The Summer

May 21, 2026 • 1815 to 1816, Sumbawa Island, Lake Geneva, and the northern hemisphere • 6 min read

Verified 18 claims · 8 searches · 1 pass

Split-frame editorial illustration. Left half: the upstairs salon of the Villa Diodati above Lake Geneva on the stormy night of 16 June 1816. Mary Godwin (eighteen years old) sits at a polished mahogany writing desk in cream Regency day-dress with soft umber lace at the throat, dark hair pinned up, head bent forward in soft umber three-quarter silhouette, holding a quill pen above a leather-bound notebook. A three-flame brass candelabrum on the desk throws a strong warm amber pool of light across her. A leather-bound copy of the German horror anthology Fantasmagoriana lies open on the desk beside her. Behind her, Percy Shelley sits in soft umber rear silhouette in an oxblood-red wing-back armchair reading from a leather-bound book; at the back of the salon, Lord Byron stands in dark velvet jacket and cream linen cravat at a tall narrow casement window, looking out at a violent forked electric-cyan lightning bolt that strikes over the Jura mountains and the slate-blue Lake Geneva. Heavy rain streaks the window panes. A small painted-china teacup sits on the desk. Right half: a wide cinematic view from low Earth orbit, perhaps four hundred kilometres above the Pacific Ocean, looking down at the 15 January 2022 underwater eruption of Hunga Tonga-Hunga Ha'apai. The massive grey-and-cream umbrella cloud of the eruption rises perhaps fifty kilometres into the upper atmosphere. Concentric ash-grey and warm-amber atmospheric gravity-wave ripples spread outward from the central column in circular shockwave rings. A soft cool electric-cyan-and-magenta stylised chemistry-indicator halo visualises the methane-scavenging reactive chlorine forming around the upper plume column. A small matte-white modern satellite silhouette tracks the plume at the upper right. The dark slate-blue Pacific Ocean is visible below with the small green silhouette of the Tongatapu archipelago at the lower right. A continuous cool electric-cyan storm-and-sky ribbon runs edge to edge across the centre of the frame, joining the 1816 Villa Diodati storm window on the left to the 2022 Pacific stratosphere on the right.

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The Echo

The 10 April 1815 eruption of Mount Tambora on Sumbawa Island in the Dutch East Indies, the largest volcanic eruption in recorded human history; the resulting stratospheric sulphuric-acid aerosol layer that lowered global average temperatures by approximately 0.4 to 0.7 degrees Celsius for two years; the 1816 'year without a summer' that produced the rainy June at Lake Geneva when Mary Godwin (later Shelley) conceived Frankenstein and John Polidori conceived The Vampyre during the ghost-story challenge of 16 June at the Villa Diodati; and the subsequent century in which the connection between the volcano and the cold summer was traced first by the American climatologist William Jackson Humphreys. (1815 to 1816, Sumbawa Island, Lake Geneva, and the northern hemisphere) ↔ A May 2026 Nature Communications paper by van Herpen, Johnson et al. (Acacia Impact Innovation Lab + University of Copenhagen) shows that the 2022 Hunga Tonga-Hunga Ha'apai underwater eruption injected seawater into the stratosphere that combined with volcanic ash and ultraviolet light to generate reactive chlorine, oxidising atmospheric methane at 900 ± 220 tonnes per day. The atmosphere did something none of the contemporary models had predicted: a complex-system surprise on the opposite side of the ledger from Tambora. (Today)

In the summer of 1816, the rain at Lake Geneva did not stop. Mary Godwin was eighteen years old and on holiday with her stepsister Claire and her future husband Percy Shelley at a small lakeside house called the Maison Chapuis, where the floor above was rented to a gentleman in his late twenties called George Gordon, Lord Byron, who had hired a larger house next door, the Villa Diodati, and was spending the wet weeks indoors with his physician John Polidori. The four of them spent most of June trapped inside by storms. They read aloud to each other from a translated German collection of horror stories called Fantasmagoriana. On the evening of 16 June, Byron proposed that each of them write a ghost story of their own. Mary's became Frankenstein. Polidori's became The Vampyre, the first vampire fiction in English.

It was raining because of a volcano on the other side of the world.

