Study: volcanic eruptions diminished recent warming. March 3, 2013.
Average global temperatures fluctuate in response to many different influences, and while some of these "forcings" are now affected by humans, others are shaped entirely by natural causes. Articles on this website have considered whether sulfur released into the atmosphere by volcanic eruptions stimulated the prolonged cooling of the so-called Little Ice Age in the centuries before 1850. Deposited in the stratosphere, volcanic sulfur dioxide interacts with other chemicals to form sulfuric acid and water, which in turn reflects solar radiation. Other articles on the site have introduced research revealing that the reflective properties of man made aerosol pollution in the twentieth century likely sheltered swaths of North America and, later, parts of China from the influence of global warming. More
Debate tests accuracy of tree ring data. February 6, 2013.
For those interested in climates past and present, trees do more than absorb carbon dioxide. Seasonal changes in cellular growth near the bark of a tree leave rings buried in its wood. The size of those records is tied to the growth of the tree; a good year will imprint a thick ring, while hard times leave mere slivers. Anyone who's ever owned a plant will understand that most trees need abundant sun, moderate temperatures and sufficient water. Of course, gardeners are aware that different plants - from weeds to trees - respond to different conditions. By researching the peculiar tastes of various tree species climatologists can use tree trunks to reconstruct yearly fluctuations in temperature and precipitation, sometimes over hundreds of years. More
Climate change research: now for historians. January 13, 2013.
Most scholars study something important to their societies. The walls of the ivory tower are, in fact, quite porous. It's no surprise that the genre of history that deals with environmental issues - environmental history - grew out of the debates surrounding the use of DDT. No surprise, either, that academics within disciplines from anthropology to economics are increasingly considering the influence of climate change just as the effects of global warming are becoming painfully obvious. Now more than ever, research into past climates is not just for scientists.
If environmental history grew steadily in the decades since its conception, so too did its semi-autonomous, interdisciplinary cousin: climate history, or historical climatology. This site regularly describes some of the more interesting work published by historical climatologists, before considering how it can reframe today's environmental issues. More
If environmental history grew steadily in the decades since its conception, so too did its semi-autonomous, interdisciplinary cousin: climate history, or historical climatology. This site regularly describes some of the more interesting work published by historical climatologists, before considering how it can reframe today's environmental issues. More
Climate change and ice cover in one Arctic lake. December 16, 2012.
Average air temperatures have risen across much of the globe in recent decades, nowhere more quickly than in the Arctic. However, the consequences of rapid warming for the environmental conditions that shape life in the Arctic remain poorly understood. A new article published in the journal Climatic Change by an international team of scholars under lead author Ruibo Lei uses 44 years of ice data fromLake Kilpisjärvi, in the Northwestern fringe of Finland, as a case study to improve our understanding of recent shifts in Arctic ice cover. Because the workings of lake ice can be easily related to large-scale atmospheric changes, past ice records can shed new light on local and regional climate change. Extensive regional ice monitoring dates back to 1964, and the remoteness of the lake ensures that human influences other than anthropogenic change likely had little to no impact on the ice data. More
Study: drought triggered Mayan collapse. November 9, 2012.
For seven centuries the Classic Maya dominated central America, developing a unique society that in its complexity rivaled the greatest civilizations of contemporary Asia or Europe. For over three decadessome scholars attempted to link the gradual collapse of Mayan population centers between 800 and 1000 CE to sustained drought influenced by a change in the regional climate. However, their conclusions remained controversial, in part because climatic reconstructions compiled usingpaleoclimatic records were not yet sufficiently precise. More recent articles supported the drought hypothesis for the collapse of Mayan Civilization, but environmental circumstances like human-caused deforestation complicated attempts to piece together what happened near the most important cities of Mayan antiquity. More
Study: methane emissions linked to human activity for millennia. October 6, 2012.
Methane in the upper troposphere, 2011.
Using new data from the NEEM and EUROCORE ice core drilling programs, researchers from the Niels Bohr Institute have published a study in the journal Nature that reconstructs how different natural and anthropogenic activities contributed to methane emissions over the last two millennia. An important but frequently ignored greenhouse gas, methane is released into the troposphere from three sources: biogenic (wetlands or rice paddies, for instance), geological (for example, mud volcanoes) or pyrogenic (including biofuel or coal burning). Different methane sources have different isotopic signatures, meaning that scientists can use ice cores to trace how and why methane rose and fell over time. More
Pollution cooling summers in one part of China. September 30, 2012.
