Rock Doc: Climate change and population collapse
By E. Kirsten Peters, College of Agricultural, Human & Natural Resource Sciences
PULLMAN, Wash. – Climate is always changing. That’s one truth that stands out from the record around the world of natural samples of Earth materials, tree rings, ice layers and so much more. But how much has past climate change influenced human affairs?
In anthropology it’s been relatively commonplace to look at the twists and turns of ancient human history and assign at least some major population collapses to climate change. It certainly stands to reason that climate stress may have impacted early human populations – the only real question is how often.
One collapse of an early human society that has often been linked to climate change happened at the end of the Bronze Age in northwestern Europe. Many archeologists have believed that a shift in climate to cold, wet conditions ushered in the end of the late Bronze Age, stifling its complex societies, so that a poorer culture with a smaller population started off the early Iron Age.
But now it looks like climate may not have been to blame for what befell humans at that time.
Economics, not climate, the culprit
European researchers from the University of Bradford, the University of Leeds, the University of College Cork and Queen’s University Belfast are making the case that the human population collapsed about a century earlier than the climate changed. Their work was recently published in the Proceedings of the National Academy of Sciences.
“Our evidence shows definitively that the population decline in this period could not have been caused by climate change” because the climate change came later, Ian Armit told ScienceDaily. He is a University of Bradford professor and lead author of the PNAS paper.
What, then, caused societies to fall apart in the late Bronze Age? That is less clear, but Armit speculates that economic changes were most likely the culprit.
Bronze is made of copper and tin, relatively rare metals. Bronze Age societies had to trade with one another, over large distances, to supply themselves with the metals that make bronze. Controlling those trade routes led to the growth of complex societies dominated by a warrior elite, Armit said.
When more commonplace iron started to replace bronze as the metal from which implements and weapons were made, the trade networks fell apart. That in turn led to societal collapse. Thus, Armit argues, changing economics and all that went along with those changes may have led to the fall in population.
Climate change a contributing factor
“Although climate change was not directly responsible for the collapse, it is likely that the poor climate conditions would have affected farming,” Armit is quoted in ScienceDaily. “This would have been particularly difficult for vulnerable communities, preventing population recovery for several centuries.”
Skipping up to the present, this research does not say that the production of greenhouse gases won’t stress the environment – and human societies – in the remainder of this century. But the argument can be made that climate change wasn’t the reason for widespread population decrease as the Bronze Age was succeeded by the Iron Age in Europe.
Dr. E. Kirsten Peters, a native of the rural Northwest, was trained as a geologist at Princeton and Harvard. This column is a service of the College of Agricultural, Human and Natural Resource Sciences at Washington State University.