Wednesday, August 21, 2013 8:14:08 AM
Warming climate drives human conflict
Conflicts among cattle-herding ethnic groups in east Africa can be linked to climate change.
UNICEF/GEORGINA CRANSTO/epa/Corbis
Temperature and rainfall extremes linked to more frequent feuds and wars.
Lauren Morello
01 August 2013
Tempers flare as temperatures rise — across the globe and throughout human history, researchers have found. The result is consistent with a growing body of research suggesting that climate change somehow incites human conflict.
Small changes in temperature and rainfall substantially raise the risk of conflict of many types, from interpersonal spats — such as aggressive horn-honking by automobile drivers — to full-blown civil war and societal collapse, researchers report today in Science1. They reviewed data from 60 studies on environmental change and human aggression that spanned six continents and more than 12,000 years.
The researchers found that a temperature rise of one standard deviation — which, in the United States today, occurs when the average temperature for a given month is about 3° Celsius higher than usual — increases the frequency of interpersonal violence by 4%, and the risk of intergroup conflict, such as civil war or rioting, by 14%.
Floods and drought also have an effect, although it is smaller than that of temperature, the researchers report. And the effects are apparent worldwide, in developed and developing countries.
“The level of consistency in how people are responding was surprising to us,” says Solomon Hsiang, an econometrician at the University of California Berkeley, who led the study. He and his team warn that climate’s influence on behaviour is likely to become more apparent as the planet warms and precipitation patterns change.
The researchers did not attempt to explain how climate exerts its apparent influence on human behaviour. They linked climate extremes to many types of conflict, from the fall of the fractious Classic Maya empire in the ninth century, to professional baseball pitchers purposely hitting opposing batters with balls. But the lack of causal mechanisms leaves many political scientists sceptical about the environment’s role in conflicts, which they say are driven by a complex array of social factors.
“It’s hard to see how the same causal mechanism that would lead to wild pitches would be linked to war and state collapse,” says Idean Salehyan, who studies political violence at the University of North Texas in Denton.
Similarly, Halvard Buhaug, a political scientist at the Peace Research Institute Oslo in Norway, says that the latest study does little to sway his belief that the climate–conflict link is weak and inconsistent. He has found that major conflicts in Africa have declined over the past few decades, despite noticeable warming there2, 3 — bucking the trend sketched in the latest study and in earlier, similar studies4, 5.
The contradictory results point to the need for researchers to test the links between climate and conflict in case studies where more variables can be tracked, says Andrew Solow, an environmental statistician at the Woods Hole Oceanographic Institution in Massachusetts.
Without that focus, he warns, researchers may unintentionally exaggerate the climate–conflict relationship by tweaking the definition or historical bounds of a conflict. “In the aggregate, if you work the data very hard, you do find relationships like this,” he says. “But when you take a closer look, things tend to be more complicated.”
Nature
doi:10.1038/nature.2013.13464
*
References
1. Hsiang, S. M., Burke, M. & Miguel, E., Quantifying the Influence of Climate on Human Conflict, Science [ http://dx.doi.org/10.1126/science.1235367 ] (2013).
http://www.sciencemag.org/content/early/2013/07/31/science.1235367
2. Buhaug, Reply to Burke et al.: Bias and climate war research, H. Proc. Natl. Acad. Sci. USA 107, E186–E187 [ http://dx.doi.org/10.1073/pnas.1015796108 ] (2010).
http://www.pnas.org/content/107/51/E186
3. Theisen, O. M., Holtermann, H. & Buhaug, Climate Wars? Assessing the Claim That Drought Breeds Conflict, H. Int. Secur. 36, 79–106 [ http://dx.doi.org/10.1162/ISEC_a_00065 ] (2011).
http://www.mitpressjournals.org/doi/abs/10.1162/ISEC_a_00065
4. Hsiang, S. M. , Meng, K. C. & Cane, M. A., Civil conflicts are associated with the global climate, Nature 476, 438–441 [ http://dx.doi.org/10.1038/nature10311 ] (2011).
http://www.nature.com/nature/journal/v476/n7361/full/nature10311.html
5. O'Loughlin, J. et al., Climate variability and conflict risk in East Africa, 1990–2009, Proc. Natl. Acad. Sci. USA 109, 18344–18349 [ http://dx.doi.org/10.1073/pnas.1205130109 ] (2012).
