“AROUND mid-morning on Pentecost, June 8th of 1783, in clear and calm weather, a black haze of sand appeared to the north of the mountains. The cloud was so extensive that in a short time it had spread over the entire area and so thick that it caused darkness indoors. That night, strong earthquakes and tremors occurred.”

Thus begins the eyewitness account of one of the most remarkable episodes of climate change ever seen. It was written by a Lutheran priest, Jon Steingrimsson, in the Sida district of southern Iceland. At nine o'clock that morning, the earth split open along a 16-mile fissure called the Laki volcano. Over the next eight months, in a series of vast belches, more lava gushed through the fissure than from any volcano in historic times—15 cubic kilometres, enough to bury the whole island of Manhattan to the top of the Rockefeller Centre.

Pentecost is the Christian festival celebrating the appearance of the Holy Spirit to the Apostles with the sound, the Bible says, “as of a mighty rushing wind” and an appearance “like as of fire”. But there was nothing metaphorical or festive about the winds and fire of the Laki eruption. It was the greatest calamity in Iceland's history.

“The flood of fire”, Steingrimsson writes, “flowed with the speed of a great river swollen with meltwater on a spring day.” It was rather as if the world's largest steelworks had begun pouring molten metal all over the neighbourhood. When the lava stream ran into water or marshes, “the explosions were as loud as if many cannon were fired at one time.” When it hit an obstacle, such as older lava fields, great gouts of molten metal were flung in the air, splashing back to earth, he says, “like cowpats”. But the damage to Iceland was only the start of a much greater trail of destruction that was eventually to reach halfway round the world, from the Altai mountains of Siberia to the Gulf of Mexico.

There are two sorts of volcanic eruptions, explosive and effusive. The well-known sort is explosive. It has the greater force. Explosions of this sort destroyed Pompeii and star in Hollywood films. Their sheer power throws volcanic gases and ash far into the stratosphere (the higher reaches of the atmosphere), where they absorb incoming radiation and cool the earth until they dissipate after two or three years. The eruption of Krakatoa caused record snowfalls round the world.

Effusive volcanic eruptions are different. They simmer with less force, but produce a greater volume of debris. Laki belched out clouds of volcanic gases 80 times greater than Mount St Helens, though Mount St Helens had much greater explosive power. But because Laki was weaker, three-quarters of the gas reached only as far as the lower atmosphere (the troposphere), the level at which rain, ordinary clouds and surface winds are carried. The gases included enormous quantities of sulphur dioxide; at its peak, the eruption produced as much in two days as European industry produces in a year. Part of this dissolved in the vapour of the clouds to form sulphuric acid. Within a few hours, the Laki volcano had produced a vast plume of acid rain, brooding over the skies of southern Iceland.

In the normal course of events, the prevailing winds would have blown this poisonous plume northwards, towards the Arctic Circle. But the summer of 1783 was not normal. A stable ridge of high pressure had settled over north-east Europe, pulling the winds, and the Laki cloud, south-east, towards the European mainland.

What happened next can be recreated in great detail because in the late 18th century diaries were fashionable among the newly literate middle classes and the circulation of newspapers was rising even in small towns; there was also growing scientific interest in the natural world, with educated amateurs keeping detailed notes of natural phenomena. From such records, one can track the course of the Laki cloud literally day by day (see map).

On June 10th wrote Sæmundur Magnusson Holm at the University of Copenhagen, falling ash coloured black the deck and sails of ships travelling to Denmark. The same day, a Lutheran priest in Norway, Johan Brun, reported that falling ash had withered the grass and leaves in Bergen. Six days later, Anton Strnadt reported that “the dry fog” came up over the river Moldau into Prague while Nicolas von Beguelin reported its first appearance in Berlin the day afterwards. “The sun”, he wrote, “was dull in its shine and coloured as if it had been soaked in blood.”

By June 18th the winds seem to have been blowing the cloud south and west. Robert de Lamanon, a French botanist and explorer, wrote from Laon, in northern France, that “the fog was cold and humid, with the wind coming from the south, and one could with ease look at the sun with a telescope without a blackened lens.” De Lamanon said fog—“such as the oldest men here have not seen before”—first appeared that day in Paris, Turin and Padua, from where Giuseppe Toaldo wrote that the whole of northern Italy was covered by the haze and smelled of sulphur.

The first mention of the haze in Britain came on June 22nd when Henry Bryant wrote to the Norfolk Chronicle that “there was an uncommon gloom in the air, with dead calm and very profuse dew.” Gilbert White, a Hampshire clergyman, noted in his diaries for the 23rd that “the blades of wheat in several fields are turned yellow and look as if scorched with frost.”

By June 26th Leonhard Euler, a Swiss mathematician, reported a “dry fog” in St Petersburg. By the end of the month, the cloud had reached Moscow and Tripoli in Syria, according to a Dutch professor, S.P. van Swinden, whose “Observations on the Cloud which Appeared in 1783” says that “a very thick haze covered both land and sea; the sun could be seen rarely, and always with a bloody colour, which was rare in Syria.” Finally, on July 1st, the haze appeared at Baghdad and in the Altai mountains, according to a geologist, Ivan Michaelovich Renovantz, who reported unseasonable frosts in Central Asia.