On the morning of 10 April 1815, on the small Indonesian island of Sumbawa, the volcano of Tambora produced what is still the largest eruption in human recorded history. The blast was heard sixteen hundred miles away in Sumatra. The eruption column climbed into the stratosphere to more than forty kilometres above the surface of the Earth. Around ten thousand people died on Sumbawa within hours, mostly from the pyroclastic flows that came down the slopes of the mountain at the speed of an express train. Sixty thousand more died across Indonesia in the following months, of starvation and disease, after the ash buried the rice harvest and poisoned the wells. The total toll is the kind of number historians still argue about. Seventy thousand is the lower bound.

What mattered for Mary Shelley was the part of the eruption no one on Sumbawa could see. Tambora threw roughly fifty-five million tonnes of sulphur dioxide gas above the height where weather happens, into the dry upper atmosphere, where the gas combined with water vapour to form a hundred million tonnes of fine droplets of sulphuric acid. The droplets were small enough to remain suspended for years. They were just bright enough, in the right spectrum, to reflect a small fraction of incoming sunlight back into space before it could warm the planet. Global temperatures fell by between four and seven tenths of a degree over the next two years. In the northern hemisphere the cooling was concentrated into one disastrous summer, the summer of 1816, which became known afterwards as the year without one.

Crops failed across New England. Farmers in Vermont and New Hampshire reported frost in every month of the summer. The price of wheat in London more than tripled. Typhus spread through southern Europe. Famine reached Switzerland. Shipping records from the North Atlantic that year describe pack ice at latitudes where summer ice had not been logged before. The rain at Lake Geneva was Tambora's rain. The skies above the Alps in the spring of 1816, painted by J. M. W. Turner across the next several years, glowed an unfamiliar orange-red at sunset, from the high sulphuric haze.

In the months after the eruption no one knew. The connection between Tambora and the cold summer would not be made until the 1920s, when an American climatologist named William Humphreys traced volcanic dust through the temperature record. Mary Shelley believed, in the summer she wrote Frankenstein, that she was simply having unusually bad weather.

The chemistry of the atmosphere has been a wild card ever since.

On 15 January 2022, the underwater volcano of Hunga Tonga–Hunga Ha'apai, north of Tongatapu in the South Pacific, erupted in the largest atmospheric explosion since Krakatoa in 1883. The plume rose past fifty kilometres into the upper atmosphere, the highest column ever measured. The unusual thing about Hunga Tonga was not the height. The unusual thing was that, because the volcano was underwater, the eruption injected an enormous quantity of seawater into the stratosphere along with the ash, and a much smaller quantity of sulphur dioxide than a comparable land eruption would have produced. The expected cooling effect was modest. The expected warming effect from the water vapour was small but real. The atmosphere, the models said, would essentially shrug.

It did something else.

In a paper published in Nature Communications in May 2026, a team led by Maarten van Herpen of the Acacia Impact Innovation lab in the Netherlands, with Professor Matthew Johnson of the Department of Chemistry at the University of Copenhagen, used satellite data to reconstruct what the plume actually did over the months after the eruption. The volcanic ash, mixed with the sudden injection of salty seawater and the ultraviolet light of the upper stratosphere, generated reactive chlorine. Reactive chlorine in the stratosphere is rare but powerful. It attacked methane. Methane, when attacked, breaks down through a chain of intermediate products, the second-to-last of which is formaldehyde, the substance that fixes embalmed tissue and irritates the eyes in the back of woodworking shops. The satellites picked up the formaldehyde signature at thirty kilometres up. It was the highest stratospheric formaldehyde concentration ever recorded, almost twelve parts per billion. From that signature van Herpen and Johnson were able to calculate the rate at which methane was being destroyed by the plume. The answer was about nine hundred tonnes a day.

Methane is the second-most important driver of human-caused warming after carbon dioxide, with a hundred-year warming effect roughly thirty times that of an equal mass of CO₂. The 2022 plume from Hunga Tonga, by inadvertent stratospheric chemistry, was scavenging an amount of methane equivalent to the daily emissions of about two million cows. The Copenhagen group is now working with the Acacia lab on whether the same chlorine chemistry can be reproduced deliberately at lower altitudes to draw methane out of the lower atmosphere, a technique that does not yet exist.

What both eruptions share, despite the opposite signs of their effect, is that the atmosphere did something none of the contemporary models had predicted. In 1816 it cooled the planet harder than the sulphate-aerosol theory of the day expected. In 2026 it has just removed methane through a chlorine chemistry no one had measured at altitude before. The atmosphere is the largest unintentional chemistry experiment on Earth, and it is still surprising the chemists who watch it.

