Mud is one of the signature horrors of the First World War. Photographs, paintings, and poems capture nightmarish landscapes pitted with shell craters and slick with oozing earth. Soldiers manning flooded defences risked succumbing to trench foot, while attacking troops could find themselves literally bogged down. But such haunting conditions were not an automatic consequence of the stalemate on the Western Front. While the struggle for a military breakthrough forced soldiers to live in subterranean shelters all year round, these troops were not experiencing normal weather. Instead, study of material preserved in an ice core from the heart of Europe has revealed that fighting overlapped with an extreme climatic anomaly, lasting from 1914 to 1919. This once-in-a-century event saw air arriving from the North Atlantic, bringing cold conditions and increased rainfall. Charting this anomaly sheds new light on both wartime conditions and the 1918-1919 ‘Spanish Flu’ pandemic. This, though, is only the most-recent finding from the Historical Ice Core Project, funded by the Arcadia Foundation, which is shedding extraordinary new light on human activity over thousands of years.Counting backwards
‘It started when I won an amazing award out of the blue back in 2002’, remembers Michael McCormick, Professor of Medieval History at Harvard University. ‘It was from the Mellon Foundation in New York, and was called the “Distinguished Achievement Award”. This came with a grant to spend on whatever research I wanted within three years, so I put together workshops to bring together people who wouldn’t otherwise meet. The very first one was on climate science and the human past, which involved archaeologists, historians, and climate scientists like Paul Mayewski, the great ice-core specialist. We spent a whole day brainstorming whether we could do anything with ice-core data that would have a tight-enough chronology to be of use to archaeologists and historians. So we came up with a project to use Paul’s measurements of volcanic events from a Greenland ice core alongside historical sources from Charlemagne’s time, to see if there was any connection with the written record. Lo and behold, we found a very close connection, with volcanic events leading to cold summers, harsh winters, failed harvests, famines, and political instability. So Paul and I thought how wonderful it would be to do a new ice core ourselves, with historical questions in mind.’
Securing an ice core from a region closer to where human activity was focused presented a desirable first step, and the late Dietmar Wagenbach from the University of Heidelberg successfully championed Colle Gnifetti, in the Swiss-Italian Alps. This target, though, posed significant challenges. ‘A core there was expected to cover 4,000 years, but the complication is that you don’t get very thick annual layers of ice,’ explains Paul Mayewski, director and professor of the Climate Change Institute, University of Maine. ‘There are two reasons for that. One is that there is a lot of wind, so you lose part of each year – typically the winter, when it’s windier – and, when the snow does settle and turn to ice, it compresses the earlier layers. So our core from Colle Gnifetti is 72m long, but the lowest 2m covers 2,000 years, because the individual annual layers have become so thin. The very best sampling resolution that labs had been able to attain was 1cm resolution, so that gives 100 samples per metre. That meant you couldn’t even get one sample per year in the very deep parts. So we developed a new technology, with funding from the W M Keck Foundation. Instead of 100 samples per metre, we can now use a laser and get 10,000 and, in some cases, 20,000 samples. All of a sudden, we had the ability to match the written records, to distinguish not only years but seasons, and even the number of storm events per season.’
‘When we use the laser, we have a chamber that keeps the ice cold, while a video camera shows us what is happening in real time. It looks like a worm digging an immense trench, but it’s so magnified that when you pull the ice out you can’t even see a scratch on it, the laser is taking such a small sample. So the core remains available for future study. This is very important, because many of the cores we have collected are from places where the ice has since melted and is gone. In future decades, when even more advanced techniques are available, these cores could be the climatic equivalent of a Rosetta Stone. I like to say that ice cores are like buried meteorological stations, except that, unlike meteorological stations, you also get air chemistry. This tells you where air masses are coming from, and whether or not human activity in the form of producing pollution has been important. There is a tendency to think that Europe had this beautiful, pristine environment during the Middle Ages, and that only changed with coal-burning during the Industrial Revolution. But it’s not true: the ice core shows that we’ve been impacted by things like lead pollution for a long time.’
It was a sudden fluctuation in lead pollution that helped the team establish they were successfully isolating the individual annual ice layers. ‘We moved very carefully’, says Michael, ‘to make sure that our chronology was completely robust. We were counting invisible layers, using chemical spikes from Saharan dust that was deposited every summer. We knew we were on the right track when we looked at the first run of results and saw that there was a huge drop in the lead readings in 1349. I asked Pascal Bohleber, then at the University of Heidelberg, who had done this meticulous study of the layer counting, “There are always problems with ice cores that need correcting, so tell me, what corrections did you make to get the lead fall to occur in 1349?” Pascal replied, “There were no corrections. I got it from counting backwards. Why, did something happen in 1349?” So that led us to look at the effects of the 1348-1349 Black Death.’
