Contributing Author: Benoit S. Lecavalier
August 18th, 2013 marked the start of a two week long workshop called the Advanced Climate Dynamics Course (ACDC). The venue was located in a former fishing village in the Vesterålen islands of Arctic Norway, a little place called Nyksund with a population of slightly over a dozen permanent residents. We were there for more than just hiking through the great outdoors, eating the local food, and performing local outreach. We were there to discuss what many call small talk: the climate. Organized by European and North American Universities, this event attracted internationally renowned researchers and graduate students, gathered there to discuss the climate dynamics of the last deglaciation. Twenty thousand years ago, during the last glacial maximum, the climate was cooler, the Greenland and Antarctic ice sheet were larger, and gargantuan bodies of ice rested across North America, the British Isles, and Scandinavia. Consequently, the sea-level was lower than it is today by over 120 meters. The emphasis of the workshop was to discuss how the climate system transitioned from glacial to present interglacial conditions.
The seminars began by summarizing our present understanding of climate on time-scales of thousands of years. The driver, often referred to as the pacemaker for the ice ages, is the changes in the Earth’s orbit around the sun. These gradual changes in the Earth’s orbit affect incoming solar radiation at the Earth’s surface, which can either facilitate the growth of an ice sheet or deter it. However, countless feedbacks within the climate system render the situation complex. For example, ice sheet’s reflective nature deflects radiation back into space affecting the available energy at the surface. In addition ice sheets, which can rival mountain ranges in size, affect atmospheric jet streams and deflect storm tracks as well as precipitation patterns. To understand these feedbacks within the climate system we have to look at paleoclimate records: terrestrial and marine records of past climate.
The following days were spent going over climate proxies, which preserve physical characteristics of past climatic conditions. These tell us about past temperatures on land and in the ocean, how vigorously the oceans circulated, and past sea-levels, among many other things. After being presented with collections of paleoclimate records, we could speculate on the role of the atmosphere and ocean during the deglaciation. The question that came came to mind: if the ice ages are driven by slow gradual changes in the Earth’s orbit around the sun, what processes, feedbacks, and mechanisms could punctuate the system with such abrupt and rapid climate change?
We reviewed the literature to investigate the consensus on what is currently understood and what observations lack a proper explanation. Our review emphasized the necessary role of geophysical modeling of the climate system to understand how all these complex processes are intertwined. State-of-the-art atmosphere-ocean general circulation models tell us about the state of the atmosphere and ocean, while glacial system models reveal the response of ice sheet to past climate change and the resulting change in sea-level. Atmosphere-Ocean models are predominantly applied for the past and future 100 years, so the question remains: what were the climatic conditions over the ice sheets thousands of years ago? What climate forcing led to ice sheet instabilities, causing the flow of iceberg armadas in the North Atlantic? To which extent did the fresh water from these icebergs affect the circulation of the Ocean? How have these changes in circulation affected global heat transport and the carbon cycle? What about global temperatures? Fortunately, we are beginning to answer these questions thanks to international cross-disciplinary collaborations, which are often initiated by workshops such as the ACDC.
Many atmosphere-ocean modelers take an interest in simulating the deglacial climate, with help from the glaciological community who provide past ice sheet reconstructions. These scientists have discovered that massive ice sheets show the potential to deflect atmospheric stationary waves. The ice sheets respond to climatic shifts, and in warmer conditions they can change dynamically by releasing icebergs into the ocean. Fresh water melting from those icebergs produces density differences in the Atlantic Ocean which slows down the formation of heavy deep water, affecting global circulation. This change in ocean heat transport cools the North Atlantic, while the Southern Oceans warm in a compensating fashion. The models simulate these dramatic climate events, hinting at underlying mechanisms and illuminating the observations found in paleoclimate records. This goes a long way towards explaining how the Earth as a whole warmed out of the glaciation and why records in the North Atlantic reflect quick warming with subsequent rapid and prolonged cool period before finally stabilizing to present conditions.
However, the story is far from understood, for every answer brings new questions. The workshop got everyone thinking about possible avenues of research which will have to be investigated to address our questions. That is why we gathered there in that little Norwegian village. It was to exchange ideas, data and model predictions, to work together and form collaborations, and to piece together a story that shaped humanity and still affects us today.
A week ago I returned from what was, surprisingly, my first trip to Germany. This year the European Society for Environmental History convened its biannual conference in Munich, a city I’ll remember for its beautiful architecture, sensible public transit and delicious beer. No fewer than fifteen climate history panels were part of the conference, and despite my best attempts I couldn't attend them all. Still, I decided to share some of what I learned (or remembered) while listening to papers that were good enough to keep me from exploring Munich. Note that for the purposes of this little article, the terms “climate history” and “historical climatology” are synonymous.
