Recent research at the University of California, Berkeley and Princeton University published in the journal, Science, has shown that the slightest change in temperature or rainfall leads to an increase in violence, and the relationship has been evident since ancient times. Researchers analysed studies from different fields that included archaeology, climatology, economics, political science and psychology.

A lead author of the latest study, Solomon Hsiang, told how 60 previous studies were examined and subjected to a common statistical framework, and that the results were “striking.” Conflict fell into three categories: personal violence, intergroup violence and institutional breakdown, with intergroup violence affected most by climate change. Examples were murders in the United States and Tanzania, ethnic conflict in Europe and southern Asia and civil strife in the tropics.

Another lead author, Marshall Burke, said that if conditions became hotter by a mere one standard deviation – a measure of the spread of values – then personal violence rose by four percent and intergroup conflict by 14 percent. Hence, if temperatures worldwide rise by 36 degrees Fahrenheit – two degrees Celsius – then intergroup violence could rise by as much as 50 percent. This is approximately equivalent to the warming of an African country by 33 degrees Fahrenheit (0.4 degrees Celsius) for a year or of a US state by 37 degrees Fahrenheit (three degrees Celsius) for a month. Burke remarked, “These are moderate changes, but they have a sizeable impact on societies.” Temperatures are expected to rise by around two to four standard deviations by 2050.

Luca Russo, a food security policy analyst for the UN’s Food and Agriculture Organisation, revealed that his organisation had discovered similar links. In 2007, a report by the Military Advisory Board of the CNA Corporation explicitly linked climate change with terrorism. It found that greater poverty, more forced migration and higher unemployment fomented conditions that could be exploited by extremists.

Marked cold also led to more conflict, as seen in Europe during the Little Ice Age from the 16th to 19th centuries. Extremely high or low levels of rainfall also tended to be damaging. Poor and rich regions can be affected.

Increased conflict would be a result of more frequent conflict over ever-scarcer natural resources and physiological stress caused by hotter weather. Burke said that there was a “primary channel” linking climate with group conflict in many agrarian societies. As for the immediate effect on people, higher temperature made them less trusting and more aggressive, as could be seen from placing people in a room and raising the temperature. Temperature altered people’s incentives to participate in the labour market, how they migrated and food prices. Burke added that future societies might be better at dealing with extreme temperatures, but it would be dangerous to assume this will definitely come to pass. Measures that could be taken included the adoption of crops that are more resistant to extreme weather and insurance schemes.

One more author, Edward Miguel, a professor of environmental and resource economics at Berkeley, charged that while we consider society to be mostly independent of the environment due to technology, the study challenged that notion. Hsiang affirmed that the connection between climate change and violent conflict was on a par with the link between smoking and lung cancer in the 1950s – it was only explained years later.

International Alert, which describes itself as a “peace-building” organisation, reported that 61 countries are at risk from the “double-headed” risk of climate change and conflict.

Recent research at the University of California, Berkeley and Princeton University published in the journal, Science, has shown that the slightest change in temperature or rainfall leads to an increase in violence, and the relationship has been evident since ancient times. Researchers analysed studies from different fields that included archaeology, climatology, economics, political science and psychology.

A lead author of the latest study, Solomon Hsiang, told how 60 previous studies were examined and subjected to a common statistical framework, and that the results were “striking.” Conflict fell into three categories: personal violence, intergroup violence and institutional breakdown, with intergroup violence affected most by climate change. Examples were murders in the United States and Tanzania, ethnic conflict in Europe and southern Asia and civil strife in the tropics.

Another lead author, Marshall Burke, said that if conditions became hotter by a mere one standard deviation – a measure of the spread of values – then personal violence rose by four percent and intergroup conflict by 14 percent. Hence, if temperatures worldwide rise by 36 degrees Fahrenheit – two degrees Celsius – then intergroup violence could rise by as much as 50 percent. This is approximately equivalent to the warming of an African country by 33 degrees Fahrenheit (0.4 degrees Celsius) for a year or of a US state by 37 degrees Fahrenheit (three degrees Celsius) for a month. Burke remarked, “These are moderate changes, but they have a sizeable impact on societies.” Temperatures are expected to rise by around two to four standard deviations by 2050.

Luca Russo, a food security policy analyst for the UN’s Food and Agriculture Organisation, revealed that his organisation had discovered similar links. In 2007, a report by the Military Advisory Board of the CNA Corporation explicitly linked climate change with terrorism. It found that greater poverty, more forced migration and higher unemployment fomented conditions that could be exploited by extremists.

Marked cold also led to more conflict, as seen in Europe during the Little Ice Age from the 16th to 19th centuries. Extremely high or low levels of rainfall also tended to be damaging. Poor and rich regions can be affected.

Increased conflict would be a result of more frequent conflict over ever-scarcer natural resources and physiological stress caused by hotter weather. Burke said that there was a “primary channel” linking climate with group conflict in many agrarian societies. As for the immediate effect on people, higher temperature made them less trusting and more aggressive, as could be seen from placing people in a room and raising the temperature. Temperature altered people’s incentives to participate in the labour market, how they migrated and food prices. Burke added that future societies might be better at dealing with extreme temperatures, but it would be dangerous to assume this will definitely come to pass. Measures that could be taken included the adoption of crops that are more resistant to extreme weather and insurance schemes.

One more author, Edward Miguel, a professor of environmental and resource economics at Berkeley, charged that while we consider society to be mostly independent of the environment due to technology, the study challenged that notion. Hsiang affirmed that the connection between climate change and violent conflict was on a par with the link between smoking and lung cancer in the 1950s – it was only explained years later.

International Alert, which describes itself as a “peace-building” organisation, reported that 61 countries are at risk from the “double-headed” risk of climate change and conflict.