|Image From: The London Bridge Experience|
What was learned
The seven scientists were able to demonstrate, in their words, that "climate change was the ultimate cause, and climate-driven economic downturn was the direct cause, of large-scale human crises in pre-industrial Europe and the Northern Hemisphere." In addition, they say it was cooling that triggered the chain of negative responses in variables pertaining to physical and human systems. Initially, for example, they found that agricultural production "decreased or stagnated in a cold climate and increased rapidly in a mild climate at the multi-decadal timescale," while the time course of crisis development was such that "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." Thus, the dark ages they delineated by these means were AD 1212-1381 (the Crisis of Late Middle Ages) and AD 1568-1665 (the GCSC), whereas the golden ages were the 10th to 12th centuries (the High Middle Ages), the late-14th to early 16th centuries (the Renaissance), and the late-17th to 18th centuries (the Enlightenment).
What it means
Several centuries of European and Northern Hemispheric data reveal that warming and warmth beget human wellness, while cooling and cold produce human misery.
Zhang, D.D., Lee, H.F., Wang, C., Li, B., Pei, Q., Zhang, J. and An, Y. 2011a. The causality analysis of climate change and large-scale human crisis. Proceedings of the National Academy of Sciences USA: 10.1073/pnas.1104268108.
Read More: CO2 Science.