http://www.pnas.org/content/109/45/18344
*
Related stories and links
From nature.com
Global warming: A call for peace on climate and conflict
08 May 2013 [ http://www.nature.com/doifinder/10.1038/497179a ]
http://www.nature.com/nature/journal/v497/n7448/full/497179a.html
Climate cycles drive civil war
24 August 2011 [ http://www.nature.com/doifinder/10.1038/news.2011.501 ]
http://www.nature.com/news/2011/110824/full/news.2011.501.html
'Climate wars' claims disputed
08 September 2010 [ http://www.nature.com/doifinder/10.1038/467145a ]
http://www.nature.com/news/2010/100908/full/467145a.html
Darfur's climate roots challenged
27 June 2007 [ http://www.nature.com/doifinder/10.1038/4471038b ]
http://www.nature.com/nature/journal/v447/n7148/full/4471038b.html
Climate change 'could lead to conflict with Russia'
10 Mar 2008
http://blogs.nature.com/news/2008/03/climate_change_could_lead_to_c.html
From elsewhere
Solomon Hsiang
http://www.solomonhsiang.com/
Halvard Buhaug
http://www.prio.no/People/Person/?x=3497
Idean Salehyan
http://idean.salehyan.com/
Andrew Solow
http://www.whoi.edu/profile.do?id=asolow
*
© 2013 Nature Publishing Group, a division of Macmillan Publishers Limited
http://www.nature.com/news/warming-climate-drives-human-conflict-1.13464 [with comment]
--
Hotter Weather Actually Makes Us Want to Kill Each Other
Wikimedia Commons
A new meta-analysis finds that extreme changes in temperature increase the likelihood of inter-group conflict.
Olga Khazan
Aug 1 2013, 2:00 PM ET
Farmers in Brazil are more likely to invade each others' land in years that are particularly wet or unusually dry. Americans honk their horns more at other cars when it's hot outside. Countries in the tropics are more likely to have civil wars in years that are especially hot or dry.
They may seem random, but actually, these events are all connected. New research from Princeton University and UC Berkeley published today in Science [ Hsiang, S. M., Burke, M. & Miguel, E., Quantifying the Influence of Climate on Human Conflict, Science [ http://dx.doi.org/10.1126/science.1235367 ] (2013)., http://www.sciencemag.org/content/early/2013/07/31/science.1235367 ] reveals a link between big shifts in climate and precipitation and a rise in interpersonal violence, institutional breakdown, and especially inter-group violence, such as war. Not only does the paper shed light on past bouts of global conflict, it also offers a warning about the future. The world is expected to warm by at least 2 degrees Celsius over the next few decades, unless governments do something drastic, and the researchers say that increased bloodshed could be a serious side-effect of that trend.
For this study, the researchers performed a meta-analysis of 60 studies, some of which contained data going back to 10,000 B.C. They found that as temperature increases one standard deviation from the mean -- roughly equivalent to warming a U.S. county by 5 degrees Fahrenheit in a given month -- the likelihood of interpersonal violence rises by 4 percent and that of intergroup conflict rises by 14 percent.
The results touch on nearly every world region and hold true for both periods of extreme warming and cooling. Even the collapse of the Mayan civilization and major dynastic transitions in ancient China were preceded by drought and extreme weather. During the Little Ice Age, which started at around 1550, European countries were much more likely to go to war with each other.
Solomon Hsiang, a public policy professor at Princeton and one of the study's lead authors, told me that while his team did discover that conflict and climate change are related, they still don't know why it is that temperature change makes us so belligerent. And, more importantly, they aren't saying climate change is the only or even primary cause of violence.
"We're in the position medical researchers were in in the 1930s," he told me. "Smoking was the clear proximate cause of lung cancer, but it wasn't until decades later that we understood how that was linked."
They do offer a few theories, though. Climate change causes migration, and as big populations move, they might confront existing residents in a battle for resources and land. It can also alter physical environments in a way that predisposes people to confrontation, or -- particularly in earlier eras -- might have caused people to wrongly attribute environmental conditions to the actions of their enemies. Other studies have shown that hot temperatures make us more hostile psychologically.
