Long-Term Fluctuations in Climate and Population in the Preindustrial Era

This article examines the hypothesis that longterm changes in middle latitude climate had a significant impact on population size variations in preindustrial societies. Warm periods are assumed to be associated with above average population levels while cool periods are correlated with subnormal levels. A model is presented that suggests longterm fluctuations in middle latitude temperature cause longterm fluctuations in food supply per capita and in vital rates; the effects of food supply and temperature on vital rates are independent however. Empirical analysis of data from various European countries China and archaelogical sites in North America and Europe provide support for such a model. Data from England show declines in grain yield fertility life expectancy and population growth and increases in average age at 1st marriage and net outmigration during the cooling period that extended from 1590 to 1670. The reverse trends were noted during the period of warming from 1670 to 1800. Analysis of data from China and western Europe indicate that a 10% increase in solar activity (a proxy for temperature) was associated with a 4% increase in population. In contrast to Malthusian theory which cannot account for the timing of longterm observed fluctuations in population a climate-population model effectively predicts the turning points observed in preindustrial societies. The striking synchrony in the longterm movements of temperature agricultural yield and population series across the middle latitudes in the period before the year 1800 suggest that this approach is worthy of more attention.