‘The Black Death was one of the worst pandemics in history,’ says Alexander More, of Harvard University and the Climate Change Institute. ‘And it had the worst death rate, which was 40%-60%. It’s been argued that famine caused by climate instability just before the Black Death may have contributed to this, because people were malnourished, which made them weaker. We’ve been able to use our climate data to corroborate that argument. Something we’ve always known is that the pandemic had an enormous impact on the economy, which essentially stopped, and now we know that air pollution also dropped dramatically in 1349. For five years, the air was clean, and the ice core shows that this is the only period over the last 2,000 years when that was the case. Why? Because so many people were dead.’
‘We published a paper looking at this back in 2017, and at the time we had some people criticising it, saying “No, no, that’s not possible”, but now we can see that it’s effectively a much more extreme example of what happened in Europe this March, April, and May, when pollution reduced during the COVID pandemic. Our data are also relevant for the baseline established for gauging modern levels of pollution, because that’s based on the assumption that levels before the Industrial Revolution were pretty much what was normal. Now we know that’s not true. Over the last two millennia, we’ve only had clean air for five years.’ As well as reflecting activity by past populations, this lead pollution potentially carried health implications for them, as exposure can have various harmful consequences, including reduced attention spans and heightened aggression.
It was not just an event of the magnitude of the Black Death that had a measurable impact on lead pollution. ‘Lead is a proxy for the production of silver,’ points out Christopher Loveluck, Professor of Medieval European Archaeology at the University of Nottingham. ‘During the Black Death, there was a pan-European effect on economic activity. The ice core has potential to give a true regional picture of the scale of production at different points in the past. That has never before been possible, from either textual records or archaeological sites, but ice-core records give you a macro-economic total. To capitalise on that, though, you need to source where the pollution is coming from. So I have been chasing information from peat cores and manufacturing evidence around Europe. A lot of the time, this ends up proving negatives: we look at the wind direction and climate evidence, I examine the archaeological evidence, and we rule out regions that couldn’t have produced certain pollution signatures. That allows us to arrive at the regions that could have contributed to the picture we are seeing.’
‘From that, it became apparent that a lot of our signals are coming from north-west Europe. They were basically travelling on winds following a north-west to south-east axis from Iceland over Britain and northern France, and eventually to the Alps. For example, the ice core gives us a yearly political economy from 1170-1216 for the Angevin Empire in England, which is basically the period of Henry II, Richard the Lionheart, and John. I looked at the Pipe Rolls, which record production and silver taxation payments from English mines annually, and the peaks and troughs in lead pollution from our Alpine ice core matched exactly the yearly levels of production/taxation in the Peak District, including stoppages due to war and royal succession. We’re very lucky in Britain – this was only possible because we’ve been massively bureaucratic for over 1,000 years!’
Lead pollution can also shine new light on less-well-documented eras, including the 7th century, when Europe embarked on the first large-scale production of silver coinage since the fall of the Roman Empire. ‘We have a clear chronology now,’ says Michael. ‘We can see when gold coins were being adulterated with silver in the 640s, and then the shift to full silver production between 660 and 680. That is more or less what numismatists had suspected. In the past, though, it was generally thought that this shift from gold to silver was one of desperation, because there was no new gold in the West, and the old Roman coins were wearing out. So the Carolingians were forced to melt down Roman candlesticks made of silver, and use that for coinage. That’s suggestive of a small-scale desperate measure as the economy ground to a halt. But the signature we’re seeing in the ice core is of a major new source of silver being found and exploited, which fits with a 7th-century radiocarbon date from a mine at Melle in western France. So they’re ramping up production, and they’re choosing to go with silver coins, and that suggests an expanding economy, which is big news. Then, within 20 years, you have the first mention of a wic-port at London, and trading emporia using silver pennies spreading around the North Sea.’
Winds of war
The team are now turning their attention from pollution to climate, leading them to the cold and wet spell coinciding with the First World War and the ‘Spanish Flu’ pandemic. ‘It was a tragic combination,’ says Christopher. ‘Historians have commented before that bad weather, particularly wet conditions, made things an awful lot worse. Previous scholars, though, have been hampered by the temperature records from the environs of the Western Front being – entirely understandably – very erratic. What we’ve done is scientifically identify in the ice core a specific short-term climatic anomaly that contributed the bad weather. We can see large-scale and recurrent cold and wet marine air being blown in from the North Atlantic, which very unhappily coincided with the height of the First World War, exacerbating casualty rates. You get the repetitive impact of the bad weather on key battles. This is particularly true of Passchendaele – the 3rd Battle of Ypres in 1917 – but it also affected earlier ones, such as the 1914-1915 Battle of Champagne. The consequences of this climatic anomaly were heightened by the nature of the fighting: trench warfare leaves soldiers vulnerable to the effects of wet and cold conditions. So that means millions of troops with depressed immune systems, making them highly susceptible to disease.’
