Scientists have proven definitively that climate change could not have been responsible for a huge population collapse in Europe at the end of the Bronze Age.
Archaeologists and environmental scientists from the University of Leeds, the University of Bradford, University College Cork and Queens University Belfast have shown that the changes in climate that scientists believed to coincide with the fall in population in fact occurred at least two generations later.
Their results, published today in the Proceedings of the National Academy of Sciences, show that human activity starts to decline after 900 BC, and falls rapidly after 800 BC, indicating a population collapse. But the climate records show that colder, wetter conditions didnt occur until around two generations later.
Dr Graeme Swindles, from the School of Geography at the University of Leeds and a co-author of the study, said: We found clear evidence for a rapid change in climate to much wetter conditions, which we were able to precisely pinpoint to 750 BC using statistical methods.
Fluctuations in human activity levels through time are reflected by the numbers of radiocarbon dates for a given period. The team used new statistical techniques to analyse more than 2,000 radiocarbon dates, taken from hundreds of archaeological sites in Ireland, to pinpoint the precise dates that Europes Bronze Age population collapse occurred.
The team analysed past climate records from peat bogs in Ireland and then compared the archaeological data to the past climate records to see if the dates tallied, and compared that information with evidence of climate change across northwest Europe between 1200 and 500 BC.
The research suggests that social and economic stress is more likely to be the cause of the sudden and widespread fall in numbers, rather than climate change.
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 warrior elite. As iron production took over, these networks collapsed, leading to widespread conflict and social collapse. It may be these unstable social conditions, rather than climate change, that led to the population collapse at the end of the Bronze Age.
According to study co-author Dr Katharina Becker from University College Cork, 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 study co-author Professor Armit from the University of Bradford, 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, said 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.