New Englanders and eastern Canada were hit the hardest by the reduced temperatures. In May of 1816 frost killed off much of the crops that had been planted, and in June two large snowstorms resulted in many human deaths as well. In July and August ice formed on the lakes in Canada. Farmers south of New England did succeed in bringing some crops to maturity, but maize (corn) and other grain prices rose dramatically. Oats, for example, rose from 12 cents a bushel the previous year to 92 cents a bushel.
Europe, still recuperating from the Napoleonic Wars, suffered from food shortages. Food riots broke out in Britain and France and grain warehouses were looted. The violence was worse in landlocked Switzerland, where famine caused the government to declare a national emergency.
American climatologist William Humphreys eventually determined the cause of the year without summer in 1920, after reading a treatise written by Ben Franklin in 1783 blaming the unusually cool summer of that year on volcanic dust coming from Iceland.