A commonly held assumption that climate change accounted for the significant fall in population at the end of the Bronze Age, needs a new explanation, say a group of researchers. Using new statistical techniques to analyse more than 2000 radiocarbon dates, taken from hundreds of archaeological sites in Ireland, they have shown that the changes in climate actually occurred at least two generations later then the collapse in population.
Archaeologists and environmental scientists from the University of Bradford, University of Leeds, University College Cork, Ireland (UCC), and Queen’s University Belfast have published their results in Proceedings of the National Academy of Sciences. The results show that human activity starts to decline after 900BC, and falls rapidly after 800BC, indicating a population collapse. But the climate records show that colder, wetter conditions didn’t occur until around two generations later.
Climate records from peat bogs
Fluctuations in levels of human activity through time are reflected by the numbers of radiocarbon dates for a given period, so, as well as looking at the radiocarbon dates, the team then analysed past climate records from peat bogs in Ireland and compared them to the archaeological data to see if the dates tallied. That information was then compared with evidence of climate change across NW Europe between 1200 and 500 BC.
“Our evidence shows definitively that the population decline in this period cannot have been caused by climate change,” says Ian Armit, Professor of Archaeology at the University of Bradford, and lead author of the study.
Graeme Swindles, Associate Professor of Earth System Dynamics at the University of Leeds, added, “We found clear evidence for a rapid change in climate to much wetter conditions, which we were able to precisely pinpoint to 750BC using statistical methods.”
According to Professor Armit, social and economic stress are more likely candidates for the sudden and widespread fall in numbers. Communities producing bronze needed to trade over very large distances to obtain copper and tin. Control of these networks enabled the growth of complex, hierarchical societies dominated by a warrior elite. As iron production took over, these networks fell apart, leading to widespread conflict and social collapse. It may be these unstable social conditions led to a decimation of the population at the end of the Bronze Age.
According to Katharina Becker, Lecturer in the Department of Archaeology at UCC, the Late Bronze Age is usually seen as a time of plenty, in contrast to an impoverished Early Iron Age. “Our results show that the rich Bronze Age artefact record does not provide the full picture and that crisis began earlier than previously thought,” she says.
“Although climate change was not directly responsible for the collapse it is likely that the poor climatic conditions would have affected farming,” adds Professor Armit. “This would have been particularly difficult for vulnerable communities, preventing population recovery for several centuries.”
The findings have significance for modern day climate change debates which, argues Professor Armit, are often too quick to link historical climate events with changes in population.
“The impact of climate change on humans is a huge concern today as we monitor rising temperatures globally,” says Professor Armit.
“Often, in examining the past, we are inclined to link evidence of climate change with evidence of population change. Actually, if you have high quality data and apply modern analytical techniques, you get a much clearer picture and start to see the real complexity of human/environment relationships in the past.”