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.