What is “a famine” often caused by in medieval Europe?

The story behind the answer

Medieval society lived on the edge of subsistence, with most calories coming from small, low-yield grain harvests. When weather turned against them—prolonged rains, late frosts, droughts, or plant diseases—harvests failed, granaries emptied, and prices soared. The “seed grain dilemma” worsened matters: eating the seed meant nothing to plant next season, locking communities into a downward spiral.

A famous example is the Great Famine of 1315–1317, when relentless rain rotted grain and hay. Draft animals starved, further reducing plowing and future yields. While warfare, trade disruptions, or livestock illness could aggravate shortages locally, the fundamental trigger for widespread hunger was simply that the fields did not produce enough to feed everyone in a world with minimal reserves and rudimentary transport.