A LOOK BACK: 1815 Mount Tambora and the Year Without a Summer

Written by Mark Vogan on July 2, 2016 in Rest of Europe, Summer 2016, United Kingdom & Ireland, United States of America with 0 Comments

UCAR Article

The summer of 1816 was not like any summer people could remember. Snow fell in New England. Gloomy, cold rains fell throughout Europe. It was cold and stormy and dark – not at all like typical summer weather. Consequently, 1816 became known in Europe and North America as “The Year Without a Summer.”

Why was the summer of 1816 so different? Why was there so little warmth and sunshine in Europe and North America? The answer could be found on the other side of the planet – at Indonesia’s Mount Tambora.

On April 5, 1815, Mount Tambora, a volcano, started to rumble with activity. Over the following four months the volcano exploded – the largest volcanic explosion in recorded history. Many people close to the volcano lost their lives in the event. Mount Tambora ejected so much ash and aerosols into the atmosphere that the sky darkened and the Sun was blocked from view. The large particles spewed by the volcano fell to the ground nearby, covering towns with enough ash to collapse homes. There are reports that several feet of ash was floating on the ocean surface in the region. Ships had to plow through it to get from place to place.

But the smaller particles spewed by the volcano were light enough to spread through the atmosphere over the following months and had a worldwide effect on climate. They made their way into the stratosphere, where they could distribute around the world more easily. Earth’s average global temperature dropped three degrees Celsius. The effect was temporary. Eventually, even the smallest particles of ash and aerosols released by the volcano fell out of the atmosphere, letting in the sunshine.

The Year Without a Summer had many impacts in Europe and North America. Crops were killed – either by frost or a lack of sunshine. This caused food to be scarce, and caused farmers who were able to grow crops to fear that they would be robbed. The lack of successful crops that summer made the food which was grown more valuable, and the price of food climbed. Because the price of oats increased, it was more expensive for people to feed their horses. Horses were the main method of transportation, so with expensive oats, the cost of travel increased. This may have been one of the factors that inspired a German man named Karl Drais to invent a way to get around without a horse: the bicycle.

The gloomy summer weather also inspired writers. During that summer-less summer, Mary Shelley, her husband, the poet Percy Bysshe Shelley, and poet Lord Byron were on vacation at Lake Geneva. While trapped indoors for days by constant rain and gloomy skies, the writers described the bleak, dark environment of the time in their own ways. Mary Shelley wrote Frankenstein, a horror novel set in an often stormy environment. Lord Byron wrote the poem Darkness, which begins, “I had a dream, which was not all a dream. The bright sun was extinguish’d.”

Year Without a Summer

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Year Without a Summer
1816 summer temperature anomaly compared to average temperatures from 1971–2000
Volcano	Mount Tambora
Date	April 10, 1815
Type	Ultra Plinian
Location	Lesser Sunda Islands, Dutch East Indies 8°15′S 118°0′E / 8.250°S 118.000°E / -8.250; 118.000
VEI	7
Impact	Caused a volcanic winter that dropped temperatures by 0.4 to 0.7 °C worldwide

The year 1816 is known as the Year Without a Summer (also the Poverty Year, the Summer that Never Was, Year There Was No Summer, and Eighteen Hundred and Froze to Death^[1]), because of severe climate abnormalities that caused average global temperatures to decrease by 0.4–0.7 °C (0.7–1.3 °F).^[2] This resulted in major food shortages across the Northern Hemisphere.^[3]

Evidence suggests that the anomaly was predominantly a volcanic winter event caused by the massive 1815 eruption of Mount Tambora in the Dutch East Indies, the largest eruption in at least 1,300 years after the extreme weather events of 535–536. The Earth had already been in a centuries-long period of global cooling that started in the 14th century. Known today as the Little Ice Age, it had already caused considerable agricultural distress in Europe. The Little Ice Age’s existing cooling was aggravated by the eruption of Tambora, which occurred during its concluding decades.^[4]

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Description[edit]

The Year Without a Summer was an agricultural disaster. Historian John D. Post has called this “the last great subsistence crisis in the Western world”.^[5]^[6] The unusual climatic aberrations of 1816 had the greatest effect on most of New England, Atlantic Canada, and parts of western Europe. Typically, the late spring and summer of central and northern New England and southeastern Canada are relatively stable: temperatures (average of both day and night) average between about 20 and 25 °C (68 and 77 °F) and rarely fall below 5 °C (41 °F).

