Climate change and the Plague of Justinian
Friday seminar by Neil Roberts
There are concerns that in the future changes in climate might increase the spread of diseases and threaten human health. However, detecting these changes is challenging because climate is only one of several factors which affect the prevalence of disease at the present day. An alternative approach to understanding the relationship between climate change and disease is to set up “experiments” using past disease outbreaks where the outcome in terms of infection and mortality is already known. One such is the Plague of Justinian. This, the first known global pandemic struck in AD451 and recurred until ~AD750, leading to the premature death of up to a quarter of the human population in the eastern Mediterranean region. Its likely cause was bubonic plague, which later caused the Medieval Black Death. Human plague is caused by fleas infected with the bacterium Yersinia pestis, which in turn are carried by rodent hosts. Modern studies show that wetter climatic conditions can lead to increased host and flea populations and heightened plague risk (Gage & Kosoy, Ann. Rev. Ent. 2005).
Documentary sources provide a detailed record of epidemics, famines and extreme weather events in the eastern and central Mediterranean between AD 284 and 750 (Stathakopoulos 2004). Independently, Nar crater lake in central Anatolia provides an exceptionally well-dated proxy record of climate and land use since AD280, then in the agrarian heartland of the Byzantine Empire (Jones et al. Geology 2006; England et al. Holocene 2008). Decadal or better dating precision is possible due to its annually-varved lake sediment record. Analysis of δ18O and diatom-inferred salinity shows that the largest dry-to-wet climatic shift of the last 1720 years occurred during the 6th century, centred on 530-560 AD. Inferred climate remained humid until AD 750, after which drier conditions lowered the plague risk. This record of climate history is therefore consistent with the hypothesis that an abrupt switch to a wetter climate facilitated the onset and recurrence of the plague.
School of Geography, Earth and Environmental Sciences, University of Plymouth, PL4 8AA, UK