Tambora: The Eruption That Changed the World (7 page)

THE 1810S: COLDEST OF THE COLD

While Vesuvius stood tall in the European imagination, it nevertheless had no impact whatever on global climate. Its intermittent eruptions were orders of magnitude too small. How ironic, then, that Europeans of the late 1810s, distracted by their Vesuvian sideshow, remained oblivious to the planet-wide volcanic crisis through which they lived. Given the state of science and communications, however—no steamships or telegraph, let alone satellites—it is no surprise they failed to “teleconnect” the dots.

Tambora’s violent impact on global weather patterns was due, in part, to the already unstable conditions prevailing at the time of its eruption. A major tropical volcano had blown up six years prior, in 1809. This cooling event, hugely amplified by the sublime Tambora in 1815, ensured extreme volcanic weather across the entire decade. We have seen that the historical record surrounding Tambora’s eruption is slim: a scattering of reports from Raffles’s lieutenants and translated stanzas from a Sumbawan poem are all we have. So obscured from human view is Tambora’s immediate predecessor, however, that even its location remains a mystery. The historical fact of the eruption scientists refer to as the 1809 Unknown was only established through the technology of ice core analysis developed in the 1960s.
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Ice cores are cylinder-shaped records of annual snowfall, dating back thousands of years, extracted from glaciers and ice sheets at the planet’s peaks and poles. These glittering sheaths of ice are among the most beautiful natural artifacts ever to be subject to scientific scrutiny—and the most important. Even given the bone-chilling requirements of their extraction, it is difficult not to envy the scientist whose task it is to unlock the climatic secrets of a giant ice core, suffused with tiny bubbles and dancing with blue light. While the Shelleys and their peers contemplated the work of centuries among the ruins of Pompeii, modern paleoclimatologists see millennia stretched out before them in perfect Apollonian torsos of glacial ice.

A paper published in 1991, based on ice core evidence from both poles, announced the surprising presence of a rich sulfate deposit corresponding to the 1810 and 1811 snowfalls, indicative of a major tropical eruption comparable in size to the famous Krakatau eruption of 1883 (a magnitude approximately half that of Tambora’s).
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A subsequent ice core study, based on sulfate deposits across the Greenland ice sheet, rated the 1809 Unknown the
third
largest eruption since the early 1400s, behind only Tambora and the eruption of Mount Kuwae on Vanuatu in 1452.
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Certainly, many parts of the globe felt its cooling impact the following year. In parts of England, the first days of May 1810 were the coldest in living memory, bitten with late frosts, while the lowlands hills of Scotland remained eerily white through the spring. In Manchester, morning May temperatures slipped 5 degrees below freezing.
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Such extreme, unseasonal cold was unheard of and would not be felt again until the disastrous volcanic summer of 1816.

A flurry of research since the discovery of the 1809 Unknown has resulted in the identification of the 1810–19 decade as a whole as the coldest in the historical record—a gloomy distinction. A 2008 modeling study concluded Tambora’s eruption to have had by far the largest impact on global mean surface air temperatures among volcanic events since 1610, while the 1809 Unknown ranked second over that same period, measuring just over half Tambora’s decline.
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Two papers published the following year confirmed the status of the 1810s as “probably the coldest during the past 500 years or longer,” a fact directly attributable to the proximity of the two major tropical eruptions.
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In light of this evidence, we can now be sure that the background climate conditions for Tambora were already unusually cool. Its spectacular eruption then increased that cooling to a truly dire extent, contributing to an overall decline of global average temperatures of 1.5°F across the entire decade. One-and-a-half degrees might seem a small number, but as a
sustained
decline characterized by a sharp rise in extreme weather events—floods, droughts, storms, and summer frosts—the chilled global climate system of the 1810s had devastating impacts on human agriculture, food supply, and disease ecologies, as we shall see unfold in often horrific detail in the following chapters.

Just how gloomy were those volcanic years? The Scottish meteorologist George Mackenzie kept meticulous records of cloudy skies between 1803 and 1821 over various parts of the British Isles. Where lovely clear summer days in the earlier period 1803–10 averaged over twenty, in the volcanic decade 1811–20 that figure dropped to barely five. Even that parlous average would have been lower but for the merciful return to seasonal conditions in 1819, which the poet John Keats immortalized for its “mellow fruitfulness” in his poem “To Autumn.” For 1816, the Year without a Summer, Mackenzie recorded
no clear days at all
.
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A craze for clouds developed during this relentlessly overcast, stormy period. The poetry of the 1810s (notably Shelley’s) is full of meditations on “Cloudland, gorgeous land!”—as Coleridge called it.
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Likewise in
painting, by the end of that gray decade, John Constable had given up his impressions of English landscapes for experimental canvases filled entirely with clouds and their subtle peregrinations across a muted sky.
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The 1810s also marks Charles Dickens’s first decade of life. His deep body memory of a volcanic childhood infuses his fiction: think of the “cold, biting weather: foggy withal” of
A Christmas Carol
. Though his adult life and writing career date from a sunnier, warmer England (everything’s relative!), his grim weatherscapes of the 1810s have entered the popular imagination as definitive representations of the ever-cloudy, bone-chilling atmosphere of Victorian London.

For the Tamboran decade of the 1810s to warrant the title of “longest sustained cold period” since the Middle Ages is no small thing, since the period 1250–1850 itself has long been referred to as the “Little Ice Age.” Before 1250—during the so-called Medieval Warming Period—Englishmen produced their own wine, while the Danes set up farming colonies on Greenland. From the late thirteenth century onward, however, such luxuries were denied by frequent spikes of brutally cold conditions. The English pulled up their vineyards and took to skating on the Thames. No universal glaciation occurred, of course, and bursts of warmth, sometimes decades long, interrupted the general cooling trend. Not an “Ice Age” at all, then—but more like an intermittent six-century cold snap.

