A 'volcanic winter' is the reduction in temperature caused by
volcanic ash and droplets of
sulfuric acid obscuring the
sun, usually following a
volcanic eruption.
Effects on life
The causes of the
bottleneck phenomenon, ''i.e.'', a sharp decrease in a
species' population immediately followed by a period of great genetic divergence (
differentiation) among survivors—might be attributed to volcanic winters. According to
anthropologist Stanley Ambrose, such events diminish the population size to "levels low enough for evolutionary changes, which occur much faster in small populations, to produce rapid population differentiation."
Ancient case of volcanic winters
One proposed volcanic winter happened around 71,000–73,000 years ago following the
supereruption of
Lake Toba on
Sumatra island in
Indonesia. In the following 6 years there was the highest amount of volcanic
sulphur deposited in the last 110,000 years, possibly causing significant
deforestation in
Southeast Asia and the cooling of global
temperatures by 1°C
[1] . Some scientists hypothesize the eruption caused an immediate return to a
glacial climate regime by accelerating an ongoing continental glaciation, thereby causing massive population reduction among animals and human beings on
Earth. Others argue that the climatic effects of the eruption were too weak and brief to impact early human populations to the degree proposed.
[2]
This, combined with the fact that most human differentiations abruptly occurred at that same period, is a probable case of
bottleneck linked to volcanic winters (see
Toba catastrophe theory). On average, super-eruptions with total eruptive masses of at least 10^15 kg (Toba eruptive mass=6.9
★ 10^15 kg) occur every 1 million years.
[3]
Recent cases of volcanic winter
Pinatubo early eruption 1991
The scales of recent winters are more modest but their effects can be significant. A paper written by
Benjamin Franklin in
1783 blamed the unusually cool summer of 1783 on volcanic dust coming from
Iceland, where the eruption of
Laki volcano had released enormous amounts of
sulfur dioxide, resulting in the death of much of the island's
livestock and a catastrophic
famine which killed a quarter of the population. Temperatures in the
northern hemisphere dropped by about 1°C in the year following the Laki eruption.
The
1815 eruption of
Mount Tambora, a
stratovolcano in
Indonesia, occasioned mid-summer frosts in
New York State and June snowfalls in
New England in what came to be known as the "
Year Without a Summer" of
1816.
In
1883, the
explosion of
Krakatoa (Krakatau) also created volcanic winter-like conditions. The next four years after the explosion were unusually cold, and the winter of
1888 was the first time snow fell in the area. Record snowfalls were recorded worldwide.
Most recently, the
1991 explosion of
Mount Pinatubo, another stratovolcano, in the
Philippines cooled global temperatures for about 2-3 years, interrupting the trend of
global warming which had been evident since about
1970.
[4]
References
1. C. Oppenheimer, 2002, Limited global change due to the largest known Quaternary eruption, Toba ~~ 74 Kyr BP, Quaternary Science Reviews, 21, 1593-1609
2. Oppenheimer (2002)
3. B.G. Mason, D.M. Pyle, and C. Oppenheimer, 2004, The size and frequency of the largest explosive eruptions on Earth, The Bulletin of Volcanology, 66 (8), 735-748.
4. [ Uncertainty estimates in regional and global observed temperature changes: a new dataset from 1850, Brohan, P., J.J. Kennedy, I. Haris, S.F.B. Tett and P.D. Jones, , , J. Geophysical Research, 2006 ]
Further reading
★
Volcanic winters, MR Rampino, S Self & RB Stothers, , , Annual Review of Earth and Planetary Science, 1988
★ C. Oppenheimer, 2002, Limited global change due to the largest known Quaternary eruption, Toba ~~ 74 Kyr BP, Quaternary Science Reviews, 21, 1593-1609.
See also
★
Nuclear winter
★
Climate changes of 535-536
★
Year Without a Summer
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