Changes in the environment can also cause labor productivity to decline, which is what happened with our earlier example of civil war in the tropics: There's less farm work during a drought, so there are more unemployed people. So if you're looking to build an army and overthrow a government, it's easier to do it when there are a lot of idle, would-be farm workers around, complete with pitchforks.
Some unrelated studies [ http://drrajivdesaimd.com/tag/causes-of-war/ ] have shown that armed conflict has globally declined over the past 50 years or so, even though the world has been warming the entire time. Hsiang pointed out that it's important to remember that he's looking at what would have happened had there been no climate change during those decades -- and the answer, he says, is that rates of conflict would have fallen even faster.
"By focusing only on one country at a time, all we are doing is comparing a country to itself as the population is responding to changes in its environment," he said.
So what does this say about the present day? This is one of the few studies that points to climate change's likely impact on human society, as opposed to things like melting ice caps and rising sea levels, but it also helps us think about how much we want to spend to mitigate global warming. If we add "less peace" to all of global warming's already horrific environmental impacts, it might change our calculus significantly.
Copyright © 2013 by The Atlantic Monthly Group
http://www.theatlantic.com/international/archive/2013/08/hotter-weather-actually-makes-us-want-to-kill-each-other/278282/ [with comments]
--
Wars, Murders to Rise Due to Global Warming?
An acid attack victim in Karachi, Pakistan. A new study suggests that such violence increases with abnormal temperatures.
Photograph by Izabella Demavlys, Redux
Shifts in temperature and rainfall linked to more aggression, study says.
Ker Than
for National Geographic
Published August 1, 2013
Wars, murders, and other acts of violence will likely become more commonplace in coming decades as the effects of global warming [ http://environment.nationalgeographic.com/environment/global-warming/ ] cause tempers to flare worldwide, a comprehensive new study warns.
The research, detailed [again, Hsiang, S. M., Burke, M. & Miguel, E., Quantifying the Influence of Climate on Human Conflict, Science [ http://dx.doi.org/10.1126/science.1235367 ] (2013)., http://www.sciencemag.org/content/early/2013/07/31/science.1235367 ] in this week's issue of the journal Science [ http://www.sciencemag.org/ ], synthesizes findings scattered across diverse fields ranging from archaeology to economics to paint a clearer picture of how global warming-related shifts in temperature and rainfall could fuel acts of aggression.
Though scientists don't know exactly why global warming increases violence, the findings suggest that it's another major fallout of human-made climate change, in addition to rising sea levels [ http://news.nationalgeographic.com/news/2013/07/130723-east-antarctic-ice-sheet-melt-global-warming/ ] and increased heat waves [ http://news.nationalgeographic.com/news/2012/08/120803-global-warming-hansen-nasa-heat-waves-science/ ].
"This study shows that the value of reducing [greenhouse gas] emissions is actually higher than we previously thought," said study first author Solomon Hsiang [ http://www.solomonhsiang.com/ ], an economist at Princeton University in New Jersey. (Related: "Global Warming Making People More Aggressive? [ http://news.nationalgeographic.com/news/2010/03/100324-global-warming-violence-aggression/ ]")
Leveling the Field
To perform their analysis, Hsiang and his colleagues sifted through hundreds of studies published across a number of fields, including climatology, archaeology, economics, political science, and psychology.
"[As economists], we were way out of our comfort zone," Hsiang said. "It's been quite an interesting experience. I've never done anything like this before."
The team eventually settled on 60 studies on subjects related to climate [ http://science.nationalgeographic.com/science/earth/earths-atmosphere/climate-article/ ], conflict, temperature, violence, crime, and more, and reanalyzed those studies' data using a common statistical framework. An analogy would be converting currencies from different European countries into the euro so that meaningful comparisons could be made.
They did this to account for the fact that different parts of the world experience different variabilities in temperature and rainfall. For example, an increase of 2°F (1.1°C) might not be a big deal in the United States, where temperatures can vary widely, but it might be unusual for a country in Africa.