1. Climate history must be inclusive to be effective.
There is only limited value in mining one kind of documentary source for evidence of past weather and, in turn, past climate change. Of course, the value of such work fluctuates with the source under investigation: registers of past events called chronicles are notoriously prone to exaggeration, for example, while ship logbooks provide standardized, easily quantifiable and remarkably reliable weather observations. Still, a reconstruction of past climate that makes any claim to accuracy must, where possible, employ a wide variety of documentary evidence compiled by many authors. These reconstructions are strengthened when meteorological information contained in some documentary sources can be verified using the data contained in other documents. They gain even more credibility alongside scientific evidence like model simulations, or statistics developed using natural archives (ice cores or tree rings, for example). Good climatic reconstructions are necessarily interdisciplinary, and we should think carefully about what we are really saying when we discuss observations written by a single author, in a single source. Are we reconstructing the climate of a vast region across the decades, or are we engaging in literary criticism?
If interdisciplinary work is essential to historical climatology, interactions between sub-disciplines are just as important. Climate history is often considered a sub-discipline of environmental history, which, in turn, is one genre in the broader field of history. Agricultural history, forest history and energy history are all among the sub-disciplines that together constitute environmental history. Like climate history, they lose significance when divorced from one another. Reconstructions of past climates are fascinating, but historians can also incorporate the many different sub-disciplines and genres of their profession to do something scientists can’t: weave the history of climate into the history of humanity. The narratives we get can be as valuable as the models developed by scientists as we struggle to understand our plight on a warming planet.
2. We're only scratching the surface of relevant documentary evidence.
Chronicles and weather diaries have long formed the backbone of the documentary evidence used to reconstruct past climates. Questions of interpretation hound both sources, however, and these days, correspondence and ship logbooks are increasingly in vogue. In Munich I heard scholars like Rudolf Brázdil describe how correspondence related to the collection of taxes can yield strikingly detailed climatic reconstructions. Tax records can be placed alongside court documents, toll accounts and maintenance registers as largely quantitative sources that can yield rich climatic data if interpreted using qualitative evidence. New sources – and new methods of source interpretation - can provide data about wind patterns, hailstorms, and other previously unexamined meteorological conditions, deepening our understanding of climate change.
3. We need new ways of conceptualizing the relationship between climate change and human history.
Fernand Braudel, perhaps the greatest historian of the twentieth century, introduced a revolutionary way of conceptualizing time. According to his notion of “total history,” different kinds of historical change transpire differently across time and space. Environmental or economic transformation at a vast scale spanned the centuries, yet the historical “event” was immediate. Understanding the past from this perspective allowed him to gather the entire Mediterranean world into a single narrative using the huge, lumbering structures of history.
The problem for historical climatologists – and indeed, all environmental historians – is that Braudel was wrong. Interdisciplinary research has revealed that many historical structures can be brittle; they can break quickly with immediate yet regionally specific ramifications. For example, climate change influenced by volcanic eruptions and the subsequent expansion of polar ice could alter prevailing weather patterns over the North Sea in one cruel winter. However, the same processes behind routinely cold winters in northern Europe could bring not frost but rather drought to the Mediterranean.
So different kinds of historical change can occur across many scales of time and space, and that complicates our attempt to conceptualize connections between past environments and historical events. Human history cannot be modeled – we simply lack all of the necessary variables – but in recent years environmental historians have made great progress going beyond the problematic concepts like footprint metaphor or social metabolism in their efforts to conceptualize the connections between nature and society. In this effort historical climatologists lag behind their peers, and for that reason climate histories can devolve into lists in which weather events likely stimulated by a climatic shift cause environmental changes that contribute to one event after another in the history of a particular region. Historians need to work with colleagues across many disciplines to develop ways of understanding relationships between climate, weather and human history. These ways of understanding might not completely explain the past, but they might help us conceive of historical change more clearly, with insights applicable for our future on a warming planet.
Note: originally posted on The Otter, blog of the Network in Canadian History and Environment (NiCHE).
On February 10th I embarked on the first leg of a long voyage from Toronto to Goa, a former Portuguese enclave nestled among the beaches of western India. After enduring the concrete monolith that is Frankfurt’s international airport, I finally boarded my second flight and flew south through Turkey, past Syria, across Iran and down towards Mumbai. I left the plane at an hour past midnight. Mosquitos swarming through the airport quickly prompted me to take the malaria medication that would later give me incredibly vivid dreams. Hours later the shock of a violent landing in Goa was nothing compared to the culture shock that followed. As I left the airport and stepped onto the rust-coloured soil I saw signs promoting European luxury vehicles or American cologne towering over slums and endless trash amid lush tropical beauty. After three sunrises and two sunsets without sleep I finally arrived at my hotel, ignoring for the moment the hand-sized spider dangling near my door.
With the help of funding generously provided by Network in Canadian History and Environment (NiCHE), I had travelled nearly 13,000 kilometers to attend the fourth Open Science Meeting (OSM) organized by the Past Global Changes (PAGES) initiative. A core project of the International Geosphere-Biosphere Programme, PAGES has over 5000 subscribing scientists across more than 100 countries. Because research supported by PAGES explores past environments to create a roadmap for the future, the initiative is especially concerned with climate change. Every four years its Open Science Meeting is held in a new location, and in case the Olympic parallels were not obvious enough a “PAGES lamp” was lit at the opening ceremonies. It may not have resembled London’s burning torch, but it did avoid the mishap that embarrassed my fellow Canadians at the Vancouver Olympics.
