by Judith Curry
[A] key message within Gore’s Climate Reality Project was that our recent strange weather and accompanying social problems are inextricably linked to the climate crisis. And say what you will about Gore, that part seems increasingly true. What’s more, there’s nothing new about such cause-and-effect. According to a new study, climate change has played a significant role in several of the crises of pre-industrial Europe and the rest of the Northern Hemisphere over the course of the 300 years.
Ecocentric blogs at Time has an article entitled”Climate Change Caused Crises Half a Millennium Ago, Too.” Some excerpts:
A team led by David Zhang of the University of Hong Kong collected as much data as they could find about climate, demography, agro-ecology, and the economy from the years 1500 to 1800 in Europe and found that these variables yo-yoed up and down along with the weather.
While numerous civilizations did experience the same ups and downs as global temperature over the centuries, the immediacy of the cause and effect varied. Sometimes the response to temperature change was almost instantaneous, while others time it took five to 30 years before the impact was fully felt. And as is the case with everything in the environment, a change in one area often triggered a cascade of changes in others. Take for example the cooling that occurred from 1560 to 1660—a century within the 300-year era known as the Little Ice Age: plants couldn’t grow as much or for as long, so grain prices soared, famine broke out, and nutrition sank. Poor diet means poor growth even for survivors, and the late 16th century saw a decline in average human body height by 0.8 inches. As temperatures rose again after 1650, human height crawled back up too. Before it did, however, sky-high grain prices and accompanying real wage declines brought social problems more pressing than height.
“Peaks of social disturbance such as rebellions, revolutions, and political reforms followed every decline of temperature, with a one- to 15-year time lag,” the scientists wrote, adding that many such disturbances escalated into armed conflicts. “The number of wars increased by 41% in the Cold Phase.”
There were more peaceable responses too. Poorly fed or otherwise deprived people tend to decamp from where they’re living and move somewhere else, and migration rates increased in this era along with social disturbance. The problem was, in these cases the relocation wasn’t the hearty westward-ho kind of 19th century America, when well-fed settlers could live off the land (and the buffalo) while they sought new homesteads on the frontiers. Rather, migration among the hungry or unwell often leads to epidemics. It may be too much to lay the great European plagues of 1550 to 1670 entirely at the door of global cooling, but dramatic climate shift and resultant poor health surely played a role. It was around 1650 as well that European population collapsed, bottoming out at just 105 million people across the entire continent. Wetter countries with more fertile land or those with stable trading economies tended to do better in this eras of hardship, but no one was spared.
Discovery News has a related article with the creative title “Climate change caused angry runts.” Some excerpts:
“Our findings indicate that climate change was the ultimate cause, and climate-driven economic downturn was the direct cause, of large-scale human crises in preindustrial Europe and the Northern Hemisphere,” wrote the researchers, led by David Zhang of the University of Hong Kong, in the Proceedings of the National Academy of Sciences.
Between 1500 and 1800, every change in average temperatures correlated to a change in agricultural output and food supply. The climate changes did not result in immediate changes in population growth, so even in a cold year with poor harvests, the population kept going up. More mouths to feed with less grain meant a rise in food prices and starvation.
“Peaks of social disturbance such as rebellions, revolutions, and political reforms followed every decline of temperature, with a 1- to 15-year time lag,” reported the researchers.
As the civilizations of Europe developed new technologies and began conquering and colonizing the Western Hemisphere, the health effects of climate changes became less pronounced.
According to Zhang and his colleagues, “The mild cooling in Europe in the late 18th and 19th centuries brought about an upsurge in prices, social disturbance, war, and migration but not demographic crisis, because of social buffers such as cross-continental migration, trade, and industrialization.”
The researchers concluded that the economic downturns caused by climate change were the direct causes of the human crises. When a country’s economy and agricultural output didn’t suffer, their populations didn’t either.
“This result explains why some countries did not undergo serious human crisis in the Little Ice Age: Wet tropical countries with high land-carrying capacity or countries with trading economies did not suffer a considerable shrinkage in food supply, nor did some countries, such as New World countries with vast arable land and sparse populations, experience substantial supply shortage,” the researchers reported.
Wired Science article
I just spotted aother orticle that is worth reading on this, at Wired Science, entitled “Climate Shifts Sparked 17th Century Conflicts.” Some critiques of the work:
Halvard Buhaug, a political scientist at Peace Research Institute Oslo, calls the research “good work with a lot of good data.” But he adds that it was “really surprising” and “unfortunate” that the authors didn’t discuss whether the findings continued to apply in the industrial period, when trade, technological development, and other processes have made societies less sensitive to the climate. It remains unclear, he says, whether this research is relevant for the present day, when humans are facing a period of rapid temperature changes.
The claim that this kind of analysis can pin down climate as the root of human history, particularly when the researchers examine long periods at a time, is “pretty hard to swallow for a historian,” says William Atwell, a historian at Hobart and William Smith Colleges in Geneva, New York. The authors, he says, ignore the effects of religion, trade, and other factors. For instance, during the “Little Ice Age” of 1500 to 1559, North American natives were dying en masse from diseases imported from the Old World, leading partly to the start of the African slave trade which, he argues, affected human history in a major way unrelated to climate shifts. “Not that [the researchers] don’t have interesting things to say,” he says, “but they’re attempting to be too precise” by putting dates and numbers on conflicts.