North America[edit]

In the spring and summer of 1816, a persistent “dry fog” was observed in parts of the eastern U.S. The fog reddened and dimmed the sunlight, such that sunspots were visible to the naked eye. Neither wind nor rainfall dispersed the “fog”. It has been characterized as a “stratospheric sulfate aerosol veil”.^[7]

At higher elevations, where farming was problematic in good years, the cooler climate did not quite support agriculture. In May 1816,^[1] frost killed off most crops in the higher elevations of Massachusetts, New Hampshire, and Vermont as well as upstate New York. On June 6, snow fell in Albany, New York, and Dennysville, Maine.^[8]

Many commented on the phenomenon. Sarah Snell Bryant, of Cummington, Massachusetts, wrote in her diary, “Weather backward.”^[9]

At the Church Family of Shakers in upstate New York, near New Lebanon, Nicholas Bennet wrote in May 1816, “all was froze” and the hills were “barren like winter”. Temperatures went below freezing almost every day in May. The ground froze solid on June 9. On June 12, the Shakers had to replant crops destroyed by the cold. On July 7, it was so cold, everything had stopped growing. The Berkshire Hills had frost again on August 23, as did much of the upper northeast.^[10]

A Massachusetts historian 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 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.^[11]

In Cape May, New Jersey, frost was reported five nights in a row in late June, causing extensive crop damage.^[12]

In July and August, lake and river ice was observed as far south as northwestern Pennsylvania. Frost was reported as far south as Virginia on August 20 and 21.^[13] Rapid, dramatic temperature swings were common, with temperatures sometimes reverting from normal or above-normal summer temperatures as high as 95 °F (35 °C) to near-freezing within hours. The weather was not in itself a hardship for those accustomed to long winters. The real problem lay in the weather’s effect on crops and thus on the supply of food and firewood. Thomas Jefferson, retired from the presidency and farming 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”.^[14] A Norfolk, Virginia Newspaper complained:

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.^[15]

Regional farmers did succeed in bringing some crops to maturity, but corn and other grain prices rose dramatically. The price of oats, for example, rose from 12¢ a bushel ($3.40/m³) in 1815 (equal to $1.55 today) to 92¢ a bushel ($26/m³) in 1816 ($12.83 today). Crop failures were aggravated by an inadequate transportation network: with few roads or navigable inland waterways and no railroads it was expensive to import food.^[16]

Europe[edit]

Cool temperatures and heavy rains resulted in failed harvests in Britain and Ireland. Families in Wales travelled long distances as refugees, begging for food. Famine was prevalent in north and southwest Ireland, following the failure of wheat, oats, and potato harvests. In Germany, the crisis was severe; food prices rose sharply. With the cause of the problems unknown, people demonstrated in front of grain markets and bakeries, and later riots, arson, and looting took place in many European cities. It was the worst famine of 19th-century Europe.^[8]^[17]

The effects were widespread and lasted beyond the winter. In western Switzerland, the summers of 1816 and 1817 were so cool that an ice dam formed below a tongue of the Giétro Glacier high in the Val de Bagnes. Despite engineer Ignaz Venetz‘s efforts to drain the growing lake, the ice dam collapsed catastrophically in June 1818.^[18]

Asia[edit]

In China, the cold weather killed trees, rice crops, and even water buffalo, especially in the north. Floods destroyed many remaining crops. Mount Tambora’s eruption disrupted China’s monsoon season, resulting in overwhelming floods in the Yangtze Valley. In India, the delayed summer monsoon caused late torrential rains that aggravated the spread of cholera from a region near the River Ganges in Bengal to as far as Moscow.^[19]

Causes[edit]

The aberrations are now generally thought to have occurred because of the April 5–15, 1815, Mount Tambora volcanic eruption^[20]^[21] on the island of Sumbawa, Indonesia (then part of the Dutch East Indies, but under French rule during Napoleon’s occupation of the Netherlands), described by Thomas Stamford Raffles.^[22] The eruption had a volcanic explosivity index (VEI) ranking of 7, a supercolossal event that ejected immense amounts of volcanic ash into the upper atmosphere. It was the world’s largest eruption since the Hatepe eruption in 180 AD.

