Volcanic Eruptions and Climate Change


A news blurb about recent increased volcanic
activity in Alaska renewed a question for me.
Then a new entry posted at Real Climate brought
the question even closer. And then an overview in
Science News put me over the brink, so here I’ll
stick my neck out.

My question comes in two parts. First, what
happens if we do find some safe and reasonable
way to “geoengineer” a cooling of the atmosphere,
only to find out with deep regret that we’ve set
ourselves up for a dangerous cooling — beyond
the intended, engineered cooling — when a
volcanic eruption deepens our engineered chill to
even deeper and, for many, to lethal levels?

Second, while even a major volcanic cooling is
widely accepted as a relatively temporary thing,
lasting only a few years if not only a few
months, might it relieve the heat in ways we
don’t dare voice aloud? Put crudely, my second
question is: Might some major and violent
volcanic eruption “save” us from the dangerous 3C
or 4C heat scenario by eliminating zillions of

“So what are the problems? Robock’s study looks at
a subset of the potential ones – in particular, the impacts on

A new entry titled ‘Climate change methadone?’
has been posted to RealClimate.org.


“The eruption of Indonesia’s Tambora in 1815
triggered agricultural failures in North America
and Europe, caused the worst famine of the 19th

“Today, by comparison, the world’s surplus food
supply would last only about 90 days, a number
that’s steadily dropping as population increases

“What happens if another major eruption happens
today?” Verosub asks. “If we lower the growing
season globally, are we looking at a food crisis?
Š We’ve got a really stressed system, and if we
hit it hard, is it going to collapse? I think
that’s worth thinking about.”

Science News
August 30th, 2008; Vol.174 #5

Disaster Goes Global
By Sid Perkins

Small disturbances can eventually have immense
consequences. In the namesake example of the
butterfly effect, the vortex spun from a
butterfly’s wing creates tiny changes in the
atmosphere that result in a hurricane half a
world away. While that’s theoretically possible,
no one has yet tried to blame the insect world
for triggering a cyclone.

But a strong link does exist between the small
particles suspended high in Earth’s atmosphere,
such as those spewed from erupting volcanoes, and
the overall climate down at the planet’s surface.
High-altitude aerosols, especially in large
numbers, block sunlight from reaching the ground
and scatter it back into space, thereby cooling
the planet for months or even years (SN: 2/18/06,
p. 110). The 1991 eruption of Mount Pinatubo in
the Philippines, for example, caused the global
average temperature to briefly drop about 0.4
degrees Celsius. The eruption of Indonesia’s
Tambora in 1815 triggered agricultural failures
in North America and Europe, caused the worst
famine of the 19th century and cooled the planet
so much that 1816 became known as “the year
without a summer.”

While many eruptions in historic times caused
real climatic changes, previously only Tambora
had been linked to significant social
disruptions, says Kenneth Verosub, a geophysicist
at the University of California, Davis. Now,
however, analyses by Verosub and colleague Jake
Lippman suggest a connection between the 1600
eruption of Huaynaputina, a little-known peak in
Peru, and one of the greatest famines ever to
strike Russia.

“People have long known about the eruption and
have long known about the famine, but no one has
previously linked the two,” Verosub says.

Other volcanic eruptions of approximately
Huaynaputina’s size or larger have occurred more
recently, including Pinatubo in 1991 and
Indonesia’s Krakatau in 1883, but they didn’t
cool Earth as much and didn’t trigger societal
upheavals. The reason, researchers say, may stem
from the immense volumes of sulfur-rich fluids
that fueled Huaynaputina’s eruption, which
released an exceptional amount of planet-cooling

Krakatau and Pinatubo also took place in a more
industrialized world in which nations were more
connected than they were when Tambora blew its
top. So perhaps technology and globalization have
rendered modern society more resilient to the
effects of a worldwide catastrophe such as a
massive volcanic eruption.

Unfortunately, though, overpopulation and
humanity’s consumption of a large fraction of the
world’s biological productivity mean that even
today a large eruption could deal humanity a
significant blow, some scientists say.

Trouble down south

The Andes, the world’s longest mountain chain,
stretch along the western edge of South America
and are chock-full of volcanoes. In February
1600, Huaynaputina, a relatively inconspicuous
peak in southern Peru with no known history of
eruption – in the local language, the name means
“new volcano” – catastrophically exploded. The
eruption, the largest in South America in written
or oral history, lasted at least two weeks and
belched as much as 12 cubic kilometers of ash,
much of that spewing into the atmosphere during
the first two days.