By then, back in Europe, the cloud had thickened. This was not a plume like that from Chernobyl, which appeared in one vast belch, spread over Europe and blew away. After its initial effusion, Laki erupted again, more violently, on June 11th and with still greater force on the 14th. Ferenc Weiss, a Hungarian meteorologist, was right to speculate that “the thick fog was being continually replenished”. There were to be ten big eruptions between June 8th and the end of October, followed by a series of rumblings that exhausted themselves only in February 1784.

As the cloud approached western Europe, it was sucked down in a spiral pattern towards the Earth's surface, producing a thick haze near ground level. By mid-summer, the “dry fog” had settled on Europe like a blanket; it was to stay there throughout the summer.

Europeans reacted in different ways. Steingrimsson was in no doubt: the eruption was “the Lord's chastisement”. On the fourth Sunday after Pentecost, with the lava advancing down the valley towards his church “which was shaking and quaking from the cataclysm”, he gathered his flock for Sunday service, as usual. “Both myself and all the others in the church were completely unafraid,” he writes. “No one showed any signs of leaving during the service, which I had made slightly longer than usual.” On emerging, the congregation found that two rivers, blocked by the lava flow, had changed course and poured down, dousing the lava and stopping it yards from the church door. (Two centuries later, Icelanders created the same obstacle by artificial means to save a town threatened by another eruption.) “From this day onwards the fire did no major damage to my parish in any way.”

“The miracle of the fire sermon” became well known and sermons on the freakish cloud common. “You stare at the sky and at the horizon veiled in dark exhalations,” Johann Georg Gottlob Schwarz admonished his audience in Alsfeld, Germany. “The Lord speaks daily to us and reveals in Nature his omniscience.”

The end is nigh

The expressions of faith were driven partly by alarm, even terror. “Some fear to go to bed, expecting an Earthquake; some declare that [the sun] neither rises nor sets where he did, and assert with great confidence that the day of judgment is at hand,” wrote an English poet, William Cowper. Parishioners near Broué, in northern France, dragged their priest out of bed and forced him to perform a rite of exorcism on the cloud. After rains brought temporary relief in Antwerp, the Gazette van Antwerpen reported that public prayers were held to bring more.

Alarm and misapprehension were not confined to the illiterate. The British government, fearing a plague outbreak, drew up plans to close the ports to traffic from the continent. Nor were popular fears mere superstition. The parish records of the English midlands reveal a spike in the number of deaths during July and August 1783, though summer is normally the time of lowest mortality in agricultural societies. Around 23,000 more English people died than would have been expected that year, doubling the normal death toll. In France, on some estimates, 5% of the population died that summer. Unusually, the deaths included young men and women working in the fields, breathing polluted air in stifling heat.

In Japan, the famine was so severe that special crews had to be hired to clear the roads of the dead

In general, though, “the Connoscenti”, (Cowper's term) sought rational explanations for the haze, rather than the consolations of religion. A French naturalist was the first to connect the fog to volcanic activity in Iceland in a lecture at Montpellier as early as August 7th. In Paris, meteorologists “desirous of making some observations of the atmosphere, had a sort of kite flown to a great height after which it was drawn in, covered with innumerable small black insects.” In an apparent attempt to allay panic, a French astronomer, Jerome de Lalande, wrote a paper arguing the unusual weather was “nothing more than the very natural effect from a hot sun after a long supersession of heavy rain” (he was wrong). Everywhere, educated men left detailed descriptions of the cloud cover; of the unusual appearance of the sun (“ferruginous” said White; “the face of a hot salamander” said Cowper); and of the scorching of leaves and grass and the state of the harvest and livestock.

By the end of October, the last of the big eruptions at Laki was over, and the haze began to dissipate, blown by the autumn winds. It was the end of the cloud but not the end of the damage. One of the gases the volcano threw up was fluorine, which fell quickly back to earth as hydrofluoric acid. In Iceland, this had horrible results. “The horses lost all their flesh,” Steingrimsson wrote, “the skin began to rot off along the spines. The sheep were affected even more wretchedly. There was hardly a part on them free of swellings, especially their jaws, so large that they protruded through the skin...Both bones and gristle were as soft as if they had been chewed.”

Half the horses and cattle and three-quarters of the sheep on the island died. As famine took hold, social bonds began to fray. To protect his remaining cattle, Steingrimsson slept in the cowshed “since thieves were on the prowl.” In all, a quarter of Iceland's population was to die of starvation, including Steingrimsson's beloved wife of 31 years. “When I lost my wonderful wife”, he writes, “everything, so to speak, collapsed around me.”

In Europe, the summer of 1783 had been unusually warm, the warmest recorded in England before 1995. White called the season “an amazing and portentous one, full of horrible phenomena”, and complained of the abnormal number of wasps. The heat may have been a short-term greenhouse-gas effect from high concentrations of sulphur dioxide. Or it may have just been natural variation.

