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The risk of civil conflict doubles in tropical countries during El Niño years, and around one-fifth of all civil wars between 1950 and 2004 may have been influenced by its weather patterns, according to a study.
The El Niño climate cycle, which periodically warms up the Pacific Ocean and affects weather patterns in many countries, has influenced 21 per cent of civil wars around the world and almost 30 per cent in the countries where El Niño has a high impact — the tropical parts of Africa, Asia-Pacific and South America.
The findings were reported by a team from Columbia and Princeton universities, United States, in Nature this week (24 August).
"We find that it is the poorest countries that respond to El Niño with violence," said Solomon Hsiang, lead author and a researcher at Columbia University. Countries that have been particularly affected are Angola, Congo, El Salvador, Eritrea, Haiti, Indonesia, Myanmar, Peru, the Philippines, Rwanda, Sudan and Uganda.
Hsiang and colleagues analysed more than 230 civil conflicts that took place globally between 1950 and 2004.
El Niño occurs every two to seven years, but Hsiang noted that it is now possible to forecast it up to two years in advance, allowing for preventative measures.
Nick Nuttall, a spokesperson for the UN Environment Programme, told SciDev.Net: "Governments should take this study as a red flag in terms of co-operating on climate policy and coming up with some decisive trajectories for reducing emissions".
Halvard Buhaug, a conflict researcher at the Peace Research Institute Oslo, in Norway, said: "The reported correlation between El Niño cycles and conflict risk in El Niño-sensitive countries is remarkably strong".
Buhaug had previously criticised a controversial 2009 study that sought to link the local climate in Africa to conflict outbreaks and published a study last year showing no link between climate change indicators and civil wars in Africa.
He said of the new study: "The statistical analysis is quite comprehensive and the results appear robust".
But he added: "Until we can establish the causal links that might be at play I find it advisable to exercise restraint in embracing the notion that El Niño drives civil wars in the tropics".
Although the study did not reveal how or why changing weather affects outbreaks of violence, El Niño is known to be correlated with crop losses, natural disasters and the spread of infectious diseases.
So the team hypothesises that income inequality, declining employment, governments incapable of enforcing law, or even the physiological effects of heat could tip volatile situations over the edge.
Although climate change may also make weather patterns more extreme, the study did not look at its effects.
But Mark Cane, one of the co-authors and professor of earth and climate sciences at Columbia University, said the pattern they found may also apply to a world disrupted by global warming.
Nature 476, 438-411 (2011)