Avalanches of volcanic ash and hot boulders
spilled east and southeast of the peak, and
lahars – flows of ash and mud with the
consistency of wet cement – destroyed several
villages on the way to the Pacific coast, about
120 kilometers away. Significant quantities of
ash smothered the region, says Charles Walker, a
historian at UC Davis. “Some people didn’t see
the sun for months, and agricultural production
was devastated for the next two years,” he notes.

As many volcanic eruptions do, Huaynaputina
lofted immense amounts of sulfur dioxide into the
atmosphere. That gas reacts with water vapor in
the air and then condenses into Earth-cooling
droplets of sulfuric acid, which can destroy
high-altitude ozone. Eventually the droplets are
cleansed from the air by natural processes. The
amount of sulfur-bearing compounds deposited on
ice in Greenland and Antarctica in the months
after the eruption suggests that Huaynaputina
spewed between 16 million and 32 million metric
tons of sulfur into the air, says Hannah
Dietterich, a geologist at Pomona College in
Claremont, Calif.

Most of that sulfur came not from the lava, but
rather from pressurized fluids that accumulated
in the volcano’s magma chamber before the
eruption, she and her colleagues proposed in
December 2007 at a meeting in San Francisco of
the American Geophysical Union. Geochemical
analyses of trace elements in the apatite
minerals recovered recently from rocks made of
Huaynaputina’s ash suggest that the magma could
have contained no more than 4.1 million metric
tons of sulfur. The tests also hint that as much
as 5 percent of the material that erupted from
the peak could have been fluid rich in sulfur
dioxide, carbon dioxide and water – substances
that, as they rose to Earth’s surface, would have
violently expanded and fueled the eruption.

The big chill

Several studies indicate that the sulfur dioxide
emissions from Huaynaputina were roughly
comparable to those of Tambora. Therefore, says
Verosub, the climatological consequences of the
two volcanoes should be similar. Indeed, the
chilling effects of Huaynaputina’s eruption in
1600 were substantial and were felt worldwide, he
and Lippman report in the April 8 Eos.

To wit: Tree ring data gathered throughout the
Northern Hemisphere indicate that 1601 was, on
average, the coldest year out of the last 600. In
Switzerland, 1600 and 1601 were among the coldest
years between 1525 and 1860. In Estonia, the
winter of 1601-1602 was the coldest in a 500-year
period. In Latvia, the late date of ice breakup
in the harbor at Riga indicates the winter was
the worst in the 480 years before today. In
Sweden, record amounts of snow in the winter of
1601 were followed in the spring by record
floods. People around the world felt the effects
of Huaynaputina’s changes to climate.

Through a chance meeting on an airplane, Verosub
found that Huaynaputina may have triggered
substantial social upheaval as well. While he
chatted with a seatmate about his research on the
effects of volcanic eruptions, a fellow seated in
the row behind – Chester Dunning, a historian
specializing in Russian history at Texas A&M
University in College Station – overheard the
conversation and introduced himself.

“So,” Verosub asked Dunning later in the chat,
“did anything interesting happen in Russia in
1601?” The reply: “Oh, yeah. That was a terribly
cold time in Russia.” That cold spell was just
the beginning of the nation’s woes, Dunning

Large portions of Russia received heavy rains in
the summer of 1601, and by the end of the growing
season it was clear that most crops would fail.
In that age, Dunning explains, most farmers
expected to occasionally experience a bad year
and stockpiled accordingly, so farmers and their
families didn’t suffer immediately. However,
another agricultural failure the following year
led to widespread starvation in both 1602 and

This lengthy famine – Russia’s worst, says
Dunning – claimed the lives of an estimated 2
million people, or about one-third of the
population, and more than 100,000 died in Moscow
alone. Government inability to alleviate both the
calamity and the subsequent unrest eventually led
to the overthrow of Czar Boris Godunov, a
defining event in Russian history.

Many volcanoes, besides killing local residents
during their eruptions, have caused indirect
deaths by triggering famines in the surrounding
regions, says Lee Siebert, a volcanologist at the
Smithsonian Institution in Washington, D.C. In
1783, for example, the clouds of volcanic ash and
poisonous gases lofted during the eruption of
Laki in Iceland killed more than half of the
nation’s livestock, which in turn led to a food
shortage that resulted in the death of about
one-quarter of the population there. Also that
year, an eruption of Asama, one of Japan’s most
active volcanoes, may have contributed to a local
famine that lasted four years and killed between
300,000 and 1 million Japanese, Siebert says.

