Graphic detail | Europe’s economic history

Arctic lead levels shed new light on Europe’s history

Lead trapped in Arctic ice tracks Europe’s money supply over the past two millennia

TODAY JACHYMOV is a small Czech town nestling in a valley on the German border. In 1534, though, it was Joachimsthal, the largest city in Bohemia apart from Prague and home to the almighty thaler—a weighty silver coin that became the de facto currency of Europe and the New World. The thaler lent an English version of its name, “dollar”, to the money of the United States and a score of other jurisdictions. Joachimsthal’s silver rush began in 1512. By the middle of the century the local mines were the most prolific in Europe.

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Joachimsthal’s mines left another legacy, however: lead. Silver and lead often co-mineralise, and refining silver from its ore releases some of that lead into the atmosphere, where winds can carry it far and wide. Lead transported in this way to the Arctic often ends up trapped in layers of glacial ice. That is where a team of researchers led by Joseph McConnell of the Desert Research Institute, in Reno, Nevada found it, in ice cores pulled from glaciers in Greenland and Siberia.

In their new study, published in the Proceedings of the National Academy of Sciences, Dr McConnell’s team used coring to analyse lead emissions and produce a record of the European economy from Roman to modern times. Moreover, by comparing records from Greenland and Siberia, Dr McConnell could distinguish mines in western and eastern Europe. Eastern mines left more lead in Siberia than in Greenland, and western ones the reverse.

The data illuminate the historical record. As Charlemagne conquered most of western Europe, his mints turned out huge quantities of new silver currency. After his reign, his empire disintegrated and smaller potentates took over minting. Silver production rose gradually but steadily through the prosperous medieval warm period. Conflict punctuates the record, as combatants fought over mining regions.

Disease, too, makes its terrible impact plain. Major modern economic shocks, like the Great Depression, have taken a decade or so to recover from. By comparison, the Black Death halved lead levels, and it took 100 years for them to recover afterwards. The implication is that silver mines were unprofitable—either because of a lack of demand, or of a shortage of affordable labour, or both—well into the Renaissance. When plague recurred across Europe in the late 16th and 17th centuries, growth in lead emissions stalled as well.

After 1750, industrial processes overtook silver production as the chief source of lead pollution. Leaded gasoline, introduced in the 1930s, sent lead levels still higher. Starting in the 1970s, environmental policies in America and Europe decoupled lead pollution from economic growth. Arctic lead levels have since fallen by more than 80%—but they remain 60 times higher than in the medieval era.

This article appeared in the Graphic detail section of the print edition under the headline "Plumbing the glaciers"

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