Last year might have been the hottest year ever recorded by our instruments. Average global temperatures were at least 0.27° C warmer than the average between 1981 and 2010, which was in turn up from the preindustrial norm. Overall, the past 17 years have been very warm, and since 2002 temperatures have been consistently well above the 1981-2010 average. However, that consistency is not clearly reflected in Arctic sea ice trends. In fact, the winter extent of Arctic sea ice has expanded in the last two years, seemingly defying projections of its imminent collapse.

Arctic sea ice is extremely complex and comes in many forms that respond more or less aggressively to seasonal changes and temperature anomalies. Currents, wind patterns, and even subtle differences in Earth’s gravitation also influence sea ice extent, although temperature usually plays a dominant role. As a result, Arctic sea ice coverage rises in winter and falls in summer. Its minimum and maximum yearly extent reflect shifts in average annual temperature, and in turn climate change. 

In the winter of 2010/11, Arctic sea ice reached its lowest-recorded extent (above). Satellite data reveals that, in December 2010, average Arctic sea ice covered just 12 million square kilometers. While that may sound like a lot, it is some 1.35 million square kilometers below the 1979-2000 average, and 270,000 square kilometers below the previous record low (set in 2006).

The sharp decline in Arctic sea ice coincided with very high global temperatures. In fact, scientists are still determining whether 2014 was actually warmer than 2010. In the wake of the winter of 2010/11, it seemed as though even the direst projections of Arctic sea ice decline had been too optimistic. Perhaps a threshold had been crossed, a tipping point had been reached, and Arctic sea ice would soon vanish. 

However, since the winter 2010/11 Arctic sea ice extent has haltingly recovered. Satellite maps demonstrate that Arctic sea ice currently covers 12.52 million square kilometers, about 520,000 square kilometers more than the 2010/11 maximum (above). The greatest change relative to 2010/11 is in the Canadian Arctic and Subarctic, where the Hudson and Baffin Bays are now completely covered with ice.

If Arctic warming has persisted since 2010, why has Arctic sea ice recovered? One possible explanation lies in the recent history of the Arctic Oscillation (AO), a band of winds that circle the Arctic in a counter clockwise direction. When the AO is in a positive phase, its winds move quickly, tightly sealing frigid air in the Arctic. When it is in a negative phase, its winds move more slowly and the band is distorted, allowing Arctic air to descend towards lower latitudes. There appears to be a correlation between a negative AO and reductions in Arctic sea ice extent. The AO, which was in a strongly negative phase in 2010, is now apparently in a weakly positive setting. 

Recent research also suggests that Arctic sea ice has a very low “memory” of previous trends. If, for example, Arctic sea ice extent is very low in September, winter heat loss is high, encouraging the formation of more sea ice. Such processes explain high year-to-year fluctuations in sea ice, yet they do not preclude  long-term trends. 

The apparent recovery of Arctic Sea Ice therefore does not counter long-term developments in either regional sea ice decline or global warming. Sea ice extent in December was still 540,000 kilometers below the 1981-2010 average, which means that sea ice coverage in the Arctic is still declining by 3.4%/decade. Most model simulations still project an accelerating decline in Arctic sea ice extent, even in optimistic scenarios in which our civilizations sharply reduce their greenhouse gas emissions (above). 

Model simulations, scientific proxy data, and documentary evidence assessed by interdisciplinary scholars can contextualize sea ice in the modern Arctic in light of the distant past. My own recent research suggests that sea ice extent in the Arctic north of Europe during December 2014 is not dissimilar to what was encountered by European polar explorers during summer expeditions at the height of the Little Ice Age. This reflects climate change on a remarkable scale, given the vast annual difference between summer and winter sea ice coverage in the Far North.

For example, I traced sea ice recorded by Henry Hudson and his crew, during their first Arctic expedition. In the above map, the outbound journey is depicted with a black solid line, while the return journey portrayed in a blue, dashed line. The part of the voyage in which ice was sighted is in white; a solid white line for the outbound journey, and a dashed line for the return. Compare the summer sea ice sighted in the Hudson journey with the edge of winter sea ice today (the second map provided in this article). 

