire continents to look more like Europe. We are still reckoning with and contributing to the resulting, massive decline in plant and animal biomass and diversity. Not for nothing do some date the “Anthropocene,” the proposed geological epoch distinguished by human dominion over the natural world, to the sixteenth century. 

All of these issues also shed much-needed light on the Little Ice Age. Whatever its cause, we now know that climatic cooling had profound consequences for contemporary societies. Cooling and associated changes in atmospheric and oceanic circulation provoked harvest failures that all too often resulted in famines. In community after community, the malnourished repeatedly fell victim to outbreaks of epidemic disease, and mounting misery led many to take up arms against contemporary governments.​ Some communities and societies were resilient, even adaptive in the face of these calamities, but often partly by taking advantage of the less fortunate. ​Whether or not the New World genocide led to cooling, the sixteenth and seventeenth centuries offer plenty of warnings for our time.

Works Cited:

Archer, S. "Colonialism and Other Afflictions: Rethinking Native American Health History." History Compass 14 (2016): 511-21.

Crosby, Alfred W. “Conquistador y pestilencia: the first New World pandemic and the fall of the great Indian empires.” The Hispanic American Historical Review 47:3 (1967): 321-337.

Crosby, Alfred W. The Columbian Exchange: Biological and Cultural Consequences of 1492. Westport: Greenwood Press, 1972. Alfred W. Crosby, Ecological Imperialism: The Biological Expansion of Europe, 900-1900, 2nd Edition. Cambridge: Cambridge University Press, 2004.

Degroot, Dagomar. “Climate Change and Society from the Fifteenth Through the Eighteenth Centuries.” WIREs Climate Change Advanced Review. DOI:10.1002/wcc.518

Degroot, Dagomar. The Frigid Golden Age: Climate Change, the Little Ice Age, and the Dutch Republic, 1560-1720. New York: Cambridge University Press, 2018.

Gade, Daniel W. “Particularizing the Columbian exchange: Old World biota to Peru.” Journal of Historical Geography 48 (2015): 30.

Goldewijk, Kees Klein, Arthur Beusen, Gerard Van Drecht, and Martine De Vos, “The HYDE 3.1 spatially explicit database of human‐induced global land‐use change over the past 12,000 years.” Global Ecology and Biogeography 20:1 (2011): 73-86.

Jones, Emily Lena. “The ‘Columbian Exchange’ and landscapes of the Middle Rio Grande Valley, AD 1300– 1900.” The Holocene (2015): 1704.

Kelton, Paul. "The Great Southeastern Smallpox Epidemic, 1696-1700: The Region's First Major Epidemic?". In R. Ethridge and C. Hudson, eds., The Transformation of Southeastern Indians, 1540-1760. 

Koch, Alexander, Chris Brierley, Mark M. Maslin, and Simon L. Lewis. “Earth system impacts of the European arrival and Great Dying in the Americas after 1492.” Quaternary Science Reviews 207 (2019): 13-36

McCook, Stuart. “The Neo-Columbian Exchange: The Second Conquest of the Greater Caribbean, 1720-1930.” Latin American Research Review 46: 4 (2011): 13.
​
McNeill, J. R. “Woods and Warfare in World History.” Environmental History, 9:3 (2004): 388-410.

Melville, Elinor G. K. ​A Plague of Sheep: Environmental Consequences of the Conquest of Mexico. Cambridge: Cambridge University Press, 1997.

PAGES2k Consortium, “A global multiproxy database for temperature reconstructions of the Common Era.” Scientific Data 4 (2017). doi:10.1038/sdata.2017.88.

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

Sigl, Michael et al., "Timing and climate forcing of volcanic eruptions for the past 2,500 years." Nature 523:7562 (2015): 543.

Riley, James C. "Smallpox and American Indians Revisited." Journal of the History of Medicine and Allied Sciences 65 (2010): 445-77. 

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

Williams, Michael. Deforesting the Earth: From Prehistory to Global Crisis. Chicago: University of Chicago Press., 2002. 

To grasp the significance of global warming, and to confirm its connection to human activity, you have to know how climate has changed in the past. Scholars of past climate change know that understanding how climate has varied over historical timescales requires access to robust long-term datasets. This is not a problem for regions such as Europe and North America, which have a centuries-long tradition of recording meteorological data using weather instruments (thermometers, for example). However, for large areas of the world the ‘instrumental period’ begins, at best, in the late 19th or early 20th century. This includes Africa, where, with the exception of Algeria and South Africa, instrumental data for periods earlier than 1850 are sparse. To overcome such data scarcity, other approaches are used to reconstruct past climates, most notably through analyses of accounts of weather events and their impacts in historical documents.

Compared to the wealth of documentary evidence available for areas such as Europe and China, there are relatively few collections of written materials that allow us to explore the historical climatology of Africa. Documents in Dutch exist from the area around Cape Town that date back to the earliest European settlers in 1652, and Arabic- and Portuguese-language documents from northern and southern Africa, respectively, are likely to include climate perspectives from even further back in time. However, the bulk of written evidence for Africa stems from the late 18th century onwards, with a proliferation of materials for the 19th century following the expansion of European colonial activity.

These documents are increasingly used by historical climatologists to reconstruct sequences of rainfall variability for the African continent. This focus on rainfall isn’t surprising, given that rainfall was – and is – critical for human survival. As a result, people tended to write about its presence or absence in diaries, letters, and reports. In turn, these rainfall reconstructions are now used by historians as a backdrop when exploring climate-society relationships for specific time periods. It is therefore critical that we understand any issues with rainfall reconstructions in case they mislead or misinform.

This article will take you under the hood of the practice of reconstructing past climate change. Its aim is to: (a) provide an overview of historical climatology research in Africa at continental to regional scales; and (b) point out how distinct approaches to rainfall reconstruction in different studies can potentially produce very different rainfall chronologies, even for the same geographical area (which of course alters the kinds of environmental histories that can be written about Africa). The article concludes with some personal reflections on how we might move towards a common approach to rainfall reconstruction for the African continent.
 
Different approaches to rainfall reconstruction in Africa

Most historical rainfall reconstructions for Africa use evidence from one or more source type (Figure 1). A small number of studies are based exclusively upon early instrumental meteorological data. Of these, some (the continent-wide analysis by Nicholson et al. in 2018, for example) combine rain gauge data published in 19th-century newspapers and reports with more systematically collected precipitation data from the 19th to 21st centuries, to produce quantitative or semi-quantitative time series. Others, such as Hannaford et al. (2015), for southeast Africa, use data digitized from ship logbooks to generate quantitative regional rainfall chronologies. 

