Tambora: The Eruption That Changed the World (21 page)

Bernard O’Reilly was one such loose end. In a
Quarterly Review
article of April 1818, Barrow eviscerates O’Reilly’s
Greenland
as among “the most barefaced attempts at imposition which has occurred to us in the whole course of our literary labours,” a book full of “nonsense,” “falsehood,” and “glaring folly,” and motivated throughout by a “mischievous tendency.”
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At first blush, Barrow’s vituperation of O’Reilly seems perplexing. After all, had not O’Reilly done great service to the naval cause in publishing his eyewitness account of an open polar sea in precisely that region to which Captain Ross was now preparing to sail in search of a northwest passage?

Fatefully for him, however, O’Reilly openly rejected the notion of a northwest passage to be found anywhere but along the Canadian north coast (where no expedition had been sent) and flatly rejected Barrow’s theory of polar warming and an open Arctic sea. Worse still,
O’Reilly dared to mock Barrow himself for believing in such chimeras. He called the new Admiralty expeditions a “utopian paper-built plan,” destined to “futility”:

Sailing to the north pole has been long a very favourite subject for closet lucubration; and as long as a man, in such circumstances, chooses to amuse himself harmlessly, or entertain his friends with his effusions through the medium of a magazine, such pursuits are altogether allowable; but where such visionary schemes are in contemplation as would mislead the public mind, in the same manner as the writer misleads himself, not pausing over facts, and maturely weighing their consequences, the prudent will be careful how they admit his opinions, however plausibly dressed up.
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O’Reilly (like Mary Shelley, as we shall see) reveals himself a polar skeptic, a Barrow critic, and hence an enemy of the Royal Navy. And because the impudent Irishman brought to his skepticism the authority of eyewitness, Barrow—who had never been to the Arctic—calls him a fraud and a plagiarist, a peddler of “absurdities, too mad for reason, too foolish for mirth.”
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The final straw? O’Reilly had the gall to publish his book as a lavish, expensive quarto targeted to Britain’s elite circles. From Barrow’s point of view, the claims of uppity amateur naturalists over Arctic science must be denied as emphatically as those of professional whalers—Scoresby, too, found himself unceremoniously excluded from the new polar mission. Only Britannia, in her full naval glory, should rule the Arctic waves.

Barrow’s scathing review did its work well. O’Reilly’s
Greenland
disappeared from sight, crushed beneath the wheels of Barrow’s Arctic juggernaut. In subsequent years, this unfortunate Irishman traveled the south seas as a ship’s surgeon, compiling scientific observations on Java, Australia, and India for future volumes that never appeared. Bernard O’Reilly was found dead in a rented room in London in 1827, probably by his own hand, his desk cluttered with desperate letters to would-be patrons. In one, he takes credit for Britain’s renewed quest for the northwest passage, a blatant untruth he nevertheless had good reason to believe might have been true … but for his nemesis John Barrow.
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CAPTAIN SCORESBY’S MARINE DIVER

So how did tropical Tambora—distant and faceless—launch her thousand ships into the Arctic? More pointedly, how could a period of drastic global cooling, precipitated by Tambora’s eruption, be consistent with warming of the polar seas and the release of thousands of square miles of Arctic ice into the shipping lanes of the Atlantic? William Scoresby, unwittingly, provides a key piece to the puzzle in his whaling journal of 1816.

Scoresby cut a legendary figure among the whalers of Yorkshire for his superb seamanship and physical charisma: he was capable, it was said, of staring down polar bears. In addition to these Ahab-like acquirements, he was a naturalist of rare gifts. In the whaling off-season, he studied with the renowned natural historian Robert Jameson at the University of Edinburgh and corresponded, as we have seen, with Sir Joseph Banks. His compilation of a lifetime’s study of the polar region, published in 1820 as
An Account of the Arctic Regions
, remains a classic foundational text of Arctic science. Charles Darwin, a fellow student of Robert Jameson, kept a well-thumbed copy by his bedside onboard the
Beagle
.

The main theme of Scoresby’s correspondence with Banks prior to 1817 is the design of an instrument for measuring seawater temperature at depth. Banks commissioned a slim bucket made of glass and wood for Scoresby to collect samples, but the whaler found that, at three hundred fathoms, the wood swelled and broke the glass. Scoresby then himself designed an upgraded model of the water sampler—an elegant, self-closing, octagonal cylinder made of brass, with a single window. The contraption weighed twenty-three pounds and sank by itself without the need of ballast. Scoresby called it his “Marine Diver.” It was Scoresby’s habit to take advantage of any lull in the hunt for whales to conduct experiments with his diving machine and record observations in a journal.

