The famine of 1740–41 was due to extremely cold and then rainy weather in successive years, resulting in food losses in three categories: a series of poor grain harvests, a shortage of milk, and frost damage to potatoes. At this time, grains, particularly oats, were more important than potatoes as staples in the diet of most workers.
Deaths from mass starvation in 1740–41 were compounded by an outbreak of fatal diseases. The cold and its effects extended across Europe, but mortality was higher in Ireland because both grain and potatoes failed. This is now considered by scholars to be the last serious cold period at the end of the Little Ice Age of about 1400–1800.
By the mid-19th century's better-known Great Famine of 1845–1852, potatoes made up a greater portion of the Irish diets, with adverse consequences when the crops failed. This famine differed by "cause, scale and timing:" it was caused by an oomycete infection which destroyed much of the potato crop for several years running. The crisis was exacerbated by insufficient relief and extreme government regulations.
In 1740 Ireland had a population of 2.4 million people, most of whom depended on grains (oats, wheat, barley and rye) and potatoes as their staple foods. Half their expenses for food went for grain, 35% for animal products and the remainder for potatoes. Some survived only on oatmeal, buttermilk and potatoes. Over a year, daily consumption of potatoes was estimated at 2.7 to 3.2 kg (6 to 7 lb) per person. Diets varied according to village locations and individual income, with many people supplementing these staples with river, lake or sea fish, especially herring, and small game such as wild duck. Most social welfare, such as it was, was provided locally on the parish or village level. The government was not organized for large-scale relief efforts.
An extraordinary climatic shock, the "Great Frost", struck Ireland and the rest of Europe between December 1739 and September 1741, after a decade of relatively mild winters. Its cause remains unknown. Charting its course sharply illuminates how climate events can result in famine and epidemic disease, and affect economies, energy sources, and politics.