Ultimately, Arctic sea ice fluctuates from year to year in ways that can temporarily mask gradual climate change. The world is warming, and the Arctic is warming faster than anywhere else. It is important to keep an eye on the recent recovery in Arctic sea ice, but all indications are that it is just a momentary reprieve in a very worrisome trend. 

~Dagomar Degroot

In Europe, the “Bronze Age” lasted nearly 2,000 years, from approximately 3200 BCE to roughly 600 BCE. In this period, bronze tools were forged for the first time, revolutionizing how Europeans manipulated their world and competed for resources. The first trading networks connected the continent, as navigational knowledge reached heights that Europeans would not exceed until the fifteenth century.

Centralized “palace economies” flourished throughout Europe and the Middle East, in ancient civilizations we remember today: on Minoan Crete, in Mycenaean Greece, in the Mesopotamian conquests of the Hittites and Akkadians, and of course in Egypt. Then, in the centuries around 1000 BCE, populations collapsed across Europe and the Middle East, sometimes in remarkably sudden events that must have been even more traumatic than the fall of the Roman Empire. In many regions, small, scattered villages were all that remained of the great Bronze Age civilizations. In Europe, it would be centuries before societies of similar complexity would rise again.

Those who study past climates are drawn to disaster, and not without reason. If we can establish that social crises coincided with periods of abrupt climate change, we can be pretty sure that further investigation will turn up connections between climate and human history. Historians, archaeologists, anthropologists, and scientists often find that connections between climate and human activity are particularly clear, and especially well-documented, in times of crisis. It is no surprise, then, that scholars have sought to link the Bronze Age collapse to climate change.

For example, while surveying 250,000 years of climate history, historian John Brooke of Ohio State University argues in an ambitious new book that the onset of a “cold, dry climate has to be a fundamental explanation of the demise of the Bronze Age of the greater Mediterranean.” (Brooke, 2014) Harvests failed in a changing climate, and subsequent food shortages undermined palace economies while provoking mass migration. Civilizations clashed, populations mingled and therefore spread disease, and piracy spread across the Mediterranean. Other scholars have tied roughly synchronous collapse in Northwestern Europe to changing climatic conditions. (Raftery, 1994; Tipping et al., 2008)

It is a compelling story, especially because it appears to offer a vivid warning for us today. However, like many straightforward narratives that tie climate change to historical collapse, that story is being revised by cutting-edge, interdisciplinary scholarship. In a paper recently published in Proceedings of the National Academy of Sciences, a team of scientists under lead author Ian Armit of the University of Bradford set out to reconstruct the late Bronze Age climate with unprecedented precision. Archaeological activity has surged across Ireland, offering abundant new sources for radiocarbon dating. Altogether, the researchers analyzed 2,023 radiocarbon dates in data from peat bogs and archaeological sites to build their new climate record.

They found that, in Northwestern Europe, populations began to decline more than a century before the late Bronze Age climate started to cool. Collapse in this part of Europe therefore cannot be tied to climate change. In fact, the authors argue that, all along, social and economic shifts were more than sufficient to explain the fall of regional Bronze Age civilizations. Trading networks and, in turn, stratified civilizations based around bronze production could not survive the advent of the Iron Age, when metals stronger than bronze were suddenly widely accessible.

Not surprisingly, this thesis is not quite as straightforward as the scientists suggest, because in many places people only gradually transitioned from bronze to iron. Nor does the climatic history of Northwestern Europe necessarily translate to southern Europe and the Middle East. Moreover, historians like Brooke have long acknowledged that climate change is but one possible explanation among many for the late Bronze Age collapse.