Other large volcanic eruptions (with VEIs at least 4) around this time were:

1812, La Soufrière on Saint Vincent in the Caribbean
1812, Awu in the Sangihe Islands, Dutch East Indies
1813, Suwanosejima in the Ryukyu Islands, Japan
1814, Mayon in the Philippines

These eruptions had already built up a substantial amount of atmospheric dust. As is common after a massive volcanic eruption, temperatures fell worldwide because less sunlight passed through the stratosphere.^[23]

According to a 2012 analysis by Berkeley Earth Surface Temperature, the 1815 Tambora eruption caused a temporary drop in the Earth’s average land temperature of about 1 °C. Smaller temperature drops were recorded from the 1812–1814 eruptions.^[24]

This period also occurred during the Dalton Minimum (a period of relatively low solar activity), specifically Solar Cycle 6, which ran from December 1810 to May 1823. May 1816 in particular had the lowest sunspot number (0.1) to date since record keeping on solar activity began. The lack of solar irradiance during this period was exacerbated by atmospheric opacity from volcanic dust.

Effects[edit]

As a result of the series of volcanic eruptions, crops in the aforementioned areas 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 food shortages. Food riots broke out in the United Kingdom and France, and grain warehouses were looted. The violence was worst in landlocked Switzerland, where famine caused the government to declare a national emergency. Huge storms and abnormal rainfall with flooding of Europe’s major rivers (including the Rhine) are attributed to the event, as is the August frost. A major typhus epidemic occurred in Ireland between 1816 and 1819, precipitated by the famine caused by the Year Without a Summer. An estimated 100,000 Irish perished during this period. A BBC documentary, using figures compiled in Switzerland, estimated that the fatality rates in 1816 were twice that of average years, giving an approximate European fatality total of 200,000 deaths.

New England also experienced major consequences from the eruption of Tambora. The corn crop was significantly advanced in New England and the eruption caused the crop to fail. In the summer of 1816, corn was reported to have ripened so badly that no more than a quarter of it was usable for food. The crop failures in New England, Canada, and parts of Europe also caused the price of wheat, grains, meat, vegetables, butter, milk, and flour to rise sharply.

The eruption of Tambora also caused Hungary to experience brown snow. Italy’s northern and north-central region experienced something similar, with red snow falling throughout the year. The cause of this is believed to have been volcanic ash in the atmosphere.

In China, unusually low temperatures in summer and fall devastated rice production in Yunnan, resulting in widespread famine. Fort Shuangcheng, now in Heilongjiang, 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, located at around 30°N. In Taiwan, which has a tropical climate, snow was reported in Hsinchu and Miaoli, and frost was reported in Changhua.^[25]

Cultural effects[edit]

Hong Kong sunset circa 1992 after the eruption of Mount Pinatubo

High levels of tephra in the atmosphere led to unusually spectacular sunsets during this period, a feature celebrated in the paintings of J. M. W. Turner. This may have given rise to the yellow tinge predominant in his paintings such as Chichester Canal circa 1828. Similar phenomena were observed after the 1883 eruption of Krakatoa, and on the West Coast of the United States following the 1991 eruption of Mount Pinatubo in the Philippines.

The lack of oats to feed horses may have inspired the German inventor Karl Drais to research new ways of horseless transportation, which led to the invention of the draisine or velocipede. This was the ancestor of the modern bicycle and a step toward mechanized personal transport.^[26]

The crop failures of the “Year without a Summer” may have helped shape the settling of the “American Heartland“, as many thousands of people (particularly farm families who were wiped out by the event) left New England for what is now western and central New York and the Midwest (then the Northwest Territory) in search of a more hospitable climate, richer soil, and better growing conditions.^[27] British historian Lawrence Goldman has suggested that this migration into the Burned-over district was responsible for the centering of the anti-slavery movement in that region.^[28]

Chichester Canal by J. M. W. Turner (1828)

According to historian L. D. Stillwell, Vermont alone experienced a decrease in population of between 10,000 and 15,000, erasing seven previous years of population growth.^[6] Among those who left Vermont were the family of Joseph Smith, who moved from Norwich, Vermont (though he was born in Sharon, Vermont) to Palmyra, New York.^[29] This move precipitated the series of events that culminated in the publication of the Book of Mormon and the founding of the Church of Jesus Christ of Latter-day Saints.^[19]

