As Imperialism goes about the world pillaging Nature and Humanity,
Nature is finding a way to adjust to this negative environmental
impact. Within the next ten years, we will be facing one of the
most horrific environmental disaster periods in humna history.
The superrich have at least two alternatives: (1) envelope themselves
in an environmentally controlled environment in Denver or Mexico
City or another high elevation region... and watch billions of
people and animals drown and/or choke to death on bad air. Or
(2) leave earth and colonize Mars or the Moon... and watch billions
of people and animals drown and/or choke to death on bad air.
We, the unrich, within our fight to be free from capitalism,
have this additional duty to struggle to at least halt the deterioration
of the environment. Its no longer a "60's" abstraction or Hippie
concern. The Earth's life-giving eco-system is in deep trouble,
and it's adjusting itself to another level of stability that
does not include the "human" factor.
In Struggle,
Sam Anderson
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Antarctic Ice Shelf Collapses
Via NY Transfer News * All the News that Doesn't Fit
Source - Antarctic Meteorlogical Research Center
http://uwamrc.ssec.wisc.edu/amrc/iceberg.html
19 March 2002 - updated 11:58 MST
Recent Moderate Resolution Imaging Spectroradiometer (MODIS)
satellite imagery analyzed at the University of Colorado's National
Snow and Ice Data Center revealed that the northern section of
the Larsen B ice shelf, a large floating ice mass on the eastern
side of the Antarctic Peninsula, has shattered and separated
from the continent. The shattered ice formed a plume of thousands
of icebergs adrift in the Weddell Sea. A total of about 3,250
km2 of shelf area disintegrated in a 35-day period beginning
on 31 January 2002. Over the last five years, the shelf has lost
a total of 5,700 km2, and is now about 40 percent the size of
its previous minimum stable extent.
Ice shelves are thick plates of ice, fed by glaciers, that float
on
the ocean around much of Antarctica. The Larsen B shelf was about
220m thick. Based on studies of ice flow and sediment thickness
beneath the ice shelf, scientists believe that it existed for
at least 400 years prior to this event, and likely existed since
the end of the last major glaciation 12,000 years ago (see more
about Dr. Eugene Domack's research).
For reference, the area lost in this most recent event dwarfs
Rhode Island (2717 km2) in size. In terms of volume, the amount
of ice released in this short time is 720 billion tons, enough
ice for about 12 trillion 10 kg bags.
This is the largest single event in a series of retreats by ice
shelves in the Peninsula over the last 30 years. The retreats
are
attributed to a strong climate warming in the region. The rate
of
warming is approximately 0.5 degrees Celsius per decade, and
the trend has been present since at least the late 1940s. Overall
in the Peninsula, extent of seven ice shelves has declined by
a total of about 13,500 km2 since 1974. This value excludes areas
that would be expected to calve under stable conditions.
Ted Scambos, a researcher with the National Snow and Ice Data
Center (NSIDC) at University of Colorado, and a team of collaborating
investigators, developed a theory of how the ice disintegrates.
The theory is based on the presence of ponded melt water on the
surface in late summer as the climate has warmed in the area.
Meltwater acts to enhance fracturing of the shelf by filling
smaller cracks and forcing them through the thickness of the
ice due to the weight of the water. The idea was suggested in
model form by other researchers in the past (Weertman, 1973;
Hughes, 1983); satellite images have provided substantial observational
proof that it is in fact the main process responsible for the
Peninsula shelf disintegrations. Christina Hulbe of Portland
State University and Mark Fahnestock of University of Maryland
collaborated with Scambos on the research.
A number of international scientists have also cooperated in
the
general study of the demise of the shelves and the climatic trend
in the Antarctic Peninsula. As early as November of last year,
Pedro Skvarca, Head of the Glaciological Division of the Instituto
Ant=E1rtico Argentino, warned of a possible impending breakup,
due to very warm spring temperatures and a dramatic 20 percent
increase in the rate of flow of the ice shelf. He and his team
were the last people to set foot on the northern portion of the
shelf. Later in the summer, the Argentine group returned to their
base at Marambio, near the shelf, to await what they anticipated
would be the final disintegration event. They flew over the shelf
repeatedly, measuring its extent with GPS during the course of
the breakup event. (See Dr. Skvarca's photos of the ice front
line towards Cape Foyn and the broken ice shelf south of the
Seal Nunataks.)