Ian Armit and his coauthors conclude that, in an age of global warming, “it is easy to view climate as the primary driver of past cultural change,” but “such assumptions need to be critically assessed using high-precision chronologies” that “guard against misleading correlations.” Sometimes historical work could use a little more methodological rigour, and certainly scientists, archaeologists, and historians should be prepared to work together in uncovering the climate history of the distant past.

However, at other times excellent historical work is grounded on cutting-edge scientific data that is revised by later studies. That can undermine some compelling narratives, but that does mean those narratives were never worth telling. Scholarship is a conversation, and that conversation gains depth through daring, provocative stories.  

~Dagomar Degroot

Sources: 

Armit, Ian et al., “Rapid climate change did not cause population collapse at the end of the European Bronze Age.” PNAS 111:48 (2014): 17045–17049.

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

Raftery, Barry. Pagan Celtic Ireland. The Enigma of the Irish Iron Age. London: Thames and Hudson, 1994.

Tipping, Richard et al., “Response to late Bronze Age climate change of farming communities in north-east Scotland.” Journal of Archaeological Science 35 (2008): 2379–2386.

Last month, world leaders met at UN Headquarters in New York City for Climate Summit 2014. As protests raged across the globe, diplomats established the framework for a major climate change agreement next year. The aim will be to limit anthropogenic warming to no more than 2 °C, a threshold established by scientists and policymakers, beyond which climate change is increasingly dangerous and unpredictable.

Just days after the 2014 summit, policy expert David Victor and influential astrophysicist Charles Kennel published an article in Nature that called on governments to “ditch the 2 °C warming goal.” Kennel and Victor argue that the rise in average global temperatures has stalled since 1998, as warming is increasingly absorbed by the world’s oceans. Variations in global temperature therefore do not directly reflect climate change, and governments should adopt other benchmarks for action. Atmospheric concentrations of carbon dioxide, they contend, more accurately reveal the relentless advance of climate change. In any case, limiting the rise in global temperatures to just 2 °C would impose unrealistic costs on national economies. 

Not surprisingly, responses to Victor and Kennel have been swift and comprehensive. For example, physicist and oceanographer Stefan Rahmstorf argues that short-term temperature variability does not undermine the case for a 2 °C limit, especially when there is little evidence for a “pause” in global warming. He explains how scientists and policymakers selected the limit, and cites studies synthesized by the IPCC, which conclude that holding the rise in planetary temperatures to 2 °C would cost no more than 0.06% of the world’s annual GDP. Kevin Anderson, Deputy Director of the Tyndall Centre for Climate Change Research, claims that Victor and Kennel have confused the roles that should be pursued by scientists in international climate change negotiations. Like Rahmstorf, he maintains that the 2 °C limit is neither misplaced nor unachievable. As a climate change advisor to the British government, he explains that, “the UK, almost overnight, conjured up over £350b to bail out the banks and stimulate the economy – but it has earmarked just £3.8b for its Green investment bank!” Physicist Joe Romm argues that a new study, which finds that scientists may have underestimated the extent of global warming, only strengthens the case for a 2 °C limit. To their credit, Victor and Kennel wrote a lengthy response in the New York Times to these and other critiques.

Missing from this debate are perspectives from those who study the past: the ways in which natural climate change has actually influenced human history. This is unfortunate, because historical relationships between climate and society can yield important insights on the usefulness of a 2 °C limit.

Take, for example, the sixteenth and seventeenth centuries, when Europeans entered the Arctic and Subarctic as never before. Journeys of exploration gradually transformed scholarly understandings of the Far North and shaped popular attitudes towards nature and empire. They paved the way for new settlements and laid the groundwork for the exploitation of marine resources that would alter European diets, stimulate the continent’s northern economies, and transform Arctic environments. All this during an early modern “Little Ice Age” that cooled temperatures across the Arctic and Subarctic by at least 0.5 °C, relative to the twentieth-century norm.

