As plague swept through Europe in the mid-1300s, wiping out more than a third of the region’s population, a glacier in the Alps was recording the upheaval of medieval society.
While tens of millions of people were dying, pollen from the plants, trees and crops growing in Western Europe were being swept up by the winds and carried toward the Alps.
They became trapped in snowflakes and fell onto the region’s highest mountain, the Monte Rosa massif. Over time, the snow flattened into ever-growing layers of ice, storing a blow-by-blow record of regional environmental change.
Centuries later, the crop pollens trapped in the ice reveal the collapse of agriculture associated with the pandemic, as bad weather led to poor harvests and fields lay fallow because there was no one left to work them.
For more than 50 years, scientists have drilled ice cores in the Arctic and Antarctica to reconstruct uninterrupted records of climate change over hundreds of thousands of years. But these glaciers can be difficult to get to and they are far from where most people on Earth live.
Margit Schwikowski, an atmospheric chemist, with a sample ice core on the Colle Gnifetti glacier.CreditPaul Scherrer Institute
Mid- to low-latitude glaciers, on the other hand, tend to be more accessible and lie at the heart of thousands of years of human activity. The Colle Gnifetti glacier, sitting near the Swiss-Italian border, and with a central location on the continent, has put it on a crash course with Europe’s dust for roughly 10,000 years.
Sandra Brügger, a climate scientist at the Institute of Plant Sciences and the Oeschger Centre for Climate Change Research at the University of Bern, developed a technique to study the pollen, fungal spores, charcoal and soot locked in an ice core drilled from this Swiss glacier. She is aiming to disentangle the ways extreme weather, innovation, crop failures and pollution have shaped Europe since 1050, when Macbeth ruled Scotland.
Pollen levels rise and fall during the century, but their most pronounced peaks and valleys coincide with notable events. Europe suffered through a spate of calamities during the 14th century. Before the Black Death, there was the Great European Famine. Historical accounts tell of the relentless rains that spoiled back-to-back harvests in parts of Europe from 1315 through 1317, and may have helped bolster the plague’s grip.
Ms. Brügger tracked the cereal and hemp pollen over time, noting their rise and fall. In the early 1300s, these crop pollen levels drop precipitously. “People were starving and there wasn’t much agricultural activity anymore,” Ms. Brügger said.
The Black Death took greater hold of Europe from 1347 to 1351, killing 75 million people, and the pollens vanished as agriculture came to a halt. “There’s just nothing for five to 10 years,” she said. Then, as villages recovered, the pollen levels rebound.
The ice core reveals more than Europe’s 14th century agricultural crises. It chronicles the expansion of pastureland, the increasing globalization of the economy, the onset of industrialization and the occurrence of extensive wildfires through the ages. The results, presented at the Polar 2018 meeting in Switzerland in June, may be the first continuous study of pollen and fungal spores in a European ice core to be captured at intervals of once every decade.
Few people have conducted detailed studies of pollen in ice cores before, said Raymond Bradley, a geoscientist at the University of Massachusetts, Amherst, and an expert in using lake-bed sediment cores to reconstruct past climates. “Most ice cores are polar and they are a long way from major vegetation regimes. Those studies that were done were pretty boring, they didn’t show much,” he said.
In the fall of 2015, a six-person crew flew by helicopter from Zermatt, Switzerland, to the saddle of the Colle Gnifetti glacier. They carried with them a ton of equipment, including tents, cookstoves, food and a solar-powered drill.
“It’s a bit risky,” said Margit Schwikowski, an atmospheric chemist at the Paul Scherrer Institute and the Oeschger Centre, who is leading the study of the ice core. “You’re at 4,500 meters and you have the risk of high-altitude sickness. You don’t have time to acclimatize.”
For four days, the drill bored into the ice — and back in time — until it hit bedrock. The team flew home with two ice cores, each spanning the entire thickness of the glacier and covering 10,000 years. The ice is more compressed near the bottom of the core, so the top 65 meters of the core contain data from 1050 until 2015, with the remaining 9,000 years crammed into 50 meters of ice.
Back in the lab, Dr. Schwikowski and her colleagues dated the different sections of the ice core using water, lead and carbon isotopes, and by identifying “dating horizons” such as well-known volcanic eruptions, Saharan dust transport and nuclear weapons tests. Once the timeline was in place, Ms. Brügger began tracking pollen, spores and soot in the samples using a light microscope. In all, she counted more than 40,000 pollen grains in the ice core.
Grass pollens were abundant in the segments that corresponded to the years 1100 to 1200. During the Medieval Warm Period, temperatures in Europe and the nearby North Atlantic were as warm or warmer than they are now, and crops and forests flourished. The spike in grass pollens corresponded to the expansion of open landscapes, a transition from forests to pastures. She also found the highest levels of a spore from a fungus called Sporormiella that grows only on dung.
“It’s a sign that it’s not only an open landscape, but that we also have a lot of cattle,” she said.
[Like the Science Times page on Facebook. | Sign up for the Science Times newsletter.]
The record becomes more complex in 1750, which marks the expansion of the European economy and the start of the Industrial Revolution.
Historical records tell us that Columbus introduced maize to Europe in 1493, but maize pollen doesn’t show up in the ice core until the mid-1700s, a sign that its large-scale regional production didn’t take off immediately. It was also around this time that European society started to become more industrial and urban. This is mirrored in the ice core with the first traces of small spherical carbon particles, evidence of a transition from wood to coal burning in Central Europe.
Although poets, landowners, chroniclers and others noted these historical events, manual record-taking can be imperfect and limited in geography, and they don’t quantify their scale over the whole region. Coupling ice-core data with historical records can yield new insights, said Alexander More, historian and climate scientist at Harvard University and the Climate Change Institute at the University of Maine in Orono. “The combination provides a level of insight that is just not matched by either type on their own,” he said.
Many scientists, including Dr. Schwikowski, are concerned about the fate of these glaciers under climate change. Some glaciers are beginning to melt as temperatures rise. Meltwater from the upper layers of the glacier trickle through the airspaces between the snow granules, smearing the chemical signals and making the core unusable. Colle Gnifetti has, thus far, been spared, because of its high altitude.
“It is becoming more and more difficult to find a glacier that is not melting and that can still be used for research,” said Dr. Schwikowski. “The object for our research is melting away.”
