The Year Without Summer (3 page)

On April 19, the
Benares
reached Bima. The coastline was barely recognizable; what had been one of the most
beautiful and regular harbors in Asia now was an obstacle course, littered with masses
of black pumice stone, tree trunks burnt and splintered as if by lightning, and the
prows of previously sunken ships which the ocean had thrown onto land. The village
had only a small supply of rice to stave off starvation. When the
Benares
departed several days later, it sailed past Mount Tambora, which had been one of
the highest peaks in the archipelago, often used by sailors as a landmark. Clouds
of smoke and ash still obscured the volcano’s peak. Even at a distance of six miles,
sailors could see patches of lava steaming along the mountainside.

A heavy rainstorm on April 17 had left the air cleaner and cooler, and probably saved
a substantial number of lives on the more distant islands as the rain washed the ash
off crops and provided fresh drinking water to help stem an incipient epidemic of
fever. But nothing could save those closer to Tambora. Over the following month, thousands
more perished—some from severe respiratory infections from the ash that remained in
the atmosphere in the aftermath of the eruption, others from violent diarrhoeal disease,
the result of drinking water contaminated with acidic ash. The same deadly ash poisoned
crops, especially the vital rice fields, raising the death toll higher. Horses and
cattle perished by the hundreds, mainly from a lack of forage. Lieutenant Owen Phillips,
dispatched by Raffles to investigate conditions and provide an emergency supply of
rice to the inhabitants, arrived in Bima several weeks after the eruption and reported
that “the extreme misery to which the inhabitants have been reduced is shocking to
behold. There were still on the road side the remains of several corpses, and the
marks of where many others had been interred: the villages almost entirely deserted
and the houses fallen down, the surviving inhabitants having dispersed in search of
food.” In the nearby village of Dompo, residents were reduced to eating stalks of
papaya and plantain, and the heads of palm. Even the Raja of Sanggar lost a daughter
to hunger.

In the end, perhaps another seventy to eighty thousand people died from starvation
or disease caused by the eruption, bringing the death toll to nearly ninety thousand
in Indonesia alone. No other volcanic explosion in history has come close to wreaking
disaster of that magnitude.

And yet there would be more casualties from Tambora. In addition to millions of tons
of ash, the force of the eruption threw 55 million tons of sulfur-dioxide gas more
than twenty miles into the air, into the stratosphere. There, the sulfur dioxide rapidly
combined with readily available hydroxide gas—which, in liquid form, is commonly known
as hydrogen peroxide—to form more than 100 million tons of sulfuric acid. The sulfuric
acid condensed into minute droplets—each two hundred times finer than the width of
a human hair—that could easily remain suspended in the air as an aerosol cloud. The
strong stratospheric jet streams quickly accelerated the particles to a velocity of
about sixty miles per hour, blowing primarily in an east-to-west direction. The sheer
power of the jet stream allowed the aerosol cloud to circumnavigate Earth in two weeks;
but the cloud did not remain coherent.

Variations in the wind speed and the weight of the particles caused some parts of
the cloud to travel faster or slower than others, and so the cloud spread as it moved
around Earth, until it covered the equator with an almost imperceptible veil of dust
and sulfurous particles. It also began to spread north and south, albeit far more
slowly. While it took only two weeks for the aerosol cloud to cover the globe at the
equator, it was likely more than two months before it reached the North and South
Poles.

Rather than a slow, steady broadening of the equatorial cloud into the Northern and
Southern Hemispheres, the cloud expanded in fits and starts. As some pieces of the
cloud were blown away from the equator, they were quickly caught up in the dominant
stratospheric jet streams—which in May blow east to west in the Northern Hemisphere,
and west to east in the Southern Hemisphere. The cloud soon began to resemble streamers
or filaments, with small portions regularly pushed off the equator and into the middle
latitudes in each hemisphere. Eventually, these filaments coalesced into a single,
coherent cloud that covered Earth.