This apparent paradox is a focus of my recent research. I have learned that it can be tempting to assume that global cooling or warming will have straightforward impacts at the regional or local level, but such assumptions are often wrong. It often feels as though climate history is the study of bewildering, sometimes infuriating complexity. I frequently find myself using eclectic sources to trace, for example, how changes in solar radiation altered global temperatures, regional cyclonic activity, a series of storms above a town, damage sustained in that town, and how people understood what was going on. This is a part of what makes climate historians so useful to the broader historical discipline: we are always coming up with new ways of understanding how the local reflects the global, of discerning how – and why - things change over time.

Lately, I have used cutting-edge scientific data to reinterpret journals written by Arctic and Subarctic explorers in the sixteenth and seventeenth centuries. I discovered that some expeditions to the Far North benefitted from unusually warm ocean currents and hot summers that actually reflected counter-intuitive links between local environments and the globally cool Little Ice Age.

I have also started to investigate the seventeenth-century rise of the Dutch and English whaling industry around the island of Spitsbergen in the seas north of Norway. It might seem obvious that Arctic whaling expeditions would suffer in colder decades, and indeed the pack ice between Spitsbergen and Greenland would expand as regional temperatures cooled. However, at the same time bowhead whales prized by hunters would congregate near the pack ice, which made them much easier to hunt. The whaling industry therefore enjoyed its best years during the coldest phases of the Little Ice Age.

In other words, my research has revealed that when our focus is strictly on warming or cooling trends, we can lose sight of how climatic shifts actually affect people. 

Note: originally posted on The Otter, blog of the Network in Canadian History and Environment. 

Like the research that inspired it, this article is a cultural consequence of climate change.

Seven years ago, I was on a bus, reading a book about ancient climates. I looked out the window at a sunset so brilliant, it seemed to ignite Toronto's skyscrapers. I thought of global warming, and wondered: had anyone searched for connections between human history and climate change? Over the next seven years I found out that they had, but that there was still plenty of room for a new perspective.

The book I was reading was the product of an academic culture increasingly affected by the growing manifestations of global warming. Years ago, its importance to me was shaped by my place among a tangle of different cultures that all included discourses about climate change. The sunset that helped me imagine new connections between ideas triggered by these cultures led to a dissertation, which explored the climate history of the Dutch Golden Age. Now completed, the dissertation reveals, in part, that culture is inextricable from the material influence of climate change.

Simply put: we cannot comprehend the human consequences of climate change, past, present, and future, without understanding culture.

That insight was central to the papers of my panel at the World Congress of Environmental History, which recently concluded in beautiful Guimarães, Portugal. Panelists discussed how climate change can upend delicate relationships between humans and local environments, in ways that ultimately influence culture.

Thanks to funding generously provided by the Network in Canadian History and Environment, I was there to chart the ways in which a cooler early modern climate, known as the “Little Ice Age,” influenced the famous Dutch culture of the seventeenth century. My paper drew both from the last chapter of my dissertation, and from my more recent articles on Arctic environmental history.  

Strangely, projected relationships between climate and culture rarely feature in the reports regularly published by the Intergovernmental Panel on Climate Change or the World Meteorological Organization. Moreover, scholars of past climates who consider cultural consequences have too often assumed that a worsening climate inspired melancholic cultural responses. Those narratives are easily dismissed by cultural historians who can readily find alternative explanations for changing artistic tastes, or shifting patterns of gendered persecution, during even the coldest decades of the Little Ice Age.

Because the Dutch Republic flourished during the nadir of the Little Ice Age, examining its richly documented culture provides a rare opportunity to refine narratives that connect climate change to culture. My paper argued that literate Dutch observers, writing within a maritime culture that produced detailed records of daily weather, discerned changes in prevailing patterns of extreme weather in the seventeenth century. This partial understanding of climate change might have informed cultural responses, but I believe that we must be careful in making these connections. 

