Alexandra Witze and Jeff Kanipe are finalists for the 2016 PEN/E.O. Wilson Literary Science Writing Award for Island on Fire: The Extraordinary Story of a Forgotten Volcano That Changed the World. The book centers on the story of Laki, Iceland’s largest volcano, whose 1783 eruption had devastating consequences for humans. Incorporating larger discussions of super-volcanoes and recent volcanic eruptions, Witze and Kanipe analyze the potential consequences of a future Laki eruption. The following is an excerpt from the book.

In 1783, Benjamin Franklin was living in Passy, as the United States’ main diplomatic representative to France. Although Franklin had other weighty matters on his mind—notably, hammering out a British-American peace treaty following the Revolutionary War—he became fascinated, inevitably, by the oddities of the weather that summer. Franklin was many things—a politician, a writer, and America’s first postmaster. At heart, though, he was a scientist.

No record exists of exactly when Franklin first spotted the dry fog that descended over France, but a key document survives that describes how he thought about it. In May 1784, Franklin sent a letter to his friend Thomas Percival, a physician in Manchester, who corresponded with him regularly on meteorological topics. The contents became public that December, when Percival read it in front of the Manchester Literary and Philosophical Society.

Never one to let a natural phenomenon pass him by, Franklin had seized the opportunity to think about the mysterious haze. As usual, he had thoughtful and insightful things to say about where such a fog might have come from—things that cemented his reputation in the history of volcanology. In his letter to Percival, Franklin described the event:

During several of the summer months of the year 1783, when the effect of the sun’s rays to heat the earth in these northern regions should have been greatest, there existed a constant fog over all Europe and great part of North America. This fog was of a permanent nature; it was dry, and the rays of the sun seemed to have little effect towards dissipating it, as they easily do a moist fog, arising from water. They were indeed rendered so faint in passing through it, that when collected in the focus of a burning glass, they could scarce kindle brown paper. Of course, their summer effect in heating the earth was exceedingly diminished. Hence the air was more chilled, and the winds more severely cold. Hence perhaps the winter of 1783-4 was more severe than any that had happened for many years.

Franklin was far from the only scientist to note the bitter winter of 1783-84, nor was he the first to link it to the dry fog that spread across Europe the previous summer. But in a typical Franklin twist, it appears as if he had been intrigued enough to try a little backyard experiment, to see whether the haze had attenuated sunlight to the point that a magnifying glass (a ‘burning glass’) could not ignite a fire. Such a minor test would not have been a stretch for a man who famously flew a kite into a thunderstorm to verify the nature of electricity. In his essay, Franklin goes on to probe where the dry fog might have come from:

The cause of this universal fog is not yet ascertained. Whether it was adventitious to this earth and merely a smoke proceeding from the consumption by fire of some of those great burning balls or globes which we happen to meet with in our rapid course round the sun, and which are sometimes seen to kindle and be destroyed in passing our atmosphere, and whose smoke might be attracted and retained by our earth: or whether it was the vast quantity of smoke, long continuing to issue during the summer from Hecla [sic] in Iceland, and that other volcano which arose out of the sea near that island, which smoke might be spread by various winds over the northern part of the world, is yet uncertain.

Here Franklin proposes two ideas, one perhaps more outlandish than the other. The ‘great burning balls or globes’ he refers to are the meteors, such as the fireball that soared across Europe on 18 August 1783. Richard Payne, a geographer at Manchester Metropolitan University, has argued that Franklin’s suggestion is the first time any scientist drew a link between an extraterrestrial impact and climate change.

But Franklin has a second possible explanation for the dry fog: that it issued from a volcano in far-off Iceland. Franklin had never been to that exotic island, but if he thought a volcano might be to blame he would naturally think of the country with the mighty fire-mountains. Of those, Hekla was by far the most famous and among the most active, and so he proposed it as a possible source. But if Hekla was not the culprit, another possibility might be ‘that other volcano which arose out of the sea near the island’. That other volcano was Nyey (‘New Island’), a short-lived land that passing sailors had seen rising above the waves off Iceland’s southwest coast in the spring of 1783. Tales of its dramatic birth would have quickly spread to the continent, and in the absence of any information about the Laki eruption, Franklin was taking his best guesses as to which Icelandic volcano might have produced the menacing dry fog.