Most reconstructions, however, draw on European traditions by using narrative accounts of weather and related phenomena contained within documentary sources (such as personal letters, diaries/journals, reports, newspapers, monographs and travelogues) to develop semi-quantitative relative rainfall chronologies. Some of the most widely available materials are those written by early explorers, missionaries, and figures of colonial authority. The use of such evidence permits the reconstruction of rainfall for periods well before the advent of meteorological data collection.
​
The greatest numbers of regional documentary-based reconstructions are available for southern Africa, which forms the focus of this article. These draw on documentary evidence from a combination of published and unpublished sources, often using available instrumental data for verification and calibration, and span much of the 19th century. Where information density permits, it has been possible to reconstruct rainfall variability down to seasonal scales (see, for example, a study by Nash et al. in 2016). There are, in addition, continent-wide series that integrate narrative information from mainly published sources with available rainfall data (Nicholson et al., 2012, for 90 homogenous rainfall regions across mainland Africa).

An important point to note is that the various reconstructions adopt slightly different methodologies for analyzing documentary evidence. For example, all of the regional studies in southern Africa noted above use a five-point scale to classify annual rainfall (from –2 to +2; extremely dry to extremely wet). Scholars decide how to classify a specific rainy season in a region through qualitative analysis of the collective documentary evidence for that season. In other words, they take into account all quotations describing weather and related conditions. This contrasts with the approach used by Nicholson and colleagues in a 2012 continent-wide rainfall series. In that reconstruction, scholars attributed a numerical score on a seven-point scale (–3 to 3) to each individual quotation according to how wet or dry conditions appear to have been. They then summed and averaged the scores for each item of evidence for a specific region and year. As we will see, these distinct analytical approaches, which may draw on different documentary evidence, may introduce significant discrepancies between rainfall series.
 
Comparisons between rainfall series

A compilation of all the available annually-resolved rainfall series for mainland southern Africa is shown in Figure 2. This includes seven series (g-m) based exclusively on documentary evidence, four regional series (c-f) from Nicholson et al. (2012) based on combined documentary evidence and rain gauge data, the 19th-century portion of the ships’ logbook reconstruction series (b) by Hannaford et al. (2015), and, for comparison, the 19th-century section of a width-based tree ring rainfall reconstruction (a) for western Zimbabwe by Therrell et al. (2006). With the exception of the Cape Winter Rains series, all are for areas of southern Africa that receive rainfall predominantly during the summer months.

This compilation shows that, in the 19th century, rainfall varied from place to place across southern Africa. However, we can identify a number of droughts that affected large areas of the subcontinent. Droughts, for example, stretched across southern Africa in the mid-1820s, mid-1830s, around 1850, early-mid-1860s, late-1870s, early-mid-1880s and mid-late-1890s. We can also pinpoint a smaller number of coherent wetter years: in, for example, the rainy seasons of 1863-1864 and 1890-1891. Analyses that use many different climate "proxies" - that is, sources that register but do not directly measure past climate change - indicate that the early-mid 1860s drought was the most severe of the 19th century, and that of the mid-late-1890s the most protracted (see, for example, studies by Neukom et al., 2014, and Nash, 2017).
​
The inset map in Figure 2 reveals that a number of rainfall series overlap in their geographical coverage, which allows a direct comparison of results. In some cases, the overlap is between series created using very different methodologies. For the most part, there is good agreement between these overlapping series, but there are some significant differences. The rest of this article will focus on two of these periods of difference: the 1810s in southeast Africa, and the 1890s in Malawi.
 
How dry was the first decade of the 19th century in southeast Africa?

Four rainfall series are available for southeast Africa for the first decade of the 19th century (Figure 3) – documentary series for South Central Africa and the Kalahari (by Nicholson et al., 2012), a tree-ring series for Zimbabwe (Therrell et al., 2005), and a ships’ log series for KwaZulu-Natal (Hannaford et al., 2015). Collectively, these series suggest that there was at least one major drought that potentially affected much of the region.

This was a very important time in the history of southeast Africa. The multi-year drought is remembered vividly in Zulu oral traditions as the ‘mahlatule’ famine (translated as the time we were obliged to eat grass). Scholars have seen it as a trigger for political revolution and reorganization, one that ultimately led to the dominance of the Zulu polity. 

Yet there are some discrepancies between the overlapping records, which have important implications for our understanding of relationships between climate change and society. For example, while the documentary-based South Central Africa series in Figure 3 suggests protracted drought from 1800 to 1811, the overlapping tree ring series for Zimbabwe infers periods of average or above-average rainfall, alternating with drought. A similar contrast is shown between the documentary-based Kalahari series (which encompasses the southern Kalahari but extends to the east coast of South Africa) and the overlapping ships’ logbook-based reconstruction for Royal National Park, KwaZulu-Natal.
​
Since these series are based on different evidence, it is impossible to tell which is more likely to be ‘right’. However, the rainfall series based on documentary evidence are clearly less sensitive to interannual rainfall variability than those based on ships’ log data or tree rings, at least for the early 19th century. This is surprising, as a major strength of documentary evidence is normally the way that it captures extreme events.

The reasons for these discrepancies are unclear, but are likely to be methodological. The Africa-wide rainfall series by Nicholson and colleagues, from which the South Central Africa and Kalahari series in Figure 3 are derived, is a model of research transparency – it identifies the evidence base for every year of the reconstruction, with all documentary and other data made available via the NOAA National Climatic Data Center. Inspection of this dataset indicates that the reconstructions for the early 1800s in southern Africa are based on a limited number of published monographs and travelogues, written mainly by explorers. While these are likely to include eyewitness testimonies, there is potential for bias towards drier conditions. The majority of authors were western European by birth and, in some cases, their writings reflected their first travels in the subcontinent. It wouldn’t be at all surprising if they found southern Africa significantly drier than home.
 
How dry was the last decade of the 19th century in Malawi?

The collective evidence for rainfall variability around present-day Malawi during the mid-late 19th century is shown in Figure 4. Here, two rainfall reconstructions overlap: the first, a reconstruction for three regions of the country based primarily on unpublished documentary evidence by Nash et al. (2018); and the South Central Africa series and adjacent rainfall zones of Nicholson et al. (2012). 

Extreme events, such as the droughts of the early-1860s, mid-late-1870s, and mid-late-1880s, and a wetter period centred around 1890-91, are visible in both reconstructions. However, there are discrepancies in other decades, most notably during the 1890s where the Nicholson series indicates mainly normal to dry conditions, and the Nash series a run of very wet years.
​
Delving deeper into the documentary evidence underpinning the Nicholson series suggests that the discrepancies may again be methodological, and strongly influenced by source materials. As with the other regional reconstructions for southern Africa, the Nash study bases annual classifications on average conditions across a large body of mainly unpublished primary documentary materials. Nicholson, by contrast, uses smaller numbers of mainly published documentary materials, combined with rain gauge data. An over-emphasis of references to dry conditions in these documents, combined with an absence of gauge-data for specific regions and years, could therefore skew the results. 
 
