The Chinese civilization is among many other things one of record keeping farmers, warring dynasties and outstanding scholars.
This paper is a modern day scientist's take on history and it's clues towards correctly analyzing conflicts. It clearly shows how climate change is a major factor. Traditionally, like elsewhere, the Chinese have explained their wars by political, social, psychological and other anthropocentric causes. And the apparent cycles of warfare by pseudo-scientific rules of thumb about the aging of empires. Zhang's study is a thorough mathematical correlation from climate to war frequency done on a macro-historical level. The idea isn't new since 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 by correlating temperature data reconstructed from extra- and interpolating a number of methods with the meticulously described wars. 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. Other studies are cited for already having shown how agricultural harvests usually went up during warm periods, down during cold periods and how double cropping rice was only possible during warm periods. Today's China is warm enough for double cropping but many agricultural outputs world wide are limited by climatic factors. Extreme anecdotal evidence from a particularly ecologically fragile area says a 2°C drop in average temperature shortens the growing season of grass by as much as 40 days in turn leading to the death of 90% of the area's domestic animals. 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. Both impressive academic feats. The war data was pruned to 899 wars between year 1000 and 1911. The weather data synchronized with emphasis on the most reliable methods - studies of tree rings, corals, ice core studies, historical documents etc. all of which correlate beautifully in regard to oscillations. Population data are available from year 1741 to 1851 "only". Interestingly, the cold periods are characterized by incidents of
extreme summer heat as well as other weather abnormalities. The cold
periods are defined by time frames of significantly low average
temperatures. Six such periods of various lengths are identified. The cyclical pattern and the correlation is not just an abstract figure somewhat closer to 1 than 0. It's in your face. Looking at Zhang's graphs it is quite obvious how cold phases coincide with periods of high war frequency. All periods of high war frequency are in cold phases, all cold phases have high war frequency, the coldest periods have the most extreme war frequencies and all dynasty collapses occurred in or right after cold phases. 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. A series of major events in Chinese history is put in perspective of this present climate study and quite convincingly so. Zhang argues past research has been simplifying history, reducing causes of warfare to financial, political and ethnic ones while largely ignoring the ecosystem. Finally the current climate changes are discussed briefly in light of the conclusions of the study. Zhang emphasizes how current global warming is different from the warm phases of his study, as it is both natural and anthropogenic, highly unpredictable and affecting an entirely different society. 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.