Island on Fire Page 12
Laki was particularly sulphur-rich because of the magma that fed the eruption. In 1996, Thor Thordarson and his colleagues published a seminal paper that used geologic detective work to hunt down the chemistry of the original magma. By looking at tiny bubbles within rocks erupted from the Laki fissure, the scientists calculated the chemical makeup of the original magma. They discovered that Laki was particularly efficient at separating out sulphur and other volatile elements (such as chlorine and fluorine) from the molten rock, and spitting them into the air.
Gases separate out of magma as it rises toward the surface, depressurizing along the way. Laki’s magma rocketed upward with the force of a jet engine. By the time anyone in Iceland realized what was happening, Laki was fountaining fire more than 1,400 metres into the air. This suggests the magma was gushing out at up to 170 metres per second – maybe even twice as fast in the early stages of the eruption. At these speeds, Thordarson’s team estimated, half to three-quarters of the gases contained in the magma would have separated out.
But how high did Laki’s sulphate aerosols reach? Were they really high enough to penetrate the stratosphere and thus be transported around half the planet? Most experts on the eruption, including Thordarson, think the Laki plume was high enough to reach the stratosphere. Analysis of eyewitness reports suggest the plume must have risen at least nine kilometres and probably went as high as thirteen kilometres. At Laki’s latitude of 64 degrees north, that would place it just past the tropopause and into the lower stratosphere.
This claim gets some solid support from ice cores drilled into the Greenland ice sheet. Every year, snow falls atop Greenland in winter and melts a little in summer, compacting and building up layer after layer of ice. Gas bubbles trapped within the ice preserve ancient air, which researchers can use to trace changes in the planet’s atmosphere over time. Chemical elements within the ice itself also provide clues to other environmental changes, from the rise of industrial pollution to wildfires.
Several international expeditions have drilled cores from Greenland’s ice sheet, and many of those cores contain layers rich in volcanic sulphur. Most such layers can be traced back to particular eruptions, such as Krakatau in 1883. Others are mysterious peaks of sulphur with no known volcano to blame them on. Ice layers dated to the year 1258, for instance, show a huge spike in sulphur that implies a volcano eight times as big as Krakatau must have gone off around that time — though no one knows which volcano that might have been. The ice core record of Laki, however, is clear.
Many of these precious ice cores are preserved in Denver, Colorado. Inside a huge building at the Denver Federal Center – once the largest warehouse west of the Mississippi River – sits the National Ice Core Laboratory. All federally financed U.S. drilling projects send their ice cores to be stored here. It’s sort of a frozen library, with row after row of silvery one-metre-long core tubes taking the place of books on floor-to-ceiling shelves. In this case the library represents a precious storehouse of information about past climate.
On a cloudy February morning, we make our way to the ice core lab to see the remains of Laki for ourselves. Our guide is chief curator Geoff Hargreaves, who trained as an oceanographic technician and spent years escorting complex scientific equipment on and off research vessels. Now he puts his talents to work creating new ways to prepare and store ice cores for posterity.
Before seeing Hargreaves’ ice, though, we have to bundle up. On go a pair of thick coveralls, protective ‘bunny boots’, a warm hat and gloves. To enter the freezer itself, we go through a series of heavy doors, with increasingly dire warnings about the temperatures ahead. The main core storage is at a bone-chilling -38 degrees Celsius – the kind of temperature that renders people what Hargreaves calls ‘cold-stupid’. Reflexes slow down, talking seems difficult and thinking just as arduous. We’re glad to have someone experienced in deep cold to escort us through.
Quickly we stumble into the ‘warm’ room that clocks in at only 24 degrees below. With high white walls and various preparatory tables sitting around, this is the area where technicians and scientists actively work with cores. It’s cold enough to keep the ice safely frozen, but those extra few degrees above the deep-freeze temperature is enough to make working here simply uncomfortable rather than dangerous. Some workers can stay in the ‘warm’ room for up to four hours; Hargreaves says he usually bails after about thirty minutes. For our purposes, the sooner we see the Laki core the better.
Hargreaves leads us over to a black-curtained alcove, which looks something like a photo booth at a train station. He pulls aside the drape and the first thing we see is Arnold Schwarzenegger staring back at us. A lifesize cut-out of the actor, dressed as Mr. Freeze from the movie Batman & Robin, is on guard here. Mr. Freeze watches over whatever ice core happens to be placed on the metal tray in front of him – which today is a half-core of ice drilled by the American GISP2 project in the early 1990s. The Denver lab has 3,000 metres of ice cores from this site in Greenland, starting at the top of the ice sheet and going down to bedrock. We are interested in only the uppermost part of the core, the part that holds ice just over 200 years old. The particular segment Hargreaves lays out for us once rested between 71 and 72 metres deep. It lies in front of us, a half-moon of ice a metre long, formed as the American Revolutionary War was ending and the first balloonists were taking to the skies over France.
But it’s really hard to see the remains of Laki here: it all looks like pale blue ice to us. Fortunately, Hargreaves has already passed this core through a machine that measures electrical conductivity, and he can see that something very odd happens about 0.095 metres into it. So we look at the core’s left edge and scan our eyes to the right by about ten centimetres. And there it is, barely visible but corresponding to the spike in conductivity that Hargreaves has measured: a dusky band a few centimetres wide crosses the core. It looks as if someone had spilled a bit of cigarette ash on the ice and forgotten to clean it up.
The deep freezer of the National Ice Core Laboratory, near Denver, Colorado, contains polar environmental history stretching back hundreds of thousands of years.
We are looking at some of the particles that Jón Steingrímsson would have seen rising as black clouds above the hills behind Klaustur. The particles danced upward and were caught in the great circulation vortex over the Arctic. Eastward they went, sweeping across Scandinavia and northern Asia and then circling all the way around again, to settle out in snow falling over central Greenland. Year after year the thin ash layer got buried, compressed, and crushed down in the ice core until scientists, finally, retrieved it.
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 modelling 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. T
he year after the 1980 eruption of Mount St. Helens, he published a paper in Science explaining why it would have little to no global climatic 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 Luke Oman and others, Robock combined a popular NASA climate model with another that specialized in atmospheric sulphur chemistry. The scientists first tested the approach by loading it with information about sulphur 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 sulphur erupted from the fissures. The model assumed that the erupted particles would have been injected some nine to thirteen kilometres high.
Calculations showed that Laki’s sulphur dioxide emissions would have reached their peak in late June 1783 and then converted to sulphate aerosols over the next few weeks. By late August the atmosphere’s sulphate 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.
Laki’s haze played havoc with temperature and weather patterns, causing levels of rivers such as the Nile to drop precipitously.
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 life-giving floods never came, and neither did they arrive the following summer. With no water, crops failed and famine ensued.
Travelling through 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 the 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 sulphur into the stratosphere to make a global impact.)
The cooling effect of volcanic eruptions can be seen in this chart of land temperatures from 1750 to the present.
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 sulphur-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. Which may mean that Laki is 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 modeller 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 under
standing 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 got 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 modellers 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 dry fog. But scientists can’t 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.