Take the famous Dutch “winter landscapes” of the sixteenth and seventeenth centuries. The rise of these paintings during the onset of a particularly cold phase of the Little Ice Age appears, at first, like an especially direct cultural consequence of climate change. Certainly many scholars of past climates have argued as much. However, on closer inspection, connections between climate and culture are not so straightforward. The painters of winter landscapes often painted indoors, during years that were not especially cold, and their paintings were often heavy with mythology and allegory. Certainly they did not directly reflect contemporary weather or climate. Moreover, winter landscapes were often part of a series, which included depictions of other seasons. Finally, they were attuned to a market that had dried up by the late seventeenth century, another period of extreme cold that was nevertheless not accompanied by paintings of winter landscapes.

The Dutch example therefore reveals that, in order to link climate change to cultural responses, we must carefully establish relationships between climate, weather, individuals, markets, and more. Scholars who examine the human consequences of climate change must range across so many disciplines that making assumptions can be very tempting. However, too easily connecting climate to culture can undermine other conclusions founded on more sturdy ground.

Ultimately, there were some elements of Dutch Golden Age culture that probably reflected the influence of climate change. Among them: poems and illustrations that responded to distinct weather events rendered more frequent during the coldest (or warmest) decades of the Little Ice Age. Technologies like new heating devices and “ice wagons” that travelled speedily across the ice likely also reflected the cultural influence of a cooler climate. So too did the uniquely egalitarian cultures that emerged from winter carnivals, which were held on ice that was more extensive and lasted longer in the chilliest phases of the Little Ice Age.

Overall, concrete cultural responses to climate change in the Dutch Republic were consequences of, or contributed to, the broader societal resilience of the Dutch to the Little Ice Age. At the WCEH, my paper and panel demonstrated once again that relationships between climate change and humanity are inexplicable without a rigorous analysis of culture. 

~Dagomar Degroot

According to the most recent summary for policymakers published by the Intergovernmental Panel on Climate Change (IPCC), “climate change can indirectly increase risks of violent conflicts” by exacerbating the socially destabilizing influence of poverty and economic shocks. While the IPCC attaches “medium confidence” to this claim, it is hardly controversial. Similar conclusions were made in the IPCC’s 2007 assessment reports. Since then, several studies have established that warfare is correlated to climatic stress, although their methods ignore social and cultural contexts. Many of the world’s most advanced militaries are now at the forefront of state adaptation to global warming. The American military, for example, is not only curbing its greenhouse emissions, but is also actively preparing for conflict stimulated by future climate change.

But how is the conduct of war – not just its origins – actually influenced by climate change? In the latest issue of the journal Environment and History, I published an article that explores this question. In the seventeenth century, three wars between England and the Dutch Republic – then the leading maritime powers of their day – were fought during the onset of an especially chilly stretch of the Little Ice Age in Europe. In my article, I argue that the weather that accompanied the coming of this “Maunder Minimum” affected military operations during the wars in complex and often counter-intuitive ways.

The First Anglo-Dutch War, contested between 1652 and 1654, actually preceded the cooling of the Maunder Minimum. I used ship logbooks, correspondence, intelligence reports, and diary entries written during the war to demonstrate that frequent westerly winds can be associated with warmer temperatures during the early 1650s. That usually allowed English fleets sailing from the west to claim the “weather gage,” the windward position from the enemy that, in naval combat, granted initiative in attack and, occasionally, retreat.

The English navy had developed revolutionary tactics in which ships of great size would bombard enemy hulls while sailing past them in line formation. By contrast, Dutch tactics still mandated grappling, boarding, and firing at enemy rigging (ironic, since a Dutch admiral had first debuted “line of battle” tactics some 15 years earlier). English tactics required favourable winds, and English fleets got them in the first Anglo-Dutch War. The Dutch Republic was rich enough to survive several naval reversals, and its shipyards productive enough to stave off defeat. However, on the balance the First Anglo-Dutch War was far more costly for the Dutch than it was for the English.