When the team converted the data and compared them, the results were striking: They found that even relatively minor departures from normal temperatures or rainfall amounts substantially increased the risk of conflict on a variety of levels, ranging from individual aggression, such as murder and rape, to country-level political instability and international wars.
The study data covered all major regions of the world and different time spans as well, from hours and years to decades and centuries. Across the data, the researchers found similar patterns of human aggression fueled by climate factors.
Examples included spikes in domestic violence in India and Australia, increased assaults and murders in the United States and Tanzania, ethnic violence in Europe and South Asia, land invasions in Brazil, and police using force in the Netherlands.
Ancient Insights
The effect wasn't limited to just modern societies, either. Among the research Hsiang and his team looked at was a study that linked increased political instability and warfare in the ancient Maya civilization around A.D. 900 to prolonged droughts brought about by global warming-related climate shifts in lands near the Pacific Ocean. (Related: "Why the Maya Fell: Climate Change, Conflict—And a Trip to the Beach? [ http://news.nationalgeographic.com/news/2012/11/121109-maya-civilization-climate-change-belize-science/ ]")
"That's when the classical period of Mayan civilization ends," said study co-author Edward Miguel [ http://emiguel.econ.berkeley.edu/ ], a professor of economics at the University of California, Berkeley.
Another study linked the 14th-century collapse of Cambodia's ancient Khmer civilization, which built the temple of Angkor Wat [ http://news.nationalgeographic.com/news/2007/08/070813-angkor-wat.html ], to decades of drought interspersed with intense monsoon rains.
"Archaeologists can actually observe how [Khmer] engineers were trying to adapt," Hsiang said. "They were trying to keep up with the climatic changes, but in the end, even though they were the most sophisticated water engineers in the region at the time, it still seemed too much."
Hsiang says his team included these historic case studies in their analysis in order to understand how populations adapted—or didn't—to the kinds of gradual climate changes that climatologists predict for the future. But he thinks there are also lessons to be learned from the past.
"A lot of the civilizations that were nailed by climatic shifts were the most advanced societies in their region or on the planet during their day, and they probably felt they could cope with anything," he said.
"I think we should have some humility [and] recognize that people in the past were very innovative and they were trying to adapt to these changes as well."
Why Does Warming Make People Mad?
Brad Bushman [ http://www.comm.ohio-state.edu/people/the-lantern-soc/userprofile/67.html ], a professor of communication and psychology at Ohio State University who specializes in human aggression and violence, called the study "impressive."
"The convergence of findings across so many different disciplines increases your confidence that you've got a pretty reliable effect here," said Bushman, who was not involved in the research.
"Hopefully, this study will increase awareness that climate change spans many different domains of human activity, including conflict." (See "6 Ways Climate Change Will Affect You [ http://news.nationalgeographic.com/news/2013/01/pictures/130115-climate-change-superstorm-atmosphere-science/ ].")
While the new study helps strengthens the case for climate change influencing human aggression, it was not designed to address the question of why it does.
Other scientists have speculated on possible mechanisms. For example, Bushman thinks dramatic changes in temperature and rainfall are unpleasant and naturally make people more cranky. "When people are in a cranky mood, they're more likely to behave aggressively," he said.
Another theory is that too much or too little rain can negatively affect a country's agriculture and lead to economic ruin.
"When individuals have very low income or the economy of the region collapses, that changes people's incentives to take part in various activities," study first author Hsiang said. And "one activity they could take part in is joining a militant group."
The team thinks researchers will eventually discover that multiple mechanisms are at play simultaneously.
Hsiang compared modern scientists studying the relationship between climate and aggression to medical doctors in the 1930s who knew that smoking and lung cancer were linked but had not yet uncovered the mechanism.
"It took decades, but people did eventually figure out what was going on, and that helped us design policies and institutions to help mitigate the harmful effects [of smoking]," Hsiang said.
Similarly, co-author Miguel said, pinning down the mechanisms behind how global warming affects aggression will be the "next key frontier" for this area of research.
© 2013 National Geographic Society
http://news.nationalgeographic.com/news/2013/08/130801-global-warming-violence-climate-change-science-environment/ [with comments]
--
(linked in):
http://investorshub.advfn.com/boards/read_msg.aspx?message_id=91207416 (and any future following)
http://investorshub.advfn.com/boards/read_msg.aspx?message_id=91231387 and preceding and following
http://investorshub.advfn.com/boards/read_msg.aspx?message_id=91231886 and preceding (and any future following)
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Conflicts among cattle-herding ethnic groups in east Africa can be linked to climate change.