The local and regional effects of volcanoes are
common and often well-documented. However, the
purported long-distance link between Huaynaputina
and the subsequent famine and social unrest in
Russia marks the only instance besides Tambora in
which a specific volcano has been blamed for
causing global misery, Verosub says.

Future shock?

In general, the larger the volcanic eruption, the
bigger the cooling effect and the longer that
effect lasts, sulfur content of its aerosols
notwithstanding. Scientists categorize eruptions
according to the Volcanic Explosivity Index, a
parameter that depends on factors such as how
much material is thrown from the peak and the
height of the ash plume that’s produced.

The Huaynaputina eruption of 1600 falls into VEI
category 6, which denotes an eruption with an
ejecta volume greater than 10 cubic kilometers
and a plume height that exceeds 25 kilometers. By
comparison, Tambora has been tagged as a VEI
category 7 eruption, which signifies an eruption
that produces a similarly lofty ash plume but
generates more than 100 cubic kilometers of

Since 1601, there have been five category 6
eruptions, including Laki (1783), Krakatau (1883)
and Pinatubo (1991). However, none of these
events spawned adverse societal effects on a
global scale as Huaynaputina did. In part,
Huaynaputina’s sulfur-rich plume could have
rendered the peak’s eruption inordinately

Climate at the time could have played a role as
well, says Verosub: In 1600, the world was in the
midst of the Little Ice Age, typified by harsh
winters, springs and summers much cooler and
wetter than normal, and shorter-than-average
growing seasons. A large volcanic eruption during
that period would have depressed average
temperatures even further – adding insult to
injury, as it were.

The demographics of the era also played a role,
Dunning speculates. During the 1500s, the
population in many regions had doubled, and as
the century progressed, the proportion of young
males had grown even faster. As a result, many of
the younger sons of the late 1500s ended up not
receiving their fathers’ land, jobs or titles,
producing what Dunning terms “a surplus
population of angry young men.” And in general,
food production wasn’t keeping up with population

By the 1590s, Dunning notes, many parts of the
world were experiencing a wave of starvations,
rebellions and unrest. Then, he adds, “at this
most excruciating moment, this other thing comes
along to take things where they’d never gone
before.” None of the countries of early modern
Europe were equipped to deal with such crises,
Dunning says.

Is the situation any better today? Would modern
technology and an increased global
interconnectedness enable 21st century humans to
better survive an immense, Earth-chilling
eruption? Surprisingly, the answer to both
questions may be no.

In the past, Verosub notes, most of a society’s
foodstuffs were grown locally and in wide
variety, so not every crop required the full
growing season to mature. Therefore, any event
that shortened a region’s growing season didn’t
necessarily doom the entire harvest. Staples that
formed the bulk of the diet were, for the most
part, homegrown.

Today, on the other hand, most large-scale
agricultural production focuses on a single crop
that’s chosen to take full advantage of a
region’s climate in order to realize maximum
output – a severe disadvantage if the growing
season is significantly trimmed by, say, a
volcanic eruption.

Not only were preindustrial farming practices
possibly more resilient to total agricultural
failure, people then “were used to living on the
margin,” Dunning says. “Everybody knew hunger Š
and the idea that you should plan for a bad year
was ingrained in these societies.”

Today, by comparison, the world’s surplus food
supply would last only about 90 days, a number
that’s steadily dropping as population increases.
Additional pressure on food, water and other
resources in some nations, such as China, stem
from a rapidly increasing standard of living and
the resulting changes in dietary preferences (SN:
1/19/08, p. 36).

Humans are consuming an ever-increasing fraction
of the biological productivity at the base of
Earth’s food chain, in some regions almost
two-thirds of the biomass that would be available
if humans weren’t clearing forests, farming or
otherwise occupying the land (SN: 10/13/07, p.
235). Rising population, plus the shift in some
areas to divert agricultural production to
produce inedible commodities such as ethanol, has
led many to suggest a modern-day food crisis is
at hand.

“What happens if another major eruption happens
today?” Verosub asks. “If we lower the growing
season globally, are we looking at a food crisis?
Š We’ve got a really stressed system, and if we
hit it hard, is it going to collapse? I think
that’s worth thinking about.”


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