The Year Without a Summer

Summary

In 1816 the summer failed across western Europe and north-eastern North America, with June snow, killing frosts and ruined harvests. The cause, the April 1815 eruption of Mount Tambora in Indonesia, was named about a century later and formally tested only in 2019.

At the time the cold was not connected to Tambora. The press blamed comets and sunspots. Beside Lake Geneva, a party of English writers kept indoors by the rain began writing ghost stories, and one of them became Frankenstein.

What is documented

The eruption. On Sumbawa, explosions were heard on the evening of 5 April 1815. The climactic phase began at about 19:00 local time on 10 April, and explosions continued intermittently until 15 July (Oppenheimer, 2003, drawing on accounts collected at the time for Stamford Raffles). The Smithsonian's Global Volcanism Program rates it VEI 7, "history's largest explosive eruption", which left a caldera 6 kilometres wide and 1,250 metres deep. Oppenheimer estimated that it put about 60 megatonnes of sulphur into the stratosphere, some six times as much as Pinatubo in 1991.

The dead in Indonesia. Estimates differ. Zollinger (1855) put the deaths at about 10,000 during the eruption, 38,000 from starvation on Sumbawa and 10,000 from disease and hunger on neighbouring Lombok. A 1998 revision by Tanguy and colleagues gave 11,000 killed by the eruption and 49,000 by famine and disease; the Global Volcanism Program uses about 60,000. Oppenheimer's review gives more than 71,000. On every count, most of the dead were killed by the famine and disease that followed, not by the eruption itself.

North America, June 1816. On 6 June 1816 snow fell at Albany, New York, and at Dennysville, Maine, and there were killing frosts at Fairfield, Connecticut. At Williamstown, Massachusetts, the observer recorded a temperature of about 44 °F (about 7 °C) through the day and snow several times. Near Quebec City about 30 centimetres of snow accumulated between 6 and 10 June. The Williamstown record goes on to note frost on 29 and 30 June, a frost on 9 July that killed part of the cucumbers, and another on 22 August that killed them. Oppenheimer describes the killing frosts as having all but destroyed New England's main crops, and the failure as contributing to accelerated emigration from New England. The year was later remembered there as "eighteen hundred and froze to death".

Europe. The Met Office's Central England Temperature series, which begins in 1659, records a summer mean of 13.38 °C for 1816. Of the 368 summers in the series to 2026, only 1725 and 1695 were colder. The figure is about 1.9 °C below the average of the thirty summers before it, 15.29 °C (the registry's calculation from the Met Office series). Across western and central Europe the summer was both cold and unusually wet (Schurer and colleagues, 2019). Grain prices roughly doubled between 1815 and 1817 (Post, as cited by Oppenheimer). In the Czech lands, documentary sources record an extremely cold summer in 1816, poor grain harvests and widespread price rises in 1817 (Brázdil and colleagues, 2016). In Ireland, a typhus epidemic followed; a contemporary estimate by Harty put the number infected at about 800,000 and the dead from famine, dysentery and fever at 44,300.

The hemisphere. The anomaly was large in places and modest overall. Reconstructions cited by Oppenheimer put the Northern Hemisphere summer temperature anomaly for 1816 at about half a degree. A 2016 review by Raible and fourteen colleagues found the global and Northern Hemisphere cooling well constrained by proxies, and "no strong signal" in Southern Hemisphere proxies. The whole decade was cold: Cole-Dai and colleagues (2009) used ice-core sulphate to show that a large eruption in 1809, from an unidentified volcano, reached the stratosphere, and attributed the cold of 1810 to 1819 to it and Tambora together.

The villa by the lake. In the summer of 1816 Mary Godwin, later Mary Shelley, and Percy Bysshe Shelley were neighbours of Lord Byron beside Lake Geneva; Byron was at the Villa Diodati with his physician, John Polidori. In her 1831 introduction to Frankenstein, Mary Shelley wrote: "But it proved a wet, ungenial summer, and incessant rain often confined us for days to the house." Byron proposed that each of them write a ghost story. Hers became Frankenstein, published anonymously in London on 1 January 1818. Polidori's became The Vampyre, published in the New Monthly Magazine on 1 April 1819.

What people blamed at the time. Czech documentary sources make no direct mention of Tambora. The reasons offered in the contemporary press were comets, sunspot activity and long-term cooling, and, only in 1817, earthquakes and volcanic eruptions in general (Brázdil and colleagues, 2016). Brönnimann and Krämer (2016) write that the causes of the European anomaly remained unknown for another century. In 1913 the US Weather Bureau physicist W. J. Humphreys mentioned, in passing, that the "year without a summer" had followed the eruption of "Tomboro".

Leading explanations

Sulphate aerosol from Tambora. Established. Sulphur injected into the stratosphere formed a veil of sulphate droplets that reflected sunlight and cooled the Northern Hemisphere summer of 1816. The eruption left a sulphate layer in polar ice, the cooling is seen in instrumental records and proxies, and climate models reproduce it (Raible and colleagues, 2016). In 2019 Schurer and colleagues applied formal event attribution to the European summer. In their models the Tambora forcing made the cold anomaly up to 100 times more likely; the pressure pattern of 1816 alone accounts for only about a quarter of the cold.

Weather variability. Peer-reviewed; enough on its own for the wet, not for the cold. The same study found that the circulation pattern of 1816 could produce the summer's rainfall without any external forcing. The eruption made a summer that wet between 1.5 and 3 times as likely. The cold was mostly the volcano. The rain could have come from the weather alone, though the eruption made it more likely.

A second eruption in 1809. Peer-reviewed, a contributor to the cold decade. Cole-Dai and colleagues (2009) found that a large eruption in 1809 also reached the stratosphere. Tambora came on top of a climate already cooled by it.

Current status

Later explained. The cold of 1816 in Europe and north-eastern North America is established as mainly the effect of Tambora's sulphate aerosol, on top of a decade already cooled by the 1809 eruption. The wetness of the European summer could have arisen from that year's circulation alone; the eruption made it between 1.5 and 3 times as likely. What remains open is detail: how the aerosol was distributed, and which volcano erupted in 1809. Neither is likely to change the basic explanation.

Last reviewed: September 2026. Records are provisional. Where the evidence changes, the entry changes. Found an error? Tell us.