Lead pollution levels are about 60 times higher today than at the beginning of the Middle Ages, say researchers.
They found that particles of lead trapped deep in the Arctic ice reveal the economic impact of wars and plagues for the past 1,500 years.
Results from the analysis show that the increase in lead concentration in the ice cores goes closely with periods of expansion in Europe, the rise of new technologies, and economic prosperity.
Decreases in lead, on the other hand, paralleled climate disruptions, wars, plagues, and famines.
The research team used 13 Arctic ice cores from Greenland and the Russian Arctic to measure, date, and analyze lead emissions captured in the ice from 500 to 2010 CE, a period that extended from the Middle Ages through the Modern Period to the present.
“The ice-core array provides amazing detail a continuous record of European—and later North American—industrial emissions during the past 1,500 years. It shows that before the Industrial Revolution, lead pollution was pervasive and surprisingly similar across a large swathe of the Arctic and undoubtedly the result of European emissions,” the findings say.
According to the interdisciplinary team, the findings are not just interesting to environmental scientists, who want to understand how human activity has changed the environment, the ice-core records can also help historians understand and quantify the ways societies and economies responded to external forces such as climate disruptions, plagues, or political unrest.
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. Further, 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, indicating that economic activity stalled, the findings say.
Despite the rise and fall over time due to events such as plagues, the study shows that increases in lead pollution in the Arctic during the past 1,500 years have been exponential. “The array of accurately dated ice core records documents exponential, 250- to 300-fold increase in Arctic lead pollution from the Early Middle Ages to the 1970 industrial peak, reflecting largescale emission changes from ancient European silver production, recent fossil fuel burning, and other industrial activities,” says the paper.
The researchers say the implementation of pollution abatement policies, such as the US Clean Air Act of 1970 and similar legislation in other countries, resulted in immediate and pronounced 80% declines in overall Arctic lead pollution by the end of the 20th century. “Decrease in industrial emissions associated with economic and political changes in central and eastern Europe and the 1991 dissolution of the Soviet Union probably contributed to the sharp drop in lead deposition in the Russian Arctic as well,” says the paper. However, despite such declines, “modern Arctic lead pollution remains about 60-fold higher than at the start of the Middle Ages”, says the team.
The researchers used state-of-the-art atmospheric modeling to determine the relative sensitivity of different ice-core sites in the Arctic to lead emissions. It comprised researchers from the Desert Research Institute (DRI), the University of Oxford, NILU - Norwegian Institute for Air Research, the University of Copenhagen, the University of Rochester, and the Alfred Wegener Institute for Polar and Marine Research.
“Modeling shows that the core from the Russian Arctic is more sensitive to European emissions, particularly from eastern parts of Europe, than cores from Greenland. This is why we found consistently higher levels of lead pollution in the Russian Arctic core and more rapid increases during the Early and High Middle Ages as mining operations shifted north and east from the Iberian Peninsula to Great Britain and Germany,” state the findings.
The research team explains in their findings that commercial and industrial processes have emitted lead into the atmosphere for thousands of years, from the mining and smelting of silver ores to making currency for ancient Rome to the burning of fossil fuels today.
“This lead pollution travels on wind currents through the atmosphere, eventually settling in places like the ice sheet in Greenland and other parts of the Arctic,” says the paper.
It further says, “because of lead’s connection to precious metals like silver and the fact that natural lead levels in the environment are very low, scientists have found that lead deposits in layers of Arctic ice are a sensitive indicator of overall economic activity throughout history.”
The study was published in the Proceedings of the National Academy of Sciences.