A British research vessel, the RRS James Clark Ross, was in the
area just as the event was occurring and provided images from
the ocean surface in the region of the event. Keith Nicholls
of British Antarctic Survey (BAS) provided the images.
In prior studies, Dr. David Vaughan and Chris Doake of BAS have
reported extensively on the climate warming in the area, and
have
modelled shelf stresses and possible causes of breakup. They
collaborated with Skvarca and with Austrian and German scientists,
Dr. Helmut Rott and Dr. Wolfgang Rack, who conducted detailed
satellite radar image studies and field studies in the area.
The radar study also showed ice flow increase in the years leading
to breakup and an increased velocity of the glaciers as the shelves
disappeared. Radar images have provided very detalied views of
the events of past ice shelf collapses. Dr. Rott is a professor
at the Department of Meteorology and Geophysics at Innsbruck
University; Dr. Rack is now at Alfred Wegener Institute in Bremerhaven,
Germany.
The melt water fracturing theory fared well in this last event
(See
Christina Hulbe's Larsen Ice Shelf site). Sequential images from
the MODIS sensor, a new satellite imager flying on NASA's Terra
platform, showed extensive melt ponding over the Larsen B in
late January, consistent with an unusually warm summer and extended
melt season. In a series of images taken in February, several
of the melt ponds disappeared, presumably as they drained through
opening fractures in the ice. By 23 February, 790 km2 had shattered
from the front. The next image from 5 March showed another 1960
km2 of ice gone. The event continued to 7 March with an additional
loss of 525 km2. The area lost by the shelf was was almost solely
the region covered by melt ponds in late January. The timing
of the event, at the end of a particularly warm summer, is consistent
with the theory.
Other scientists, and Scambos, continue to look for additional
mechanisms that may contribute to the breakups. One idea is that
meltwater seeping between ice crystals and warming of the shelf
as a whole, reduces the fracture toughness of the ice so that
the shelf shatters under the same stresses imposed by local geography
and the flow it used to tolerate. Another idea is that meltwater
seeps into shallow cracks and expands the cracks as it refreezes
during the winter. Ocean warming and sub-ice currents dragging
on the underside of the ice have also been cited as possible
contributors.
While the breakup of the ice shelves in the Peninsula has little
consequence for sea level rise, other shelves in the Antarctic
could have a major effect on the rate of ice flow off the continent.
Ice shelves act as a buttress, or braking system, for glaciers.
Further, the shelves keep warmer marine air at a distance from
the glaciers; therefore, they moderate the amount of melting
that occurs on the glaciers' surfaces. Once their ice shelves
are removed, the glaciers increase in speed due to meltwater
percolation and/or a reduction of braking forces, and they may
begin to dump more ice into the ocean than they gather as snow
in their catchments. Glacier ice speed increases are already
observed in Peninsula areas where ice shelves disintegrated in
prior years.
With the Peninsula shelf breakups as a guide, we can now reassess
the stability of ice shelves around the rest of the Antarctic
continent. Past assessments of stability were based primarily
on mean annual temperature; with this guideline, most shelves
outside the Peninsula were considered well within their climate
limit. Given the success of the melt pond theory, we use the
climate conditions and physical parameters of ice shelves at
the point of ponding as a guide in this assessment. In particular,
the next shelf to the south, the Larsen C, is very near the stability
limit, and may start to recede in the coming decade if the warming
trend continues. Melt ponds are occasionally observed in limited
regions of the Larsen C shelf.
More importantly, the warmest part of the giant Ross Ice Shelf
is in fact only a few degrees too cool in summer presently to
undergo the same kind of retreat process. The Ross Ice Shelf
is the main outlet for several major glaciers draining the West
Antarctic Ice Sheet, which contains the equivalent of 5 m of
sea level rise in its above-sea-level ice.
Although several recent large iceberg calving events have been
observed on the Ross and elsewhere in Antarctica, none of these
are thought to be related to ice shelf instability.
see photo at http://uwamrc.ssec.wisc.edu/amrc/iceberg.html
Caption: 05 Mar 2002
MODIS image courtesy of NASA's Terra satellite, supplied by Ted
Scambos, National Snow and Ice Data Center, University of Colorado,
Boulder.
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