Climate change may be one of the most significant threats facing humankind. A new study shows that long-term climate change may ultimately lead to wars and population decline.
By Abby Vogel for Newswise
The study, published November 19 in the early edition of the journal Proceedings of the National Academy of Sciences (PNAS), revealed that as temperatures decreased centuries ago during a period called the Little Ice Age, the number of wars increased, famine occurred and the population declined.
Data on past climates may help accurately predict and design strategies for future large and persistent climate changes, but acknowledging the historic social impact of these severe events is an important step toward that goal, according to the study’s authors.
“Even though temperatures are increasing now, the same resulting conflicts may occur since we still greatly depend on the land as our food source,” said Peter Brecke, associate professor in the Georgia Institute of Technology’s Sam Nunn School of International Affairs and co-author of the study.
This new study expands previous work by David Zhang of the University of Hong Kong and lead author of the study.
“My previous research just focused on Eastern China. This current study covers a much larger spatial area and the conclusions from the current research could be considered general principles,” said Zhang.
Brecke, Zhang and colleagues in Hong Kong, China and the United Kingdom perceived a possible connection between temperature change and wars because changes in climate affect water supplies, growing seasons and land fertility, prompting food shortages. These shortages could lead to conflict – local uprisings, government destabilization and invasions from neighboring regions – and population decline due to bloodshed during the wars and starvation.
To study whether changes in temperature affected the number of wars, the researchers examined the time period between 1400 and 1900. This period recorded the lowest average global temperatures around 1450, 1650 and 1820, each separated by slight warming intervals.
The researchers collected war data from multiple sources, including a database of 4,500 wars worldwide that Brecke began developing in 1995 with funding from the U.S. Institute of Peace. They also used climate change records that paleoclimatologists reconstructed by consulting historical documents and examining indicators of temperature change like tree rings, as well as oxygen isotopes in ice cores and coral skeletons.
Results showed a cyclic pattern of turbulent periods when temperatures were low followed by tranquil ones when temperatures were higher. The number of wars per year worldwide during cold centuries was almost twice that of the mild 18th century.
The study also showed population declines following each high war peak, according to population data Brecke assembled. The population growth rate of the Northern Hemisphere was elevated from 1400-1600, despite a short cooling period beginning in the middle of the 15th century. However, during the colder 17th century, Europe and Asia experienced more wars of great magnitude and population declines.
In China, the population plummeted 43 percent between 1620 and 1650. Then, a dramatic increase in population occurred from 1650 until a cooling period beginning in 1800 caused a worldwide demographic shock.
The researchers examined whether these average temperature differences of less than one degree Celsius were enough to cause food shortages. By assuming that agricultural production decreases triggered price increases, they showed that when grain prices reached a certain level, wars erupted. The ecological stress on agricultural production triggered by climate change did in fact induce population shrinkages, according to Brecke.
Global temperatures are expected to rise in the future and the world’s growing population may be unable to adequately adapt to the ecological changes, according to Brecke.
“The warmer temperatures are probably good for a while, but beyond some level plants will be stressed,” explained Brecke. “With more droughts and a rapidly growing population, it is going to get harder and harder to provide food for everyone and thus we should not be surprised to see more instances of starvation and probably more cases of hungry people clashing over scarce food and water.”
Climate Change Can Spark War
Andrea Thompson, LiveScience, Yahoo News 22 Nov 07;
History may be bound to repeat itself as Earth’s climate continues to warm, with changing temperatures causing food shortages that lead to wars and population declines, according to a new study that builds on earlier work.
The previous study, by David Zhang of the University of Hong Kong, found that swings in temperature were correlated with times of war in Eastern China between 1000 and 1911. Zhang's newer work, detailed in the Nov. 19 online edition of the journal Proceedings of the National Academy of Sciences, broadens its outlook to climate and war records worldwide and also found a correlation between the two.
"This current study covers a much larger spatial area and the conclusions from the current research could be considered general principles," Zhang said.
The research does not represent direct cause-and-effect, but rather suggests a link between climate and conflict.
Looking to the past
Because water supplies, growing seasons and land fertility can be affected by changes in climate, they might prompt food shortages that could in turn lead to conflicts, such as local uprisings, government destabilization and invasions from neighboring regions, the researchers speculate. These conflicts and the food shortages that cause them could both contribute to population declines, they add.
To see whether changes in climate affected the number of wars fought in the past, the researchers examined the time period between 1400 and 1900, when global average temperatures reached extreme lows around 1450, 1640 and 1820, with slightly warmer periods in between.
Using records reflected in tree rings and ice cores, the researchers compared temperature changes to a database of 4,500 wars worldwide that co-author Peter Brecke of Georgia Tech compiled with funding from the U.S. Institute of Peace.
The results of the comparison showed a cyclic pattern of turbulent periods when temperatures were low, followed by more tranquil times when temperatures were higher.
This correlation doesn't necessarily mean that all-out war is imminent, William Easterling of Pennsylvania State University, who was not affiliated with the work, had said in regards to Zhang's earlier work. However, the changing distribution of resources could certainly increase international tensions, he added.
The new study also showed population declines following each war peak. Specifically, during the frigid 17th century, Europe and Asia experienced more wars of great magnitude and population declines than in more temperate times.
Projecting into the future
To connect temperature changes of less than 1 degree Celsius (1.8 degrees Fahrenheit) to food shortages, the authors used price increases as a measure of decreases in agricultural production and found that when grain prices reached a certain level, wars erupted.
Though these historical periods of climate change featured cooler temperatures, current rising global temperatures could still cause ecological stress that damages agricultural production.
"Even though temperatures are increasing now, the same resulting conflicts may occur since we still greatly depend on the land as our food source," Brecke said.
"The warmer temperatures are probably good for a while, but beyond some level, plants will be stressed," Brecke explained. "With more droughts and a rapidly growing population, it is going to get harder and harder to provide food for everyone, and thus we should not be surprised to see more instances of starvation and probably more cases of hungry people clashing over scarce food and water."
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