Franklin was not alone in his surmises. Although he didn’t know it at the time, he wasn’t even the first to link the fog to Iceland. That honor probably belongs to French scholar Morgue de Montredon, who presented a paper about the dry fog to a learned gathering in Montpellier on 7 August 1783, more than half a year before Franklin wrote his letter. Morgue de Montredon was a distinguished member of France’s national scientific society, and his paper is a detailed and careful summary of the extraordinary meteorological properties of the fog as seen around Montpellier. He concluded that the haze was rich in sulfur and suggested that it originated with a volcano. A volcano probably meant Iceland, and so de Montredon also picked Nyey as the likely source.

Other scholars weighed in independently with similar ideas. Christian Gottlieb Kratzenstein, a physics professor at the University of Copenhagen, blamed the fog on Nyey sometime in the summer of 1783, and so may deserve the acclaim for being the first to link the haze to an Icelandic volcano. But de Montredon was the first to present his ideas in public, and he also had a greater impact among the scholars of continental Europe. Still, more than either of these two, it was Franklin who made the full link between volcanic activity and the ensuing cold winter. Richard Payne notes that unlike the others, Franklin went on to make a wilder connection:

It seems however worth the inquiry, whether other hard winters, recorded in history, were preceded by similar permanent and widely extended summer fogs, because if found to be so, men might from such fogs conjecture the probability of a succeeding hard winter, and of the damage to be expected by the breaking up of frozen rivers in spring, and take such measures as are possible and practicable, to secure themselves and effects from the mischiefs that attended the last.

With such prescient words, Franklin’s essay brought the idea of a link between volcanoes and climate change into far broader public consciousness.

***

The aerosols from Laki were lofted so high into the atmosphere that they spread not only across Europe but also, as we’ll soon see, across the rest of the northern hemisphere. To understand how Laki could have such a global impact, we’ll need to pause for a brief look at some basics of atmospheric chemistry.

The part of the atmosphere that people experience every day—through which we walk, run, drive, and fly—is called the troposphere. It makes up most of the mass of the atmosphere: four-fifths of all nitrogen and oxygen and other elements that comprise the air we breathe is concentrated here. Weather patterns arise, evolve and expire in the troposphere. Most of humanity’s population also swarms throughout this lowermost layer.

Now imagine being a balloon rising through the troposphere. As you get higher and higher, the air grows thinner and temperatures drop. Eventually, by the time you reach about -50 degrees Celsius, you get to a point where the temperature stops getting any colder. Now you’ve reached the top of the troposphere and are starting to move into a drier and more rarefied realm: the stratosphere.

Some of the planet’s most important chemistry takes place in the stratosphere. For instance, here lies a layer of the triple oxygen molecules called ozone, which shields the Earth from the sun’s searing ultraviolet rays (when not being depleted by man-made chlorofluorocarbon chemicals). More importantly for our story, the stratosphere is also where long-distance transport can happen. Any material in the atmosphere that makes it past the top of the troposphere and into the stratosphere can travel around the globe much more readily than it can lower down, where it would be washed out by rain and other everyday weather.

Therefore, the boundary between the troposphere and the stratosphere is crucial. Get past that point, and you’ll be able to stay aloft much longer and travel greater distances. But here’s a complicating point: the boundary between those two atmospheric sections, known as the tropopause, varies in elevation depending on latitude. At the equator, the tropopause is typically about eighteen kilometers above the surface, whereas at the poles it is just eight kilometers up. (This difference is thanks to circulation patterns in the atmosphere, particularly jets of air known as the subtropical and polar front jets.) Therefore, gases and aerosols ejected by volcanoes closer to the poles, such as Indonesia, have a lot further to go to reach the stratosphere. In contrast, those from volcanoes closer to the poles, such as in Iceland, have a shorter distance to travel and can more readily penetrate the stratosphere.

Volcanoes eject many things—including ash, rock and gases—but the main factor that affects climate is the amount of sulfur. It initially billows out of volcanoes as sulfur dioxide gas, but within about a month this oxidizes in the stratosphere, or combines with other compounds, to form sulfuric acid. These acid vapors, along with water vapor, then condense into sulfate aerosol particles, which are the major player in volcanic climate change.

Lower down, in the troposphere, rain washes out most sulfate aerosols within a matter of days. But particles that make it up into the drier stratosphere may survive for several years, plunging back down to the surface if they get mixed into descending air masses at mid-latitudes. They can also get sucked down through atmospheric vortices at the planet’s poles. Both processes take time, which means the volcanic particles can influence climate long after the ash plume has faded.