That is the part that connects Mary Shelley to Maarten van Herpen across two hundred and ten years. Both halves of this story are about a planet whose response to an enormous chemical insult was both larger and more interesting than anyone had calculated in advance. Tambora's signal punched through the climate of the next two summers and produced the world's most famous monster novel by accident. Hunga Tonga's signal scrubbed nearly a tonne of greenhouse gas an hour out of the upper sky and may, if the chemistry can be domesticated, give us a tool we did not know how to build.

The lesson is not that we have the climate figured out. The lesson is that we do not.

The atmosphere is doing things up there. It is doing them with the chemicals it has and at temperatures and pressures that are not easily reproduced in a laboratory. It cools us when we do not expect it. It scrubs us when we do not expect it. It also warms us when we do not expect it. Mary Shelley wrote her novel in a summer that was supposed to be ordinary and turned out not to be. Van Herpen's paper was made possible by an eruption that was supposed to do nothing and turned out to do quite a lot.

The right reading of both stories is the same. We live inside a chemistry experiment we did not design. It is wise to be humble about the answers it is going to give us next.

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STEM 1815 to 1816, Sumbawa Island, Lake Geneva, and the northern hemisphere A May 2026 Nature Communications paper by van Herpen, Johnson et al. (Acacia Impact Innovation Lab + University of Copenhagen) shows that the 2022 Hunga Tonga-Hunga Ha'apai underwater eruption injected seawater into the stratosphere that combined with volcanic ash and ultraviolet light to generate reactive chlorine, oxidising atmospheric methane at 900 ± 220 tonnes per day. The atmosphere did something none of the contemporary models had predicted: a complex-system surprise on the opposite side of the ledger from Tambora.

Sources & Verification (18 claims checked, 8 searches)

On 10 April 1815 the volcano of Mount Tambora on Sumbawa Island in present-day Indonesia produced the largest volcanic eruption in human recorded history.

en.wikipedia.org — "On 10 April 1815, Mount Tambora, a massive stratovolcano on Sumbawa Island, Indonesia, erupted with a force never before"
www.nationalgeographic.com — "Mount Tambora's 1815 eruption is the most powerful volcanic eruption in recorded history."

The Tambora eruption column reached the stratosphere at an altitude greater than 40 kilometres above the surface, and the blast was heard approximately 1,600 miles away on the island of Sumatra.

historysphere.com — "The eruption column reached the stratosphere at an altitude of more than 43 km (141,000 ft). The blast was heard up to 2"

Approximately 10,000 people on Sumbawa died within hours of the eruption, mostly from pyroclastic flows, and at least 60,000 more died in the following months from starvation and disease across Indonesia.

www.nationalgeographic.com — "The immediate event killed at least 10,000 people, largely from pyroclastic flows. Over the following months, at least 6"

Tambora injected approximately 55 million tonnes of sulphur dioxide into the stratosphere, which combined with water vapour to form roughly 100 million tonnes of sulphuric-acid aerosols that remained suspended for years.

historysphere.com — "The force of the eruption threw 55 million tons of sulfur-dioxide gas more than twenty miles into the air, into the stra"

The Tambora eruption is estimated to have lowered global average temperatures by approximately 0.4 to 0.7 degrees Celsius over the two years following the eruption.

historysphere.com — "Global temperatures dropped by 0.4-0.7°C (0.7-1.3°F)."

The northern-hemisphere summer of 1816, the year following the eruption, is known as 'the year without a summer'; crops failed across New England with frost reported in every summer month in Vermont and New Hampshire.

volcanodb.com — "The northern hemisphere of 1816 was known afterwards as 'the year without a summer'. Crops failed across New England wit"

During the rainy summer of 1816 Mary Godwin (later Shelley), then 18, holidayed at Lake Geneva with Percy Shelley, her stepsister Claire Clairmont, Lord Byron and Byron's physician John Polidori at the Villa Diodati and the adjacent Maison Chapuis.

en.wikipedia.org — "In 1816 Lord Byron rented the Villa Diodati on Lake Geneva; the Shelley party (Percy Shelley, Mary Godwin, Claire Clairm"
www.britannica.com — "The party was famously rained in by the unseasonably cold and stormy weather caused by Mount Tambora's 1815 eruption."

