A new study has shown that air pollution levels across Europe have been higher than previously thought for the last 2000 years, with the exception of a four-year period during a catastrophic pandemic.
The findings in this latest study will have significant implications for current public health and environmental policy which have so far deemed pre-industrial lead pollution levels to be ‘natural’ and so presumably ‘safe’.
The research, which is published in GeoHealth – a journal of the American Geophysical Union, is based on scientific climate data as well as detailed historical and archaeological records.
Collaborative working
The new study provides evidence that the natural level of lead in the air is essentially zero, contrary to common assumptions. The research shows lead pollution from mining and smelting was detectable well before the Industrial revolution, in fact, as far back as 2000 years ago and beyond. Only when a bubonic plague pandemic (the Black Death in 1349-1353) stopped those activities, did lead pollution in the air return to natural levels.
The research was carried out by historians and climate scientists at Harvard University in Cambridge, Massachusetts and at the Climate Change Institute (CCI) at University of Maine, in collaboration with academics from the Department of Archeology at the University of Nottingham, and glaciologists from the University of Heidelberg. The project was supported by a grant from the Arcadia Fund, a charitable fund of Peter Baldwin and Lisbet Rausing.
This is the first time that highly detailed historical records could be matched to a scientific climate/pollution record, on a yearly to monthly scale, to show human impact on the environment. The whole project was designed from the start by climate scientists, historians, and archeologists working together.
Next generation laser technology
Scientists and historians chose to examine past lead levels in the air because it is a dangerous pollutant and because it serves as a key indicator for economic activity (mined in its own right and as a by-product of silver-mining for coinage), ramping up when economies grow and tailing off when they decline.
Researchers matched new, high-resolution measurements of lead in an ice core taken from a glacier in the Swiss/Italian Alps with highly detailed historical records showing that lead mining and smelting activity plummeted to nearly zero during the Black Death.
This is the first time that next-generation laser technology has been used to study an ice core to provide climate and pollution data down to within a certain year. The ultra-high-resolution record is the first and most accurate climate/pollution record currently in existence.
The researchers found that atmospheric lead reached undetectable levels only once in the last 2,000 years of European history, according to Alexander More, an environmental historian at Harvard University and the Climate Change Institute, and lead author of the study.
“When we saw the extent of the decline in lead levels, and only saw it once, during the years of the pandemic, we were intrigued. In different parts of Europe, the Black Death wiped out as much as half the population. It radically changed society in multiple ways. In terms of the labour force, the mining of lead essentially stopped in major areas of production. You see this reflected in the ice core in the large drop in atmospheric levels, and you see it in historical records for an extended period of time.”
‘Re-defining our understanding of air pollution’
Dr Christopher Loveluck, Associate Professor and a Reader in Medieval Archaeology at the University of Nottingham, worked with the climate scientists and Harvard historians to help interpret the ice core results from Colle Gnifetti in the Alps, working on lead mining and palaeo-environmental evidence from across western Europe, together with the historical records to understand what the changes in lead levels meant.
Dr Loveluck said: “The collaborative work with other members of the team allowed the verification and sourcing of the lead signal at Colle Gnifetti, to provide a unique new insight into the impact of the Black Death in our region of England and western Europe, and to provide a world-first in demonstrating what the real ‘natural’ lead background level would be without human activity in this part of the globe. The chronology of the collapse in lead mining in 1349-51 from the ice core most closely matches the collapse sequence for British lead sources, such as the Peak District (the largest producers in western Europe when the Black Death hit). Climate modelling by the CCI confirms delivery of pollution from Britain to the Alps.
“The study has redefined our understanding of human impact on pollution from lead over the last 2000 years, and more, at a level of precision where we are able to pinpoint down to exact years. The research is opening up a new world for climate scientists, historians and archaeologists, allowing analysis and integration of different sources of evidence at a level of chronological precision (through laser technology) that we would not have thought possible 10 years ago.
“In the next few years we are going to have unprecedented new insights into climate and environmental change, and human economic, demographic and societal changes over the last millennia that will allow us to model the future as much as providing a better understanding of the past.”
Lead poisoning
Lead is one of the most dangerous environmental pollutants and is toxic to the brain at extremely low levels. No levels of lead can be considered safe in children, according to Philip Landrigan, Dean of the Global Health for the Icahn School of Medicine at Mount Sinai Medical Center in New York, who was not connected to the study.
“It is clear that lead has lasting effects on children’s lives,” said Landrigan, whose research on lead poisoning in children was instrumental in the implementation of abatement policies since the 1970s.”
The public health implications of the Colle Gnifetti ice core findings, which Landrigan called a ‘meticulously well-done’ research, will require governments to re-evaluate lead pollution standards and abatement issues
The full report can be found online.
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