THE LITTLE (VOLCANIC) ICE AGE - Tambora: The Eruption that Changed the World - page 17

Figure 2.2. Graph showing sulfate deposition, from both poles, corresponding to the 1809 and 1815 erup-
tions. Because these two major eruptions—Tambora's being “colossal”—occurred within six years, they
ensured significant suppression of global temperatures across the entire decade. (Jihong Cole-Dai et al.,
“Cold Decade [AD 1810-19] Caused by Tambora [1815] and Another [1809] Stratospheric Volcanic Erup-
tion,” Geophysical Research Letters 36 [2009]: L22703; © American Geophysical Union.)
A flurry of research since the discovery of the 1809 Unknown has resulted in the identi-
fication 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 Tam-
bora's decline. 14 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. 15
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 Au-
tumn.” For 1816, the Year without a Summer, Mackenzie recorded no clear days at all . 16
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 Col-
eridge called it. 17 Likewise in painting, by the end of that gray decade, John Constable had