.
"Scientists used to think soot was unlikely to have been carried high
enough to start the glaciers melting, but they now appear to have been
mistaken."
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9/4/13, "Soot ‘melted Alps glaciers, not heat’," ClimateNewsNetwork.net, Alex Kirby, London
"Scientists think they know why some
European glaciers started to shrink decades before climate change had
begun to raise temperatures.
It wasn’t warming that attacked the glaciers, they say in the Proceedings of the National Academy of Sciences. It was soot from industry, steam locomotives and domestic fires.
Glaciologists have for years been puzzled by the sudden start in the
middle of the 19th century of the retreat of the Alpine glaciers, which
number around 4,000.
They had survived in good condition from the 13th century throughout
the fairly cool 500-year period called the Little Ice Age. They reached
their greatest extent in the mid-1800s, about double what they are now.
But even though it remained cool the glaciers suddenly began
shrinking, leading scientists to believe that the Little Ice Age had
ended around 1850.
Average global temperatures, though, did not rise significantly –
until the end of the 19th century. In fact, Alpine climate records –
among the most extensive and reliable in the world – suggest that the
glaciers should have continued to grow for another 50 years or more,
until about 1910.
The scientists acknowledge that other parts of the world may also
have been affected, but point out that the decline was well documented
only in the Alps.
However, soot is also a big concern in the Himalayas,
at high altitudes in some regions bigger than temperature rises. The
burgeoning economies of China and India contribute huge amounts.
“Something gnawed on the glaciers that climate records don’t
capture,” said Georg Kaser, a glaciologist at the University of
Innsbruck in Austria and a member of the team that identified black
carbon, or soot, as the cause.
“A strong decline in winter snowfall was often assumed to be the culprit. But from all that we know, no such decline occurred.”
Because darker surfaces absorb more heat than lighter, more reflective ones, if enough soot is deposited on snow and ice it can accelerate melting.
Records suggest that by the mid-19th century the air in some Alpine
valleys was laden with pollution. “Housewives in Innsbruck refrained
from drying laundry outdoors,” says Kaser.
Scientists used to think soot was unlikely to have been carried high
enough to start the glaciers melting, but they now appear to have been
mistaken.
When Kaser’s team looked at ice cores previously drilled at two sites
high in the western Alps – the Colle Gnifetti glacier saddle 4,455 m up
on Monte Rosa near the Swiss–Italian border, and the Fiescherhorn
glacier at 3,900 m in the Bernese Alps – they found that in around 1860
layers of glacial ice started to contain large amounts of soot.
The team measured the effect the soot would have had on glaciers at
the time in terms of equivalent changes in air temperature. They found
that the melting effect of black carbon provided a good explanation of
the observed glacier retreat.
Andreas Vieli, a glaciologist at the University of Zurich
in Switzerland (who was not involved in the study) said: “…[T]his study
offers a very elegant and plausible explanation for the glacier
conundrum. It appears that in central Europe soot prematurely stopped
the Little Ice Age.”
Only after around 1970, when air quality began to improve, did
accelerated climate warming become the dominant driver of Alpine glacier
retreat, Kaser says.
He says that if glaciers in the region continue to melt at the rate
seen during the past 30 years, there is a risk that nearly all of them
will vanish before the end of the century." via Junk Science
.
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