Intensifying climate change will increase the future risk of violent armed conflict within countries, a study has found.
The research, published in the journal Nature, estimates climate has influenced between three and 20 per cent of armed conflict risk over the last century and that the influence will likely increase dramatically.
In a scenario with four degrees Celsius of warming, the influence of climate on conflicts would increase more than five times, leaping to a 26 per cent chance of a substantial increase in conflict risk, according to the study.
Even in a scenario of two degrees Celsius of warming beyond preindustrial levels -- the stated goal of the Paris Climate Agreement -- the influence of climate on conflicts would more than double, rising to a 13 per cent chance.
"Appreciating the role of climate change and its security impacts is important not only for understanding the social costs of our continuing heat-trapping emissions, but for prioritizing responses, which could include aid and cooperation," said Katharine Mach, from the Stanford University in the US.
Climate change-driven extreme weather and related disasters can damage economies, lower farming and livestock production and intensify inequality among social groups.
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These factors, when combined with other drivers of conflict, may increase risks of violence.
"Knowing whether environmental or climatic changes are important for explaining conflict has implications for what we can do to reduce the likelihood of future conflict, as well as for how to make well-informed decisions about how aggressively we should mitigate future climate change," said Marshall Burke, assistant professor at Stanford.
Researchers disagree intensely as to whether climate plays a role in triggering civil wars and other armed conflicts.
To better understand the impact of climate, the analysis involved interviews with and debates among experts in political science, environmental science, economics and other fields who have come to different conclusions on climate's influence on conflict in the past.
The experts agree that climate has affected organised armed conflict in recent decades.
However, they make clear that other factors, such as low socioeconomic development, the strength of government, inequalities in societies, and a recent history of violent conflict have a much heavier impact on conflict within countries.
The researchers do not fully understand how climate affects conflict and under what conditions.
The consequences of future climate change will likely be different from historical climate disruptions because societies will be forced to grapple with unprecedented conditions that go beyond known experience and what they may be capable of adapting to.
"Historically, levels of armed conflict over time have been heavily influenced by shocks to, and changes in, international relations among states and in their domestic political systems," said James Fearon, professor at Stanford.
"It is quite likely that over this century, unprecedented climate change is going to have significant impacts on both, but it is extremely hard to anticipate whether the political changes related to climate change will have big effects on armed conflict in turn," said Fearon.