Is the globe warming or is the climate changing? Policy makers and media outlets have long misunderstood the relationship between "global warming" and "climate change" as the terms are used in scientific literature, creating a false but popular dichotomy in which the planet cannot be warming if the climate is changing. Climate change, after all, must refer to both cooling and warming, but how can the planet be warming if both trends are happening at the same time? With popular confusion in mind, it is important for scholars of climate and its history to remind the public that, in scientific literature, climate change is the consequence of global warming. The world is getting hotter, but the warming influence of greenhouse gases, coupled with other pollutants, has set in motion a complex chain of atmospheric and oceanic changes that sometimes have surprising consequences.
Some of those consequences are explored in a new study written by lead author Bian He for the journal Climatic Change. Over the past decade several studies have uncovered the existence of a pocket of summer climatic cooling within rapidly warming East Asia between 1951 and 2000. More
Some of those consequences are explored in a new study written by lead author Bian He for the journal Climatic Change. Over the past decade several studies have uncovered the existence of a pocket of summer climatic cooling within rapidly warming East Asia between 1951 and 2000. More
Study: after initial extinction, biodiversity increases in warmer climates. Sept 12, 2012.
On a large scale, biodiversity decreases at a predictable rate with an increase in latitude. In other words, more species can live in hot climates than in cold climates. Strangely, analysis of fossil records dating back 540 million years previously suggested that biodiversity decreased as climates warmed. Now, a study published in the journal Proceedings of the National Academy of Sciences has used newly standardized data chronicling marine invertebrate biodiversity to refine and, in fact, contradict those earlier results. Biodiversity, in turns out, generally increases in climates marked by relatively stable warmth. Lead author Peter Mayhew and his fellow researchers are careful to note that the relationship between climatic shifts and biodiversity is not deterministic: periods of unusual biodiversity like the late Jurassic or early Cretaceous coincided with relatively cool temperatures owing to variables like sea level changes or continental dispersion. Moreover, the eventual trend towards greater biodiversity in warmer climates, which often took millions of years, was typically preceded by an initial extinction event. More
New evidence links solar activity to winter severity. August 26, 2012.
The best climatic reconstructions are compiled at the intersection of the sciences and the humanities. Climatic data from scientific "proxy data," like ice cores or tree rings, can be refined using weather descriptions in historical evidence written by contemporary observers. The most useful documents for the reconstruction of past climates are often the most simple and the easiest to quantify. In the straightforward weather observations provided in ship logbooks or financial accounts, for example, relationships between weather, its environmental consequences, and human observers are often the clearest. Describing a simple environmental phenomenon with an easily identifiable meteorological cause, easily quantifiable records of river freezing are especially valuable. Used for decades by Dutch scholars, they have recently been applied to a central European context by an international team of researchers under Frank Sirocko of Johannes Gutenberg University. More
Studies: atmospheric CO2 concentration drives climate change. August 2, 2012.
Despite its catchy name, Marine Isotope Stage 11 (MIS 11) is not a science fiction film but, instead, a climatic regime similar to our own that that endured from 424,000 to 374,000 years ago. During MIS 11 the world's orbital configuration, atmospheric greenhouse gas concentration and fauna resembled their current state, encouraging researchers to develop high-resolution climatic reconstructions of the period. Nevertheless, despite the quality of existing climatic reconstructions uncertainty has persisted regarding the major drivers of contemporary climate change. A new study by lead author S. Das Sharma, published in latest issue of the Journal of Geophysical Research, employs novel statistical techniques to interpret 15 climatic indicators - like pollen records - in a quest for the primary cause of the warmer MIS 11 climate. According to the authors, the results "unequivocally" establish that atmospheric carbon dioxide was the key influence behind the warmer climate of the period, with important consequences for our understanding of the relationship between anthropogenic greenhouse gasses and today's changing climate. More
Does tree ring data reflect global cooling? July 9, 2012.