The way forward?

There are two main take-home messages from this article. First, on the basis of a comparison of annually-resolved southern African rainfall series, documentary data appear less sensitive to precipitation variability than other types of proxy evidence, even for some extreme events. Discrepancies are most apparent for periods of the early 19th century, where documentary evidence is relatively sparse.

Second, different approaches to reconstruction may produce different results, especially where documentary evidence is combined with gauge data. The summative approach used by Nicholson and colleagues, for example, where individual quotations are classified, summed and averaged, may be much more sensitive to bias from individual sources when data are sparse.

Having identified these potential issues, one way forward might be to run some experimental studies using different approaches on the same collections of documentary evidence to assess the impact of methodological variability on rainfall reconstructions. This would be no small task, as it would mean re-analyzing some large datasets. However, it would confirm or dismiss the suggestions made here about the relative effectiveness of different methodologies.

These experimental studies would help us to identify the "best practice" for reconstructing African rainfall. They would allow us to improve the robustness of the baseline data available for understanding historical rainfall variability in the continent likely to be most severely impacted by future climate change. They would also permit us to refine our understanding of past relationships between climatic fluctuations and the history of African communities. These relationships may offer some of our best perspectives on the future of African societies in a warming planet. 

Works Cited: 

Brázdil, R. et al. 2005. "Historical climatology in Europe – the state of the art." Climatic Change 70: 363-430.
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Grab, S.W. and Zumthurm, T. 2018. "The land and its climate knows no transition, no middle ground, everywhere too much or too little: a documentary-based climate chronology for central Namibia, 1845–1900." International Journal of Climatology 38 (Suppl. 1): e643-e659.

Hannaford, M.J. and Nash, D.J. 2016. "Climate, history, society over the last millennium in southeast Africa." Wiley Interdisciplinary Reviews-Climate Change 7: 370-392.

Hannaford, M.J. et al. 2015. "Early-nineteenth-century southern African precipitation reconstructions from ships' logbooks." The Holocene 25: 379-390.

Kelso, C. and Vogel, C.H. 2007. "The climate of Namaqualand in the nineteenth century." Climatic Change 83: 257-380.

Nash, D.J., 2017. Changes in precipitation over southern Africa during recent centuries. Oxford Research Encyclopedia of Climate Science, doi: 10.1093/acrefore/9780190228620.013.539.

Nash, D.J. and Endfield, G.H. 2002. "A 19th century climate chronology for the Kalahari region of central southern Africa derived from missionary correspondence." International Journal of Climatology 22: 821-841.

Nash, D.J. and Endfield, G.H. 2008. "'Splendid rains have fallen': links between El Nino and rainfall variability in the Kalahari, 1840-1900." Climatic Change 86: 257-290.

Nash, D.J. and Grab, S.W. 2010. "'A sky of brass and burning winds': documentary evidence of rainfall variability in the Kingdom of Lesotho, Southern Africa, 1824-1900." Climatic Change 101: 617-653.

Nash, D.J. et al. 2018. "Rainfall variability over Malawi during the late 19th century." International Journal of Climatology 38 (Suppl. 1): e649-e642.

Nash, D.J. et al. 2016. "Seasonal rainfall variability in southeast Africa during the nineteenth century reconstructed from documentary sources." Climatic Change 134: 605-619.

Neukom, R. et al. 2014. "Multi-proxy summer and winter precipitation reconstruction for southern Africa over the last 200 years." Climate Dynamics 42: 2713-2716.

Nicholson, S.E. et al. 2012. "Spatial reconstruction of semi-quantitative precipitation fields over Africa during the nineteenth century from documentary evidence and gauge data." Quaternary Research 78: 13-23.

Nicholson, S.E. et al. 2018. "Rainfall over the African continent from the 19th through the 21st century." Global and Planetary Change 165: 114-127.

Pfister, C. 2018. "Evidence from the archives of societies: Documentary evidence - overview". In: White, S., Pfister, C., Mauelshagen, F. (eds.) The Palgrave Handbook of Climate History. Palgrave Macmillan, London, pp. 37-47.

Therrell, M.D. et al. 2006. "Tree-ring reconstructed rainfall variability in Zimbabwe." Climate Dynamics 26: 677-685.

Vogel, C.H. 1989. "A documentary-derived climatic chronology for South Africa, 1820–1900." Climatic Change 14: 291-307.

​Until recently, it was notoriously difficult to connect today’s extreme weather with the gradual trends of climate change. Scientists shied away from saying, for example, that catastrophic droughts or severe hurricanes reflected the influence of anthropogenic global warming. Yet today, scientists use big data from satellites and weather stations to inform supercomputer simulations that reveal the extent to which warming trends have raised the odds for previously unusual weather. Scientists now report, for instance, that the drought that crippled Syria between 2006 and 2009 was between two and three times more likely in today’s climate than it would have been a century earlier. They feel comfortable concluding that the rains of Hurricane Harvey were perhaps 20 times more likely now than they once were. Armed with these statistics, many scholars and journalists now conclude that events like the Syrian Civil War, which unfolded in the wake of that devastating drought, can be convincingly connected to climate change.
 
Yet how can we link past climate change – change that happened before the advent of big weather data – to human affairs? Many historians and archaeologists favor qualitative methods. They identify weather events in surviving documents, or in paleoclimatic proxy data (such as tree rings, ice cores, or lakebed sediments) that register the influence of temperature or precipitation. Next, they carefully study texts or ruins to determine how these weather events influenced human activities – such as farming, hunting, or sailing – that clearly depended on favorable weather. By looking at enough of these relationships, over a long enough timeframe, they ultimately reach conclusions about the influence of weather trends – that is, climate change – on the human past.
 
Environmental historians might be most familiar with these qualitative methods. They inform a raft of new books and articles in climate history, on diverse topics that range from the fall of Rome to the colonization of Australia; from the origins of apocalyptic Norse mythology to the travails of Arctic whalers.

​But these qualitative methods are much less influential beyond the historical profession. Today, there is a large and rapidly growing “quantitative” school of climate history that instead relies on statistical means to discern the impact of climate change on human history. Papers in this school are cited more frequently in the latest IPCC assessment report, for example, than publications written by historians who prefer more qualitative means of doing history. 

Natural scientists, economists, and historical geographers in the quantitative school of climate history quantify diverse social variables in particular regions, then graph their highs and lows over decades, centuries, even millennia. Next, they develop or make use of temperature or precipitation reconstructions for those same regions across identical timescales. Finally, they use statistical methods to find covariance between their graphs of social and climatic trends.
 