In June 1816, “incessant rainfall” during that “wet, ungenial summer” forced Mary Shelley, John William Polidori, and their friends to stay indoors at Villa Diodati overlooking Lake Geneva for much of their Swiss holiday.^[28]^[30]^[31] They decided to have a contest to see who could write the scariest story, leading Shelley to write Frankenstein, or The Modern Prometheus and Lord Byron to write “A Fragment“, which Polidori later used as inspiration for The Vampyre^[32] — a precursor to Dracula. In addition, Lord Byron was inspired to write the poem “Darkness“, by a single day when “the fowls all went to roost at noon and candles had to be lit as at midnight”.^[28]

Justus von Liebig, a chemist who had experienced the famine as a child in Darmstadt, later studied plant nutrition and introduced mineral fertilizers.

Comparable events[edit]

Toba catastrophe 70,000 to 75,000 years ago
The 1628–26 BCE climate disturbances, usually attributed to the Minoan eruption of Santorini
The Hekla 3 eruption of about 1200 BCE, contemporary with the historical Bronze Age collapse
The Hatepe eruption (sometimes referred to as the Taupo eruption), around 180 CE
Extreme weather events of 535–536 have been linked to the effects of a volcanic eruption, possibly at Krakatoa, or Ilopango in El Salvador.
The Heaven Lake eruption of Paektu Mountain between North Korea and the People’s Republic of China, in 969 (± 20 years), is thought to have had a role in the downfall of Balhae.
An eruption of Mount Rinjani on the island of Lombok in 1257
An eruption of Kuwae, a Pacific volcano, has been implicated in events surrounding the Fall of Constantinople in 1453.
An eruption of Huaynaputina, in Peru, caused 1601 to be the coldest year in the Northern Hemisphere for six centuries (see Russian famine of 1601–1603); 1601 consisted of a bitterly cold winter, a cold, frosty, late (possibly nonexistent) spring, and a cool, wet summer.
An eruption of Laki, in Iceland, caused thousands of fatalities in Europe, 1783–84.
The eruption of Mount Pinatubo in 1991 led to odd weather patterns and temporary cooling in the United States, particularly in the Midwest and parts of the Northeast. An unusually mild winter and a warm, early spring were followed by an unusually cool, wet summer and a cold, early autumn in 1992. Enhanced rainfall occurred across the West Coast of the United States, particularly California, during the 1991–92 and 1992–93 rainy seasons.

1815 eruption of Mount Tambora

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1815 Eruption of Mount Tambora
False color image of Mount Tambora, taken from the Space Shuttle Endeavour on 13 May 1992 (for orientation, the top of the image is towards the East).
Volcano	Mount Tambora
Date	1815
Type	Ultra Plinian
Location	Sumbawa, Lesser Sunda Islands, Dutch East Indies 8°15′S 118°00′E / 8.25°S 118°E / -8.25; 118Coordinates: 8°15′S 118°00′E / 8.25°S 118°E / -8.25; 118
VEI	7
Impact	Reduced global temperatures, leading the following year, 1816, to be called the Year Without a Summer.

The 1815 Eruption of Mount Tambora was one of the most powerful eruptions in recorded history and is classified as a VEI-7 event. The eruption of the volcano, on the island of Sumbawa in the Dutch East Indies (present-day Indonesia), reached a climax on 10 April 1815^[1] and was followed by between six months and three years of increased steaming and small phreatic eruptions.

The eruption column lowered global temperatures, and some experts believe this led to global cooling and worldwide harvest failures, sometimes known as the Year Without a Summer in 1816.^[2] The eruption resulted in a brief period of significant climate change that led to various cases of extreme weather. Several climate forcings coincided and interacted in a systematic manner that has not been observed since, despite other large eruptions that have occurred since the early Stone Age. Although the link between the post-eruption climate changes and the Tambora event has been established by various scientists, the understanding of the processes involved is incomplete.^[3]

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Chronology of the eruption[edit]

Current topography of Sumbawa

The estimated volcanic ashfall regions during the 1815 eruption. The red areas show thickness of volcanic ash fall. The outermost region (1 cm (0.39 in) thickness) reached Borneo and Sulawesi.