UNICEF/GEORGINA CRANSTO/epa/Corbis
Temperature and rainfall extremes linked to more frequent feuds and wars.
Lauren Morello
01 August 2013
Tempers flare as temperatures rise — across the globe and throughout human history, researchers have found. The result is consistent with a growing body of research suggesting that climate change somehow incites human conflict.
Small changes in temperature and rainfall substantially raise the risk of conflict of many types, from interpersonal spats — such as aggressive horn-honking by automobile drivers — to full-blown civil war and societal collapse, researchers report today in Science1. They reviewed data from 60 studies on environmental change and human aggression that spanned six continents and more than 12,000 years.
The researchers found that a temperature rise of one standard deviation — which, in the United States today, occurs when the average temperature for a given month is about 3° Celsius higher than usual — increases the frequency of interpersonal violence by 4%, and the risk of intergroup conflict, such as civil war or rioting, by 14%.
Floods and drought also have an effect, although it is smaller than that of temperature, the researchers report. And the effects are apparent worldwide, in developed and developing countries.
“The level of consistency in how people are responding was surprising to us,” says Solomon Hsiang, an econometrician at the University of California Berkeley, who led the study. He and his team warn that climate’s influence on behaviour is likely to become more apparent as the planet warms and precipitation patterns change.
The researchers did not attempt to explain how climate exerts its apparent influence on human behaviour. They linked climate extremes to many types of conflict, from the fall of the fractious Classic Maya empire in the ninth century, to professional baseball pitchers purposely hitting opposing batters with balls. But the lack of causal mechanisms leaves many political scientists sceptical about the environment’s role in conflicts, which they say are driven by a complex array of social factors.
“It’s hard to see how the same causal mechanism that would lead to wild pitches would be linked to war and state collapse,” says Idean Salehyan, who studies political violence at the University of North Texas in Denton.
Similarly, Halvard Buhaug, a political scientist at the Peace Research Institute Oslo in Norway, says that the latest study does little to sway his belief that the climate–conflict link is weak and inconsistent. He has found that major conflicts in Africa have declined over the past few decades, despite noticeable warming there2, 3 — bucking the trend sketched in the latest study and in earlier, similar studies4, 5.
The contradictory results point to the need for researchers to test the links between climate and conflict in case studies where more variables can be tracked, says Andrew Solow, an environmental statistician at the Woods Hole Oceanographic Institution in Massachusetts.
Without that focus, he warns, researchers may unintentionally exaggerate the climate–conflict relationship by tweaking the definition or historical bounds of a conflict. “In the aggregate, if you work the data very hard, you do find relationships like this,” he says. “But when you take a closer look, things tend to be more complicated.”
Nature
doi:10.1038/nature.2013.13464
*
References
1. Hsiang, S. M., Burke, M. & Miguel, E., Quantifying the Influence of Climate on Human Conflict, Science [ http://dx.doi.org/10.1126/science.1235367 ] (2013).
http://www.sciencemag.org/content/early/2013/07/31/science.1235367
2. Buhaug, Reply to Burke et al.: Bias and climate war research, H. Proc. Natl. Acad. Sci. USA 107, E186–E187 [ http://dx.doi.org/10.1073/pnas.1015796108 ] (2010).
http://www.pnas.org/content/107/51/E186
3. Theisen, O. M., Holtermann, H. & Buhaug, Climate Wars? Assessing the Claim That Drought Breeds Conflict, H. Int. Secur. 36, 79–106 [ http://dx.doi.org/10.1162/ISEC_a_00065 ] (2011).
http://www.mitpressjournals.org/doi/abs/10.1162/ISEC_a_00065
4. Hsiang, S. M. , Meng, K. C. & Cane, M. A., Civil conflicts are associated with the global climate, Nature 476, 438–441 [ http://dx.doi.org/10.1038/nature10311 ] (2011).