Credit: Institute of Geography, JGU
In a study published in the journal Nature Climate Change and sure to be widely misinterpreted, a team under lead author Jan Esper has used new dendrochronological (tree ring) data from sub-fossil pine trees to reconstruct Finnish temperatures back to 138 BC. The results faithfully record past climatic fluctuations from the Roman warm period to the Little Ice Age, but they also seem to reflect a surprising trend: the cooling of European temperatures by 0.31 degrees Celsius for each of the last two millennia prior to the onset of anthropogenic climate change. Tree ring data is derived from measurements of the distance between growth rings in the trunk of a tree. It not only reflects variability in temperature but also precipitation, with some trees responding more strongly to a particular meteorological variable than others. Researchers must take this into account, and since the 1970s historical climatologists have carefully reconstructed Scandinavian temperatures using dendrochronological data. However, the new study appears to reveal a general cooling trend missing from previous records, with results now fitting coupled general circulation models. Esper and his co-authors conclude that cooling over the past two millennia was driven by a gradual reduction in solar radiation driven by changes in Earth's orbit around the sun. According to Esper, these findings are "significant with regard to climate policy, as they will influence the way today's climate changes are seen in the context of historical warm periods." Sure, but how? More
Studies explore social and cultural consequences of extreme weather. June 26, 2012.
Two new studies in the journal Climatic Change explore relationships between extreme weather events and socio-cultural responses in early to mid-twentieth century Britain. Increasingly, projections of a warmer future and its ramifications have prompted interdisciplinary scholars to contribute the insights of ever more diverse disciplines to the quest for a better understanding of how life - especially human life - copes with climatic fluctuation. Consequently, the first article, by Mike Hulme of the University of East Anglia, considers how to make sense of climate in different disciplines by examining cultural responses to a heatwave that lingered over Norfolk in July, 1900. Hulme describes how the heatwave can be traced in three different worlds unlocked by three different disciplines: that which was imagined by contemporary author H.P. Hartley, that which was lived historically in Victorian Norfolk, and that which is quantified by climate scientists. More
Study refines how climatologists use past to predict future. June 17, 2012.
Global warming is understandable only in the context of the past. Without a record of temperatures in the recent past there would be no way to measure change in global temperatures; without historical evidence there would be no way to grasp how humans respond to climatic fluctuations; without an analysis of the (often) distant past there would be no way to develop the models that help predict the possible nature of a warmer climate. The Eemian Warm Period, a 10,000-year epoch that began about 125,000 years ago, is often used to design climatic models. With temperatures several degrees warmer than they are today, much of Greenland's ice sheet had melted, and Earth's sea level had risen substantially. Now, German scholars Henning Bauch, Evgeniya Kandiano and Jan Helmke have published an article in the journal Geophysical Research Letters that reveals a critical difference between the Eemian Warm Period and the hotter climate of the near future. More
Study reconstructs millennium of Australian climate. May 23, 2012.
A team of researchers under historical climatologist Joëlle Gergis has published a new article in the Journal of Climate that uses data from tree rings, ice cores, coral and 24 other natural indicators to reconstruct a millennium of Australian climatic history. The study, the Australasian region’s contribution to the fifth IPCC assessment report, collects and synthesizes the work of more than 30 scholars, conducted over many decades. Although plentiful records of past climatic fluctuations are available for the Northern Hemisphere over the past two millennia, the limited availability of long proxy records for the Southern Hemisphere has undermined attempts at global reconstructions. Uncertainty continues to surround how periods of prolonged warmth or cold, like the Medieval Climatic Anomaly (MCA, also called the Medieval Warm Period) or Little Ice Age (LIA), were expressed globally. Australian researchers have now revealed that a warmer climatic regime peaked in Australia just after its maximum in Europe, while demonstrating that Australia also experienced the cool weather of the Little Ice Age, even if its coldest periods were felt in different decades. The Australian record is part of the Past Global Changes Regional 2K (PAGES) initiative, which endeavours to reconstruct the past 2000 years of climatic fluctuation in every part of the world to minimize uncertainty in projections of global warming. Ultimately Gergis concludes that the study “revealed that recent warming [of 0.9 degrees Celsius since 1960] in a 1000 year context is highly unusual and cannot be explained by natural factors alone.” The full article can be found here.
