IF ALIENS had been watching the Earth during 1815 the chances are
they would not have noticed the cannon fire of Waterloo, let alone the
final decisions of the Congress of Vienna or the birth of Otto von
Bismark. Such things loom larger in history books than they do in
astronomical observations. What they might have noticed instead was
that, as the year went on, the planet in their telescopes began to
reflect a little more sunlight. And if their eyes or instruments had
been sensitive to the infrared, as well as to visible light, the curious
aliens would have noticed that as the planet brightened, its surface
cooled.
Mount Tambora (pictured), a volcano on the Indonesian island of
Sumbawa, was once similar in stature to Mont Blanc or Mount Rainier. But
in April 1815 it blew its top off in spectacular fashion. On the 10th
and 11th it sent molten rock more than 40 kilometres into the sky in the
most powerful eruption of the past 500 years. The umbrella of ash
spread out over a million square kilometres; in its shadow day was as
night. Billions of tonnes of dust, gas, rock and ash scoured the
mountain’s flanks in pyroclastic flows, hitting the surrounding sea hard
enough to set off deadly tsunamis; the wave that hit eastern Java,
500km away, two hours later was still two metres high when it did so.
The dying mountain’s roar was heard 2,000km away. Ships saw floating
islands of pumice in the surrounding seas for years.
In his book “Eruptions that Shook the World”, Clive Oppenheimer, a
volcanologist at Cambridge University, puts the number killed by the ash
flows, the tsunamis and the starvation that followed them in Indonesia
at 60,000-120,000. That alone would make Tambora’s eruption the
deadliest on record. But the eruption did not restrict its impact to the
areas pummelled by waves and smothered by ash.
When the sulphur hits the stratosphere
The year after the eruption clothes froze to washing lines in the New
England summer and glaciers surged down Alpine valleys at an alarming
rate. Countless thousands starved in China’s Yunnan province and typhus
spread across Europe. Grain was in such short supply in Britain that the
Corn Laws were suspended and a poetic coterie succumbing to cabin fever
on the shores of Lake Geneva dreamed up nightmares that would haunt the
imagination for centuries to come. And no one knew that the common
cause of all these things was a ruined mountain in a far-off sea.
While lesser eruptions since then have had measurable effects on the
climate across the planet, none has been large enough to disrupt lives
to anything like the same worldwide extent. It may be that no eruption
ever does so again. But if that turns out to be the case, it will be
because the human world has changed, not because volcanoes have. The
future will undoubtedly see eruptions as large as Tambora, and a good
bit larger still.
Mixed in with the 30 cubic kilometres or more of rock spewed out from
Tambora’s crater were more than 50m tonnes of sulphur dioxide, a large
fraction of which rose up with the ash cloud into the stratosphere.
While most of the ash fell back quite quickly, the sulphur dioxide
stayed up and spread both around the equator and towards the poles. Over
the following months it oxidised to form sulphate ions, which developed
into tiny particles that reflected away some of the light coming from
the sun. Because less sunlight was reaching the surface, the Earth began
to cool down.
The sulphate particles were small enough to stay aloft for many
months, so the cooling continued into the following year. By the summer
of 1816 the world was on average about 1ºC cooler than it had been the
year before—an average which hides much larger regional effects. Because
the continents are quicker to cool than the heat-storing seas are, land
temperatures dropped almost twice as much as the global average.
This cooling dried the planet out. A cooler surface meant less
evaporation, which meant less water vapour in the lower atmosphere and
thus less rain. Rainfall over the planet as a whole was down by between
3.6% and 4% in 1816.
If such numbers seem suspiciously accurate, considering that most of
the world of 1816 was devoid of thermometers and rain gauges, it is
because they come from recent computer modelling of the climate that
seeks to mimic the conditions Tambora created. Like all modelling
results, such numbers need caveats. These results, though, and similar
ones from other models, can be accorded the credence that comes from
having been proved right in similar situations.