http://www.nature.com/nature/journal/v476/n7361/full/nature10311.html
5. O'Loughlin, J. et al., Climate variability and conflict risk in East Africa, 1990–2009, Proc. Natl. Acad. Sci. USA 109, 18344–18349 [ http://dx.doi.org/10.1073/pnas.1205130109 ] (2012).
http://www.pnas.org/content/109/45/18344
*
Related stories and links
From nature.com
Global warming: A call for peace on climate and conflict
08 May 2013 [ http://www.nature.com/doifinder/10.1038/497179a ]
http://www.nature.com/nature/journal/v497/n7448/full/497179a.html
Climate cycles drive civil war
24 August 2011 [ http://www.nature.com/doifinder/10.1038/news.2011.501 ]
http://www.nature.com/news/2011/110824/full/news.2011.501.html
'Climate wars' claims disputed
08 September 2010 [ http://www.nature.com/doifinder/10.1038/467145a ]
http://www.nature.com/news/2010/100908/full/467145a.html
Darfur's climate roots challenged
27 June 2007 [ http://www.nature.com/doifinder/10.1038/4471038b ]
http://www.nature.com/nature/journal/v447/n7148/full/4471038b.html
Climate change 'could lead to conflict with Russia'
10 Mar 2008
http://blogs.nature.com/news/2008/03/climate_change_could_lead_to_c.html
From elsewhere
Solomon Hsiang
http://www.solomonhsiang.com/
Halvard Buhaug
http://www.prio.no/People/Person/?x=3497
Idean Salehyan
http://idean.salehyan.com/
Andrew Solow
http://www.whoi.edu/profile.do?id=asolow
*
© 2013 Nature Publishing Group, a division of Macmillan Publishers Limited
http://www.nature.com/news/warming-climate-drives-human-conflict-1.13464 [with comment]
--
Hotter Weather Actually Makes Us Want to Kill Each Other
Wikimedia Commons
A new meta-analysis finds that extreme changes in temperature increase the likelihood of inter-group conflict.
Olga Khazan
Aug 1 2013, 2:00 PM ET
Farmers in Brazil are more likely to invade each others' land in years that are particularly wet or unusually dry. Americans honk their horns more at other cars when it's hot outside. Countries in the tropics are more likely to have civil wars in years that are especially hot or dry.
They may seem random, but actually, these events are all connected. New research from Princeton University and UC Berkeley published today in Science [ Hsiang, S. M., Burke, M. & Miguel, E., Quantifying the Influence of Climate on Human Conflict, Science [ http://dx.doi.org/10.1126/science.1235367 ] (2013)., http://www.sciencemag.org/content/early/2013/07/31/science.1235367 ] reveals a link between big shifts in climate and precipitation and a rise in interpersonal violence, institutional breakdown, and especially inter-group violence, such as war. Not only does the paper shed light on past bouts of global conflict, it also offers a warning about the future. The world is expected to warm by at least 2 degrees Celsius over the next few decades, unless governments do something drastic, and the researchers say that increased bloodshed could be a serious side-effect of that trend.
For this study, the researchers performed a meta-analysis of 60 studies, some of which contained data going back to 10,000 B.C. They found that as temperature increases one standard deviation from the mean -- roughly equivalent to warming a U.S. county by 5 degrees Fahrenheit in a given month -- the likelihood of interpersonal violence rises by 4 percent and that of intergroup conflict rises by 14 percent.
The results touch on nearly every world region and hold true for both periods of extreme warming and cooling. Even the collapse of the Mayan civilization and major dynastic transitions in ancient China were preceded by drought and extreme weather. During the Little Ice Age, which started at around 1550, European countries were much more likely to go to war with each other.
Solomon Hsiang, a public policy professor at Princeton and one of the study's lead authors, told me that while his team did discover that conflict and climate change are related, they still don't know why it is that temperature change makes us so belligerent. And, more importantly, they aren't saying climate change is the only or even primary cause of violence.
"We're in the position medical researchers were in in the 1930s," he told me. "Smoking was the clear proximate cause of lung cancer, but it wasn't until decades later that we understood how that was linked."
