Quantitative Analysis of Climate Change and Human Crises in History - Space-Time Integration in Geography and GIScience - page 236

followed by a relatively tranquil one (Fig. 14.2 b). Two periods plagued by unrest
and warfare and three relatively peaceful periods inversely followed the temperature
undulation. This pattern appeared not only at a continental scale, but also in three
war databases with different violence thresholds at the global scale 8 (Fig. 14.2 c). In
short, synchronous periods of relative peace and turbulence during those 500 years
were a global phenomenon seemingly linked to temperature change.
At the century time scale, war frequencies and the ratio of wars per year in
different centuries were calculated at various geographic scales (global, continental,
and country). 9 Those calculations demonstrated that the number and ratio of wars
in the mild eighteenth century were the lowest compared with other centuries. The
results indicate that the worldwide war ratio during cold centuries was 1.93 times
greater than that of the mild eighteenth century, and 1.77, 1.91, 1.50, and 2.24
times greater for the Northern Hemisphere, Asia, the arid areas of the Northern
Hemisphere, and Europe, respectively. At the country scale, only 27 of 170 countries
and areas around the world had higher war ratios in the eighteenth century than in
the fifteenth to seventeenth and nineteenth centuries. Most of the 'exceptional cases'
are located near the Equator, where there was no obvious Little Ice Age and the
resulting cooling that would have a significant effect on agriculture.
To refine the analysis, a series of Pearson's correlation analyses were carried
out at the much lower scale of an annual level time-frame. 10 The results show
that the numbers of wars per year, in all war classifications, were significantly
negatively correlated with the annual changes of the temperature anomalies at the
global level (Table 14.2 ). The number of wars in the Northern Hemisphere and the
Southern Hemisphere also correlated significantly with their temperature variations.
Further analysis of the frequency of wars in Europe, Asia, and the arid areas of
the Northern Hemisphere also shows significant correlations with the Northern
Hemisphere temperature anomaly for their geographical patterns (Table 14.2 ). The
values of the coefficients at the annual scale also reflect environmental vulnerability
and population density. As arid regions are the most vulnerable to climate change,
the highest coefficient should and does appear in the war frequencies for the arid
areas of the Northern Hemisphere. Values are lower for Asia, probably because
much of the continent for which there is conflict data is subject to a wet tropical

wars include all recorded violent conflicts that meet Richardson's magnitude 1.5 criterion ( 32

deaths). The geographical locations of wars in the dataset are divided by their natural locations.
8 Apart from Brecke's Conflict Catalog , we also included another two global war datasets for
comparison: Wright's ( 1942 ) dataset, which documents all hostilities involving members of the
family of nations, whether international, civil, colonial, or imperial, which were recognized as
states of war in the legal sense or which involved over 50,000 troops; and Luard's ( 1986 )
dataset, which documents those encounters that involved at least one sovereign state and involved
substantial, organized fighting over a significant period (also known as principle wars).
9 The calculation of the war frequencies and the ratio of wars was based on Brecke's ( 1999 ) Conflict
Catalog .
10 Data were smoothed by the 40-year Butterworth low-pass filter to remove fluctuations on time-
scales <40 year prior to statistical analysis.