Most published work in this vein finds statistically significant correlations between these trends. In study after study, Chinese historical geographers have found striking correlations between climatic cooling and the wars, rebellions, and dynastic transitions of Imperial China. European scholars have found equally impressive correlations between cool, wet conditions and conflict in northwestern Europe over the past five centuries. In southeastern and central Europe, by contrast, correlations exist between conflict and warm, dry weather. Another, even more ambitious study finds strong correlation between European wars and climate changes over 2,600 years.
 
Quantitative climate historians often focus on China and Europe, and not only because most of them live in these regions. People across much of China and Europe have long relied on rain-fed agriculture, which should have been especially sensitive to fluctuations in temperature or precipitation. They also kept unusually detailed, and unusually continuous, records of their activities. Yet a growing group of quantitative researchers now concentrates on the much more recent history of sub-Saharan Africa, where millions continue to rely on rain-fed agriculture. Many studies correlate warming, drying trends across Africa to twentieth-century civil wars, although some emphasize that these correlations only existed under the right socioeconomic conditions.
 
The great appeal of quantitative approaches to climate history is that they seem to replace the messiness of the historian’s craft, and the subjectivity of the qualitative findings, with scientific objectivity and certainty. Quantitative historians have used statistical correlation not only to confidently explain the past, but also to predict the future. Already in 2007, historical geographers concluded, for example, that Chinese “war-peace, population, and price cycles in recent centuries have been driven mainly by long-term climate change.” Two years later, another group controversially concluded that the frequency of civil wars in sub-Saharan Africa would likely increase as the continent warmed, since a regional correlation between temperature and violence existed in the past.

​But have quantitative scholars really found a better way of doing climate history, one that at last permits predictions of the kind that always remain frustratingly out of reach for historians and archaeologists? Well, not quite. On close examination, the soaring claims made by many quantitative scholars in fact rest on assumptions that remain frustratingly subjective . . . and at times, simply misguided.
 
Most importantly, the correlations identified in quantitative work are meaningless unless their trends reflect the right data. Some studies of this kind use weather observations in surviving documents to graph centuries-long trends in temperature or precipitation. Decades ago, the great meteorologist Hubert Lamb relied on much the same method to identify a hot climatic regime that he called the “Medieval Warm Period.” The medieval centuries, Lamb concluded, were at least as warm as the late twentieth century.
 
While some deniers of anthropogenic global warming still use Lamb’s graph, scholars have changed the name of his period to the “Medieval Climate Anomaly.” It turns out that Lamb, unversed in the art of reading historical sources, simply took medieval references to weather at face value. When the legitimate weather observations examined by Lamb are read more carefully, and used alongside climate reconstructions compiled with more reliable tree ring or ice core data, they reveal a period of modest but erratic warming in the high medieval centuries. Nothing comparable, in other words, with late twentieth-century warming.
 
The lesson here is that references to weather in ancient documents do not always simply reveal the state of the atmosphere in a particular time and place. The problem is much more acute when considering very long timescales. Before the instrumental era, even seemingly reliable weather observations over decades or centuries are really the product of many observers, some of whom might use different methods to record weather. Moreover, sources that may seem especially dependable at a glance – such as many European chronicles – in fact refer to weather metaphorically, or use fabricated weather events to justify the course of human affairs.
 
Researchers should therefore strive to use weather observations in historical documents as a starting point – only a starting point! – in a long process of reconstructing a region’s climate. Where possible, documentary evidence should be used alongside climate reconstructions compiled with tree rings, ice cores, lakebed sediments, and the many other proxy sources in natural archives. The best climate reconstructions often use the most proxies. Of course, many excellent reconstructions have now been published for most parts of the world. There is often little need to develop a regional climate reconstruction from scratch.
 
In quantitative climate history, multi-proxy climate reconstructions should also reveal climatic trends on the same spatial scale as the social variables under consideration. Even some scholars who do use so-called “multiproxy” climate reconstructions to find their correlations go on to match trends of global or hemispheric temperature or precipitation with trends of local or regional historical events. Yet before the onset of anthropogenic global warming, climatic trends rarely unfolded at the same time in every part of the globe. A general cooling trend across the northern hemisphere, for example, did not always lead to colder temperatures in China.  
 
If quantitative climate historians face problems when choosing which climate reconstructions to use – or how to make them – these pale in comparisons to those that bedevil their attempts to quantify social variables. Quantitative studies of war, for example, have used makeshift and now defunct websites to determine when wars began and ended. Others have relied on historical scholarship that is well over a century old. It is as though the historical geographers, political scientists, natural scientists, and economists who typically write quantitative climate history do not recognize that the disciplines of history and archaeology are as rigorous and dynamic as their own. Naturally, correlations that rely on obsolete or untrustworthy data about the human past can tell us little about the influence of climate change on human history.
 
Jan de Vries, Philip Slavin, and I have also flagged a second big problem faced by quantitative approaches to climate history. Studies that find correlations over centuries, let alone millennia, rarely appreciate that social variables change through time. A statistically significant correlation between warming and economic growth in the high medieval centuries, for example, does not necessarily hint at the same kind of relationship between climate change and human affairs as a similar correlation several hundred years later. Over the course of those centuries, the cultural, economic, social, and political pathways by which climate change affects human life may have fundamentally changed, and the individuals who control those pathways will have obviously died. The question becomes: what are quantitative approaches to climate change really measuring?
 
That gets us into a third, and related, problem of quantifying the human past. It is one thing to quantify a particular kind of agricultural production over long timespans. Though agricultural practices can change dramatically over those timespans, even in pre-modern societies, scholars may still find correlations between agricultural yields and climatic trends that can suggest something new about the human past. Yet it is quite another matter to quantify the number or intensity of a major social event, such as a war.
 
Attempts to link the number of wars by decade to decadal temperature or precipitation, for example, face the challenge of quantifying long and complex wars: precisely the kind of war that often placed the greatest strain on agricultural resources also affected by climate change. Scholars might consider the Thirty Years’ War, for instance, as either a single war or a series of wars, and their subjective choice would determine the correlation identified in a study between seventeenth-century climate change and European conflict. In some of these studies, the early seventeenth century may look like a time of relative peace in Germany!
 
Scientists have also used arbitrary numbers to decide when violence amounts to a war. Does violence rise to the status of war when at least 1,000 people have died, as some studies assume? Presumably the standard would be higher in very populous societies and lower in less populated ones, but this distinction is never made in quantitative studies. Graphing wars by quantity can also lead scholars to misrepresent changes in quality. Scholars might easily count the First and Second World Wars as only two wars, for example, yet of course their material and human costs dwarfed those of any previous conflict. If problems of this nature plague the superficially simple task of correlating the number of wars to temperature trends, imagine the challenges of determining similar correlations with, for example, economic development or cultural efflorescence! 