Mount Tambora experienced several centuries of dormancy before 1815, as the result of the gradual cooling of hydrous magma in a closed magma chamber.^[4] Inside the chamber at depths between 1.5 and 4.5 km (0.93 and 2.80 mi), the exsolution of a high-pressure fluid magma formed during cooling and crystallisation of the magma. Overpressure of the chamber of about 4,000–5,000 bar (400–500 MPa; 58,000–73,000 psi) was generated, and the temperature ranged from 700 to 850 °C (1,300–1,600 °F).^[4] In 1812, the volcano began to rumble and generated a dark cloud.^[5]

On 5 April 1815, a huge eruption occurred, followed by thunderous detonation sounds, heard in Makassar on Sulawesi, 380 km (240 mi) away, Batavia (now Jakarta) on Java 1,260 km (780 mi) away, and Ternate on the Molucca Islands 1,400 km (870 mi) away. On the morning of 6 April, volcanic ash began to fall in East Java with faint detonation sounds lasting until 10 April. What was first thought to be the sound of firing guns was heard on 10 April on Sumatra more than 2,600 km (1,600 mi) away.^[6]

At about 7 pm on 10 April, the eruptions intensified.^[5] Three columns of flame rose up and merged.^[6] The whole mountain was turned into a flowing mass of “liquid fire”.^[6] Pumice stones of up to 20 cm (7.9 in) in diameter started to rain down around 8 pm, followed by ash at around 9–10 pm. Pyroclastic flows cascaded down the mountain to the sea on all sides of the peninsula, wiping out the village of Tambora. Loud explosions were heard until the next evening, 11 April. The ash veil had spread as far as West Java and South Sulawesi. A “nitrous” odour was noticeable in Batavia and heavy tephra-tinged rain fell, finally receding between 11 and 17 April.^[5]

The first explosions were heard on this Island in the evening of 5 April, they were noticed in every quarter, and continued at intervals until the following day. The noise was, in the first instance, almost universally attributed to distant cannon; so much so, that a detachment of troops were marched from Djocjocarta, in the belief that a neighbouring post was being attacked, and along the coast boats were in two instances dispatched in quest of a supposed ship in distress.

—Sir Stamford Raffles‘ memoir.^[6]

The explosion is estimated to have been a VEI-7.^[7] An estimated 41 km³ (9.8 cu mi) of pyroclastic trachyandesite were ejected, weighing about 10000 million tonnes. This has left a caldera measuring 6–7 km (3.7–4.3 mi) across and 600–700 m (2,000–2,300 ft) deep.^[5] The density of fallen ash in Makassar was 636 kg/m³.^[8] Before the explosion, Mount Tambora was about 4,300 m (14,100 ft) high,^[5] one of the tallest peaks in the Indonesian archipelago. After the explosion, it measured only 2,851 m (9,354 ft) (about two thirds of its previous height).^[9]

The 1815 Tambora eruption is the largest observed eruption in recorded history (see Table I, for comparison).^[5]^[10] The explosion was heard 2,600 km (1,600 mi) away, and ash fell at least 1,300 km (810 mi) away.^[5] Pitch darkness was observed as far away as 600 km (370 mi) from the mountain summit for up to two days. Pyroclastic flows spread at least 20 km (12 mi) from the summit. Due to the eruption, Indonesia’s islands were struck by tsunami waves reaching heights up to 4 m (13 ft).

Aftermath[edit]

On my trip towards the western part of the island, I passed through nearly the whole of Dompo and a considerable part of Bima. The extreme misery to which the inhabitants have been reduced is shocking to behold. There were still on the road side the remains of several corpses, and the marks of where many others had been interred: the villages almost entirely deserted and the houses fallen down, the surviving inhabitants having dispersed in search of food.
…
Since the eruption, a violent diarrhoea has prevailed in Bima, Dompo, and Sang’ir, which has carried off a great number of people. It is supposed by the natives to have been caused by drinking water which has been impregnated with ashes; and horses have also died, in great numbers, from a similar complaint.

—Lt. Philips, ordered by Sir Stamford Raffles to go to Sumbawa.^[6]

All vegetation on the island was destroyed. Uprooted trees, mixed with pumice ash, washed into the sea and formed rafts up to 5 km (3.1 mi) across.^[5] One pumice raft was found in the Indian Ocean, near Calcutta on 1 and 3 October 1815.^[10] Clouds of thick ash still covered the summit on 23 April. Explosions ceased on 15 July, although smoke emissions were still observed as late as 23 August. Flames and rumbling aftershocks were reported in August 1819, four years after the event.

