The Year Without a Summer was an agricultural disaster; historian John D. Post called it "the last great
subsistence crisis in the Western world". The climatic aberrations of 1816 had their greatest effect on
New England (US),
Atlantic Canada, and Western Europe. The main cause of the Year Without a Summer is generally held to be a
volcanic winter created by the April 1815
eruption of Mount Tambora on
Sumbawa. The eruption had a
volcanic explosivity index (VEI) ranking of 7, and ejected at least of
dense-rock equivalent material into the atmosphere. It remains the most recent confirmed VEI-7 eruption to date. Other large volcanic eruptions (of at least VEI-4) around this time include: • The
1808 mystery eruption in the southwestern Pacific Ocean • 1812,
La Soufrière on
Saint Vincent in the Caribbean • 1812,
Awu in the Sangihe Islands,
Dutch East Indies • 1813,
Suwanosejima in the
Ryukyu Islands • 1814,
Mayon in the
Philippines These eruptions had built up a substantial amount of atmospheric dust, and thus temperatures fell worldwide as the airborne material blocked sunlight in the
stratosphere. According to a 2012 analysis by
Berkeley Earth, the 1815 Tambora eruption caused a temporary drop in the Earth's average land temperature of about one degree Celsius; smaller temperature drops were recorded from the 1812–1814 eruptions. The Earth had already been in a centuries-long period of cooling that began in the 14th century. Known today as the
Little Ice Age, it had already caused considerable agricultural distress in Europe. The eruption of Tambora occurred near the end of the Little Ice Age, exacerbating the background global cooling of the period. This period also occurred during the
Dalton Minimum, a period of relatively low
solar activity from 1790 to 1830. May 1816 had the lowest
Wolf number (0.1) to date since records on solar activity began. It is not yet known, however, if and how changes in solar activity affect Earth's climate, and this correlation does not prove that lower solar activity produces global cooling.
Africa No direct evidence for conditions in the
Sahel region have been found, though conditions from surrounding areas have implied above-normal rainfall. Below the Sahel, the coastal regions of West Africa likely experienced below-normal levels of precipitation. Severe storms affected the South African coast during the Southern Hemisphere winter. On July 29–30, 1816, a violent storm occurred near
Cape Town, South Africa, which brought forceful northerly winds and
hail and caused severe damage to shipping.
Asia The
monsoon season in China was disrupted, resulting in overwhelming floods in the
Yangtze Valley. Fort
Shuangcheng reported fields disrupted by frost and conscripts deserting as a result. Summer snowfall or otherwise
mixed precipitation was reported in various locations in
Jiangxi and
Anhui. In
Taiwan, snow was reported in
Hsinchu and
Miaoli, and frost was reported in
Changhua. A large-scale famine in
Yunnan helped reverse the fortunes of the ruling
Qing dynasty. In India, the delayed summer monsoon caused late torrential rains that aggravated the spread of
cholera from a region near the
Ganges in
Bengal to as far as Moscow. In Bengal, abnormal cold and snow was reported in the winter monsoon. concentration in
ice cores from
Greenland. An
unknown eruption occurred before 1810. The peak after 1815 was caused by Mount Tambora.
Europe As a result of the series of volcanic eruptions in the 1810s, crops had been poor for several years; the final blow came in 1815 with the eruption of Tambora. Europe, still recuperating from the
Napoleonic Wars, suffered from widespread food shortages, resulting in its worst famine of the century. Low temperatures and heavy rains resulted in failed harvests in Great Britain and Ireland. Famine was prevalent in north and southwest Ireland, following the failure of wheat,
oat, and potato harvests.
Food prices rose sharply throughout Europe. With the cause of the problems unknown, hungry people demonstrated in front of grain markets and bakeries.
Food riots took place in many European cities. Though riots were common during times of hunger, the food riots of 1816 and 1817 were the most violent period on the continent since the
French Revolution. Widespread flooding of Europe's major rivers is attributed to the event, as is frost in August. Hungary experienced snowfall colored brown by volcanic ash; in northern Italy, red snow fell throughout the year. In
Switzerland, famine was limited to the east, which was densely populated and more industrialized. Harvests were not affected everywhere. In Scandinavia and the northern Baltic regions were almost normal, as they were in eastern Europe and western Russia. Indeed, the Russian Emperor
Alexander I was able to donate grain to western Europe.