​It turns out that quantitative approaches to climate history often obscure more than they reveal. Far from providing a more objective, “scientific” way of understanding the impact of climate change on the human past, they really rely on assumptions that are every bit as subjective as those made in more qualitative work. Yet unlike many qualitative climate historians, they leave those assumptions unacknowledged.
 
I am convinced that quantitative climate historians could fruitfully address at least some of these problems by interacting more with qualitative scholars, most of whom work in the humanities. Unfortunately, many historians, at least, have not heard of quantitative approaches to climate history, while most quantitative scholars have little inkling of qualitative approaches to their subject. Remarkably, I have never seen a work of qualitative climate history cited within a paper that aims to identify correlation. Part of the problem is that quantitative and qualitative scholars often work in different media. While historians prioritize books, most scientists, economists, and geographers value short, multi-authored studies.
 
Yet collaboration is surely possible, and if so it would undoubtedly prove productive. Quantitative scholars have recently used statistical means to identify not only how climate change might be correlated to human activities, but also how it might have partly accounted for – that is, caused – those activities. Such studies have yielded models that are really variants of models that qualitative scholars had already developed. What if they had worked with qualitative scholars from the start? Meanwhile, qualitative scholars often use statistics to support their conclusions, without always understanding what those statistics actually reveal (or what they don’t). What if qualitative scholars consulted colleagues in more quantitative disciplines while developing these statistics?
 
At the Climate History Network, we will strive to incorporate more quantitative scholars within our ranks. Perhaps we will be able to build a shared community in the coming years, one that will yield a more comprehensive kind of climate history.

Works Cited:
​
Buhaug, Halvard. “Climate not to blame for African civil wars.” Proceedings of the National Academy of Sciences 107:38 (2010): 16477-16482.
 
Büntgen U. et al. “2500 years of European climate variability and human susceptibility.” Science 331:6017 (2011): 578-582.
 
Burke, Marshall B. et al. “Climate robustly linked to African civil war.” Proceedings of the National Academy of Sciences 107:51 (2010): E185-E185.
 
Burke, Marshall B. et al. “Warming increases the risk of civil war in Africa." Proceedings of the National Academy of Sciences 106:49 (2009): 20670-20674.

​Degroot, Dagomar. “Climate Change and Conflict,” in The Palgrave Handbook of Climate History, eds. Christian Pfister, Franz Mauelshagen, and Sam White. Basingstoke: Palgrave Macmillan, 2018. 

​Slavin, Philip. “Climate and famines: a historical reassessment.” Wiley Interdisciplinary Reviews: Climate Change 7:3 (2016):

Theisen, Ole Magnus. “Climate clashes? Weather variability, land pressure, and organized violence in Kenya, 1989-2004.” Journal of Peace Research 49:1 (2012): 81-96.
 
Theisen, Ole Magnus, Helge Holtermann, and Halvard Buhaug. “Climate wars? Assessing the claim that drought breeds conflict,” International Security 36:3 (2011): 79-106.

Tol, Richard and Sebastian Wagner. “Climate change and violent conflict in Europe over the last millennium,” Climatic Change 99 (2010): 65-79.

Zhang, David. “Climate Change and War Frequency in Eastern China over the Last Millennium,” Human Ecology 35 (2007): 403-414.

Zhang, David and Harry Lee, “Climate Change, Food Shortage and War: A Quantitative Case Study in China during 1500-1800,” Catrina 5:1 (2010): 63-71.

Zhang, David et al., “Climatic change, wars and dynastic cycles in China over the last millennium,” Climatic Change 76 (2006): 459-477.

Zhang, David, Peter Brecke, Harry F. Lee, Yuan-Qing He, and Jane Zhang. “Global climate change, war, and population decline in recent human history.” Proceedings of the National Academy of Sciences 104:49 (2007): 19214-19219.

Zhang, David. “The causality analysis of climate change and large-scale human crisis,” Proceedings of the National Academy of Sciences 108:42 (2011): 17296-17301.

Zhang, Dian et al., “Climate change, social unrest and dynastic transition in ancient China,” Chinese Science Bulletin 50:2 (2005): 137-144.

Zhibin Zhang, “Periodic climate cooling enhanced natural disasters and wars in China during AD 10-1900,” Proceedings of the Royal Society 277 (2010): 3745-3753.

​Earth’s climate is changing with terrifying speed. Humanity has added several hundred billion tons of carbon dioxide to the atmosphere, strengthening a greenhouse effect that has now warmed the planet by roughly one degree Celsius. The scale, speed, and causes of today’s global warming have no precedent, but of course natural forces have always changed Earth’s climate. We now know that these changes were big enough to shape the fates of past societies. Most confronted disaster, but a few seemed to prosper in spite of – and in some cases because of – climate changes. Perhaps the most successful of all emerged in the coastal fringes of the present-day Netherlands. It has left us with lessons that may offer new perspectives on our fate in a warmer world.  
 
To contextualize present-day warming, paleoclimatologists have scoured the globe for signs of past climate change. They have found layers buried deep in glacial ice and cave stalagmites, sediments embedded in lakebeds and ocean floors, and rings wound around tree trunks and stony corals. All bear silent testament to ancient weather. Together, they reveal that, sometime in the thirteenth century, Earth’s climate started cooling.
 
Huge volcanic eruptions lofted dust high into the stratosphere that blocked incoming sunlight. The Sun itself slipped into a dormant phase, sending less energy to the Earth. A long-running shift in Earth’s axial tilt gradually reduced the amount of solar energy that reached the northern hemisphere. Sea ice expanded, wind patterns changed, and ocean currents altered their flow. Patterns of precipitation fluctuated dramatically, bringing torrential rains to some places, and unprecedented droughts to others. A long “Little Ice Age” had begun. 

In the closing decades of the sixteenth century, this Little Ice Age reached its chilliest point across much of the northern hemisphere. By then, the world had cooled by nearly one degree Celsius, relative to average temperatures in the twentieth century. In many places, weather had also grown more volatile and less predictable from year to year, season to season. Despite its name, the Little Ice Age involved more than constant cooling.
 
Historians, historical geographers, and archaeologists have argued that the onset of the coldest and most erratic phase of the Little Ice Age could not have come at a worse time. For centuries, populations in the greatest empires of the day had steadily increased. By the sixteenth century, millions depended on crops stubbornly cultivated in arid, unproductive farmland. When falling temperatures shortened growing seasons, when monsoons failed, or when storms flooded fields, harvests in these regions failed again and again.
 
