Quantitative Analysis of Climate Change and Human Crises in History - Space-Time Integration in Geography and GIScience - page 251

socioeconomic, human ecological, and demographic variables corresponded very
well with temperature change and were in successive order. The variables of the
bio-productivity, agricultural production, and food supply per capita (FSPC) sectors
responded to temperature change immediately, whereas the social disturbance, war,
migration, nutritional status, epidemics, famine, and population sectors responded
to the drop in FSPC with a 5- to 30-year time lag. The adverse effect of the two
short-term, minor cooling episodes in Mild Phase 2 (Fig. 14.6 , blue dotted lines)
also was reflected by the variables' fluctuations in annual and decadal units, such
as Northern Hemisphere tree-ring width, grain yield, grain price, and agricultural
production index.
Cooling in the Cold Phase dampened agro-ecosystem output by shortening plant
growing seasons and shrinking the cultivated land area (Galloway 1986 ). The ratio
of grain yield to seed decreased along with temperature decline (Fig. 14.6 b, red
line). Tree-ring width (a variable of bio-productivity) also varied in response to
temperature change, decreasing rapidly in AD 1560-1650 (Fig. 14.6 b, black line).
Grain yield links directly to agricultural production, which is represented by the
agricultural production index. Although in the long term the agricultural production
index moved upwards with population size, it decreased or stagnated in a cold
climate and increased rapidly in a mild climate at the multi-decadal time-scale
(Fig. 14.6 c, black line).
Although agricultural production decreased or stagnated in a cold climate, pop-
ulation size continued to grow. Hence, two variables of FSPC - grain price and real
wages of labor - changed considerably, and economic crisis followed. Grain price is
determined by both demand and supply and is an important indicator of the boom-
and-bust cycle in an agrarian economy. The detrended grain price (Fig. 14.6 c, red
line) was inversely correlated with every fluctuation of the agricultural production
index and temperature. Real wages of labor (Fig. 14.6 d, red line) varied inversely
with grain price and followed agricultural production and temperature change
closely. Given the low FSCP, famine became more frequent (Fig. 14.6 d, black
line), resulting in deteriorating nutritional status and ultimately in reduced human
body height (Koepke and Baten 2005 ). The average height of Europeans followed
temperature closely (Fig. 14.6 f, red line) and declined 2 cm in the late sixteenth
century. It increased slowly with rising temperatures only after AD 1650.
Inflating grain prices and declining real wages bred unbearable hardship in
all walks of life, triggering many social problems and intensifying existing
social conflicts. Peaks of social disturbance such as rebellions, revolutions, and
political reforms followed every decline of temperature, with a 1-15-year time
lag (Fig. 14.6 e, black line). Many disturbances eventually developed into armed
conflicts. The number of wars increased by 41 % in the Cold Phase (Fig. 14.6 e, red
line). Although the number of wars decreased in the interval AD 1620-1650, these
wars were comparatively more lethal and longer lasting (e.g., the Thirty Years War)
(Brecke 1999 ). Annual war fatalities from AD 1620-1650 were >12 times those in
the period AD 1500-1619 (Fig. 14.6 g, red line).
More frequent and severe economic chaos, famine, social disturbance, and war
pushed people to emigrate. In Europe, migration (Fig. 14.6 g, black line) peaked