And there they remained. Had the aerosol cloud ascended only into the lowest part
of the atmosphere, the troposphere, where clouds form, rain would soon have cleansed
the ash from the air. But in the more stable stratosphere, conditions mitigate against
the formation of clouds of water droplets. The coldest air already is at the bottom
of the stratosphere, with warmer air above it, so air rarely rises from the troposphere
into the stratosphere. With no rising plumes of warm air to carry moisture into the
stratosphere, clouds almost never form; the stratosphere is drier than most deserts.
With no clouds, there could be no rain to wash away the stratospheric aerosol veil.
Only the slow action of gravity and the occasional circulation of air between the
stratosphere and the troposphere could drag the droplets back to the earth. And so
the extraordinarily fine sulfur particles from Tambora that reached the stratosphere
remained suspended in the air for years, freely transported around the globe by the
winds. By the winter of 1815–16, the nearly invisible veil of ash covered the globe,
reflecting sunlight, cooling temperatures, and wreaking havoc on weather patterns.

2.

PORTENTS

“The country has all the appearance of the middle of winter…”

F
ROM
T
ERAMO IN
central Italy, near the Adriatic coast, came reports in late December 1815 of “the
heaviest snow ever known in that country.” According to one account, over a six-hour
period “a greater quantity of snow [fell] than has been known in the memory of man.”
More astonishing was the nature of the precipitation. The snow “was of a red and yellow
color … [which] excited great fear and apprehension in the people.” Believing that
“something extraordinary has taken place in the air,” the local residents organized
religious processions to placate God; in the meantime, provincial authorities summoned
a professor of physical science from Parma (who was also a Jesuit priest) to study
the phenomenon. For the rest of the winter, the Abruzzo region remained cold, with
significantly more snow and freezing rain than usual.

Several weeks later, an intense blizzard raged across northeastern Hungary for two
days. The snow reportedly covered houses to the rooftops, and killed more than ten
thousand sheep and hundreds of oxen. Despite the magnitude of the storm, news accounts
focused primarily on the fact that “the snow was not white, but brown or flesh colored.”
April brought reports of another colored snowfall in Italy, this time around the Tonale
Pass, in the Italian Alps: “It was brick red and left an earthy powder, very light
and impalpable, unctuous to the touch … [with an] astringent taste.” The colored snow
almost certainly was the result of ice droplets forming with ash particles from Tambora
as their nuclei. The deepest clouds associated with severe storms occasionally are
able to reach into the stratosphere, which is consistent with the colored snow falling
in particularly extreme weather events. Over the course of months—and, in this case,
years—gravity also slowly dragged the stratospheric sulfur particles into the upper
reaches of the troposphere, where the particles could more easily form the centers
of ice crystals.

No contemporary accounts appear to have made the connection between the phenomenon
of colored snow in Italy and Hungary and the eruption of Mount Tambora nearly halfway
around the world, although reports of Tambora had reached London by the end of 1815,
and a few amateur scientists—most famously Benjamin Franklin—had previously essayed
a connection between volcanic eruptions and unusual atmospheric conditions. Following
the eight-month-long eruption of Laki in southern Iceland in June 1783, Europe and
North America experienced highly unusual weather, including a persistent dry haze
during the summer and an extremely cold and snowy winter that killed thousands of
people across Europe. Although Franklin, who was living in Europe at the time, acknowledged
in a 1784 lecture to the Manchester Literary and Philosophical Association that “the
cause of this universal fog is not yet ascertained,” he suggested that it may have
been “the vast quantity of smoke, long continuing, to issue during the summer [from
Laki] … which smoke might be spread by various winds, over the northern part of the
world.” And the frigid temperatures, he proposed, probably resulted from this fog
blocking the rays of the sun, thereby reducing the amount of solar energy that reached
Earth.

Throughout the winter of 1815–16, the spreading aerosol cloud from Mount Tambora had
been doing precisely that: cooling global temperatures by reflecting and scattering
sunlight. Although the cloud reflected only one half to one percent of the incoming
energy, it reduced the Northern Hemisphere average temperature in 1816 by about three
degrees Fahrenheit. This seemingly small cooling had a considerable impact on global
weather patterns, with devastating consequences for agriculture on both sides of the
Atlantic. Ironically, however, the effects of Tambora’s aerosol cloud could have been
far worse if the eruption had been slightly weaker. While immense in size and scope,
Tambora’s aerosol cloud was not particularly efficient at reflecting sunlight. Stronger
volcanic eruptions tend to eject more sulfur dioxide into the stratosphere than weaker
eruptions, which leads to more sulfuric acid droplets within the same volume of atmospheric
gases. A greater number of droplets increases the chance that droplets will meet and
collide, forming larger droplets that will be removed more quickly from the stratosphere
by gravity. A single, larger droplet also has less total surface area than two smaller
droplets, and so is less effective at scattering sunlight. There is therefore a balance
to be struck between eruptions that are too weak to penetrate into the stratosphere—and
so produce small, short-lived cooling—and eruptions that produce large, less effective
sulfuric acid droplets. By measuring the remnants of Tambora’s aerosol cloud in ice
cores and lake sediments, modern scientists have determined that the climatic consequences—while
undoubtedly devastating—could have been far worse if the particles had been roughly
half their size.