Human and environmental structures had shifted by the onset of the Second Anglo-Dutch War in 1664. Seasonal temperatures were more variable but generally cooler, storms had become more frequent and more severe, and easterly winds had grown more common. Meanwhile, the Dutch had adopted many of the most effective elements of the English naval system. Dutch fleets sailing to battle from the east now did so with the weather gage, and they were often victorious. Moreover, because English vessels had three tiers of guns while the Dutch only had two, many English guns were located near the water, and had to be retracted in high winds that were more common in a cooler climate. Easterly winds also allowed the Dutch fleet to raid up the Medway River in 1667, forcing the English crown into a peace that clearly benefitted the Dutch. 

In the Third Anglo-Dutch War, the climate of the Maunder Minimum manifested in weather that was defined less by easterly winds than incessant storminess. This time, the Dutch Republic was invaded by French and German armies while besieged at sea by a united Anglo-French fleet. However, in the summer of 1672 relentless gales kept the allied fleet from supporting a naval invasion, just as the Dutch fleet was partially disbanded so its soldiers and artillery could defend against invasion on land. Thereafter, Dutch admiral Michiel de Ruyter conducted a remarkably successful guerrilla campaign, aided by frequent easterly winds. The Dutch Republic survived its greatest crisis of the seventeenth century, and England signed another concessionary peace in 1674.

So, what does this seventeenth-century story tell us about war and climate change today?

First, it demonstrates again that climate change is mediated by human decisions, institutions, and cultures. The Dutch Admiralties might not have prevailed in the second and third wars had they not learned from the success of the English, who might have won the third war were it not for the leadership of De Ruyter. Second, the article reveals that military operations are influenced by short-term weather, which is often but certainly not inevitably affected by long-term climate change. The distinction is important, because the weather that most influences a battle can actually be an exception to the climatic trend.

Ultimately, far more studies are required that explore not only how climate change contributes to the cause of war, but also how it shapes wars once they begin.

~Dagomar Degroot

Note: this article is a greatly condensed version of dissertation chapters that also examine how climate influenced weather that affected shipbuilding, marine intelligence networks, privateering, and warfare on land during the Anglo-Dutch Wars. 

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. 

United States Department of Defense, Quadrennial Defense Review Report. February 2010.

In 2012 the Canadian government infamously announced changes to Library and Archives Canada (LAC) that made it much harder for researchers to access their country’s documentary heritage.  The LAC’s mandate was transformed: rather than acquiring and maintaining a “comprehensive” collection, it now aimed merely to gather a “representative” assembly of Canadian documents. Funding was slashed, employees were laid off, new acquisitions were paused, documents were sold to private bidders, and resources were decentralized across Canada.

In the last month, interviews with scientists by The Tyee have revealed how the conservative regime’s attitude towards the environment meant that environmental archives suffered the most. Government scientists, who have asked to remain anonymous, report that the chaotic closure of world-class environmental libraries resulted in the destruction of priceless documents relevant to environmental and climate history. The same scientists allege that the government falsely assured that all documents were preserved through digitalization.

 "The cuts were carried out in great haste apparently in order to meet some unknown agenda,” one scientist told The Tyee. “No records have been provided with regard to what material has been dumped or the value of this public property. No formal attempt was made to transfer material to libraries of existing academic institutions."  

The rich resources for environmental research at the St. Andrews Biological Station in New Brunswick are gone, as is the Freshwater Institute Library in Winnipeg, and the Northwest Atlantic Fisheries Centre in Newfoundland. At a time when historical climatology has increasingly turned to ship logbooks, the 50-volume logbook of the HMS Challenger has been destroyed. In 1876 the Challenger completed the first global marine research expedition, and its logbooks contain priceless data about the contemporary biosphere, hydrosphere and atmosphere. A copy of its logbooks exists outside of Canada, but it is less accessible for Canadian researchers.

The attack on environmental and, in particular, climate history by Canada’s Harper government demonstrates yet again that scientific or historical research into the environment is inherently political. Sadly, Canadian researchers cannot take even their archives for granted. We must do our best to digitalize what we can, ourselves, before it is lost forever.

