Climate change and the Plague of Justinian

There are concerns that in the future changes in climate might increase the spread of diseases and threaten human health. For example, a warmer and wetter climate could lead to disease-carrying creatures which thrive in warm, moist environments spreading to new regions. However, detecting changes such as these is challenging because climate is only one of several factors which affect the prevalence of disease at the present day; (other factors include immunisation programmes, easier transport of infected humans, etc...). 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. Another strain of bubonic plague later caused the Medieval Black Death.

This project will examine the changes in climate that took place at the same time as the Plague of Justinian. We will do this using evidence of past climate preserved in lake muds. Until recently, climatic evidence from the Mediterranean region for this time period has not been very precisely dated or detailed in time. However, the muds at the bottom of Nar lake in central Turkey are annually-banded, similar to tree rings, which offers the chance to reconstruct year-by-year variations in climate. So far, sediment core samples from Nar have been analysed at 5 to 20 year time intervals, and they show that the onset of the plague seems to have coincided with a very large switch from a drier to a wetter climate. Similarly, the Justinian plague era came to the end around AD750, when the climate became drier once again. The wetter climate would have increased the numbers of rats and other rodents which carry fleas, which in turn carry the plague bacterium. In order to test this idea more rigorously, we aim to measure climatic indicators in our cores for each individual annual layer during the critical time period around the start and end of the plague. We will use chemical isotopes, chemical element composition and other changes in the sediment layers to reconstruct how fast the climate changed and whether there was any lag between this and spread of the disease. The sediment cores can also tell us, indirectly, about the consequences of the plague for rural agriculture, via the different types of pollen that are preserved. We will analyse pollen for adjacent 3-year samples of banded mud (the minimum that is practicable) to see if the reduction in human population also led to a fall in the proportion of pollen from crop plants, such as cereals and fruit trees. Finally, we will compare our results with information from historical texts which record the date and place of plague outbreaks, to see how well they match up.

We will engage with the palaeoclimate and epidemiological research communities via agencies including the IGBP Past Global Changes program, specifically the PAGES 2k initiative (http://www.pages-igbp.org/science/last2millennia.html) and the IPCC WP II (Impacts, Adaptation and Vulnerability). After publication, our data will be made available to the wider scientific community via the WDC-A archive. For historians and archaeologists, for students and for wider public engagement, we plan to develop a web-based historical and climatic time line, which will cover the last 2,000 years, including a strong focus on the events surrounding the Plague of Justinian. This will be interactive, visual and innovative in showing the relationship in time between wider historical events and changes in climate and the physical environment, demonstrating how the latter can be reconstructed using natural archives, such as pollen analysis. The time line web-site will be developed in conjunction with the British Institute in Ankara (project partner), as part of their Climate History of Anatolia Strategic Research Initiative.