The 1991 eruption of Mount Pinatubo in the Philippines was about a
sixth as large as Tambora’s in terms of the volume of lava, rock and
ash, and about a third as large in terms of sulphur emissions.
Satellites showed that in the summer of 1992 the sulphur it had spewed
into the atmosphere was reducing the amount of sunlight getting to the
Earth’s surface by well over three watts per square metre; for
comparison, the warming effect of the 40% increase in the atmosphere’s
carbon-dioxide level since the age of Tambora is just two watts per
square metre.
With the energy absorbed by the Earth reduced, temperatures fell by
around half a degree in the year after Pinatubo; rainfall dropped off
significantly, too. Computer models run after the eruption but before
these effects became visible captured the effects reasonably accurately
(though they had a tendency to overestimate the cooling). This is one of
the best reasons for thinking that such models capture the workings of
the climate quite well.
The historical record largely bears out what the models suggest
Tambora did. Across Europe the summer of 1816 was cold and wet, and the
harvest terrible. The effects were most notable around the Alps; in
Saint Gallen, in Switzerland, the price of grain more than quadrupled
between 1815 and 1817. Starving migrants took to the roads in their
hundreds of thousands; mortality rates climbed due to starvation and
disease. Death also stalked Yunnan, where Tambora’s cooling shut down
the monsoon and cold days in summer killed the rice harvest for three
years running.
Monsoons, which are driven by the difference in temperature between
hot land and cooler sea, are particularly vulnerable to the excessive
cooling of the land that volcanoes bring. Their weakening can have
effects on more than crops. In his excellent account of the global
impacts of the 1815 eruption, “Tambora”, Gillen D’Arcy Wood of the
University of Illinois draws on the writings of James Jameson, a doctor
in Calcutta, who held the lack of fresh water which followed the failure
of the 1816 monsoon responsible for the cholera epidemic that swept
through Bengal the following year.
Was this all down to one volcano? Not entirely; nothing in the
climate has a single cause. The global climate shifts in various ways on
a number of timescales, and its particular disposition at the time a
volcano strikes will influence the way the volcano’s effects play out.
The fact that an El Niño event—a swing in the global climate driven by
the slopping of warm water east across the Pacific towards South
America—was getting under way at the time of the Pinatubo eruption in
1991 undoubtedly modulated its climatic effects.
Alan Robock, an expert on links between volcanoes and climate at
Rutgers University, notes a particularly intriguing initial condition
that could have influenced the world’s response to Tambora. There had
been another large eruption—larger than Pinatubo—just six years before.
No one knows where this 1809 eruption was, but its signature can clearly
be seen in the Greenland and Antarctic ice sheets. The sulphur put into
the stratosphere by volcanoes shows up quite clearly in the
year-by-year records of what was going on in the atmosphere that climate
scientists extract from polar ice cores. These records make it possible
to give dates to large eruptions in the past even if no one recorded
the event at the time (see chart).
Cooling Mr Knightley
The ice cores show that the 1809 eruption was easily large enough to
have had effects on the climate, and there is some evidence of cooling
in subsequent years. In Jane Austen’s “Emma”, which according to Euan
Nisbet, a geologist at Royal Holloway, London, seems to follow the
weather of 1814, spring is remarkably late, with apple trees blossoming
in the middle of June. Pre-cooling along these lines might have made
some of the subsequent effects of Tambora more marked, while possibly
lessening others. Some researchers believe that a number of eruptions
close together might be able to trigger a climate downturn that lasts
considerably longer than the few years models normally predict; a set of
eruptions in the late 13th century, this idea suggests, may have been
part of the reason for the subsequent global cooling known as the
“little ice age”.
If the prior state of the climate system constrains an eruption’s
effects, so does that of the human world. The damage done to Europe by
the preceding quarter-century of revolutionary and Napoleonic war could
have left it particularly vulnerable to 1816’s “year without a summer”.
The situation in Yunnan would hardly have been as dire had the
population not been hugely expanded by the Qing dynasty’s encouragement
of new settlers.
