Quantitative Analysis of Climate Change and Human Crises in History - Space-Time Integration in Geography and GIScience - page 232

of hypotheses, as follows: in the pre-industrial period, the main source of livelihood
was agriculture; traditional agriculture was very much dictated by the whims of
climate and weather conditions; any deterioration of climate would trim agricultural
production; yield reduction would trigger famine, tax revolt, and a weakening of
state power; the deficit in livelihood resources was aggravated by the population
expansion accumulated in the previous favorable climate. Thus, human crises were
likely to erupt during the period of deteriorating climate. Given the above set of
hypotheses, our basic premise in previous studies was that, if empirically observed
human crises were correlated with climate change in a statistically significant
manner (i.e., human crises became more frequent in a deteriorating climate), then
we could confirm the connection between climate change and human crises. Three
major types of human crises were covered in our previous studies: population
checks, population collapses, and socio-political chaos. Our research findings about
the climate-crisis connection could be summarized as follows.

14.2.1 Population Checks

In Thomas Malthus' ( 1798 ) classic treatise, An Essay on Population , three types
of population checks are mentioned: wars, famines, and epidemics. Of these three
types of population checks, we put more emphasis on wars because of their
catastrophic and long-lasting social consequences. We found that in China in AD
1000-1911, like climate variations 3

(Fig. 14.1 a), the war frequency in China 4

3 BriffaandOsborn( 2002 ) chose five representative climate series of the last millennium in the
Northern Hemisphere (Jones et al. 1998 ;Mannetal. 1999 ;Briffa 2000 ; Crowley and Lowery 2000
and Esper et al. 2002 ) to discuss differences between the records of various independent paleo-
temperature studies. The five recalibrated temperature anomaly series were arithmetically averaged
to give the Northern Hemispheric temperature anomaly series (in ı C, from the AD 1961-1990
mean) (Fig. 14.1 a). Although there are China-wide temperature reconstructions with a millennium
year length of record (Wang et al. 2001 ;Yangetal. 2002 ), they did not reach the annual scale
that is required by our research. Given that the major long-term cooling events revealed by the
temperature reconstructions of China and the Northern Hemisphere were basically synchronous
in the past millennium, Briffa and Osborn's ( 2002 ) 'averaged' Northern Hemisphere temperature
anomaly series was chosen as the standard paleo-temperature record to quantitatively delineate
the cold and warm phases. The boundaries of the warm and cold phases were delineated at the
mean temperature point between minimum and maximum values of two contiguous phases on
Briffa and Osborn's ( 2002 ) averaged series. A cold or warm phase would be determined if the
average temperature change had an amplitude >0.14 ı C, in order to obtain an equal aggregate
duration of cold and warm periods. Based on the averaged series, six major cycles of warm and
cold phases were identified between AD 1000 and 1911. The cold phases spanned AD 1110-1152,
1194-1302, 1334-1359, 1448-1487, 1583-1717, and 1806-1911, while the warm phases spanned
AD 1000-1109, 1153-1193, 1303-1333, 1360-1447, 1488-1582, and 1718-1805 (Fig. 14.1 a).
4 Our war data was elicited from a multi-volume compendium which scrupulously records the wars
that took place in China from 800 BC to AD 1911 (Editorial Committee of Chinese Military
History 1985 ). There were 1,679 wars during the period AD 1000-1911, including 682 rebellions
(Fig. 14.1 b).