Many farmers responded by swapping crops that prefer warm, stable weather for those that cope better with cold, volatile conditions. Some diversified their fields. Yet often there was just no dealing with droughts, torrential rains, or cold snaps that lasted for longer than a year or two. Famine and then starvation spread from the plains of the Aztec Empire to the woodlands of the Mutapa Kingdom, from the steppes of the Grand Duchy of Moscow to the rice fields of the Ming Dynasty.
 
The worst was yet to come. Temperature and precipitation extremes sickened plants and animals alike, compounding food shortages. As temperatures dropped, farmers huddled in huts with their ailing livestock. In those conditions, diseases spread easily from animals to people. Malnourished human bodies, meanwhile, have weak immune systems, which makes them easy prey for bacteria and viruses. Changing weather patterns also altered the range of insects that carried disease pathogens, bringing new and deadly ailments to the previously unexposed. In empire after empire, millions fled from the famine-stricken countryside, unwittingly infected by diseases that they carried to cities. Where famine lingered, epidemic outbreaks often followed.
 
In one empire after another, the sick and starving blamed governments for their misery. They were usually right. Few governments responded constructively to the crises they faced, and most made them worse by, for example, increasing taxes or embarking on wars. The coldest stretch of the Little Ice Age therefore coincided with an unprecedented surge of revolts and civil wars. Rebel and state armies alike conscripted farm laborers from the already overburdened countryside, imposed new demands on marginal farmland, and joined refugees in spreading disease. In the end, millions died.
 
Yet remarkably, inhabitants of the Dutch Republic – the precursor state to today’s Netherlands – enjoyed a Golden Age that perfectly coincided with the chilliest century of the Little Ice Age. Somehow, a country with about as many people as Providence, Rhode Island emerged as a European great power, with a navy that went from victory to victory, an army that held the mighty Spanish Empire at bay, and a commercial fleet that dwarfed all others. Today, the art of Rembrandt and Vermeer – painted in the coldest years of the Little Ice Age – gives a distant echo of the energy and prosperity of those incredible times.
 
The Dutch Republic was something of an oddball in the seventeenth-century world. The overwhelming majority in most societies toiled in rural fields, growing crops for local markets. Many Dutch farmers, by contrast, cultivated cash crops for distant consumers. The republic therefore depended on a steady flow of grain imports from the rich and diverse farmland along the Baltic Sea. Over time, a growing share of Dutch citizens worked in commercial interests and industries with headquarters in or near port cities that would have been underwater, were it not for an extensive network of dikes and sluices. Urbanization rates were soon higher in the republic than they were just about anywhere else. Meanwhile, tens of thousands of sailors plied Dutch trades that reached deep into the Arctic, the Americas, Africa, and Asia.

Sailing depended on two things: favorable winds and open, ice-free water. By changing currents and cooling temperatures in the atmosphere and oceans, the chilliest stretches of the Little Ice Age therefore affected sailing as much as farming. Yet the impact was very different. New wind patterns actually sped up ships that left the republic for Asia or America, shortening their journeys.
 
In the waters off northern Europe, storms were unusually frequent and severe in the coldest stretches of the Little Ice Age. Many ships foundered, and many sailors drowned. Yet crews aboard the republic’s biggest merchant ships – ones that carried the richest cargo from distant markets – weathered storms much better than sailors aboard other European ships. In fact, storms often benefitted Dutch sailors by further increasing the speed of these big ships. 
 
Even sea ice aided the Dutch, including in the Arctic. It took plenty of sea ice – but not too much – to redirect Dutch voyages of northern exploration towards the rich bowhead whale feeding grounds off the archipelago of Svalbard, which lies between the northern coast of Norway and the North Pole. Whalers from all over Europe soon set up shop there. For a long time, the edge of the Arctic pack ice lingered near Dutch whaling stations, and since whales gathered along the edge of the ice, the Dutch benefited. By following the ice edge west, Dutch whalers even found whale breeding grounds off the little island of Jan Mayen.
 
The Dutch fought most of their wars on or around water. Climatic cooling may have benefited their armies and fleets even more than their merchants. The Dutch flooded their own farmland to thwart Spanish and later French invasions. Some of these floods would not have succeeded without torrential rains that reflected new atmospheric realities.
 
Later in the seventeenth century, cooling coincided with a shift in the strength of atmospheric high and low pressure zones over the Atlantic Ocean, which sharply increased the frequency of easterly winds over northern Europe. Sailors aboard Dutch warships heading into battle from the republic often had what was then called the “weather gage:” the upwind position from a downwind opponent. That allowed them to decide exactly how and when to deploy new “line of battle” tactics, in which warships would sail by each other in single file while firing broadsides. New wind patterns played a role in helping the Dutch win wars they might otherwise have lost. 

Still, climate change did not always aid the Dutch. In the Arctic, sea ice crushed ships, drowned sailors, and screened whales from whalers. Sailors in small ships that carried grain and timber from the Baltic Sea endured violent storms and confronted thick sea ice that blocked their way. Cold snaps in the Baltic occasionally led to harvest failures that imperiled the republic’s precious grain imports. Ice repeatedly blocked the waterways of the republic, suffocating travel between cities and raising the specter of flooding when the ice thawed. Sometimes, ice froze rivers that otherwise served as barriers to invasion. Left unattended, candles and stoves in cold winter weather kindled fires that swept through the cities of the republic.
 
Time and again, the Dutch responded creatively. Shipwrights fortified the hulls of whaling ships and greased them until they slid off ice. Civilians and soldiers hacked through ice to preserve open water in their defensive rivers. Guilds and city governments bought icebreakers that not only kept waterways open, but actually manufactured ice blocks for use in cellars. When the ice was too thick, the Dutch used skates and sleds to turn frozen canals into busy thoroughfares. Merchants divided their goods between different ships, and invested in marine insurance. They stockpiled Baltic grain in good years, and sold it for healthy profits whenever food shortages plagued Europe. Charities maintained a steady supply of food for the urban poor.  Inventors pioneered new firefighting tactics and equipment, and made good money selling them across Europe.

The Dutch, in short, were lucky to benefit from environmental changes that favored their unusual economy. But they also made their own luck. The society they built ended up being remarkably resilient in the face of new weather patterns that spelled disaster elsewhere in Europe. By relying so heavily on farmers scratching out a meagre existence on marginal farmland, other civilizations developed vulnerabilities to climate change that simply did not exist in the Dutch Republic.
 
In fact, the Dutch may even have adapted their technologies and policies to exploit the Little Ice Age, though they may not have recognized the trends in weather that we call climate change. Why were they so flexible in the face of changing environmental circumstances? In part, the answer may lie in their long history of draining and damming the Low Countries. The Dutch long understood that environments can change, and that societies can either adapt or succumb.
 