Article links climatic shifts to smallpox in the Great Plains. May 8, 2012.
In the latest issue of Environmental History environmental historian Adam Hodge argues that the climatic fluctuations of the Little Ice Age affected the productivity of the Great Plains grasslands, bison populations and, in turn, how migratory Native American tribes experienced smallpox. Between 1780 and 1782 smallpox killed more than half of natives living in the Great Plains, with mortality rates rising to 80% in the crowded villages of the Mandans, Hidatsas and Arikaras. While the historical spread of Old World diseases through densely packed, largely sedentary New World settlements should come as no surprise, high mortality rates among migratory tribes with low, scattered populations is more baffling. Trade and warfare had carried smallpox to the Great Plains by 1780, but Hodge argues that to understand why smallpox ravaged migratory tribes we need to understand their relationships with the environment of the Northern Plains. Using scientific and documentary evidence Hodge reconstructs how the climate of the Little Ice Age and the increased incidence of La Nina events influenced the extraordinary variability of seasonal precipitation and temperature across the Great Plains from the late 1770s to the early 1780s. According to Hodge, by stressing bison numbers, diminishing herd sizes and changing migration patterns the unreliable weather stimulated starvation among migratory native tribes. Starved individuals searched more widely for food, and increased interactions between native groups encouraged the spread of smallpox. Meanwhile, starvation compromises immune systems, rendering many among the migratory tribes more vulnerable to the disease. Climatic fluctuations did not cause the smallpox epidemic of 1780-1782, but they did affect why, according to historian Walter Prescott Webb, “the buffalo and the Plains Indians lived together, and together passed away.”
Study: aerosol pollution delayed warming in Eastern US. April 26, 2012.
A team of scientists at the Harvard School of Engineering and Applied Sciences has discovered that particulate pollution over the eastern United States created a “warming hole” that delayed the onset of global warming in the late twentieth century. Unlike greenhouse gases, aerosol pollution has a very short lifespan, and its distribution across the earth is uneven. Until the Clean Air Act was passed in 1970 and strengthened in 1990, aerosol particles cloaked most of the central and eastern United States. Not only do aerosol particles reflect incoming sunlight, cooling surface temperatures, but they also act as nucleation sites for cloud droplets, exacerbating the cooling by reflecting even more light. The team, under lead author Eric Leibensperger, used pollution information derived from the GEOS-Chem model developed at Harvard, and compared it with climate data from NASA’s general circulation model (for a good book on modelling climate, see A Vast Machine by Paul Edwards). More
Are slave economies comparable to fossil fuel economies? April 15, 2012.
In a recent book, a paper in the journal Climatic Change, an article in The Guardian and another in Active History, historian Jean-François Mouhot of Georgetown University has popularized the idea that there are links between past slave societies and today's fossil fuel economies. Meanwhile, James Hansen, head of the NASA Goddard Institute for Space Studies, has recently received significant media attention for similarly suggesting that climate change is a moral issue on par with slavery. Mouhot is careful to admit that there are important differences between slave and fossil fuel economies: while slaves suffered directly, the human toll of global warming, while increasingly severe, is nevertheless indirect, removed from those who cause it. Then again, Mouhot concedes that the desire to injure or dehumanize hardly accompanies the burning of fossil fuels. More
Study: atmospheric CO2 change precedes temperature shift. April 4, 2012.
A team of researchers under Jeremy Shakun have published an article in the journal Nature that explores the relationship between atmospheric carbon dioxide and the world’s climate as the last great ice age came to an end. By looking at the distant past, the study reveals that the rise in carbon dioxide that accompanied this rapid shift slightly preceded increases in global temperature. “At the end of the last ice age, CO2 rose from about 180 parts per million (ppm) in the atmosphere to about 260; and today we’re at 392,” Shakun explained. “It’s not a small amount. Rising CO2 at the end of the ice age had a huge effect on global climate.” This finding appears to contradict an earlier article that relied on an analysis of Antarctic ice to conclude that changes in Antarctic temperatures actually preceded fluctuations in temperature. By suggesting that the link between changes in carbon dioxide concentrations were more loosely linked to shifts in global temperature, the study provided fodder for global warming sceptics. However, the new study’s more comprehensive analysis of the past, incorporating data from all over the world, undermines the hopeful findings of the previous article. By using sources from ice cores to plankton buried in sediment, Shakun’s team developed an explanation for both Antarctic and global records. Warming was first stimulated by the Milankovitch “wobble,” a minor shift in the nature of the Earth’s orbit around the sun that exposes the north to more sublight and triggered the collapse of major ice sheets. The torrents of fresh water that accompanied the melting of the hemisphere’s ice upset the North Atlantic’s ocean circulation, rebounding the heart welling up from the equator and warming the South. That triggered more changes to atmospheric and ocean circulation, releasing carbon dioxide from the Southern Ocean and, in turn, stimulating a sustained global rise in temperature that culminated in a much warmer climate. This critical and alarming study has received significant media attention, but it remains to be seen whether its findings will inspire changes to national and global environmental policies.