They do offer a few theories, though. Climate change causes migration, and as big populations move, they might confront existing residents in a battle for resources and land. It can also alter physical environments in a way that predisposes people to confrontation, or -- particularly in earlier eras -- might have caused people to wrongly attribute environmental conditions to the actions of their enemies. Other studies have shown that hot temperatures make us more hostile psychologically.
Changes in the environment can also cause labor productivity to decline, which is what happened with our earlier example of civil war in the tropics: There's less farm work during a drought, so there are more unemployed people. So if you're looking to build an army and overthrow a government, it's easier to do it when there are a lot of idle, would-be farm workers around, complete with pitchforks.
Some unrelated studies [ http://drrajivdesaimd.com/tag/causes-of-war/ ] have shown that armed conflict has globally declined over the past 50 years or so, even though the world has been warming the entire time. Hsiang pointed out that it's important to remember that he's looking at what would have happened had there been no climate change during those decades -- and the answer, he says, is that rates of conflict would have fallen even faster.
"By focusing only on one country at a time, all we are doing is comparing a country to itself as the population is responding to changes in its environment," he said.
So what does this say about the present day? This is one of the few studies that points to climate change's likely impact on human society, as opposed to things like melting ice caps and rising sea levels, but it also helps us think about how much we want to spend to mitigate global warming. If we add "less peace" to all of global warming's already horrific environmental impacts, it might change our calculus significantly.
Copyright © 2013 by The Atlantic Monthly Group
http://www.theatlantic.com/international/archive/2013/08/hotter-weather-actually-makes-us-want-to-kill-each-other/278282/ [with comments]
--
Wars, Murders to Rise Due to Global Warming?
An acid attack victim in Karachi, Pakistan. A new study suggests that such violence increases with abnormal temperatures.
Photograph by Izabella Demavlys, Redux
Shifts in temperature and rainfall linked to more aggression, study says.
Ker Than
for National Geographic
Published August 1, 2013
Wars, murders, and other acts of violence will likely become more commonplace in coming decades as the effects of global warming [ http://environment.nationalgeographic.com/environment/global-warming/ ] cause tempers to flare worldwide, a comprehensive new study warns.
The research, detailed [again, Hsiang, S. M., Burke, M. & Miguel, E., Quantifying the Influence of Climate on Human Conflict, Science [ http://dx.doi.org/10.1126/science.1235367 ] (2013)., http://www.sciencemag.org/content/early/2013/07/31/science.1235367 ] in this week's issue of the journal Science [ http://www.sciencemag.org/ ], synthesizes findings scattered across diverse fields ranging from archaeology to economics to paint a clearer picture of how global warming-related shifts in temperature and rainfall could fuel acts of aggression.
Though scientists don't know exactly why global warming increases violence, the findings suggest that it's another major fallout of human-made climate change, in addition to rising sea levels [ http://news.nationalgeographic.com/news/2013/07/130723-east-antarctic-ice-sheet-melt-global-warming/ ] and increased heat waves [ http://news.nationalgeographic.com/news/2012/08/120803-global-warming-hansen-nasa-heat-waves-science/ ].
"This study shows that the value of reducing [greenhouse gas] emissions is actually higher than we previously thought," said study first author Solomon Hsiang [ http://www.solomonhsiang.com/ ], an economist at Princeton University in New Jersey. (Related: "Global Warming Making People More Aggressive? [ http://news.nationalgeographic.com/news/2010/03/100324-global-warming-violence-aggression/ ]")
Leveling the Field
To perform their analysis, Hsiang and his colleagues sifted through hundreds of studies published across a number of fields, including climatology, archaeology, economics, political science, and psychology.
"[As economists], we were way out of our comfort zone," Hsiang said. "It's been quite an interesting experience. I've never done anything like this before."
The team eventually settled on 60 studies on subjects related to climate [ http://science.nationalgeographic.com/science/earth/earths-atmosphere/climate-article/ ], conflict, temperature, violence, crime, and more, and reanalyzed those studies' data using a common statistical framework. An analogy would be converting currencies from different European countries into the euro so that meaningful comparisons could be made.
They did this to account for the fact that different parts of the world experience different variabilities in temperature and rainfall. For example, an increase of 2°F (1.1°C) might not be a big deal in the United States, where temperatures can vary widely, but it might be unusual for a country in Africa.