A moderate-sized tsunami struck the shores of various islands in the Indonesian archipelago on 10 April, with a height of up to 4 m (13 ft) in Sanggar around 10 pm.^[5] A tsunami of 1–2 m (3.3–6.6 ft) in height was reported in Besuki, East Java, before midnight, and one of 2 metres (6.6 ft) in height in the Molucca Islands. The total death toll has been estimated to be around 4,600.^[11]

The eruption column reached the stratosphere, an altitude of more than 43 km (27 mi).^[10] The coarser ash particles fell one to two weeks after the eruptions, but the finer ash particles stayed in the atmosphere from a few months up to a few years at altitudes of 10–30 km (6.2–18.6 mi).^[5] Longitudinal winds spread these fine particles around the globe, creating optical phenomena. Prolonged and brilliantly coloured sunsets and twilights were frequently seen in London between 28 June and 2 July 1815 and 3 September and 7 October 1815.^[5] The glow of the twilight sky typically appeared orange or red near the horizon and purple or pink above.

The estimated number of deaths varies depending on the source. Zollinger (1855) puts the number of direct deaths at 10,000, probably caused by pyroclastic flows. On Sumbawa island, 38,000 deaths were due to starvation, and another 10,000 deaths occurred due to disease and hunger on Lombok island.^[12] Petroeschevsky (1949) estimated about 48,000 and 44,000 people were killed on Sumbawa and Lombok, respectively.^[13] Several authors use Petroeschevsky’s figures, such as Stothers (1984), who cites 88,000 deaths in total.^[5] However, Tanguy et al.. (1998) claimed Petroeschevsky’s figures to be unfounded and based on untraceable references.^[14] Tanguy revised the number solely based on two credible sources, q.e., Zollinger, who himself spent several months on Sumbawa after the eruption, and Raffles‘s notes.^[6] Tanguy pointed out that there may have been additional victims on Bali and East Java because of famine and disease. Their estimate was 11,000 deaths from direct volcanic effects and 49,000 by posteruption famine and epidemic diseases.^[14] Oppenheimer (2003) stated a modified number of at least 71,000 deaths in total.^[10] Reid takes note of the total direct and indirect deaths caused beyond Sumbawa, in Bali and elsewhere, and suggests that a figure of perhaps 100,000 deaths is an appropriate estimate.^[15]

Disruption of global temperatures[edit]

The conditions during the northern hemisphere summer of 1816 were the result of the largest observed eruption in recorded human history, one during which global temperatures decreased by an average of 0.53 °C, and related human deaths were reported to be about 90,000. The importance of volcanic eruptions during this anomaly, specifically the eruption of Mount Tambora, cannot be overlooked. It is the most significant factor in this important climate anomaly across the globe.^[16] While there were other eruptions during the year of 1815, Tambora is classified as a VEI-7 and an eruption column 45 km tall, eclipsing all others by at least one order of magnitude.

The Volcanic Explosivity Index (VEI) is used to quantify the amount of ejected material with a VEI-7 coming in at 100 km³. Every index value below that is one order of magnitude less. Furthermore, the 1815 eruption occurred during a Dalton Minimum, a period of unusually low solar radiation.^[17] Volcanism plays a large role in climate shifts, both locally and globally. This was not always understood and did not enter scientific circles as fact until Krakatoa erupted in 1883 and tinted the skies orange.^[16]

The scale of the volcanic eruption will determine the significance of the impact on climate and other chemical processes, but a change will be measured even in the most local of environments. When volcanoes erupt they eject CO₂, H₂O, H₂, SO₂, HCl, HF, and many other gases (Meronen et al. 2012). CO₂ and H₂O are greenhouse gases, responsible for 0.0394% and 0.4% of the atmosphere respectively. Their small ratio disguises their significant role in trapping solar insolation and reradiating it back to Earth.

