Zhang's study is a thorough mathematical correlation from climate to war frequency done on a macro-historical level. Warfare has already been theoretically described as an adaptive ecological strategy of humankind in situations of limited resources. Zhang provides some empirical evidence to go with the theory. The hypothesis of the study is that climate changes has catalyzed historical events by it's importance for agricultural productivity, and that temperature is the most important climatic factor due to it's very direct effect on growing season lengths, precipitation reliability, summer warmth etc.
The data used for the analysis are comprised of China's extensive historical records literally body counting 3 millennia back in time and a set of five different weather data measurements merged into one. The war data was pruned to 899 wars between year 1000 and 1911. The weather data synchronized with emphasis on the most reliable methods all of which correlate beautifully in regard to oscillations. Population data are available from year 1741 to 1851 "only".
The cold periods are defined by time frames of significantly low average temperatures. The cyclical pattern and the correlation is not just an abstract figure somewhat closer to 1 than 0. It is quite obvious how cold phases coincide with periods of high war frequency. The war periods generally lag the onset of cold phases by 10 to 30 years which makes sense since it would take some time for the reduced agricultural productivity to manifest as resource limitations and overpopulation.
The study goes into more detail; ie correlations are particularly strong for wars of type "rebellion" and stronger in the (wet, warm) south than in the (arid, cold) north. The north-south difference is explained by historical attitudes towards migration. Population growth is seen to rise (to 1.3%) during the 1741-1805 warm phase and drop (to 0.6%) during the 1806-1850 cold phase.
Zhang argues past research has been simplifying history, reducing causes of warfare to financial, political and ethnic ones while largely ignoring the ecosystem. Zhang emphasizes how current global warming is different from the warm phases of his study. However, his last words are that even if the developed world gets by most people still rely on simple farming techniques that are highly susceptible to ecological stress and that shortages of essential resources may "very likely" trigger future conflicts among groups of people.
So, what does Zhang tell Ecowar? "Keep blogging"! Zhang must have been looking at some inconclusive data wondering pretty much the same thing I'm wondering when looking at the news of the world.
I have posted a bit about Jared Diamond who's straight out explaining some violence with what's basically "ecological stress". While Zhang highlights temperature drops, what we're mostly seeing right now is issues sparked from a temperature rise, ie drought. My Darfur: Drought or Islamism? post has the whole issue in it's little nutshell. Just like the Chinese food shortages inspired "rebellion", rising food prices gets today's consumers "up in arms". The UN has read the writing on the wall and has analyzed the Security risk of climate change. Et cetera, click backwards in time on my blog if you like. There are also more peer reviewed research on the subject out there which I plan to blog some time.
My enthusiasm when beginning this blog was fueled by the publication of Zhangs study. Although all I'd read was a journalist's interpretation. That article has now been pulled from the web. At the same time I have grown as weary of pseudo-science and political rants dressed as science in the blogosphere. So what better opportunity to introduce my flashy new Research Blogging icon!?
Zhang, D.D., Zhang, J., Lee, H.F., He, Y. (2007). Climate Change and War Frequency in Eastern China over the Last Millennium. Human Ecology, 35(4), 403-414. DOI: 10.1007/s10745-007-9115-8
This basically means my post is about a piece of peer reviewed scientific work that I have read and understand myself. As well as a number of other criteria you can check out at Research Blogging. Anyway, I hope I just reinserted my cornerstone.