Economist: Cool heads or heated conflicts?

Economist:

A lesson from history on how to prevent climate-induced wars

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.

The chart shows the correlation between the number of conflicts and the average temperature during most of the second half of the millennium, the period for which the data are best. Until the mid-18th century, this correlation is continuously and significantly negative (the line remains close to the 95% confidence level, suggesting there is only one chance in 20 that it is an accidental, random effect). In other words, lower temperatures mean more wars. Then, suddenly, the negative correlation vanishes. The line goes into positive territory, but not enough to be statistically meaningful. The inverted correlation between temperature and conflict has therefore disappeared.

Dr Tol and Dr Wagner suggest that in the more remote past the effects of cold weather on harvests led to supply shortages, and that these increased the likelihood of people fighting over food and the land needed to produce it. They argue that the reason the relationship between warfare and cold vanishes in the mid-18th century is that this is the moment when the industrial revolution began. Both agriculture and transport improved rapidly at this time. Systematic plant breeding, the introduction of new crops and new forms of crop rotation, and better irrigation increased the food supply. Improvements in roads and the large-scale construction of canals allowed food to be transported from areas of plenty to areas of scarcity.

These developments meant farmers could often produce reasonable yields during colder weather—and even when they could not, long-distance trade provided a buffer against crop failure. Meanwhile, the growth of cities and non-agricultural occupations meant there was money to buy such traded crops.

Just because cold, rather than heat, caused problems in Europe during the millennium that Dr Tol and Dr Wagner examined does not mean rising temperatures pose no threat. The lesson, rather, is that the way to minimise the likelihood of climate-induced conflict in the future is to continue the process of crop improvement (for example, by taking advantage of the potential of genetic engineering) so that heat- and drought-tolerant varieties are available; to make farmers aware of these new crops and encourage their use; and to promote free trade and non-agricultural economic development. That way people will have no cause to fight, and tyrants no excuse to stir them up.