It’s easy for historians to forget that we don’t have a monopoly over the interpretation of the past. There’s nothing like a scientific conference to remind us that we can only access a tiny sliver of the very recent past, that other disciplines can find voices which speak to the present in sources beyond the documents we hold sacred. Many of the scientists at the OSM reconstructed past climates to measure the significance of modern warming, to unravel how climatic shifts influence different environments, and to provide a clearer picture of the world’s natural history.
In papers and posters scientists presented results derived from the exhaustive analysis of, for example, changes in the growth of trees, the thickness of permanent ice cover and the scope of lakebed deposits. Conclusions were compared with other data that measured shifts in animal ranges, tree lines or glacial extent, all of which can be used to reconstruct changes in regional temperature or precipitation. Evidence from these so-called “proxies” was weighed against a range of sophisticated models, enabling projections of climates past that move seamlessly into the present and future.
Not surprisingly, correlating fluctuations in diverse proxy records and tying them to climatic trends is hardly straightforward. Physicist Ashoka Kumar Sinhvi gave an opening keynote address that exposed the frequently overlooked complexity of linking different kinds of data between different environments at different scales, revealing the limitations of our understanding of past and future climates. Later in the day that concept was echoed by André Berger, who explained how the intricate constellation of influences that shapes the global climate is never stable, complicating the attempt to find historical analogues for our present condition. Sinhvi, Berger and others helped frame the rich data presented in the papers and posters that followed by demonstrating yet again that in science, as in history, the past is opaque, unstable, and forever subject to interpretation.
Of course, that never stops us from seeking more information and, in turn, greater clarity. Some particularly fascinating papers explored past Antarctic climates at a time when the Antarctic Peninsula is warming at a rate of 5.3° C per century. Michael Weber presented findings that reveal how the Antarctic ice sheet is much more reactive to atmospheric Carbon Dioxide than previously believed. Robert Mulvaney then described how the rate of Antarctic melting, unprecedented in the past millennium, likely had analogues in the distant past when ice shelves were entirely absent. Medieval warmth and early modern cooling, familiar to historians of climates past, apparently were not felt in Antarctica. On the other hand, Guillaume Leduc presented exhaustive findings that, while skewed towards the Atlantic region, nevertheless suggested that the “Little Ice Age” between the fourteenth and nineteenth centuries strongly affected global sea surface temperatures. Those results may have critical implications for the nascent field of marine environmental history, which until now has not adequately considered climatic fluctuation.
To unravel histories that bridge culture and nature, environmental historians require some scientific literacy, yet I wasn’t sure what to expect as I prepared to give at a talk at a conference where formulas were ubiquitous and historiography unheard of. I argued that documentary evidence can improve the accuracy of reconstructions of temperature or precipitation, giving us a way of testing meteorological patterns recorded by the kinds of sources unearthed by scientists. Accustomed to the critical analysis of diverse documents, historians are ideally situated to filter documents through the kind of methodology that lets us quantify past weather observations and, in turn, reconstruct the climatic past. Moreover, while tree rings or ice cores rarely provide much more than seasonal resolution, surviving documents can record weather with far greater temporal precision, and some even chart hourly changes.
Most importantly, documentary evidence grants us access to past wind intensity or direction, weather conditions that are less easily measureable through the analysis of scientific proxy data. For centuries it was necessary for European mariners to estimate longitude by calculating a ship’s speed, direction and any leeway in its course, for which the most important influence was wind. Hence many logbooks kept aboard ships abound with reliable and quantifiable meteorological information taken several times on virtually every day of the vessel’s journey. The bulk of my talk presented results from English and Dutch ship logbooks, which suggest that easterly winds increased in the late seventeenth century as the climate cooled across the North Sea.
I was relieved and delighted by the reception I received from the scientists in the audience. More importantly, it was heartening to see the importance of interdisciplinary cooperation in the new “Future Earth” project spearheaded by the International Geosphere-Biosphere Programme. Still, many scholars in both the sciences and the humanities continue to take a passive approach to building connections between disciplines. Conferences like the PAGES OSM have existed for decades, yet many historians fail to realize that their insights are needed and desired. Similarly, most presenters at the upcoming ASEH conference are historians, and scientists or engineers remain underrepresented. Establishing connections between institutions like NiCHE, the ASEH, PAGES and the Climate History Network (CHN) can help move us forward, but what’s even more valuable is feedback from those who have benefitted from conferences in another discipline.
After the conference in Goa I spent a few days in the vast metropolis of Mumbai. My plane was delayed, and as it finally approached the city our pilot was forced to circle the airport for a few minutes before we could land. The slums in Mumbai are so vast that their full extent can only be grasped from the air. As I shifted in my leather seat I glimpsed the innumerable shanties, clustered around open sewage, barely visible through the purple smog. The impoverished people far below, and countless millions like them, will suffer most as our planet continues to warm, yet their voices are never heard in academic or political conferences. The quest to understand climate change must become more inclusive, not just of other academic disciplines, but of all voices, past and present, learned and “unlearned,” rich and poor.