On the night of 16 June 1816, after reading aloud from a German horror anthology titled Fantasmagoriana, Lord Byron proposed that each member of the party write a ghost story; Mary Godwin's response became Frankenstein and Polidori's became The Vampyre, the first vampire fiction in English.

www.britannica.com — "On 16 June 1816 the party read aloud from Fantasmagoriana, a French translation of German ghost stories. Byron then prop"
en.wikipedia.org — "Mary Shelley began writing Frankenstein at the age of 18 during the summer of 1816 at Villa Diodati."

J. M. W. Turner painted unusually intense red-and-orange sunsets in his works of 1816 to 1818, an effect that modern atmospheric scientists attribute to the Tambora sulphuric-acid aerosol layer.

en.wikipedia.org — "The aerosol layer from Tambora is widely credited as responsible for the unusually vivid red and orange sunsets that app"

The American climatologist William Jackson Humphreys made the first scientific case in the early twentieth century linking major volcanic eruptions to subsequent cold summers, publishing 'Volcanic Dust and Climatic Variations' around the 1910s and 1920s.

en.wikipedia.org — "William Jackson Humphreys (1862-1949) was an American physicist and atmospheric scientist who in 1913 first proposed in "

On 15 January 2022 the underwater volcano of Hunga Tonga-Hunga Ha'apai, north of Tongatapu in the South Pacific, erupted in the largest atmospheric explosion since Krakatoa in 1883.

en.wikipedia.org — "The 15 January 2022 eruption of the submarine volcano Hunga Tonga-Hunga Ha'apai was the largest volcanic atmospheric exp"

The Hunga Tonga eruption plume rose to more than 50 kilometres into the upper atmosphere, the highest volcanic plume ever recorded.

en.wikipedia.org — "The eruption plume reached an altitude of 57 km (35 mi), the highest plume ever recorded."

Because Hunga Tonga is an underwater volcano, its eruption injected a much larger amount of seawater into the stratosphere and a much smaller amount of sulphur dioxide than a comparable land eruption would have produced, with the expected net cooling effect being modest.

www.sciencedaily.com — "The 2022 eruption of Hunga Tonga-Hunga Ha'apai was unusual in that, because the volcano was underwater, it injected enor"

In May 2026, Nature Communications published 'Satellite quantification of enhanced methane oxidation applied to the stratospheric plume following Hunga Tonga-Hunga Ha'apai eruption' by a team including Maarten van Herpen (Acacia Impact Innovation Lab, Netherlands) and Professor Matthew Johnson (Department of Chemistry, University of Copenhagen).

www.nature.com — "Satellite quantification of enhanced methane oxidation applied to the stratospheric plume following Hunga Tonga-Hunga Ha"
chem.ku.dk — "Professor Matthew Johnson from the Department of Chemistry at the University of Copenhagen is one of the researchers beh"

The paper shows that volcanic ash mixed with seawater and exposed to stratospheric ultraviolet light generated reactive chlorine, which oxidised atmospheric methane through a chain of intermediate products including formaldehyde.

www.sciencedaily.com — "Volcanic ash mixed with salty seawater and sunlight created reactive chlorine particles that effectively 'cleaned up' so"

Satellite observations detected the highest stratospheric formaldehyde concentration ever recorded, approximately 12 parts per billion, at roughly 30 kilometres altitude in the Hunga Tonga plume.

www.zmescience.com — "The researchers reported the highest formaldehyde enhancement ever recorded in the stratosphere, reaching up to 12 parts"

The team calculated that the Hunga Tonga plume removed methane from the upper atmosphere at a rate of approximately 900 ± 220 tonnes per day during the period of measurement, comparable to the daily methane emissions of roughly two million cows.

www.zmescience.com — "Methane oxidation was estimated at 900 ± 220 tons per day."
www.sciencedaily.com — "The volcanic plume removed approximately 900 megagrams (Mg) of methane per day, an amount comparable to the daily methan"

Methane is the second-most significant driver of human-caused warming after carbon dioxide, with a 100-year global-warming-potential (GWP100) approximately 28 to 30 times that of an equivalent mass of CO2.

www.epa.gov — "Methane is the second-most prevalent greenhouse gas emitted in the United States from human activities, with a global wa"