Paleoclimatologist Sebastian Wagner of Helmholtz Zentrum Geesthacht in Germany agrees that the time frames are too broad but for a different reason. The researchers prepared the data for analysis by “smoothing” it into 40-year chunks that, he says, could alter the significance level of the statistics. Additionally, he says, the paper looked only at temperature, not at other factors, such as changes in rainfall, that can drastically influence human society.
Here are several of David Zhang‘s papers, the first one is the trigger for the news item:
The causality analysis of climate change and large-scale human crisis
David D. Zhang, Harry F. Lee, Cong Wang, Baosheng Li, Qing Pei, Jane Zhang, Yulun An
Abstract. Recent studies have shown strong temporal correlations between past climate changes and societal crises. However, the specific causal mechanisms underlying this relation have not been addressed. We explored quantitative responses of 14 fine-grained agro-ecological, socioeconomic, and demographic variables to climate fluctuations from A.D. 1500–1800 in Europe. Results show that cooling from A.D. 1560–1660 caused successive agro-ecological, socioeconomic, and demographic catastrophes, leading to the General Crisis of the Seventeenth Century. We identified a set of causal linkages between climate change and human crisis. Using temperature data and climate-driven economic variables, we simulated the alternation of defined “golden” and “dark” ages in Europe and the Northern Hemisphere during the past millennium. Our findings indicate that climate change was the ultimate cause, and climate-driven economic downturn was the direct cause, of large-scale human crises in preindustrial Europe and the Northern Hemisphere.
Published online before printOctober 3, 2011, doi:10.1073/pnas.1104268108. Link to full paper [here}.
Global climate change, war, and population decline in recent human history
David D. Zhang, Peter Brecke, Harry F. Lee, Yuan-Qing He, Jane Zhang
Abstract. Although scientists have warned of possible social perils resulting from climate change, the impacts of long-term climate change on social unrest and population collapse have not been quantitatively investigated. In this study, high-resolution paleo-climatic data have been used to explore at a macroscale the effects of climate change on the outbreak of war and population decline in the preindustrial era. We show that long-term fluctuations of war frequency and population changes followed the cycles of temperature change. Further analyses show that cooling impeded agricultural production, which brought about a series of serious social problems, including price inflation, then successively war outbreak, famine, and population decline successively. The findings suggest that worldwide and synchronistic war–peace, population, and price cycles in recent centuries have been driven mainly by long-term climate change. The findings also imply that social mechanisms that might mitigate the impact of climate change were not significantly effective during the study period. Climate change may thus have played a more important role and imposed a wider ranging effect on human civilization than has so far been suggested. Findings of this research may lend an additional dimension to the classic concepts of Malthusianism and Darwinism.
PNAS December 4, 2007 vol. 104 no. 49 19214-19219, link to full paper [here].
Climate change and large scale human population collapses in the pre-industrial era.
Zhang, D.D., Lee, H.F., Wang, C., Li, B., Zhang, J., and Chen, J. (2010)
Aim It has long been assumed that deteriorating climate (cooling and warming above the norm) could shrink the carrying capacity of agrarian lands, depriving the human population of sufficient food. Population collapses (i.e. negative population growth) follow. However, this human–ecological relationship has rarely been verified scientifically, and evidence of warming-caused disaster has never been found. This research sought to explore quantitatively the temporal pattern, spatial pattern and triggers of population collapses in relation to climate change at the global scale over 1100 years.
Location Various countries/regions in the Northern Hemisphere (NH) during the pre-industrial era.
Methods We performed time-series analysis to examine the association between temperature change and country-wide/region-wide population collapses in different climatic zones. All of the known population collapse incidents in the NH in the period ce 800–1900 were included in our data analysis.
Results Nearly 90% of population collapses in various NH countries/regions occurred during periods of climate deterioration characterized by shrinking carrying capacity of the land. In addition, we found that cooling dampened the human ecosystem and brought about 80% of the collapses in warmer humid, cooler humid and dry zones, while warming adversely affected the ecosystems in dry and tropical humid zones. All of the population collapses and growth declines in periods of warm climate occurred in dry and tropical humid zones. Malthusian checks (famines, wars and epidemics) were the dominant triggers of population collapses, which peaked dramatically when climate deteriorated.
Main conclusions Global demographic catastrophes and most population collapse incidents occurred in periods with great climate change, owing to overpopulation caused by diminished carrying capacity of the land and the resultant outbreak of Malthusian checks. Impacts of cooling or warming on land carrying capacity varied geographically, as a result of the diversified ecosystems in different parts of the Earth. The observed climate–population synchrony challenges Malthusian theory and demonstrates that it is not population growth alone but climate-induced subsistence shortage and population growth working synergistically, that cause large-scale human population collapses on the long-term scale.
Global Ecology and Biogeography. Oxford: Blackwell Science. DOI:10.1111/j.1466-8238.2010.00625x. [Link] to abstract.
JC comments: this is the first time I have come across David Zhang’s research, which addresses some very interesting links between climate, weather and society. I was particularly interested in the assessment of the role that vulnerability played in the climate-society: “When a country’s economy and agricultural output didn’t suffer, their populations didn’t either.”