Past and future climates of the Near East and Europe. March 23, 2012.
A team of researchers led by J. Lelieveld has published a study in the latest issue of Climatic Change that compares Intergovernmental Panel on Climate Change (IPCC) projections of the late twenty-first century climate in the Near East and Eastern Europe with 500-year records of its climatic past. By comparing these different datasets the study concludes that a gradual warming of 3.5-7 degrees Celsius is probable in the century between 1961-1990 and 2070-2099. Lelieveld and his fellow scholars acknowledge that the region is diverse, but with extreme climatic events already common the influence of a warmer climate will likely be especially severe. Daytime maximum temperatures will probably increase most rapidly in the northern periphery of the region, with hot summers that were extreme in the historical record becoming the norm by the conclusion of the twenty-first century. The study describes how precipitation in most seasons will likely decrease in southern Europe, while it may increase in the Arabian Gulf. Lelieveld and the other co-authors conclude that the climatic changes anticipated in the coming century will exacerbate heat stress, particularly in urban areas, while increasing shortages of fresh water in the Levant. Ultimately the article reveals with particular clarity how the consideration of climates undertaken by historical climatologists relates to a better understanding of a warmer future.
Key global temperature record updated. March 20, 2012.
As published in the Journal of Geophysical Research, a team of scientists led by Colin Morice have updated HadCRUT, one of the three major global temperature records used by climatologists. Compiled by the Hadley Centre of the UK Met Office and the Climatic Research Unit at the University of East Anglia, HadCRUT dates back to 1850 and relies on direct observation. Although the previous version was plagued by a lack of Arctic sources, the new record fills that gap by using observations from over observation stations across the rapidly warming Arctic. Meanwhile, the more accurate electronic sensors ships now use to detect sea surface temperature revealed a systematic anomaly in the way data was collected in the past. Differences in buckets used aboard ships and variations in the locations where data was collected have were corrected as scientists recalculated the older data. However, while HadCRUT is now more accurate and more comprehensive than ever before, the bottom line remains unchanged. As described on BBC News, the new version agrees with the old in recording a warming of 0.75C (1.4F) since 1900.
Henry Thoreau's journals reveal consequences of global warming. March 14, 2012.
Richard Primack, a biologist at Boston University, has used the journals of Henry David Thoreau and another naturalist to reconstruct the flowering dates of common plant species in mid to late nineteenth century Massachusetts. Primack compared these records to today's flowering patterns in an article published in the February 2012 issue of the journal BioScience, arguing that 43 species now flower an average of 7 days earlier than they did in Thoreau's time. Thoreau wrote just after the conclusion of the Little Ice Age; since then temperatures have risen by 2.4 degrees Celsius in urban areas like metropolitan Boston, which includes Thoreau's Concord. While some species are capable of changing their flowering times in response to the shifting climate, their less flexible counterparts are vanishing from Massachusetts. In fact, Thoreau described some 21 different species of orchid, and just 6 remain today. "What that result tells us is climate change is not only affecting flowering time but also affecting the abundance of species in Concord," Primack concluded. "Warming temperature is causing some species to be winners and some species to be losers." Primack's study has received significant media attention, part of an ongoing surge in the profile of work related to historical climatology. One of the most fascinating aspects of that media attention: the reference to volunteers tracking seasonal events for the USA National Phenological Network, whose efforts may corroborate some Primack's claims regarding early flowering times in today's Massachusetts. Crunching numbers is often an important part of both scientific and historical research; outsourcing that work to eager volunteers on the internet offers some very exciting possibilities for future study.