Similarly uncaptured in models, but even more fascinating to
speculate about, are the after-effects of the Tambora downturn. In
America, the spike in grain prices caused by Europe’s hunger drove a
wave of farmers across the Appalachians to where the Ohio Valley was
enjoying far more clement weather, with barges taking exports for Europe
down the Mississippi in ever larger amounts. The collapse in the grain
price when Europe’s harvest recovered contributed to the American
economy’s first major depression.
The historian John Post, in a study of Tambora’s effects published in
1977, “The Last Great Subsistence Crisis in the Western World”, held
that the volcano reshaped European politics. The disorder that sprang up
in the bad weather from 1816 to 1818, and its subsequent repression,
created a climate for authoritarian rule that held sway until the middle
of the century. Mr D’Arcy Wood points out that it was in the aftermath
of the Tambora famines that farmers in Yunnan started to plant opium
poppies, the value of which as a cash crop offered some insurance
against future failures of the grain harvest.
On top of such structural shifts, there are the personal stories. If
Shelley, Byron and their romantic entourage had not been cooped up in a
Swiss villa by incessant rain, would they have amused themselves by
writing horror stories for each other—including John Polidori’s “The
Vampyre”, the first novel to deal with seductive bloodsucking
aristocrats, and Mary Shelley’s “Frankenstein”, which has shaped fears
of scientific innovation from that day to this? If the summer frosts of
“Eighteen-hundred-and-froze-to-death” had not driven Joseph Smith, a
farmer, from Norwich, Vermont to Palmyra, New York, a place of vigorous
religious enthusiasms, would his son Joseph junior still have been able
to find the golden tablets to which the angel Moroni led him a few years
later, or would the history of Mormonism have been very different?
Reappraising the risks
And what if this happened again? In general, volcanoes are not
something people around the planet worry about very much. In lists of
the 40 most expensive and most lethal natural disasters since 1970
recently produced by Swiss Re, a reinsurer, no eruptions feature at all.
Models of the economic losses that large eruptions could cause are
nothing like as well developed as those that the insurance industry uses
for storms, floods or earthquakes, because such losses have mattered
little. Some reinsurers, though, are beginning to put that right.
One worry is that even quite a small eruption could cost a lot if it
hit a built-up part of a developed country. A study by Willis Re
suggests that an eruption of Italy’s Vesuvius like the one which took
place in 1631 (a much smaller event than that which destroyed Pompeii)
could lead to an economic loss of well over €20 billion ($22 billion).
Most of the property damage would be down to buildings collapsing under
the weight of the ash that falls on them. The 1707 eruption of Mount
Fuji produced only 2% as much ash as Tambora did, but Christina Magill
of Macquarie University has calculated that if both eruptions were rerun
today the urban area affected by heavy ashfall would be greater in the
case of the Fuji eruption, since a great deal of that ash fell on what
is now Tokyo.
The other reason for thinking more seriously about the damage done by
volcanoes than recent history might seem to merit is that geology shows
that they need to be assessed on much longer timescales. Today’s
earthquakes, storms and floods—which make up the bulk of the natural
disasters that insurers worry about—are doing more damage than
yesterday’s did, but that is because they hit a world in which there is
more valuable property that is likely to be insured, not because the
disasters themselves are getting worse. The world’s worst storm or
earthquake over a millennium is not all that much worse than the worst
of a century. With volcanoes things get worse and worse the deeper in
time you look.
In terms of direct effects, this is still not particularly worrying
for most of the world’s population. Seven out of eight people on the
planet live more than 100km from any potential eruptions. The “Global
assessment report” (GAR) prepared for the UN summit on disaster-risk
reduction held in Sendai, Japan, in March found that 95% of those at
risk live in just seven countries. Five—Indonesia, the Philippines,
Japan, Mexico and Guatemala—are on the circum-Pacific “ring of fire”,
where clashing tectonic plates promote volcanism as well as earthquakes;
the other two are Ethiopia and Italy. Two-thirds of the exposed
population is in Indonesia.