On May 21, 1816—a calm but foggy day with no “fish” in sight—Scoresby tied together all the lead lines he could find onboard his whaler, amounting to “somewhat more than 8/10 of an English mile” in length. He then attached wood blocks of different varieties to the end to test water pressure, and placed a thermometer inside the marine diver for temperature readings. Attaching the lead lines to his machine enabled Scoresby to lower the device to a depth of 600 fathoms. After some hours’ experimentation, Scoresby observed that the maximum temperature of the water through which the marine diver passed lay well beneath the surface. Also remarkable was the fact that this maximum temperature, 37°F, was the “greatest heat of the water, which [I] have observed in these regions.” The experiment, concluded Scoresby, “proves the existence of a current from the southward running beneath, at the same time the current from the NE to the SW runs upon and near the surface, whereby the whole body of the polar ice is carried.”
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What Scoresby had unwittingly identified was, in fact, the main engine of northern hemispheric climate.

The so-called Atlantic Meridional Overturning Circulation (AMOC) is a submarine current system that transports tropical warmth to the North Pole via the gulf stream and, in the course of its many thousand miles’ journey, moderates extremes of air temperature at all latitudes. The AMOC, in turn, belongs to the conveyor belt of thermal deep sea
currents that girdle the globe from pole to pole. As warm waters flow into the North Atlantic, they grow colder and saltier, and hence more dense. The heavy water sinks, drawing lighter, deep water to the surface. With his diving machine, Scoresby was able to capture a snapshot image of this dynamic process of liquid thermal exchange, and a vivid impression of opposing southward and northward currents. Becalmed off the Greenland coast west of Spitsbergen (Svalbard), he was well situated to observe the AMOC in the deep polar basins of the Norwegian and Greenland seas where its overturning motion is in fact triggered. While the sinking northward current brought heat to the Arctic seas, melting the ice pack, the cold surface drift escorted the broken ice south into the Atlantic Ocean, wreaking havoc on transatlantic shipping lanes in 1816 and 1817. Because of his vast experience in northern waters, Scoresby was thus able not only to observe the dynamics of an overturning oceanic current funneling warm water north into the polar sea but to make note of its extreme behavior in that season.

With the redoubtable Scoresby’s marine diver experiment, we inch closer to the solution to why, in the summers of 1816 and 1817—while the inhabitants of temperate zones from China to New England shivered and starved—the Arctic Circle basked in relative warmth and shed its ice at amazing, unprecedented rates. Crucial to understanding the relation between Tambora’s eruption in 1815 and the reports of massive polar ice loss in the summers following is Scoresby’s observation that, in 1817, the Arctic water was at its “greatest heat” in his experience. A survey of ships’ logs in the period suggests environmental strains on the Arctic even beyond Scoresby’s reckoning. Godthaab in southern Greenland experienced temperatures 5.5°C above average during the entire volcanic decade of 1810–19.
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The record air temperatures in Greenland, as well as Scoresby’s observation of unusually heated water, suggest that in the aftermath of Tambora, the AMOC was operating with increased intensity.

Answers to why this should be so may be found in studies of the 1991 eruption of Mount Pinatubo in the Philippines. The Pinatubo eruption has served scientists well as a model from which environmental impacts of the nearby Tambora event, unobserved by modern scientific instruments, might be extrapolated. A notable consequence of Pinatubo’s eruption, and the global cooling it produced, was the “substantial decrease” in rainfall overland for a year following the eruption and a subsequent “record decrease” in runoff to the oceans. The cause was the chilled, volcanic atmosphere, which repressed evaporation and reduced the amount of water vapor in the air. Put in its broadest terms, reduced solar radiation in Pinatubo’s aftermath altered the flow of energy through the coupled ocean-atmosphere system, with significant implications for the global hydrological cycle. Accordingly, the first post-Pinatubo year, 1992, witnessed the largest recorded percentage of the global landmass suffering drought conditions. A recent computer simulation of the influence of volcanic activity on global climate since 1600 produced the same “general precipitation decrease” in the high latitudes of the northern hemisphere, especially pronounced over land.
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In the case of Tambora, a volcanic event six times the magnitude of Pinatubo, hydrological disruption at the hemispheric scale must have been nothing short of catastrophic. In 1816 and 1817, with extreme
drought conditions prevailing across the high North American landmass, the Atlantic Ocean received only a fraction of its standard allotment of warm freshwater discharge from rivers and streams. As a result, surface waters in the North Atlantic became colder and saltier, sinking with greater force. The subsequent destabilization of the water column in turn enhanced the motive energy of the Atlantic thermohaline circulation. Convective currents released increased quantities of heat into the Arctic Circle, melting the ice cap, while a bulked-up southward current delivered great volumes of Greenland glacial ice into the Atlantic. The increased surface temperatures likewise inhibited the formation of new ice in the subpolar region, hence the magical-seeming open seas visible from the mastheads of British whalers off the coast of Greenland in 1816 and 1817.
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