Climate change was not to blame for the collapse of the Bronze Age

Scientists will have to find alternative explanations for a huge population collapse in Europe at the end of the Bronze Age as researchers prove definitively that climate change – commonly assumed to be responsible – could not have been the culprit.

Archaeologists and environmental scientists from the University of Bradford, University of Leeds, University College Cork, Ireland (UCC), and Queen’s 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 this week in Proceedings of the National Academy of Sciences, 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.

Fluctuations in levels of human activity through time are reflected by the numbers of radiocarbon dates for a given period. The team used new statistical techniques to analyse more than 2000 radiocarbon dates, taken from hundreds of archaeological sites in Ireland, to pinpoint the precise dates that Europe’s Bronze Age population collapse occurred.

The team then analysed past climate records from peat bogs in Ireland and compared the archaeological data to these climate records 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 is more likely to be the cause of 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 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 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.”

Peat moves from the bog to the generating station

Biofuel made of peat and wood could replace coal at the Atikokan Generating Station in northwestern Ontario. Photo courtesy of Mike Waddington.
Biofuel made of peat and wood could replace coal at the Atikokan Generating Station in northwestern Ontario. Photo courtesy of Mike Waddington.

For hundreds of years, peat has been used in Ireland, Sweden, Finland, Estonia, Belarus and Russia as a fuel source for thermal generating stations. Now Peat Resources Ltd. is looking at replacing the coal that fuels the province’s Atikokan Generating Station in northwestern Ontario with peat and wood.

Mike Waddington, associate professor in the Department of Geography & Earth Sciences at McMaster University, is leading the team that will assess the environmental impacts of using the new biofuel. He says Canada is a virtual peat paradise.

Canada has the world’s second-largest supply of peat; most of it around the Hudson and James Bay Lowlands and in Northern Ontario.

Says Waddington: “There are about 113 million hectares of peat in Canada — about 11 per cent of the country’s land — and if peat does become the preferred fuel of Atikokan’s Generating Station then it would use only a very small portion, about 100 hectares a year, of our total resource.”

Waddington’s first job is to determine the environmental impacts of the proposal. The greenhouse gas emissions, changes to water quantity and quality after the peat is removed from the peatlands; the rehabilitation of the peatlands, the return of process water to the peatlands, and the mercury relationships in the peatlands, all need to be explored, he says.

The process of harvesting peat for fuel involves removing the top layer of the peat, about 30 centimetres deep, and extracting from the deeper and older peat, material that is several thousand years old. Peat is a slowly renewing biofuel, says Waddington, and studies in Europe suggest it takes between 300 and 1,000 years to renew.

In Scandinavia, Ireland and Russia, peat was harvested using a dry technique that meant draining the wetlands prior to removing the peat. This method raised environmental concerns about water quality and flash flooding.

“We know how to restore dry harvest peatlands,” says Waddington, “however, with Peat Resources Ltd., we’ll be using an innovative wet harvest approach in which the peat is pumped to the processing facility through a pipeline. Once the peat is removed, the water that was removed from the peat extraction will be returned from the processing facility to the peatland.”

The proposed peat biofuel project is not the only water and peat-related energy concern in Canada.

“We’re already encountering some potential issues that will need to be hashed out,” says Waddington. “For instance, the Alberta oil sands are located under peatlands, and the hydroelectric reservoirs around James Bay region in Quebec are flooded peatlands. The question arises: Do you intrude on one resource to make room for another? It’s a tricky question.”

With 15 years experience in peatland restoration, Waddington will also be focused on how to remediate the peatlands and return them to as close to their pre-extraction state as possible. Blueberries, cranberries and wild rice are possible crops that could thrive in former peatlands.

The research for this project is being funded by the Ontario Centre of Excellence and Peat Resources Ltd.