Unlike the sudden drop in temperatures in the Indonesian archipelago that occurred
immediately after the eruption of Mount Tambora, the planet-wide cooling was a gradual
process that took up to a year to be fully realized. While air temperatures can, and
frequently do, change rapidly in response to variations in solar energy, soil and
ocean temperatures adjust much more slowly. The land and sea possess considerable
capacity to store heat, while the atmosphere has practically no storage. When the
atmosphere is cooler than the land and sea, heat will flow from these reservoirs back
into the air; but since the air cannot store heat for long, much of this is soon lost
to space. If, on the other hand, the atmosphere is warmer, some of that excess heat
will be stored in soil and water until a balance is reached. This process may be seen
clearly in summer: The warmest weather often occurs not in June, when the sun is strongest,
but in August, when the ocean and land have warmed.

As Tambora’s stratospheric aerosol cloud began to cool temperatures by subtly reducing
the amount of solar energy reaching the earth, the land and oceans would have resisted
this cooling by transferring stored heat into the atmosphere, and cooling themselves
as a result. By early 1816, the land, ocean, and atmosphere were shifting toward a
new balance of energies, largely as a result of the solar-dimming effect of the aerosol
cloud. The adjustment cooled first air, then land, and finally ocean temperatures
across the globe. Using information from tree rings—the width of each ring is related
to the growing conditions (mostly temperature and precipitation) that year—climatologists
have determined that 1816 was the second-coldest year in the Northern Hemisphere since
1400, surpassed only by 1601, following the eruption of Huaynaputina in Peru. Even
as the aerosol began to settle out of the atmosphere through gravity, it would take
years for land and ocean temperatures to return to normal. And so 1817 was the fifth
coldest, 1818 the twenty-second coldest, and 1819 the twenty-ninth coldest year in
the Northern Hemisphere since 1400.

In the meantime, the aerosol cloud had produced other noticeable optical phenomena,
most notably a series of spectacular red, purple, and orange sunsets in London in
the summer and autumn of 1815. Observers noted repeatedly that “the sky exhibited
in places a fire,” with “crimson cirri” [high-altitude cirrus clouds, composed of
fine ice particles] and “much redness in the twilight.” “The evening twilight has
been generally coloured of late,” wrote one contemporary, “and at times streaked with
converging shadows, the origin of which could not be traced to clouds intercepting
the light.” On several particularly unsettled September nights, the storm clouds continued
to glow various shades of red for half an hour after sunset.

Sunsets typically appear yellow, orange, or red because atmospheric gases scatter
blue light more effectively than other colors, skewing the visible-light spectrum
toward red. The effect is even more pronounced when the sun is low on the horizon,
since its light must pass through a thicker layer of the atmosphere to reach the ground,
resulting in less blue and more red light.

Stratospheric ash, dust, and soot particles from volcanic eruptions—or from pollution
or fires—enhance this atmospheric scattering effect, leading to brilliant red sunsets.
After the sun passes below the horizon and light no longer reaches the surface, some
sunlight still passes through the upper portions of the atmosphere. Aerosol veils
reflect this sunlight toward Earth, giving the colorful postsunset glows reported
in London. So exceptional were these sunsets that Londoners commented on them repeatedly
in letters, journals, and newspaper articles, which suggests that they likely were
caused by the Tambora aerosol cloud rather than the heavy industrial pollution that
habitually afflicted the city during that era. In fact, scientists have taken advantage
of this effect by using the amount of red in contemporary paintings of sunsets to
estimate the intensity of volcanic eruptions. Several Greek scientists, led by C.
S. Zerefos, digitally measured the amount of red—relative to other primary colors—in
more than 550 samples of landscape art by 181 artists from the sixteenth through the
nineteenth centuries to produce estimates of the amount of volcanic ash in the air
at various times. Paintings from the years following the Tambora eruption used the
most red paint; those after Krakatoa came a close second.