Note: in coming years, digitalized sources relevant to climate history will appear on this website, where permission is granted. 

~Dagomar Degroot

Links: 

1. Save Library and Archives Canada. 
2. Canadian libricide: Tories torch and dump centuries of priceless, irreplaceable environmental archives.
3. Fisheries and Oceans Library closings called loss to science. 

Established in 1988 by the UN and the World Meteorological Organization, the Intergovernmental Panel on Climate Change (IPCC) is a scientific body that periodically summarizes the scholarly understanding of the world’s climate. In 2007, the panel’s fourth assessment report outlined in stark terms the likelihood of anthropogenic global warming. Since then, severe storms and drought have ravaged North America, Australia and Africa, yet unusually wet, cold conditions have accompanied some European winters. Through it all carbon emissions have continued to rise, now driven largely by developing nations. Today, the IPCC’s highly anticipated summary for policymakers was finally released, in lieu of its fifth assessment report that will be published later this year. In this article, I explore this landmark report and the responses it has inspired from the perspective of a climate historian.

Initially, the most striking aspect of the IPCC’s new summary for policymakers was not its content but the media reaction. The banner at CNN is currently: “A town that’s melting.” Its subheading: “climate change already happening in Alaska town.” Additional titles announce: “climate change: it’s us,” and “Miama’s rising water,” while an opinion calls for “common sense.” Not surprisingly, among major news networks the BBC has provided the most informative analysis of the IPCC’s report, and its banner, while not as large as CNN’s, nevertheless reads: “UN ‘95% sure’ humans cause warming.” Of course, the Fox News headline is in substantially smaller font, and its conclusion is characteristically fair and balanced: “Hockey Schtick: UN report ignores global warming pause.” Worse still is coverage given by the Times of India, which features only a link in diminutive font buried at the bottom of its website. Meanwhile the homepage for CCTV, a major Chinese broadcaster, contains no reference at all to the report. Taken together, headlines at the big media outlets confirm the enduring importance of partisan divisions in the global warming discussion. They also suggest that scholars, journalists, the IPCC, and indeed the UN must do more to raise awareness of global warming in countries that will be most affected by its consequences. Still, the banner headlines on many centrist news outlets in the West are encouraging.

For those who have paid heed to the relentless debate about global warming, much of the action in the IPCC's fifth summary for policymakers happens in the first few pages. In previous days and weeks, so-called climate “skeptics” flooded the airwaves, encouraging rampant speculation about whether the alleged “pause” in global warming would feature prominently in the IPCC's new report. In fact, in its second page the IPCC's summary actually confirms that:

The IPCC affirmed that average global temperatures at sea and on land have risen by 0.85 degrees Celsius since 1880, although that will come as no surprise. What does impress, however, is the IPCC's explicit repudiation of the false narrative of the "pause." Climate historians know better than most that climatic reconstructions can be manipulated with ease. Start your graph of annual temperatures with a year of anomalous warmth, and you're bound to discover long-term cooling. Begin with an unusually cold year, and you'll find just the opposite. That is precisely why scholars must set their temporal and geographic parameters before reconstructing past climates. What region are we examining? For what time, and why? With what sources? What are the limitations of those sources? These questions are essential for the accurate reconstruction of past climates, and the answer can never be: "because of the expected result." Moreover, to unravel why variations in temperature occur, we must also seek the stimulus - the "forcing" - for cooling or warming. Is a volcanic eruption responsible for a few unusually cold years? Is an intense El Niño to blame for a really hot year? Neither event need contribute to a long-term climatic trend.