When the team converted the data and compared them, the results were striking: They found that even relatively minor departures from normal temperatures or rainfall amounts substantially increased the risk of conflict on a variety of levels, ranging from individual aggression, such as murder and rape, to country-level political instability and international wars.
The study data covered all major regions of the world and different time spans as well, from hours and years to decades and centuries. Across the data, the researchers found similar patterns of human aggression fueled by climate factors.
Examples included spikes in domestic violence in India and Australia, increased assaults and murders in the United States and Tanzania, ethnic violence in Europe and South Asia, land invasions in Brazil, and police using force in the Netherlands.
Ancient Insights
The effect wasn't limited to just modern societies, either. Among the research Hsiang and his team looked at was a study that linked increased political instability and warfare in the ancient Maya civilization around A.D. 900 to prolonged droughts brought about by global warming-related climate shifts in lands near the Pacific Ocean. (Related: "Why the Maya Fell: Climate Change, Conflict—And a Trip to the Beach? [ http://news.nationalgeographic.com/news/2012/11/121109-maya-civilization-climate-change-belize-science/ ]")
"That's when the classical period of Mayan civilization ends," said study co-author Edward Miguel [ http://emiguel.econ.berkeley.edu/ ], a professor of economics at the University of California, Berkeley.
Another study linked the 14th-century collapse of Cambodia's ancient Khmer civilization, which built the temple of Angkor Wat [ http://news.nationalgeographic.com/news/2007/08/070813-angkor-wat.html ], to decades of drought interspersed with intense monsoon rains.
"Archaeologists can actually observe how [Khmer] engineers were trying to adapt," Hsiang said. "They were trying to keep up with the climatic changes, but in the end, even though they were the most sophisticated water engineers in the region at the time, it still seemed too much."
Hsiang says his team included these historic case studies in their analysis in order to understand how populations adapted—or didn't—to the kinds of gradual climate changes that climatologists predict for the future. But he thinks there are also lessons to be learned from the past.
"A lot of the civilizations that were nailed by climatic shifts were the most advanced societies in their region or on the planet during their day, and they probably felt they could cope with anything," he said.
"I think we should have some humility [and] recognize that people in the past were very innovative and they were trying to adapt to these changes as well."
Why Does Warming Make People Mad?
Brad Bushman [ http://www.comm.ohio-state.edu/people/the-lantern-soc/userprofile/67.html ], a professor of communication and psychology at Ohio State University who specializes in human aggression and violence, called the study "impressive."
"The convergence of findings across so many different disciplines increases your confidence that you've got a pretty reliable effect here," said Bushman, who was not involved in the research.
"Hopefully, this study will increase awareness that climate change spans many different domains of human activity, including conflict." (See "6 Ways Climate Change Will Affect You [ http://news.nationalgeographic.com/news/2013/01/pictures/130115-climate-change-superstorm-atmosphere-science/ ].")
While the new study helps strengthens the case for climate change influencing human aggression, it was not designed to address the question of why it does.
Other scientists have speculated on possible mechanisms. For example, Bushman thinks dramatic changes in temperature and rainfall are unpleasant and naturally make people more cranky. "When people are in a cranky mood, they're more likely to behave aggressively," he said.
Another theory is that too much or too little rain can negatively affect a country's agriculture and lead to economic ruin.
"When individuals have very low income or the economy of the region collapses, that changes people's incentives to take part in various activities," study first author Hsiang said. And "one activity they could take part in is joining a militant group."
The team thinks researchers will eventually discover that multiple mechanisms are at play simultaneously.
Hsiang compared modern scientists studying the relationship between climate and aggression to medical doctors in the 1930s who knew that smoking and lung cancer were linked but had not yet uncovered the mechanism.
"It took decades, but people did eventually figure out what was going on, and that helped us design policies and institutions to help mitigate the harmful effects [of smoking]," Hsiang said.
Similarly, co-author Miguel said, pinning down the mechanisms behind how global warming affects aggression will be the "next key frontier" for this area of research.
© 2013 National Geographic Society
http://news.nationalgeographic.com/news/2013/08/130801-global-warming-violence-climate-change-science-environment/ [with comments]
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"Eternal vigilance is the price of Liberty."
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