Most eruptions never fire their aerosols high enough to reach the stratosphere, but those that do can affect climate in several ways. For one thing, the particles may warm the stratosphere by absorbing sunlight. They can also accelerate the rate of chemical changes, like the ozone depletion that happens when chlorine particles break apart ozone molecules. (Pinatubo’s 1991 eruption, in the Philippines, temporarily reduced ozone by as much as 20 per cent at certain layers in the atmosphere.) Most importantly, stratospheric particles can act as a giant sunscreen: they are just the right size to scatter incoming sunlight back into space, cooling the ground underneath as a result. In a general sense this observation is nothing new: after 44 B.C.E. eruption of Etna, Plutarch observed how the haze of particles spewed from the eruption temporarily dimmed the sun. Modern science, though, has greatly improved our understanding of how this happens.

A volcano’s climate-cooling power thus depends on two main factors: how high its gases are injected into the atmosphere, and how many sulfur aerosols are produced. Eruptions of around the same magnitude on the VEI scale can have very different climate effects. The 1980 eruption of Mount St. Helens, for instance, had relatively little sulfur dioxide in its plume and cooled the planet very little, while the similarly sized El Chichòn eruption in Mexico, two years later, cooled the planet quite a bit since it was so sulfur-rich. And that’s nothing compared to the sulfur giants. Pinatubo put about 20 million tons of sulfur dioxide into the stratosphere. But Laki spewed out more sulfur dioxide—about 122 million tons of it—than any other eruption in the past 1,000 years. That’s more than enough to wreak climate havoc well beyond Iceland and the rest of Europe.

***

Just how much of the planet Laki affected is perhaps the biggest unanswered question about the eruption. There’s no doubt that the haze itself travelled far afield. Winds blowing toward the east spread it to Africa, the Middle East and beyond. By 1 July the dry fog masked the sky above central Asia’s Altai Mountains, some 7,000 kilometers from Iceland. It may have even spread to central China, as chronicles for that year from the Henan province describe a ‘severe dry fog—sky is dark’.

Whether the volcanic haze actually spread all the way to North America is controversial. Benjamin Franklin asserted that the fog had been seen over much of the continent, and a missionary in eastern Labrador reported that the air was:

filled with the finest smoke so that the  sun shone completely pale… It is now known to be sure that this smoky air which has occurred in the summer of 1783 over nearly all Europe, has found its origin at the earth fires in Iceland at which possibly the earthquakes at Calabria might have contributed… It seems this fog has occurred over the whole northern hemisphere if not further.

We know that the Laki eruption belched a lot of material high into the air, and that this material travelled a very long way. The question that now faces us is this: how did those emissions cause the freakish weather of 1783-84, and to what extent did other meteorological patterns also play a role? For answers, we need to turn to some of modern science’s most sophisticated tools: computer climate models.

Computer models of volcanic eruptions can be used to predict where an ash cloud might spread, making it possible to plan the evacuation of residents, or the clearance of airspace. Models developed for volcanoes can also shed light on what could happen if other unwanted particles were to spread throughout the atmosphere, such as those created by a nuclear explosion or a large-scale blast of pollution.

Few scientists have thought as much about the potential of climate modeling and volcanoes as Alan Robock, of Rutgers University in New Jersey. With twinkly eyes framed by a fringe of white hair and beard, Robock looks like a jovial Santa Claus—until he starts talking about the physics of nuclear destruction. A former Peace Corps volunteer who visited the Soviet Union during the Cold War, and Fidel Castro during the US trade embargo with Cuba, he’s not shy about questioning the social relevance of his research.

For Robock, volcanoes are natural laboratories for exploring the consequences of disturbing the planet, and climate models are his main tool. The year after the 1980 eruption of Mount St. Helens, he published a paper in Science explaining why it would have little to no global climate effect; he turned out to be right. He has also helped elucidate many of the mechanisms by which Laki changed temperatures over half the planet.

In a 2006 paper written with NASA scientist Luke Oman and others, Robock combined a popular NASA climate model with another that specialized in atmospheric sulfur chemistry. The scientists first tested the approach by loading it with information about sulfur released by the 1912 Katmai eruption in Alaska and the 1991 Pinatubo eruption in the Philippines. When the model was run, it correctly showed where the aerosol clouds from those volcanoes had spread. The researchers then re-started the model with information about the Laki eruption: what time of the year it occurred, and how much sulfur erupted from the fissures. The model assumed that the erupted particles would have been injected some nine to thirteen kilometers high.

Calculations showed that Laki’s sulfur dioxide emissions would have reached their peak in late June 1783 and then converted to sulfate aerosols over the next few weeks. By late August the atmosphere’s sulfate load would have maxed out, after which the material would have drifted all the way around the northern hemisphere.

