This is important information
because it puts volcanic action in the center of considerations on climate
change in the Northern Hemisphere and pretty well rules out solar variation as
a primary driver.
I think that we can agree that
the Northern part of the hemisphere is particularly vulnerable to volcanic
cooling. Here it is argued that it can
be driven by tropical events also. With Iceland in particular and Alaska
In the meantime we now have an
exact date to claim for the beginning of the little ice age and a plausible
direction in which to determine causation.
What is badly needed is extensive work on the Alaskans to pin down the
ages of the past eruptions for at least two thousand years and as much more as
possible.
If we can now link a series of
volcanic actions to tree ring data, then we could well be onto something.
Let us hope we do not have to
evacuate Europe again as we did in 1159BC and
in the fifth century our era. There again
the temperature drop was precipitous and we lack a culprit.
Volcanic activity behind Little Ice Age
Discharge from eruptions triggered massive plant die-off, research
suggests
BY RANDY BOSWELL, POSTMEDIA NEWS JANUARY 31, 2012 2:19 AM
Melting icefields on Baffin Island, one of the clearest signs of
climate change on Earth, have yielded the strongest evidence yet for the timing
and cause of another major climate event from the planet's past: the so-called
Little Ice Age, a sudden and mysterious cooling of the globe that began about
700 years ago.
Recently exposed remains of plants that had been buried under Baffin
Island ice for centuries provided the crucial clue that has led an
international team of researchers to conclude the Little Ice Age was triggered
by volcanic eruptions between 1275 and 1300 and was sustained by changes in
Arctic sea-ice cover that lasted several centuries.
Writing in the latest issue of the journal Geophysical Research
Letters, the team of 13 scientists from the U.S., Iceland and Britain notes
that, "there is no clear consensus on the timing, duration, or controlling
mechanisms" of the Little Ice Age, which has been attributed by some
experts to the onset of a period of reduced heat from the sun.
Without fully discounting the influence of the solar radiation cycle on
the medieval cooling trend, the researchers found, however, clear
indications on Baffin Island that mosses and other plants that had thrived in
the centuries before AD 1300 were suddenly killed during a time marked by
cataclysmic discharges from volcanoes erupting in the Southern Hemisphere.
A similar series of tropical volcanic eruptions around 1450, which
initially blocked sunlight but also extended Arctic ice cover and increased
ice-berg production in the North Atlantic, coincided with another pulse of
ice-field growth and the flash-freeze killing of plants at different locations
on the Nunavut island.
Significantly, the authors note, the "entombed vegetation"
found at sites along a 1,000-km stretch of Baffin Island has only become
apparent in recent years as "rapidly melting ice caps" in Arctic Canada
"From both the Canadian evidence [many sites became ice-covered in
the late 13th Century and remained so until the past decade] and Icelandic
evidence . we can conclude that multi-decadal average summer temperatures
never returned to those of Medieval times until the 20th century," the
scientists state in the journal article. [just in case you thought
that the hockey stick was not dead - arclein]
"This is the first time anyone has clearly identified the specific
onset of the cold times marking the start of the Little Ice Age," Gifford
Miller, a geology professor at the University of Colorado, said in a summary of
the study.
"We also have provided an understandable climate feedback system
that explains how this cold period could be sustained for a long period of
time," he added, pointing to evidence that greater discharges of Arctic
ice-bergs into the North Atlantic led to
cooler surface waters and ocean circulation patterns that promoted further
sea-ice expansion.
"The dominant way scientists have defined the little Ice Age is by
the expansion of big valley glaciers in the Alps and in Norway
But the time in which European glaciers advanced far enough to demolish
villages would have been long after the onset of the cold period," Miller
stated.
However, he noted, the team's Baffin Island
study shows "if the climate sys-tem is hit again and again by cold
conditions over a relatively short period - in this case, from volcanic
eruptions - there appears to be a cumulative cooling effect."
© Copyright (c) The Vancouver
Read more:
30 January 2012 Last updated at 11:49 ET
Volcanic origin for Little Ice Age
By Richard BlackEnvironment correspondent, BBC News
Plants trapped under Iceland
The Little Ice Age was caused by the cooling effect of massive volcanic
eruptions, and sustained by changes in Arctic ice cover, scientists conclude.
An international research team studied ancient plants from Iceland and Canada
They say a series of eruptions just before 1300 lowered Arctic
temperatures enough for ice sheets to expand.
Writing in Geophysical
Research Letters, they say this would have kept the Earth cool for
centuries.
The exact definition of the Little Ice Age is disputed. While many
studies suggest temperatures fell globally in the 1500s, others suggest the Arctic and sub-Arctic began cooling several centuries
previously.
The global dip in temperatures was less than 1C, but parts of Europe
cooled more, particularly in winter, with the River Thames in London
What caused it has been uncertain. The new study, led by Gifford Miller
at the University of Colorado at Boulder, US, links back to a series of four
explosive volcanic eruptions between about 1250 and 1300 in the tropics, which
would have blasted huge clouds of sulphate particles into the upper atmosphere.
These tiny aerosol particles are known to cool the globe by reflecting
solar energy back into space.
"This is the first time that anyone has clearly identified the
specific onset of the cold times marking the start of the Little Ice Age,"
said Dr Miller.
"We have also provided an understandable climate feedback system
that explains how this cold period could be sustained for a long period of time."
The scientists studied several sites in north-eastern Canada and in Iceland
When the ice spreads, plants underneath are killed and
"entombed" in the ice. Carbon-dating can determine how long ago this
happened.
So the plants provide a record of the icecaps' sizes at various times -
and therefore, indirectly, of the local temperature.
An additional site at Hvitarvatn in Iceland
Putting these records together showed that cooling began fairly
abruptly at some point between 1250 and 1300. Temperatures fell another notch
between 1430 and 1455.
The first of these periods saw four large volcanic eruptions beginning
in 1256, probably from the tropics sources, although the exact locations
have not been determined.
The later period incorporated the major Kuwae eruption in Vanuatu
Aerosols from volcanic eruptions usually cool the climate for just a
few years.
When the researchers plugged in the sequence of eruptions into a
computer model of climate, they found that the short but intense burst of
cooling was enough to initiate growth of summer ice sheets around the Arctic
Ocean, as well as glaciers.
The extra ice in turn reflected more solar radiation back into space,
and weakened the Atlantic ocean circulation commonly known as the Gulf Stream .
"It's easy to calculate how much colder you could get with
volcanoes; but that has no permanence, the skies soon clear," Dr Miller
told BBC News.
"And it was climate modelling that showed how sea ice exports into
the North Atlantic set up this self-sustaining
feedback process, and that's how a perturbation of decades can result in a
climate shift of centuries."
Analysis
of the later phase of the Little Ice Age also suggests that changes in
the Sun's output, particularly in the ultraviolet part of the spectrum, would
also have contributed cooling.
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