Historical climatology's expanding media profile. March 2, 2012.
A new article by Richard Black of BBC News examines the development of the discipline of historical climatology “in the last couple of decades” by exploring how a team under Fernando Dominguez-Castro is reconstructing the weather of ancient Baghdad. The article describes some of the methodologies used by historical climatologists, and mentions sources from ship logbooks to parish ledgers of grape harvests. In recent years journalists from outlets like BBC news or The Guardian have devoted considerable attention to studies relevant to historical climatology, and it is encouraging to see that the workings of the discipline and the kind of work undertaken by its scholars have begun to find a voice in the mainstream media.
Is volcanism sufficient to explain the onset of the Little Ice Age? January 31, 2012.
As has been documented on this website, two important questions have inspired interdisciplinary debates about the origin of the Little Ice Age. The first: when did it begin? The second: why did it endure for so long? Now an important new study purports to answer both questions. Publishing in the journal Geophysical Research Letters, a team under Gifford Miller have used vegetation entombed by expanding ice sheets to argue that increased volcanism was the primary culprit behind a global cooling between 1250 and 1300. That argument has been made before, but as the study authors admit explosive volcanoes, by releasing aerosol particles into the atmosphere, usually only cool the world's climate for a few years. Hence, they have been considered insufficient to explain the longevity of the Little Ice Age. However, Miller and his fellow researchers have used a transient climate model to reveal that at a time when Earth’s orbit stimulated low summer insolation across the Northern Hemisphere the initial 50-year episode of four sulphur-rich volcanic eruptions was sufficient to dramatically expand ice cap growth. Increased ice reflected more sunlight into space and weakened the Atlantic Gulf Stream, allowing colder temperatures to endure long after the volcanic eruptions ended. Unmentioned in most media reports: the authors do acknowledge that reduced solar radiation exacerbated the effects of volcanism, but conclude that a Little Ice Age would have occurred regardless of solar activity.
La Nina events may increase the likelihood of flu pandemics. January 17, 2012.
A new study in Proceedings of the National Academy of Sciences has uncovered that the migratory patterns of flu-carrying birds are susceptible to changes in the surface temperature of the eastern Pacific stimulated by La Nina events. Researchers examined the Spanish Flu beginning in 1918, the Asian Flu in 1957, the Hong Kong Flu of 1958 and the swine flu in 2009, revealing that all were preceded by La Nina events. These pandemics all featured new strains of the influenza virus to which people had not developed immunity, which typically emerge when existing strains exchange genetic material. There is no obvious or direct link to La Nina conditions, which are a regularly recurring feature of Earth's climate that does not necessary coincide with flu pandemics. Nevertheless, previous research has demonstrated that patterns of flights and stopovers in the migrations of some wild birds change between El Nino and La Nina years, suggesting that birds that usually don't mix can be brought together during La nina conditions, facilitating genetic exchange and, in turn, a devastating flu pandemic. Media articlesgenerated by the study have emphasized how the research lists La Nina conditions as just one possible influence behind the development of new pandemics. With so many scientific articles arguing for direct, unproblematic connections between, for example, warfare and climatic fluctuation, the more nuanced and more realistic approach of this paper and, even more remarkably, the media coverage it has received offers some hope.
NASA/Caltech computer model predicts dramatic changes to Earth's ecosystem by 2100. December 23, 2011.
Credit: NASA/JPL-Caltech
A new computer model developed by a team of scientists under Jon Bergengren and published in the journal Climatic Change has suggested that by 2100 a warmer climate will influence change in plant communities covering nearly half the world's surface, while driving 40% from one major ecological type to another. Overall, biomes will likely migrate towards the poles and higher elevations. The study, which has received significant media attention, also predicts that the severing of ties between closely connected and often endangered plant and animal seasons will lower biodiversity and change Earth's natural cycles. The model employs the intermediate scenario described by the IPCC Fourth Assessment Report, which initial returns suggest has dramatically understated the future emissions of greenhouse gases. Of course, the essential weakness of these models rests in their inability to accommodate for changes in vegetation driven by other human activities. Furthermore, what is needed is a better understanding of how changes vegetation have accompanied climatic fluctuations in the past. When examining the influence of climatic changes historical climatologists generally explore relationships between human populations and prevailing weather, and shifts in flora or fauna are considered either for their influence on human beings or their ability to provide further insight into atmospheric developments. If changes in plant and animal life were considered important in their own right - and worthy of the kind of interdisciplinary insights historical climatologists can provide - our ability to model or, at least, conceptualize the future could be much improved.