Not surprisingly, skeptics eager to discredit the scientific consensus around global warming have ignored these questions. Instead, they have arbitrarily started their climatic reconstructions at 1998, a year of extreme warmth, in order to highlight supposed cooling since then.  Unfortunately for them, the scholars of the IPCC have included this paragraph: 

In other words, the presence of short-term fluctuations in climate does not throw into doubt the existence of long-term climatic trends. If anything, the impact of strong El Niño in 1998 reveals what can happen when an entirely natural event that stimulates warming compounds the the influence of anthropogenic greenhouse gases. Still, the IPCC's fifth summary did include these passages: 

Those paragraphs will probably be manipulated by skeptics and misinterpreted by many journalists. While they seem to suggest that there has been a  pause in the warming trend, the context matters. The surrounding passages confirm that model accuracy has improved, further strengthening projections of future warming. However, in 10 or 15-year intervals, natural signals can mask the anthropogenic warming trend. In other words, volcanic eruptions can stimulate short-term cooling, but, again, that hardly rules out long-term warming. In short intervals some natural influences will surprise scientists and confound models, because we are still learning more about the intricacies of our world's climate. Nevertheless, the big conclusions are still the same: the earth is warming, we're to blame. 

The IPCC's summary for policymakers also addresses climates in the more distant past. Another argument frequently advanced by skeptics holds that the Medieval Climate Anomaly - previously known as the Medieval Warm Period - was actually accompanied by hotter temperatures than we face today. Their conclusion is that modern warming isn't a big deal, and falls within natural variability. Of course, the cause of current warming is more important to climate scientists than the scale of warming to date, because it is precisely that cause which will trigger future warming far beyond anything humanity has encountered. Nevertheless, the IPCC's report also discredits the idea that medieval warmth exceeded or matched modern temperatures: 

In subsequent pages, the IPCC's report describes the worrying findings presented in thousands of scientific papers during the past six years. Oceans are warming, polar ice caps are shrinking and sea levels are rising, while the atmospheric concentration of carbon dioxide, methane, and nitrous oxide have risen to levels unseen in over 800,000 years. In its most important conclusion, the panel's report reveals that greenhouse gases emitted by human activity are now 95% certain to have caused recent warming. These emissions have affected carbon cycle processes, stimulating further warming from natural sources (for example, methane hidden under melting permafrost). Meanwhile, the ocean has absorbed 30% of anthropogenic carbon dioxide, causing dangerous ocean acidification. 

The IPCC's fifth summary concludes that warming in the coming century will likely fall between 1.5-4 degrees Celsius. Moreover, it is more likely that warming will exceed a catastrophic 6 degrees Celsius than fall beneath 1 degrees Celsius. The lower range of this estimate is 0.5 degrees Celsius lower than it was in the IPCC's fourth assessment in 2007, owing in part to the slight divergence between model projections and climatic trends in the past decade. It is possible that the range will be adjusted upward in the IPCC's next report, as model simulations and average global warming converge again. Either way, our best guess for the future hasn't changed much: we probably face warming of approximately 3 degrees Celsius worldwide by the end of the century. 

Of course, a 3 degree Celsius rise in average global temperatures does not mean each day will be three degrees warmer, no matter where we are. In many regions, warming will be expressed in extremes: a doubling, or tripling, of days accompanied by severe heat, along with far more dangerous storms and flooding. Moreover, warming in some countries will far outstrip the global average, and demographic, social or environmental conditions already increase the vulnerability of many of these countries to climate change. In 2011, scholars at Maplecroft,  a global risk analytics company, created the above map of global climate change vulnerability by analyzing 42 social, economic and environmental variables. News outlets in China and India take note: it is precisely the countries that increasingly contribute most to warming that have the most to lose. In that context, let us hope that the dire projections in the IPCC's fifth summary help moderates bridge the partisan divide to inspire concrete responses to climate change in the developed west. 

~Dagomar Degroot

Further reading: 

Climate scientist Michael Mann, author of The Hockey Stick and the Climate Wars, measures claims by climate skeptics in light of the IPCC's fifth summary for policymakers.

On September 28th, the scientists of the International Geosphere-Biosphere Programme respond to the IPCC's fifth summary.

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. 

~Dagomar Degroot