The good news for the people who are at risk is that volcanoes—unlike
earthquakes—provide a fair amount of warning before doing their thing.
Scientists are increasingly good at looking out for such warnings, and
most volcanoes that are close to lots of people are now pretty carefully
monitored, though there are exceptions—the GAR points to the
Michoacan-Guanajuato cinder-cone field in Mexico as a worrying one.
Satellites and seismology are likely to pick up some signs of imminent
eruptions from almost all the others. When the warnings seem to merit
it, action can be taken. During the 2010 eruptions of Mount Merapi in
Indonesia, the largest so far this century, 350,000 people were
evacuated; as a result the death toll was only a few hundred.
Evacuations kept the casualties at Pinatubo similarly small.
Unfortunately, predicting really large eruptions may be harder than
predicting smaller ones like Merapi’s. Before a very large eruption you
can expect a volcano to have been dormant for centuries; it takes time
for the infernal forces to build up. But that does not mean that the
first eruption of any long-dormant volcano will be catastrophic. It
might have decades of throat-clearing to go through before it really
lets rip. It might go back to sleep.
It was with this in mind that geologists embarked on a project to try
to understand long-dormant Pinatubo’s history soon after it started to
show signs of life in 1990. They found that the volcano seemed not to be
the throat-clearing type, specialising instead in dramatic eruptions.
Stephen Sparks of Bristol University says that understanding did a lot
to make people feel justified in calling for a big evacuation.
Wherever the next big eruption happens, though, and whether predicted
or not, it will, like Tambora, have global effects—and this time there
will be a greater range of them. The climate is not the only global
system now open to interruption.
All disasters now reverberate more than they would once have done.
Disrupted supply chains transmitted the losses from the Japanese
earthquake and tsunami in 2011 far and wide; tourism meant many more
Swedes died in the Indian Ocean tsunami of 2003 than in any recent
disaster on their home soil. Volcanoes, though, have the added ability
to interfere with one of the ways in which such connections between
far-off places are supported. As Eyjafjallajokull in Iceland showed five
years ago, a quite small eruption’s ash cloud can have a big impact on
air traffic if it is in an inconvenient place.
A really big eruption would shut down large swathes of airspace for a
couple of weeks. If the airspace in question were hard to reroute
around, that would have both direct impacts on the aviation
industry—Eyjafjallajokull cost it about $1.7 billion—and indirect
impacts on its users—valued at about twice the direct effects in that
case. The losses would not be evenly spread or easily predictable. The
Kenyan women who provide most of the labour for the country’s cut-flower
industry suffered disproportionately when Eyjafjallajokull kept their
blooms from market.
Another problem not seen when Tambora erupted would be damage to the
ozone layer. The reactions by which chlorine destroys ozone are
encouraged by the sulphate particles produced by volcanoes. In the 19th
century that didn’t matter; there wasn’t any chlorine in the
stratosphere. Now, thanks to human intervention, there is. Pinatubo saw
global reductions in stratospheric ozone levels and a marked deepening
of the “ozone hole” over Antarctica. If a Tambora-scale eruption were to
happen in the near future it would have even stronger effects.
Warmer house on the prairie
And then there is the climate. If, like Tambora and Pinatubo, the
volcano in question is close to the equator, Mr Robock says models
predict an average cooling of perhaps 2ºC in the summer of the next year
over much of North America, Europe, Asia and Africa, and decreased
precipitation over the Amazon, southern Africa, India, South-East Asia
and China. The models also make predictions about the weather in the
intervening winter: the particles that cool the surface warm the
stratosphere, which sets up a strong Arctic jet stream in a particular
configuration. Expect a peculiarly warm winter in America’s prairies,
western Europe and Central Asia, and a very cold one in eastern Canada,
the Middle East and southern China.