Global effects[edit]

Effects of volcanism[edit]

Volcanism affects the atmosphere in two distinct ways: short-term cooling due to reflected insolation, and long-term warming due to increased CO₂ levels. Most of the water vapor and CO₂ is collected in clouds within a few weeks to months because both are already present in large quantities, so the effects are limited (Bodenmann et al. 2011^{[citation needed]}). SO₂, along with other aerosols and particulates, is responsible for global cooling, nullifying the effects of the greenhouse gas emissions due to its ability to be found higher in the atmosphere and its efficiency at bonding with any water vapor found in the upper “dry” atmosphere. Sulfuric acid is exceptional at blocking solar radiation and it usually takes months to years for it to acquire enough water vapor to fall back to Earth. It has been suggested that a volcanic eruption in 1809 may have previously contributed to a reduction in global temperatures.^[18]

Impact of the eruption[edit]

By most calculations, the eruption of Tambora was at least a full order of magnitude larger than that of Mount Pinatubo in 1991 (Graft et al. 1993). It is estimated that the top 1,220 metres (4,000 ft) of the mountain was reduced to rubble ash, effectively reducing its height^{[clarification needed]} by 33%. Around 100 cubic kilometers of rock was blasted into the air, eclipsing the estimated 10 cubic kilometers by its counterpart in Italy, Vesuvius (Williams 2012). Not only were rocks and ash expelled into the atmosphere, but toxic gases were pumped into the atmosphere as well. Many of the residents who survived the resulting tsunami, eruption, or ash cloud became sick due to all of the sulfur, which caused lung infections (Cole-Dai et al. 2009). Volcanic ash was documented to be over 100 cm deep in areas within 75 km of the eruption, while areas within a 500 km radius saw a 5 cm ash fall, and ash could be found as far away as 1300 km.^[10] With this much volcanic ash on the ground, any crops or viable vegetation sources were smothered at a minimum and burned if they were close to the volcano itself. This created an immediate shortage of food in Indonesia, one that only compounded the regular shortage during the winter season (Cole-Dai et al. 2009). The ejection of these gasses, especially HCl, caused the precipitation that followed in the region to be extremely acidic, killing much of the crops that either survived or were rebudding during the spring. The food shortage was compounded by the Napoleonic wars, floods, and cholera.^[10]

The presence of ash in the atmosphere for several months after the eruption reflected significant amounts of solar radiation, causing unseasonably cool summers which further drove populations to a food shortage.^[10] China, Europe, and North America all had well-documented cases of abnormal temperatures, devastating their harvests. These climatic shifts also altered the monsoon season in China and India, forcing thousands of Chinese to flee coastal areas due to regional flooding of the Yangtze Valley (Granados et al. 2012). The gases also reflected some of the already-decreased incoming solar radiation, causing a notable decrease in global temperatures throughout the decade, between 0.4-0.7 °C globally. It was so dramatic that that an ice dam was formed in Switzerland during the summer of 1816 and 1817, earning 1816 the title “Year without a Summer” or YWAS (Bodenmann et al. 2011). The winter months of 1816 were not very different from years previous, but the spring and summer maintained the cool-to-freezing temperatures. However, the winter of 1817 radically differed, reaching temperatures below -30 °F in central and northern New York, which were cold enough to freeze lakes and rivers used for transporting supplies. Both Europe and North America suffered late freezes that lasted well into June with snow accumulating up to 32 cm in August, which killed recently planted crops, crippling the food industry. Unseasonably cool temperatures reduced the output of crops worldwide: the growing seasons in parts of Massachusetts and New Hampshire were less than 80 days in 1816, citing freezing temperatures as the reason for harvest failure (Oppenheimer 2003). These were visually connected to unique sunsets observed in western Europe and red fog found on the Eastern Seaboard of the US. These unique atmospheric conditions persisted for the better part of 2.5 years (Robock 2000).

Ice cores have been used to monitor atmospheric gases during the cold decade (1810-1819) and the results are puzzling. The SO₄ concentration found in both Siple Station, Antarctica and Central Greenland bounced from 5.0^{[clarification needed]} in January 1816 to 1.1^{[clarification needed]} in August 1818.^[18] This means that 25-30 Tg of sulfur was ejected into the atmosphere, most of which would come from Tambora, and was equalized back by natural processes on Earth rather quickly. Another unique factor is that Tambora represents the largest shift in sulfur concentration in the ice cores for the past 5000 years, potentially becoming the single most disruptive event in recorded history. Estimates of the sulfur yield vary from 10 Tg (Black et al. 2012) to 120 Tg (Stothers 2000). The difference between the models are drastic, but many estimates will either average in or agree on a number between 25-30 Tg. The high concentration might explain the stratospheric warming of ~15 °C, resulting in surface cooling that would be a delayed reaction lasting for the next nine years. It is estimated that the stratospheric warming event only lasted four years, but cooler temperatures were documented until 1825 (Cole-Dai et al. 2009). The data presented did not state whether it was a statistically significant difference or just temperatures cooler than “normal.” This has been dubbed a “volcanic winter“, similar to a nuclear winter, due to the overall decrease and abysmal farming conditions.^[10]

