It seems a warmer climate might be bad, but a colder one is deadly.
Once upon a time, people thought that overpopulation triggered crashes, but in this study by Lee and Zhang the hard numbers suggest instead that it was climate, and of course, it’s not the warmer kind of climate that causes the problems but the colder kind.
Malthusian cycles of population boom and bust aren’t the drivers here (though presumably having a large population means there is little buffer when the deadly cold spells hit).
From NIPCC: Cold Periods caused population crashes in China over the last millenium
…there were 5 major population contractions in China between 1000 CE and 1911, and all of them occurred in periods with a cold climate, when mortality crises triggered population collapses. [Abstract]
How much fun can you have in a long frost? Almost every kind of uprising, pain or plague.
In one population crash, the losses were as high as 49% of the peak. In the face of a 50:50 death rate, “perspective” doesn’t seem like quite the right word.
Data on Chinese history, including temperature, wars and rebellions, epidemics, famines, and population for the past millennium were examined. Over the study interval of 911 years, it was found that nomad migrations, rebellions, wars, epidemics, floods, and droughts were all higher in cold periods. All of these factors tended to act to disrupt population growth or cause mortality. Overall, 5 of 6 population contractions, with losses of 11.4 to 49.4% of peak population, were associated with a cooling climate. The 6th cool period evinced a great reduction in growth rate during a cool phase, but not a collapse. None of the population contractions were associated with a warming climate. (My emphasis)
In an earlier paper Zhang showed that colder weather was linked to wars, probably due to less food.
In analyzing the linkages they found to exist among these different factors, the international (Chinese, French, German, Norwegian) team of researchers concluded that “food production during the last two millennia has been more unstable during cooler periods, resulting in more social conflicts,” while specifically noting that “cooling shows direct positive association with the frequency of external aggression war to the Chinese dynasties mostly from the northern pastoral nomadic societies, and indirect positive association with the frequency of internal war within the Chinese dynasties through drought and locust plagues,” which have typically been more pronounced during cooler as opposed to warmer times.
What luxury it is to argue over esoteric theories instead of wondering how far we can eek out that last kilogram of mouldy rice, tree bark of grass soup?
Though for all the devastation wrought by climate, the worst Chinese famine, at least in sheer numbers, was not caused by climate, but by government.
Lee, H.F. and Zhang, D.D. 2010. Changes in climate and secular population cycles in China, 1000 CE to 1911. Climate Research 42: 235-246.
Zhang, Z., Tian, H., Cazelles, B., Kausrud, K.L., Brauning, A. Guo, F. and Stenseth, N.C. 2010. Periodic climate cooling enhanced natural disasters and wars in China during AD 10-1900. Proceedings of the Royal Society B 277: 10.1098/rspb.2010.0890.