Long before the advent of modern industry, humans enjoyed a long and rich history of pumping pollutants into the Arctic. The remnants of lead pollutants trapped deep in the Arctic ice are now being used by scientists to trace a detailed history of human activity, detailing everything from the Black Death and famines to wars and the smelting of silver in the Roman Empire.
As reported in the Proceedings of the National Academy of Sciences, scientists led by the Desert Research Institute (DRI) in Nevada have studied 13 ice cores, long cylinders of ice bored out of an ice sheet or glacier, from sites above the Arctic Circle.
The layers within the ice cores showed that levels of lead in the atmosphere escalated 250 to 300-fold from the start of the Middle Ages to the 1970s. There was then a prominent decrease, believed to be linked to the introduction of the 1970 Clean Air Act in the US and other environmental initiatives in Europe.
"Still, lead levels are about 60 times higher today than they were at the beginning of the Middle Ages," Nathan Chellman, a doctoral student at the DRI and coauthor on the study, explained in a statement.
Since lead is linked to the production of precious metals like silver, the ice cores also managed to provide some clear insights into populations, wars, plagues, famines, economic changes, and technology from the Middle Ages onwards.
One of the biggest rises, aside from the Industrial Revolution, was around the reign of Charlemagne, King of the Franks and Christian "Emperor of the Romans" in the latter half of the 8th century CE. This spike in 750 CE, according to the research, coincides with the establishment of a major mint in the German city of Melle, suggesting there was substantial silver smelting and mining at the time.
A colossal dip can also be found from 1349 to 1360 CE. By no coincidence, this was when the Black Death, one of the most devastating pandemics in human history, was reaching its peak. As you can imagine, the world’s population suddenly being slashed by 50 million people takes its toll on the world's economy – and this can be seen in the levels of lead found in the ice cores.
"What we're finding is interesting not just to environmental scientists who want to understand how human activity has altered the environment," concluded co-author Andrew Wilson, Professor of the Archaeology of the Roman Empire at the University of 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."