Climate models have shown that the cool conditions of the Little Ice Age lie outside the range of natural variability, so climatologists have been compelled to seek out its anomalous causes. One long-popular school of thought has focused on the irregularity of solar radiation, traceable in the historical record through accounts of sunspot activity. Although recent NASA studies support a minor link between solar minima and cooler winters, there have long been skeptics of a solar trigger for the Little Ice Age.
¹⁹
The renowned climatologist Alan Robock, among others, has shown that fluctuations in sunspot activity have little impact on global climate on decadal, let alone centennial, scales.
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According to Robock, as well as a 2012 paleoclimatological study in the Canadian Arctic and Iceland, responsibility for launching the Little Ice Age lies instead with a spasm of major volcanic eruptions
in the late thirteenth century, possibly beginning with a massive tropical eruption in 1258 (precise location again “unknown”). This concentrated sequence of volcanic blasts in the late 1200s altered the baseline conditions of global climate by a degree or more, beyond the threshold at which colder temperatures became self-reinforcing through expansion of the Arctic ice pack: a classic climate change feedback loop.

Individually, volcanoes of the magnitude that sustained the Little Ice Age have the capacity to influence climate for two to three years, until their aerosol cloud washes from the atmosphere. Volcanoes erupting in clusters, however—as they did in the thirteenth century and in the Tambora period of the early nineteenth century—achieve a cumulative chilling power over global climate by virtue of the slow thermal recovery of the world’s oceans, which continue to depress temperatures for a decade or more after the volcanic dust of any one eruption has vanished from the atmosphere.
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Thus regular eruptions during the 1250–1850 period reinforced the initial cooling events. Six centuries after the 1258 Great Unknown, with global volcanic activity on the wane and temperatures on the upswing, the celebrated Krakatau eruption, which grabbed world attention in 1883, thus stands as a last hurrah, or encore, of the Little “Volcanic” Ice Age.

In the chilling case of the volcanic 1810s, the global ocean-atmospheric system had not yet recovered from the cooling effect of the 1809 Unknown event when the colossal eruption of Tambora occurred. The aftermath of that eruption, spanning the second half of the decade, stands as the most catastrophic sustained weather crisis of the millennium. The year following Tambora, 1816, has long enjoyed the folkloric status of the “Year without a Summer.” But this is faint praise (or blame), indeed. The celebrity of 1816, as a year apart, obscures the greater climatological and social history of the 1810s, of which Tambora’s eruption is the explosive centerpiece. Nor should we view Tambora’s global impact “merely” as an extreme weather regime limited to the late 1810s. Just as the influence of volcanism on climate may extend centuries, as in the case of the Little Ice Age, so the social changes wrought by climatic upheaval on the scale of 1815–18 may be traced decades into the future, as the following chapters will show.

Fast forward to the twentieth century, and we find only Alaska’s Mount Katmai in 1912 and Mount Pinatubo in the Philippines in 1991 erupting on a scale so frequently reached during the Little Ice Age. Even mighty Pinatubo, the century’s largest volcanic event, rates an order of magnitude smaller than Tambora, lower even than Tambora’s little brother, the 1809 Unknown.
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Living in New York as I was during the snowy winter of 1991–92, Pinatubo’s grip on global climate felt sharp enough! Just arrived from balmy southern Australia, battling the snow and frigid wind in my wholly inadequate outerwear, I wondered how it had occurred to anyone to establish a civilization in such an inhospitable place. In the Tambora year 1816, many residents of New England and the Atlantic seaboard came to the same conclusion, with profound consequences for the history of the United States (a story that must wait for
chapter 9
).

SCALING TAMBORA

Tambora, in its decapitated state, stakes a serious claim as the most destructive volcano in human history. In light of this, the celebrity of Krakatau’s more modest eruption in 1883 seems undeserved. Only the historical accident of the telegraph’s invention allowed news of it to travel almost instantly across the globe. Perhaps now, with its bicentenary upon us, Tambora will at last achieve a popular recognition equal to its vaunted reputation among scientists.

But how big was the Tambora event on a geological timescale? According to the Global Volcanism Program at the Smithsonian Institution, the so-called Holocene Period—the approximately twelve thousand years since the last glacial epoch—marks the “official” time frame of volcanic history. Not coincidentally, the consistent, more moderate temperatures characteristic of the Holocene—which have not fluctuated more than a degree in warmth or cold in those twelve millennia—have witnessed great leaps forward for the human race, from a precarious existence in nomadic hunter bands, to literate settler farmer
communities, to the advanced technological mass societies of the twenty-first century—a planet literally teeming with humanity.

According to the methodology employed by the Smithsonian—which measures magmatic output deduced from geological sediments and historical accounts—Tambora belongs to an elite group of some half-dozen Holocenic volcanoes that rate 7 on the Volcanic Explosivity Index (VEI), a size officially termed “colossal.”
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Volcanologists are quick to concede the limitations of the index, which gets fuzzier the further back in time one goes. Many important volcanoes are simply missing from the Smithsonian tables, including the great “Unknowns” of 1258 and 1809. Furthermore, paleoclimatologists complain, the VEI measures explosive power only,
not
the climatic impact of the volcano. The famous Mount St. Helens eruption in 1980, for example, rates a respectable 3 on the VEI, but since its volcanic matter ejected sideward and not upward into the stratosphere, its impact on climate was nil. As we have seen, the latitude of volcanoes is also crucial to their climatic impact: tropical volcanoes are capable of influencing global weather patterns while high-latitude volcanoes, such as Iceland’s Laki in 1783, impact only the northern hemisphere. But the VEI takes no account of latitude.