Up in the stratosphere, Laki’s particles began their climate changing work. By absorbing outgoing radiation from the ground, they began warming the air around them. By reflecting incoming solar radiation, they began cooling the planet’s surface below. (Despite the extraordinary heat in Europe, for most of the rest of the hemisphere that summer was a chilly one.) Those changes, in turn, would have triggered a cascade of other modifications to the atmosphere, as weather patterns shifted around the globe in response to this new climate forcer in their midst.

In a follow-up paper to the original Laki modelling, Oman, Robock, and colleagues took a step further to find out what had happened next. Once again they fed information about Laki into a computer model, then looked to see what it told them about changing atmospheric conditions and how those affected the African and Indian monsoons, crucial weather systems that provide desperately needed rainfall to millions of people.

Oman’s team showed precisely how Laki would have set off a devastating chain of events. Normally, differences in temperature between the land and the oceans set up strong wind patterns that allow monsoons to develop seasonally. But Laki’s eruption cooled land masses in the northern hemisphere significantly, by one to three degrees Celsius. Suddenly the land was not all that much warmer than the ocean, and the monsoon didn’t have much surface heat to fuel its winds. In Africa in particular, the monsoon simply failed to materialize in the summer of 1783.

With no monsoon, Africa began to dry out. In the western part of the continent, the level of the Niger River began to drop. More importantly, to the east the Nile, too, began to dwindle. For millennia, farmers eking out their livelihood along the Nile had relied on the mighty river’s annual flood to replenish and irrigate their lands. That summer, the live-giving floods never came, and neither did they arrive the following summer. With no water, crops failed and famine ensued.

Traveling northern Africa, French nobleman Constantin de Volney wrote of the disaster:

Soon after the end of November, the famine carried off, at Cairo, nearly as many as the plague; the streets, which before were full of beggars, now afforded not a single one: all had perished or deserted the city…Nor shall I ever forget that, when I was returning from Syria to France, in March 1785, I saw, under the walls of ancient Alexandria, two wretches sitting on the dead carcase [sic] of a camel, and disputing its putrid fragments with the dogs.

By January 1785, Volney reported, one-sixth of Egypt’s population had either died or left the country because of the failure of the Nile.

Beyond Africa, Laki’s climatic effects are trickier to trace. One reason for this is that many confounding climate factors were at play in 1783-84, such as El Niño. The El Niño Southern Oscillation is an occasional climate pattern in which the eastern Pacific warms up while the central and western Pacific cool down. (Its name means ‘the boy child’, a reference to the birth of Jesus, as El Niño often makes its first appearance around Christmas off the coast of Peru.) The pattern repeats every two to seven years, affecting weather around the globe. An El Niño was well underway in 1783, a fact that complicates efforts to look for wider climatic effects from Laki.

India, for instance, suffered droughts and famine in 1783 that may have killed up to eleven million people. But this climate aberration might have been driven at least partially by El Niño and not by Laki eruption. The same may be true in Japan, where the late summer of 1783 saw unusually cold temperatures along with heavy rains. The combination drowned rice paddies, leading to one of the worst famines in Japanese history, in which tens of thousands of people may have perished. Japan’s story is also complicated by the fact that its own volcano, Mount Asama, erupted for three months starting from 9 May 1783. Tens of thousands of people died in ashflows and mudflows from this eruption. (Unlike Laki, Asama doesn’t seem to have injected enough sulfur into the stratosphere to make a global impact.)

In China, too, parts of the country had an unusually cool summer in 1783, and limited data suggest that deaths spiked soon thereafter. Again, however, it remains difficult to tease out the effects of a severe El Niño year from sulfur-loading in the atmosphere due to Laki.

In fact, one Laki expert thinks that the volcano should be entirely absolved of responsibility for the cold winter of 1783-84. Rosanne D’Arrigo, a tree ring expert at the Lamont Doherty Earth Observatory outside New York City, points to the winter of 2009-10 for an analogy. That winter was one of the coldest and snowiest ever recorded in parts of western Europe and eastern North America. February blizzards in Washington DC had locals proclaiming that ‘Snowmageddon’ had arrived, while in the United Kingdom newspapers reported on the ‘Big Freeze’ that blanketed the country in white from the Isle of Skye to the English Channel. The frigid temperatures and heavy snow trace back to an unusual combination of two natural climate patterns, which D’Arrigo thinks may have also been at work in the year after Laki went off.

The first such pattern, the North Atlantic Oscillation, is a variation in surface pressure that regularly causes temperatures to seesaw across the North Atlantic. When the oscillation is in what’s known as its negative phase, temperatures in western Europe and eastern North America are usually colder than normal. At the same time, Canada and Greenland see warmer than usual temperatures.