North America In the spring and summer of 1816, a persistent "dry fog" was observed in parts of the eastern United States. The fog reddened and dimmed sunlight such that
sunspots were visible to the naked eye. Neither wind nor rainfall dispersed the "fog", retrospectively characterized by
Clive Oppenheimer as a "stratospheric
sulfate aerosol veil". The weather was not in itself a hardship for those accustomed to long winters. Hardship came from the weather's effect on crops and thus on the supply of food and firewood. The consequences were felt most strongly at higher elevations, where farming was already difficult even in good years. In May 1816,
frost killed off most crops in the higher elevations of
Massachusetts,
New Hampshire,
Vermont, and
upstate New York. On June 6, snow fell in
Albany, New York, and
Dennysville, Maine. In
Cape May, New Jersey, frost was reported five nights in a row in late June, causing extensive crop damage. Though fruit and vegetable crops survived in New England, corn was reported to have ripened so poorly that no more than a quarter of it was usable for food, and much of it was moldy and not even fit for animal feed. At the Church Family of
Shakers near
New Lebanon, New York, Nicholas Bennet wrote in May 1816 that "all was froze" and the hills were "barren like winter". Temperatures fell below freezing almost every day in May. The ground froze on June 9; on June 12, the Shakers had to replant crops destroyed by the cold. On July 7, it was so cold that all of their crops had stopped growing. Salem, Massachusetts physician Edward Holyoke—a weather observer and amateur astronomer—while in Franconia, New Hampshire, wrote on June 7, "exceedingly cold. Ground frozen hard, and squalls of snow through the day. Icicles 12 inches long in the shade of noon day." After a lull, by August 17, Holyoke noted an abrupt change from summer to winter by August 21, when a meager bean and corn crop were killed. "The fields," he wrote, "were as empty and white as October." The
Berkshires saw frost again on August 23, as did much of New England and upstate New York. Massachusetts historian William G. Atkins summed up the disaster: Severe frosts occurred every month; June 7th and 8th snow fell, and it was so cold that crops were cut down, even freezing the roots ... In the early Autumn when corn was in the milk [the
endosperm inside the kernel was still liquid] it was so thoroughly frozen that it never ripened and was scarcely worth harvesting. Breadstuffs were scarce and prices high and the poorer class of people were often in straits for want of food. It must be remembered that the granaries of the great west had not then been opened to us by railroad communication, and people were obliged to rely upon their own resources or upon others in their immediate locality. In July and August, lake and river ice was observed as far south as northwestern
Pennsylvania. Frost was reported in
Virginia on August 20 and 21. Rapid, dramatic temperature swings were common, with temperatures sometimes reverting from normal or above-normal summer temperatures as high as to near-freezing within hours.
Thomas Jefferson, by then retired from politics to his estate at
Monticello in Virginia, sustained crop failures that sent him further into debt. On September 13, a Virginia newspaper reported that corn crops would be one half to two-thirds short and lamented that "the cold as well as the drought has nipt the buds of hope". A
Norfolk, Virginia, newspaper reported: It is now the middle of July, and we have not yet had what could properly be called summer. Easterly winds have prevailed for nearly three months past ... the sun during that time has generally been obscured and the sky overcast with clouds; the air has been damp and uncomfortable, and frequently so chilling as to render the fireside a desirable retreat. Regional farmers succeeded in bringing some crops to maturity, but
corn and other
grain prices rose dramatically. The price of
oats, for example, rose from 12¢ per
bushel in 1815 to 92¢ per bushel in 1816. Crop failures were aggravated by inadequate transportation infrastructure; with few roads or navigable inland waterways and no railroads, it was prohibitively expensive to import food in most of the country. Maryland experienced brown, bluish, and yellow snowfall in April and May, colored by volcanic ash in the atmosphere.
South America A newspaper account of northeastern Brazil was published in the United Kingdom:By an arrival at Liverpool we have received accounts from
Pernambuco of the 8th of Feb. [1817], which state that a most uncommon drought has been experienced in the tropical regions of the Brazils, or that part of the country between Pernambuco and
Rio Janiero. By this circumstance all the streams had been dried up, the cattle were dying or dead, and all the population emigrating to the borders of the great rivers in search of water. The greatest distress prevailed, provisions were wanting, and the mills completely at a stand. They have no windmills, so that no corn could be ground. Vessels have been sent from Pernambuco to the United States to fetch flour, and what had tended to increase this distress was the interruption of the coasting trade through the dread of war with
Buenos Ayres. ==Societal effects==