What these shifts would mean for agriculture is hard to say. The
experience of Tambora suggests gloom, but this is not that world. For
one thing, there is more agricultural land in more places. That gives
more scope for bad harvests in some regions being offset by better ones
elsewhere. Both models and studies of the years after Pinatubo suggest
that, for various reasons, the world’s plant life as a whole gets more
productive in the cooler, drier years that follow eruptions. It is also
possible that some parts of a world stressed by global warming might
experience sudden cooling as less of a problem than it was after
Tambora—though the dryness might exacerbate their challenges.
Another reason for tempered optimism is that the world would know
what was coming. Mr Robock and his colleagues would be spreading the
word before the eruption was over. Futures markets would doubtless pay
attention. So, one would hope, would governments.
The Red Cross/Red Crescent Climate Centre is dedicated both to
providing warnings about the human impacts of climate shifts and extreme
weather and to acting as an advocate for the people who suffer from
them most. It spends a lot of time looking at how to get timely warnings
of the likely regional effects of El Niño events to the countries and
people they are most likely to harm, along with advice on how to limit
the damage. Its head, Maarten van Alst, says he thinks that the climate
impacts of a contemporary Tambora might be comparable to those of the
big El Niño of 1997-98, which have been estimated at $36 billion, with
130m lives affected and 21,000 lives lost. And as with El Niños,
forewarned would be forearmed. Mr van Alst and his colleague, Pablo
Suarez, are trying to get a programme started that would study what
actions should be given priority in that lull between the eruption and
the cooling that would follow.
Such vigilance could come into its own well before there is another
Tambora, since there is a way for considerably smaller eruptions to have
climatic effects. Eruptions that take place well away from the equator
cool only their own hemisphere, and these lopsided coolings have an
impact on the intertropical convergence zone (ITCZ), a belt of rain
around the equator. When the northern hemisphere cools the ITCZ shifts
south, and that causes droughts in Africa’s Sahel. Of the Sahel’s four
worst years of drought during the 20th century, three took place after
northern-hemisphere eruptions: in the year after the Katmai eruption in
Alaska, (1913) and the years of and after the El Chichón eruption in
Mexico (1982 and 1983).
A repeat of the Tambora-sized blast at Taupo in New Zealand that took
place 1,800 years ago, on the other hand, would push the ITCZ to the
north and bring plentiful rain to the Sahel. The Amazon, though, which
depends on the ITCZ staying put, would have a dry few years.
For a smallish volcano at high latitudes the effects on the ITCZ
would probably swamp the local and regional effects. The direct damage a
full-on Tambora would wreak in a populated region would be far greater,
and its hard-to-foresee effects further afield, like those
Eyjafjallajokull had on Kenya, might conceivably reinforce each other in
calamitous ways, multiplying the economic damage. Still, in most cases
it seems likely that here, too, the climate effects would trump the
rest.
Pinatubo—picayune by comparison
But that does not mean their impacts would be as dire as those felt
two centuries ago. As well as having a wider agricultural base and more
foresight, the world today is more developed and better governed. A lot
of the damage done in famines such as those of the 1810s comes from
agricultural workers losing income at a time of price rises and
governments doing nothing about it. Today the proportion of the
population working the land is in most places much lower than it was
then, and most governments both perceive a need to act during famines
and have the capabilities to do so. There might well be a need for
humanitarian interventions in the weird-climate years that followed; but
such interventions do now happen.
That said, there is no reason to limit concern to Tambora-sized
eruptions. There are much larger ones on offer. Some 26,500 years ago
the Taupo volcano in New Zealand erupted with well over ten times the
power it mustered 1,800 years ago. The odds of a really big eruption in
any given year are tiny. Over a century, though, they mount up to maybe a
few percent. So, though few of those alive today would perish in a
rerun of Tambora, the chances of something much worse over their
lifetimes cannot be ruled out. And though forewarning would help, there
is no way of forestalling. Humans have huge powers over the planet. But
they cannot stop a volcano whose time has come.