AP

What is more certain is that, high in the atmosphere, the volcanic gases reflected away some of the sun's radiation even after the cloud had dissipated at lower levels. This back-scattering was to have a bigger impact on the climate than the summer cloud itself. The winters that followed the Laki eruption were freakishly cold.

At the time, some people suspected the volcano might be to blame. Benjamin Franklin, then America's ambassador to Paris, wrote to the Literary and Philosophical Society of Manchester that “[the sun's] effect of heating the Earth was exceedingly diminished. Hence the surface was early frozen. Hence the first snows remained on it unmelted. Hence the air was more chilled. Hence perhaps the winter of 1783-84 was more severe than any that had happened for many years.” In speculating upon the cause, he wondered “whether it was the vast quantity of smoke, long continuing to issue during the summer from Hecla in Iceland [near Laki]”. It was.

On average, temperatures in Europe during 1784 were about 2°C below the norm of the second half of the 18th century; and the closer to Iceland, the bigger the impact. Iceland itself was almost 5°C colder than normal and saw the longest period of sea ice around the island ever recorded. Berlin and Geneva, about 1,300 miles away, were 2ºC below normal, whereas the anomaly in Vienna, 1,700 miles from Laki, was only 1.5°C. Stockholm and Copenhagen, the nearest cities at just over 1,000 miles distant, saw temperatures drop by over 3°C.

Beyond Europe Laki's biggest influence seems to have operated over the greatest distances. The light-scattering effects of volcanic gases in the upper atmosphere reduced the amount of solar energy reaching the Earth and disrupted the normal relationship between temperatures both at the upper and lower levels of the atmosphere, and between the poles and the equator. These are the engines of the weather. Disruptions to them weakened the westerly jet streams, altered the monsoons and affected the weather throughout the northern hemisphere.

The eastern United States suffered one of its longest and coldest winters, with temperatures almost 5°C below average. George Washington, who had just disbanded his victorious army and retired to Mount Vernon, complained that he was “locked up” there by snow and ice between Christmas Eve and early March, while James Madison wrote from his home in Virginia that “we have had a severer season and particularly a greater quantity of snow than is remembered to have distinguished any preceding winter.” The St Lawrence river froze for a dozen miles far inland. In Charleston, South Carolina, which nowadays grinds to a halt with a light dusting of snow, the harbour froze hard enough to skate on. Most extraordinary of all, ice floes floated down the Mississippi, past New Orleans and out into the Gulf of Mexico.

The eastern United States recovered fairly quickly, but places farther afield were not so lucky. Japan suffered one of the three worst famines in its history in 1783-86, when exceptional cold destroyed the rice harvest and as many as 1m people died. Special crews had to be hired to clear the roads of the dead. In Japan this famine is usually attributed to another volcanic eruption, that of Mount Asama, but its impact was small compared with Laki's.

Tree-ring evidence from the Urals, the Yamal peninsula in Siberia and Alaska all suggests northern areas had their coldest summer for 400 to 500 years. The oral history of the Kauwerak tribe of north-western Alaska calls 1783 “the year summer did not come”; the tribe was almost wiped out.

Because of disruption to the monsoons, rainfall in the Nile watershed was down by almost a fifth and in the Niger watershed by more than a tenth. In his “Travels through Syria and Egypt”, Count Constantine Volney, a French orientalist, wrote that “the [Nile] inundation of 1783 was not sufficient, great part of the lands therefore could not be sown for want of being watered. In 1784, the Nile again did not rise to favourable height, and the dearth immediately became excessive. Soon after the end of November, the famine carried off, at Cairo, nearly as many as the plague.” By January 1785, he says, a sixth of Egypt's population had either perished or fled.

In Europe, the Laki eruption was not to leave an indelible mark. Within a few years, weather patterns returned to normal and Europeans had forgotten the extraordinary “dry fog”. But in retrospect, the eruption can be seen to exemplify certain truths about climate change.

Polluting gases can change global temperatures a lot (in this case by cooling, not warming). Volcanic gases can do as much damage as any amount of human activity. But the poisonous cloud was only part of the story. Weather patterns mattered too. Stable anti-cyclones brought the gas to earth in Europe and stratospheric currents then spread it over a third of the globe. And the connections between pollution and weather are complex and unpredictable: people at the time understood the link between the volcano and the haze, but not the connection with events the other side of the globe. Societies are hit very differently: the impact was modest in most of Europe, but devastating in Egypt, Japan and Alaska. Lastly, people react to environmental disruption in ways that are themselves disruptive.

As the Icelanders struggled to return to normal in the summer of 1785, the country's superintendent ordered the paupers of neighbouring districts to be moved to Steingrimsson's area, though there was no food. In desperation, he says, “we held counsel and decided to head east to the beaches. A single man who was there ahead of us, a farmer from Stapafell called Eirikur, had on that day clubbed 70 adult seals and 120 pups on the beaches. I held a service in Kalfafell in the finest weather we experienced during that time where all of us gladly thanked God for His mercy in so richly providing for us in this barren land and so agreeably removing all the famine and death which otherwise awaited.”





Click here for a list of sources and acknowledgments.