The second pattern is El Niño, which typically brings more rainfall than usual to certain regions. In 2009, a fairly strong El Niño was locked in place. Essentially, the North Atlantic Oscillation provided the cold to London and Washington, while the El Niño provided the wet. D’Arrigo and her colleagues have used tree rings to reconstruct the North Atlantic Oscillations and El Niños over the past 600 years, and in 2011 they reported that a strong combination of the two caused the chilly temperatures during the winter of 1783-84. This may mean that Laki was not to blame.

Once again, the key question is how high Laki’s aerosols travelled and how long they persisted in the atmosphere. To D’Arrigo most of the aerosols would have washed out a few months after the first violent eruptions. Others disagree. Atmospheric modeler Anja Schmidt, at the University of Leeds, has calculated that the Laki aerosol cloud would have circulated long enough into the autumn to definitely contribute to winter cooling. And various other records, including additional tree rings, show that cooling lasted across the northern hemisphere for up to three years after the eruption. That’s far too long to be explained by a combination of the North Atlantic Oscillation and an El Niño.

The final complication in understanding Laki’s climatic effects is the fact that the eruption took place during an extended cold spell known as the Little Ice Age. There is no absolute agreement as to when this era began and ended, but it’s widely accepted that Europe started to cool down in the early part of the fourteenth century, and that temperatures began to rise again in the middle of the nineteenth century. The continent endured frequent spells of severely cold weather during this period, and climate-related disasters occurred several times: the ‘Great Frost’ of 1740, for example, devastated harvests and led to a famine in Ireland just as bad as the more famous one a century later.

The Little Ice Age was a complicated phenomenon, and it’s not entirely clear what caused it. Many scientists attribute it in part to an extended period of low solar activity, as if the Sun’s thermostat get stuck on low and stayed that way for hundreds of years. With less sunlight arriving at Earth, temperatures would have dropped. But that can’t be the whole story, because European temperatures fluctuated wildly throughout the whole of the Little Ice Age, driven by a complex interplay between all facets of the Earth’s weather systems. And it’s possible that volcanoes played a role in kicking off the Little Ice Age. A 2012 study, led by Gifford Miller at the University of Colorado, proposed that a five-decade-long spurt of eruptions, beginning in the mid- to late thirteenth century, could have triggered a planetary chain reaction that affected sea ice and ocean currents in a way that abruptly lowered temperatures, and kept them low.

As Robock and others have shown, the eruption of Laki almost certainly disturbed the atmosphere enough to cause some amount of climate havoc in the years following 1783. Yet climate modelers can’t explain why the summer of 1783 was so hot. Those who watched the haze descend across Europe often noted that the warmest days seemed to be correlated with the days of the thickest fog. But scientists cannot reproduce this effect in their climate models. To Robock and others, this puzzle remains the greatest unsolved, mystery of Laki. A sophisticated model that can parse the exact amount of rainfall over the Nile for months on end cannot explain why summer temperatures would have been broiling over Europe.

Such open-ended issues complicate the calculation of Laki’s final death toll. The official count, according to the authoritative reference work Volcanoes of the World, is 9,350. But tens of thousands more may have perished across Europe from the effects of breathing in the particles day after day, and if you add the famines in Egypt and possibly Japan, Laki suddenly becomes a much bigger killer. Pressed for a complete tally, Thor Thordarson suggests that more than 1.5 million people may have lost their lives as a result of the eruption. John Grattan, a geographer at Aberystwyth University who has done the most work on Loki mortality rates, speculates the death toll may even been as high as six million.

In perhaps the biggest stretch, some environmental historians have even argued that the Loki emissions may have spelled the end for French royalty. The harsh winters, cool summers and heavy rains set up a series of crop failures across France throughout the early 1780s. Bread became scarce, and peasants became angry and desperate, particularly after a drought in 1788. The following year, revolution broke out. Few people would accept this as a straightforward case of environmental determinism: complex socioeconomic and political factors were at work in the French Revolution. That said, Laki clearly disrupted life in France for years on end. Those storming the Bastille might not have known anything about the Icelandic volcano, but perhaps it was an unseen player in the events of 1789.

Excerpted with permission from Island on Fire: The Extraordinary Story of a Forgotten Volcano That Changed the World, by Alexandra Witze and Jeff Kanipe. Reprinted by arrangement with Pegasus Books. All rights reserved.

Read more from the finalists of the 2016 PEN/E.O. Wilson Literary Science Writing Award

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