There was a darker side to the republic’s prosperity. The Dutch thrived in part by preying on communities and civilizations the world over. They shattered Iberian trading monopolies in Asia, seized expansive territories in the Americas, overwhelmed English whalers in the Arctic, and infamously broke into an African slave trade that cruelly exploited millions of people. The weather extremes of the Little Ice Age had often weakened communities that the Dutch victimized. In the republic, adaptation to climate change could take the form of a parasitic kind of opportunism that leveraged vulnerabilities in other societies. 
 
What, then, can the history of the republic’s frigid Golden Age teach us today? First and perhaps most importantly, it shows us that even relatively small changes in Earth’s average temperature can have enormous social consequences. Across much of the seventeenth-century world, the gloomiest predictions for our warmer future came true. A third of humanity may have died in disasters either set in motion or worsened by climate change.
 
The world has already warmed more, relative to average temperatures in the twentieth century, than it cooled in the chilliest stretches of the Little Ice Age. Our best projections suggest that it will warm by roughly three degrees Celsius in the coming century, if and only if countries follow through on their Paris Agreement pledges. Histories of the Little Ice Age therefore give us an urgent call to arms. We have technologies that our ancestors could not have imagined. But there are far more of us, consuming unimaginably more plants and animals, metals and fuels. And we too depend on a huge network of fields and fisheries that may not survive drastic changes in temperature and precipitation.
 
That leads us to our second lesson: climate change has had, and probably will have, very unequal consequences for different societies, communities, and individuals. Many assume that rich societies cope best with climate change. Yet some of the wealthiest seventeenth-century empires actually fared worst in the coldest and most volatile years of the Little Ice Age. Climate change, it seems, imperils not only societies that have few resources to exploit, but also those that require abundant resources to prosper.
 
The Dutch thrived in the seventeenth century not because their republic was rich, but because much of its wealth derived from activities that climate change benefited. Today, we can learn from the republic by strengthening social safety nets, investing in technologies that exploit or reduce climate change, and more broadly by thinking proactively about how we will adapt to the warmer planet of our future. We can learn from the Dutch in another way too, by strengthening bonds between countries and communities, rather than preying on the most vulnerable.
 
Ultimately, the lessons of the past come to us in the form of parables: stories that hint at deeper truths but do not tell us exactly what to do. That does not make them any less valuable. We now know that we cannot ignore our changing climate, that it will shape our fortunes in the decades to come. Let us use the warnings of the past to confront the looming catastrophe in our future, while we still can.

This article summarizes some important ideas in my new book, The Frigid Golden Age: Climate Change, the Little Ice Age, and the Dutch Republic, 1560-1720. You can buy the hardcover on the Cambridge University Press website or on Amazon, and you'll soon be able to purchase the paperback. 

The Washington Post published a modified and much shorter version of this article. You can find it here. 

​Will climate change trigger widespread food shortages and result in huge excess mortality in our future? Many historians have argued that it has before. Anomalous weather, abrupt climate change, and extreme dearth often work together in articles and books on early medieval demography, economy and environment. Few historians of early medieval Europe would now doubt that severe winters, droughts and other weather extremes led to harvest failures and, through those failures, food shortages and mortality events.
 
Most remaining doubters adhere to the idea that food shortages had causes internal to medieval societies. Instead of extreme weather or abrupt climate change, they blame accidents of (population) growth, deficient agrarian technology, unequal socioeconomic relations and weak institutions. Yet only rarely they have stolen the show or dominated the scholarship. For example, Amartya Sen’s “entitlement approach” to subsistence crises, which assigns primary importance to internal processes, has made few inroads in the literature on early medieval dearth, although in later periods it has many adherents.
 
Of course, the idea that big events have a single cause – monocausality, in other words – rarely convinces historians for long. Famine theorists and historians of other eras and world regions now argue that neither external forces such as weather, nor internal forces such as entitlements, alone capture the complexity of food shortages. They propose that these two explanatory mechanisms, often labeled “exogenous” and “endogenous,” respectively, should not be considered independent of one another or mutually exclusive. To them, periods of dearth can be explained by environmental anomalies, like unusual and severe plant-damaging weather, that coincide with socioeconomic vulnerability and declining (for most people) entitlement to food.
 
These explanations are more convincing. It seems that diverse factors acted in concert to cause, prolong and worsen food shortages. But proof for complex explanations for dearth in the distant past is hard to come by. Though they can be misleading, simpler, linear explanations are much easier to pull out of the extant evidence. This is true even when the sources are plentiful, as they are, at least by early medieval standards, for some regions and decades of Carolingian Europe. Food shortages in the Carolingian period, especially those that occurred during the reign of Charlemagne, have attracted the attention of scholars since the 1960s.

​For the Carolingian period, ordinances from the royal court, capitularies, reveal hoarding and speculation, and document official attempts to control the prices and movements of grain, while annalists and hagiographers recount severe winters and droughts. All of this evidence sheds light on dearth. Yet the legislative acts point to internal pressures on food supply, while the narrative sources highlight external ones. As we have seen, neither pressure adequately explains subsistence crises alone.
 
Unfortunately, however, we rarely have evidence for endogenous and exogenous factors at the same time. Around the year 800, when Leo III crowned Charlemagne imperator, most evidence for dearth comes from the capitularies. Before and after, narrative evidence dominates. So Charlemagne’s food shortages appear to have had internal drivers, and Charles the Bald’s external ones. Or so the written sources lead us to believe.

​Fortunately, evidence from other disciplines allows historians to fill in some of the gaps. External pressures are easier to establish by turning to the palaeoclimatic sciences. Using them, we are beginning to rewrite the history of continental European dearth, weather and climate from 750 to 950 CE. We are working on a new study that combines a near-exhaustive assessment of Carolingian written evidence for subsistence crises and weather with scientific evidence for changes in average temperature, precipitation, and volcanic activity (which can influence climate).
 
We are trying to answer some big questions, such as: What role did droughts, hard winters and extended periods of heavy rainfall have in sparking, prolonging or worsening Carolingian food shortages? Were these external forces the classic triggers of dearth that many early medievalists think they were?
 
Indicators of past climate embedded in trees and ice can test and corroborate observations of anomalous temperature and precipitation. For instance, the droughts of 794 and 874 CE, documented respectively in the Annales Mosellani and Annales Bertiniani, show up in the tree ring-based Old World Drought Atlas (OWDA, see below). Additionally, as McCormick, Dutton and Mayewski demonstrated, multiple severe Carolingian winters also align fairly neatly with atmosphere-clouding Northern Hemisphere volcanism reconstructed using the GISP2 Greenlandic ice core. 

