Lead in Arctic ice reveals the economic impact of ancient plagues and wars

For thousands of years, commercial and industrial processes like mining, ore smelting, and fossil fuel burning, have emitted lead into the atmosphere. That lead travelled via wind currents to the Arctic, where it settled on the ice sheet and became a record of economic activity throughout the past 1,500 years.

Now, a team of international researchers from the Desert Research Institute (DRI), the University of Oxford, the Norwegian Institute for Air Research (NILU), the University of Copenhagen, the University of Rochester, and the Alfred Wegener Institute for Polar and Marine Research have successfully measured, dated, and analyzed lead emissions captured in Arctic ice cores taken from Greenland and the Russian Arctic. These emissions were entrapped in ice between 500 and 2010 CE — a period of time spanning from the Middle Ages through the Modern Period to present day. Their findings are published in PNAS.

These results have been added to a study published by a group of the same researchers in 2018 which showed how lead pollution in a single ice core from Greenland depicted the ebbs and flows of the European economy between 1100 BCE and 800 CE, which includes the Greek and Roman empires.

“We have extended our earlier record through the Middle Ages and Modern Period to the present,” said lead author Joe McConnell, Ph.D., Director of DRI’s Ultra-Trace Ice Core Chemistry Laboratory in Reno, Nevada. “Using an array of thirteen ice cores instead of just one, this new study shows that prior to the Industrial Revolution, lead pollution was pervasive and surprisingly similar across a large swath of the Arctic and undoubtedly the result of European emissions. The ice-core array provides with amazing detail a continuous record of European — and later North American — industrial emissions during the past 1500 years.”

Increases in lead concentration within the cores align with periods of European expansion and economic prosperity, and decreases in lead concentration aligned with wars, plagues, famines, and climate disruptions. 

“Sustained increases in lead pollution during the Early and High Middle Ages (about 800 to 1300 CE), for example, indicate widespread economic growth, particularly in central Europe as new mining areas were discovered in places like the German Harz and Erzgebirge Mountains,” McConnell said. “Lead pollution in the ice core records declined during the Late Middle Ages and Early Modern Period (about 1300 to 1680 Ce) when plague devastated those regions, however, indicating that economic activity stalled.”

Despite the rise and fall of lead concentrations, there has been a steady incline in lead pollution in the Arctic during the last 1,500 years.

“We found an overall 250 to 300-fold increase in Arctic lead pollution from the start of the Middle Ages in 500 CE to 1970s,” said coauthor Nathan Chellman, a doctoral student at DRI. “Since the passage of pollution abatement policies, including the 1970 Clean Air Act in the United States, lead pollution in Arctic ice has declined more than 80 percent. Still, lead levels are about 60 times higher today than they were at the beginning of the Middle Ages.”

“What we’re finding is interesting not just to environmental scientists who want to understand how human activity has altered the environment,” said coauthor Andrew Wilson, Ph.D., Professor of the Archaeology of the Roman Empire at Oxford. “These ice-core records also are helping historians to understand and quantify the ways that societies and their economies have responded to external forces such as climate disruptions, plagues, or political unrest.”

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By Olivia Harvey, Earth.com Staff Writer

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