The starkest views of climate change paint war as a looming threat. The idea that violence will erupt as drought and rising sea levels displace people from their homes is, in part, why the Nobel prize for peace was awarded in 2007 to the Intergovernmental Panel on Climate Change and Al Gore. Yet a newly published study analysing the historical connection between war and climate throws into question the assumption that rising temperatures and violence go hand in hand.

Aware that evidence for the link was lacking, Richard Tol of the Economic and Social Research Institute in Dublin, Ireland, and Sebastian Wagner of GKSS, a research institute near Hamburg, Germany, set out to collect data on climate and conflict in Europe over the past thousand years. Their results have just been published in Climatic Change.

The information they worked with came from a variety of sources. Thermometers and rain gauges have been used in Europe since 1500, and many of the records are now easily available on the internet. For earlier years, the two researchers relied on indirect data such as ice cores, tree rings and the growth patterns of corals that they culled from other people’s papers.

Measuring fighting proved more challenging, since the definition of “conflict” varies throughout history. Dr Tol and Dr Wagner decided to confine their efforts to those events which lasted for a year or more. They used www.warscholar.com to count the number of such contretemps that had been taking place during each year from 1000 to 2000.

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