​By marrying written and natural archives, we are able to perfect our appreciation of the scale and extent of the weather extremes that coincide with Carolingian periods of dearth. Yet instead of simply providing answers, our integrated data are raising questions, and pushing us towards a messier history of early medieval food shortage. This is because the independent lines of evidence often do not agree. For example, only two of the 15 driest years between 750 and 950 CE in the OWDA coincide with drought in Carolingian sources.
 
Admittedly, some of this dissonance may be artificial. The written record for weather and dearth is incomplete. To be sure, some places and times during the Carolingian era, broadly defined as it is here, are poorly documented. So reported drought years can appear kind of wet in the tree-based OWDA in some Carolingian regions (parts of northern Italy and Provence in 794 and 874 for instance).
 
Moreover, the detailed or “high-resolution” palaeoclimatology available now for early medieval Europe is much better for some regions than others. Tree-ring series extending back to 750 presently exist for few European regions. It is simply not possible to precisely pair some reported weather extremes or dearths to palaeoclimate reconstructions. Indeed, spatially the two lines of evidence can be mismatched. They can also be seasonally inconsistent, as the trees tell us far less about temperature and precipitation in the winter than they do for the summer.
 
Matches between historical and scientific evidence are therefore generally limited to the growing seasons, in places where written sources and palaeoclimate data overlap. That is enough to yield some surprising results. When the written record is densest, there is natural evidence for severe weather and rapid climate change, but not for food shortages.
 
Take the dramatic drop in average temperatures registered in European trees at the opening of the ninth century. According to the 2013 PAGES 2K Network European temperature reconstruction, temperatures were cooler around the time of Charlemagne’s coronation than they had been at any time between the mid sixth and early eleventh centuries. This dramatic cooling aligns well with a relatively small Northern Hemisphere volcanic eruption, detected in the recent ice-core record of volcanism led by Sigl. The eruption would have ejected sunlight-scattering sulfur aerosols into the atmosphere. Notably, larger events in the Carolingian era, like those of 750, 817 and 822, clearly had less of an influence on European temperature. The cold of 800 is equally pronounced but less unusual in a tree-based temperature reconstruction from the Alps. In this series, the late 820s are remarkably cooler.
 
Documentary sources register the falling temperatures. The Carolingian Annales regni francorum report severe growing-season frosts (aspera pruina) in 800. The Irish Annals of Ulster document a difficult and mortal winter in an entry quite possibly misdated in the Hennessy edition at 798 (799 or the 799/800 winter is more likely). Yet surprisingly, there is no contemporary record of food shortages in Europe.

Scholars tend to focus on instances when the written evidence for dearth and the natural evidence for anomalous weather align tidily. It seems that just as often, however, the two lines of evidence do not match so neatly. Severe weather may not always have triggered dearth in the early Middle Ages. Contemporary peoples could apparently cope with weather extremes in ways that allowed them to escape food shortages.
 
Early medieval vulnerability to external forces of dearth seems to have varied over space and time. We need to investigate the contrasting abilities of peoples from different early medieval regions and subperiods, participating in distinct agricultural economies with their own agrarian technologies, to withstand plant-damaging environmental extremes.
 
Several studies already suggest early medievals were capable of responding to gradual climate change. But to argue that they were not rigid or helpless when faced with marked seasonal temperature or precipitation anomalies, we must first identify, from sparse sources, potential moments of resilience. In this we run the risk of reading too much into absences of evidence. Yet the conclusion seems inescapable: when written sources are relatively abundant and there is no record of dearth during notable deviations in temperature and precipitation, early medievals must have adapted successfully.
 
Going forward, we must identify both moments and mechanisms of early medieval resilience in the face of climate change. Teasing these out from diverse sources might be tough going, but these elements are missing from the history of early medieval dearth and climate. Their omission has allowed for misleadingly neat histories of climate change and disaster in the period. Similar problems might well plague other histories that too clearly link climate changes to food shortages and mortality crises. Research that complicates these links could offer compelling new insights about our warmer future.

​Select Reading:
 
P. Bonnassie, “Consommation d’aliments immondes et cannibalisme de survie dans l’Occident du Haut Moyen Âge” Annales: Économies, Sociétés, Civilisations 44 (1989), pp. 1035-1056.
 
U. Büntgen et al, “2,500 Years of European Climate Variability and Human Susceptibility” Science 331 (2011), pp. 578-582.
 
U. Büntgen and W. Tegel, “European Tree-Ring Data and the Medieval Climate Anomaly” PAGES News 19 (2011), pp. 14-15.
 
F. Cheyette, “The Disappearance of the Ancient Landscape and the Climatic Anomaly of the Early Middle Ages: A Question to be Pursued” Early Medieval Europe 16 (2008), pp. 127-165.
 
E. Cook et al, “Old World Megadroughts and Pluvials during the Common Era” Science Advances 1 (2015), e1500561.
 
S. Devereux, Theories of Famine (Harvester Wheatsheaf, 1993).
 
R. Doehaerd, Le Haut Moyen Âge occidental: Economies et sociétés (Nouvelle Clio, 1971).
 
P.E. Dutton, “Charlemagne’s Mustache” and “Thunder and Hail over the Carolingian Countryside” in his Charlemagne’s Mustache and Other Cultural Clusters of a Dark Age (Palgrave, 2004), pp. 3-42, 169-188.
 
M. McCormick, P.E. Dutton and P. Mayewski, “Volcanoes and the Climate Forcing of Carolingian Europe, A.D. 750-950” Speculum 82 (2007), pp. 865-895.
 
T. Newfield, “The Contours, Frequency and Causation of Subsistence Crises in Carolingian Europe (750-950)” in P. Benito i Monclús ed., Crisis alimentarias en la edad media: Modelos, explicaciones y representaciones (Editorial Milenio, 2013), pp. 117-172.
 
PAGES 2k Network, “Continental-Scale Temperature Variability during the Past Two Millennia” Nature Geoscience 6 (2013), pp. 339-346.
 
K. Pearson, “Nutrition and the Early Medieval Diet” Speculum 72 (1997), pp. 1-32.
 
A. Sen, Poverty and Entitlements: An Essay on Entitlement and Deprivation (Oxford University Press, 1981).
 
M. Sigl et al, “Timing and Climate Forcing of Volcanic Eruptions for the Past 2,500 Years” Nature 523 (2015), pp. 543-549.
 
P. Slavin, “Climate and Famines: A Historical Reassessment” WIREs Climate Change 7 (2016), pp. 433-447.
 
A. Verhulst, “Karolingische Agrarpolitik: Das Capitulare de Villis und die hungersnöte von 792/793 und 805/806” Zeitschrift fur Agrargeschichte und Agrarsoziologie 13 (1965), pp. 175-189.

​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.