It has been widely thought that the current climate warming has been causing more diseases occurrences or transmissions in the world. But a recent study (Tian et al. 2017) led by Prof Zhibin Zhang (Chinese Academy of Science) and Prof. Nils Chr. Stenseth (University of Oslo) indicated that the impacts of climate change on prevalence of epidemics were scale-dependent. This study was conducted by using historical data of two millennia in ancient China extracted from A Compendium of Chinese Meteorological Records of the Last 3,000 Years. They found when data was analyzed at a large time scale, climate cooling would cause more epidemics. However, when data was analyzed at a small time scale, the association between epidemics and temperature was not consistent; both positive and negative associations were observed. Further analysis revealed that long-term trend of cool and dry climate mainly contributed to more epidemics via increased more locusts and famines. Both long-term and short-term trend of epidemics were closely and positively associated with drought, flood, locust and famine events.

The conventional theory suggests that climate warming would cause more diseases by increasing rates of development, reproduction or survival of hosts or vectors directly. Evidences supporting the traditional theory were mainly from analyses of short-term data. At large time scale, temperature not only affects hosts and vectors directly, but also indirectly by influencing precipitation, and then agricultural production, famine and finally diseases. The researchers found that long-term trend of climate cooling caused more droughts in China, probably due to the weakening monsoon. Droughts caused more locusts, and collapses of agriculture and more famines. Hungry people would become more susceptible to disease infections due to reduced immunity. The long-term trend effects of climate change were not easily captured by using short-term data. China has a long history of recording significant biological, climatic and social events, which provided an unique opportunity of studying the biological consequences of long-term climate change.

This study highlights the significance of scale-dependent effects of climate change on biological disasters as well as natural disasters. Different from the conventional view, they found that the biological consequence of climate could be non-monotonic, being a context-dependent transformation between positive and negative effect. Their findings may have some implications in disease prevention of people. For the short-term period or trend, more droughts or floods or warm climate would increase risk of disease prevalence. However, for the long-term period or trend, climate cooling would cause more epidemics as well as the other disasters. They call for an urgent need for studying the scale-dependent effects of climate change on human epidemics.

Tian H#, Yan C#, Xu L, Büntgen U, Stenseth NC*, and Zhang Z*, 2017, Scale-dependent climatic drivers of human epidemics in ancient China. www.pnas.org/cgi/doi/10.1073/pnas.1706470114 # equally contributed, * corresponding author).

Frequency-dependent effects of biological and climatic factors on prevalence of human epidemics in ancient China (from Tian et al. 2017).

Contact:
Zhibin Zhang, PhD
State Key Laboratory of Integrated Pest Management, Institute of Zoology, Chinese Academy of Sciences, 1 Beichen West Rd, Chaoyang District, Beijing 100101, China;
Email: zhangzb@ioz.ac.cn