It is even possible that the fighting managed to aggravate the negative effects of the climatic anomaly. ‘The World War I period is pretty much unique when compared to the previous 50-70 years, or the following years up until the present’, notes Paul. ‘So what is it about World War I? This is only conjecture, but perhaps we should factor in the potential climatic consequences of war. The immense destruction from shelling, gas, and burning in World War I is exactly the way you can create cooling. All the smoke shades incoming radiation from the sun, and also acts to nucleate and precipitate moisture, potentially making conditions even colder and wetter. So there is certainly a possibility that this anomalous climatic event occurred as a consequence of the devastation of World War I, at a time when there was already an unfortunate influx of North Atlantic air.’
It was into these dire circumstances that ‘Spanish Flu’ or H1N1 arrived in the winter of 1917-1918. ‘Some historians have suggested that it was carried to the Western Front by Allied soldiers recruited in Asia,’ says Alexander. ‘But no one has previously asked why it became so virulent during the second wave of the disease in the fall of 1918. We only have ballpark figures, but at least one third of the world population was infected – that’s 500 million people – and 50 million people died. Some have argued that chemical weapons – especially chlorine gas – used in battles caused the virus to mutate and become more deadly. That’s possible. There is more evidence, though, that the climatic anomaly was significant when considered alongside the main vector of this disease. In this case, we know that the major carrier is the mallard duck, where the population has a 60% infection rate every fall. Birds that survive act as a melting pot for various diseases, which create new strains that can become very virulent.’
‘Now, I’m not arguing that mallard ducks were hanging out in trenches during the war. As my colleague Prof. Loveluck says, “Ducks don’t like things that go boom”. What I am arguing is that the abundance of water from precipitation may have led to contamination from ponds frequented by ducks getting into either drinking water, or places where people were walking, like trenches. That then makes the jump from birds into humans fairly easy. Another factor is that the annual migration of mallard ducks is very, very sensitive to changes in climate, which could have resulted in more of them in Europe during this critical period. We can’t know, though – we can only guess that contaminated water was a factor. But it is easy to see how the virus could be spread by millions of troops returning home at the end of the war in 1918. What we do know for certain is that climate changes health, because climate changes the behaviour of animals, and it changes the behaviour of people. They have to start looking for food and water in new places, outside their usual habitat. And they take their diseases with them, creating new opportunities for them to spread.’
Climate is also having a major impact on the ice that preserved these records of past events. ‘It is not easy to find places in equatorial and mid-latitudes where ice cores aren’t melting rapidly,’ says Paul. ‘We’re having to look higher and higher in the mountains. Compared to when I started working in the Himalayas, you now have to go 1,000 to 1,500m higher to get the same sort of preservation. We’re losing the entire archive. It’s the equivalent of a library burning down, except in this case there aren’t going to be many other libraries you could turn to when you try to recover the lost information. Many of us are currently working to secure as many cores as we can, so that these will be available for the future.’
‘Studying the ice core allows us to see new things that we could not pick out without it’, Michael adds. ‘For instance, we can trace the signatures left by environmental conditions giving rise to bad harvests – and good harvests – back through time. All of this changes what we can extract from the existing historical and archaeological records.’
Historical Ice Core Project publications include:
A More et al. (2020) ‘The impact of a six-year climate anomaly on the “Spanish Flu” pandemic and WWI’, GeoHealth 4 (9): e2020GH000277 (https://doi.org/10.1029/2020GH000277).
C Loveluck et al. (2020) ‘Alpine ice and the annual political economy of the Angevin Empire, from the death of Thomas Becket to Magna Carta, c.AD 1170-1216’, Antiquity 94 (374): 473-490 (https://doi.org/10.15184/aqy.2019.202).
C Loveluck et al. (2018) ‘Alpine ice-core evidence for the transformation of the European monetary system, AD 640-670’, Antiquity 92 (366): 1,571-1,585 (https://doi.org/10.15184/aqy.2018.110).
A More et al. (2017) ‘Next generation ice-core technology reveals true minimum natural levels of lead (Pb) in the atmosphere: insights from the Black Death’, GeoHealth 1 (4): 211-219 (https://doi.org/10.1002/2017GH000064).
CWA is grateful to Alexander More, Christopher Loveluck, Michael McCormick, Paul Mayewski, and Katie Andrews.