Has climate's sensitivity to CO2 been overestimated? November 25, 2011.
Rendering by Thomas J. Crowley, 2010.
A new study published in the journal Science by lead author Andreas Schmittner has used paleoscientific data to argue that the last Ice Age was not as cold as previously thought. That, in turn, suggests that global temperatures are less directly linked to atmospheric carbon dioxide than previously believed. The article, which has received extensive media attention, claims that a doubling of atmospheric carbon dioxide from pre-industrial levels would lead to a rise in the world's temperature of 1.7-2.6 degrees Celsius. In another article published in the same issue of Science Gabriele Hegerl and Tom Russon caution that Schmittner and his fellow researchers have developed just one model, and further research is required to support their results. As reported by the BBC, Climatologist Andrey Ganopolski also cautioned against reading those results as definitive, warning that the relationship between carbon dioxide and global temperatures is probably different during colder periods than in warmer decades. Ultimately, it is difficult to know what to make of these results. The idea of "using the past to predict the future," as Hegerl and Russon put it, is doubtless appealing to many historical climatologists, but the notion of unproblematically linking past temperatures to past CO2 concentrations seems simplistic when so many possible climatic stimuli exist. At first glance it seems better to use sources from both cooler and warmer periods in the less distant past that can also be supplemented with documentary evidence. Meanwhile, although the authors contend that their study does not reduce the need for urgent action to mitigate global warming they do claim that their results suggest a "lower probability of imminent extreme climatic change than previously thought." That attitude is worrisome given the upheaval the accompanied, for example, the most extreme phases of the Little Ice Age - when temperatures probably did not drop as much as 2 degrees Celsius below their previous average - and the sensitivity of modern agriculture to climatic fluctuations. Either way it's telling that the first scientific assessment to uncover links between modern extreme weather events and global warming - also described in the latest issue of Science - has not received nearly as much press.
Global warming, changing winds, and a cooler Europe? November 22, 2011.
A new paper by S.D. Outten and I. Esau in the latest issue of the journal Climatic Change has supported recent studies suggesting that the rapid melting of polar ice, caused by the warming of the Arctic, can cause a decrease in zonal wind over Europe. By funnelling warmth from the Atlantic, persistent westerly winds are largely responsible for Europe's relatively mild climate. Hence, decreased zonal wind stimulated by global warming can actually cause the continent to cool. The world's temperatures are rising - indeed "global warming" remains a better term to describe the current climatic crisis than "climate change" - but Outten and Esau have highlighted how the new climatic regime of the coming century will mean different things for different societies. By uncovering links between changing patterns of prevailing wind and climatic fluctuations, the study also has potentially important ramifications for researchers exploring relationships between human and climatic histories.
Wind currents linked to Kawasaki Disease. November 12, 2011.
Kawasaki Disease is a childhood disease that is most common in Japan and can result in irreversible heart damage. Although the seasonal nature of the disease in Japan and other regions has long been understood, the reasons for changes in the spread of KD have remained shrouded in mystery. Now a team of researchers compiled by Jane Burns has published a paper in Nature Scientific Reports and received widespread media attention by revealing how fluctuations in the number of KD cases accompany shifts in patterns of prevailing wind. Climatologist Xavier Rodó, the study's first author, claims that, "the Japanese dataset revealed that a low number of KD cases were reported prior to the epidemics, a period coinciding with winds from the south which blew across Japan from the Pacific Ocean during the summer months." However, "the numbers rapidly mounted all over Japan when winds turned and blew from the northwest, a trajectory from the Asian continent. After the peaks, the winds again shifted, blowing from the south when the number of cases again decreased." These findings suggest an infectious agent is carried across the ocean by air currents in the upper troposphere, and offer hope for isolating the cause of the disease. The study also suggests new possibilities for students of the relationship between climate changes and human history, because shifts in wind currents have been associated with climatic fluctuations past and present. The need for research into changes in wind patterns - an important aspect of my own work - has never been more pressing.
