Records from ancient China reveal link between epidemics and climate change

By Chelsea Harvey
7 November 2017
(E&E News) – Scientists are worried about the effects of long-term warming on human health and infectious disease, but a new study finds a link between epidemics and a cold climate.By analyzing Chinese records throughout nearly 2,000 years of history—from between A.D. 1 and 1911—researchers have found that climate-driven disturbances like floods, droughts, and locust outbreaks were associated with disease epidemics. The findings, published yesterday in Proceedings of the National Academy of Sciences, particularly suggest that climate-related agricultural failures may have led to famines and declines in human health and nutrition, which made communities more susceptible to infection.Interestingly, the study suggests that long periods of cold, dry weather were the primary facilitators of epidemics in the past. The records suggest that cold periods in ancient and pre-modern China were associated with an increase in the frequency of droughts, as well as attacks of locusts.As a result, the scientists write, “climate cooling could have resulted in collapsed agricultural production and reduced health conditions due to famine, thereby increasing the prevalence of human epidemic events.” [more]

ABSTRACT: A wide range of climate change-induced effects have been implicated in the prevalence of infectious diseases. Disentangling causes and consequences, however, remains particularly challenging at historical time scales, for which the quality and quantity of most of the available natural proxy archives and written documentary sources often decline. Here, we reconstruct the spatiotemporal occurrence patterns of human epidemics for large parts of China and most of the last two millennia. Cold and dry climate conditions indirectly increased the prevalence of epidemics through the influences of locusts and famines. Our results further reveal that low-frequency, long-term temperature trends mainly contributed to negative associations with epidemics, while positive associations of epidemics with droughts, floods, locusts, and famines mainly coincided with both higher and lower frequency temperature variations. Nevertheless, unstable relationships between human epidemics and temperature changes were observed on relatively smaller time scales. Our study suggests that an intertwined, direct, and indirect array of biological, ecological, and societal responses to different aspects of past climatic changes strongly depended on the frequency domain and study period chosen.

SIGNIFICANCE: The lack of available data, including written historical sources and natural proxy archives, has constrained us when disentangling the effects of climate change on the prevalence of infectious diseases. We first reconstructed human epidemics in China over the last two millennia and analyzed the impacts of climate change on the prevalence of human epidemics at various time scales. We show that long-term trends of cold and dry conditions indirectly facilitated the prevalence of epidemics through locusts and famines. Nevertheless, temperature showed unstable associations with epidemics on a small time scale. Our study highlights the urgent need to investigate scale-dependent impacts of climate change on the prevalence of diseases.

Scale-dependent climatic drivers of human epidemics in ancient China