Climate data have shown that the variance between daily lows and highs may have played a role in the lower average temperature because the fluctuations were much more subdued. Generally, the mornings were warmer due to nightly cloud cover and the evenings were cooler because the clouds had dissipated. There were documented fluctuations of cloud cover for various locations that suggested it was a nightly occurrence and the sun killed them off, much like a fog^[10] The class boundaries between 1810-1830 without volcanically perturbed years was ~7.9 °C. This is contrasted by the volcanically perturbed years (1815-1817) where the delta was only ~2.3 °C. This meant that the mean annual cycle in 1816 was more linear than bell shaped and 1817 endured cooling across the board. Southeastern England, northern France, and the Netherlands experienced the greatest amount of cooling in Europe; complemented by New York, New Hampshire, Delaware, and Rhode Island in North America (Bodenmann et al. 2011).

The documented rainfall was as much as 80 percent more than the calculated normal with regards to 1816, unusually high amounts of snow were found in Switzerland, France, Germany, and Poland. This is again contrasted by the unusually low precipitations in 1818 which caused droughts throughout most of Europe and Asia (Auchmann et al. 2012). Russia had already experienced unseasonably warm and dry summers since 1815 and this continued for the next three years. There are also documented reductions in ocean temperature near the Baltic Sea, North Sea, and Mediterranean. This seems to have been an indicator of shifted oceanic circulation patterns and possibly changed wind direction and speed (Meronen et al. 2012). This is further supported by the recorded observations of a British fleet sent to explore the Arctic Circle; they found large ice sheets miles off the coast of Greenland, where two years prior they had been shoved along the east coast of Greenland. Contemporary scientists attributed the Year Without a Summer to the drifting polar ice sheets rather than the eruption of Tambora because of its proximity to England.^[10]

Taking into account the Dalton Minimum, and the presence of famine and droughts predating the eruption, the Tambora volcanic event accelerated or exacerbated the extreme climate conditions of 1815. While other eruptions and other climatological events would have led to a global cooling of about 0.2 °C, Tambora increased that number substantially.^[18]

Comparison of selected volcanic eruptions[edit]

Table I. Comparison of selected volcanic eruptions
Eruptions	Country	Location	Year	Column height (km)	Volcanic Explosivity Index	N. Hemisphere summer anomaly (°C)	Fatalities
Mount Vesuvius	Italy	Mediterranean	79	30	5	?	02001>2,000
Hatepe (Taupo)	New Zealand	Pacific Ring of Fire	186	37	7	?	00000?
Baekdu	China / North Korea	Pacific Ring of Fire	969	36	6–7	?	00000?
Huaynaputina	Peru	Pacific Ring of Fire	1600	46	6	−0.8	01400≈1,400
Tambora	Dutch East-Indies	Pacific Ring of Fire	1815	43	7	−0.5	71001>71,000
Krakatoa	Dutch East-Indies	Pacific Ring of Fire	1883	36	6	−0.3	3600036,600
Santa María	Guatemala	Pacific Ring of Fire	1902	34	6	no anomaly	070017,000–13,000
Novarupta	USA, Alaska	Pacific Ring of Fire	1912	32	6	−0.4	000022
Mt. St. Helens	USA, Washington	Pacific Ring of Fire	1980	19	5	no anomaly	0005757
El Chichón	Mexico	Pacific Ring of Fire	1982	32	4–5	YES	02001>2,000
Nevado del Ruiz	Colombia	Pacific Ring of Fire	1985	27	3	no anomaly	2300023,000
Pinatubo	Philippines	Pacific Ring of Fire	1991	49	6	−0.5	012021,202

Source: Oppenheimer (2003),^[10] and Smithsonian Global Volcanism Program for VEI.^[20]

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A LOOK BACK: 1815 Mount Tambora and the Year Without a Summer

Year Without a Summer

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