Climate change, economic fluctuations, and warfare. November 1, 2011.
The latest issue of the Proceedings of the National Academy of Sciences contains an article that appears to link climatic fluctuations with European "golden" and "dark" ages in the early modern period. According to the authors, climatic cooling directly causes economic decline, which, in turn, leads to warfare, turbulence and, supposedly, "darkness." In reality, it's articles like these that highlight the need for interdisciplinary cooperation in all areas of climate research, perhaps especially those that look into the past. As described by historian Sam White, the article never actually explains exactly how these connections work, precisely because it uses methodology that historical climatologists abandoned decades ago. Climate never directly causes human history, because climatic fluctuations are only one complicated influence among the many that colour the relationship between human societies and their environment. That understanding, vital to historical climatology, is also important as we consider our warmer future. Conflict may intensify in the coming century not because a hotter climate determines it, but because many economic, political and cultural structures in today's world contribute to global warming while exacerbating its most problematic influences.
Does anthropogenic climate change precede global warming? October 18, 2011.
In a recent article in The Holocene and a subsequent paper given at this month’s Geological Society of America meeting, Richard Nevle presented evidence that apparently links the reforestation of the Americas following the European conquest of the New World with a reduction in atmospheric carbon dioxide and, ultimately, the coldest centuries of the Little Ice Age. Nevle’s work appears to support the general conclusions of William Ruddiman, who in 2003 argued that human beings have altered the world’s climate for millennia, largely through forest clearing. It’s worth noting that the warmer climatic regime that directly preceded the Little Ice Age waxed during an era of European deforestation, and that today’s climate is rapidly heating as forests in the southern hemisphere continue to shrink. Beyond the questions it raises within historical climatology and environmental history, the work of Nevle and Ruddiman is important for challenging the idea, so often raised by global warming skeptics, that humanity is incapable of altering the world's climate. Perhaps human beings, even in relatively modest numbers and well before the advent of industrialization, unwittingly changed the world’s environment on the grandest scale.
Global Warming to cost arctic countries? October 2, 2011.
A few years ago the CIA world factbook projected a surge in Russia's agricultural production in the warmer decades to come. Like many others, the CIA's analysts apparently assumed that in arctic countries warmer temperatures translated to a general expansion in arable land. Coupled with the arctic resources unlocked by thawing ice, in economic terms Canada, Russia and Greenland stood to gain far more than they lost under the new climatic regime. Now the National Roundtable on the Environment and the Economy, a government-backed Canadian initiative, has released a lengthy report that argues the opposite. In fact, the NRTEE projects that the death of forests, flooding of low-lying regions and spread of disease it associates with global warming could cost Canada some 2.5% of its GDP by 2075. Interestingly the NRTEE members include few academic representatives, among them no environmental historians, who might have corrected sentences like "climate change will lead to warmer summers and poorer air quality, resulting in increased deaths and illnesses." (17) Either way, as a historical climatologist I study the rise of the Dutch Republic - the world's first capitalist economy - during a period of pronounced climatic cooling and general European decline. Its counterintuitive growth - founded as much on trade and financial innovation as fishing or an evolving agriculture - might suggest that countries whose economies rely on natural resources could be more susceptible to periods of climatic transition.
Weather and tropical warfare: September 23, 2011.
As my colleague Sam White recently reported through the Climate History Network, a recent article in Nature reveals that from 1950 to 2004 conflict in the tropics was twice as common during El Niño years as it was in La Niña years. The authors - an interdisciplinary team from Columbia University's Earth Institute - even suggest that El Niño, which reduces rainfall and increases temperatures every 3-7 years, might account for a fifth of all global conflict. Their statistical work - while important - nevertheless reveals the importance of a truly interdisciplinary approach to the study of the relationship between climate, weather and human history. Long-since discarded by historical climatologists, the idea that any atmospheric event determines the course of human history continually threatens to not only marginalize the work of scholars examining climate's past, but to undermine projections of our future on a warmer planet. It is far more useful to conceive of any environmental structure as narrowing or expanding the range of human action, rather than causing those actions to happen.
