Posts
"Are
IPCC projected rates of sea level rise too
conservative? "You can bet
your bottom dollar on it.
Warm
Water Rising From
the Depths: Much of
Antarctica Now Under
Threat of
Melt
9
December, 2014
Antarctica.
A seemingly impregnable fortress of cold. Ice mountains rising 2,100
meters high. Circumpolar winds raging out from this mass of chill
frost walling the warm air out. And a curtain of sea ice insulating
the surface air and mainland ice sheets from an increasingly warm
world. A world that is now on track to experience one of its hottest
years on record.
Antarctica,
the coldest place on Earth, may well seem impregnable to this
warming. But like any other fortress, it has its vulnerable spots. In
this case, a weak underbelly. For in study after study, we keep
finding evidence that warm waters are rising up from the abyss
surrounding the chill and frozen continent. And the impact and risk
to Antarctica’s glacial ice mountains is significant and
growing.ent GDP by the end of 2014.
Getting
a hold on the budget deficit – both within the government and key
state-owned companies like Naftogaz – is a requirement IMF put
forward to allow further loans to Ukraine. It also demanded a hike in
utility prices, which the Yatsenyuk government is currently putting
into place. The measures are causing understandable irritation among
the Ukrainian population, who are not thrilled to see their bills
skyrocket amid an economic slowdown plaguing the country.
(Collapse of ice structure at the leading edge of the Filchner-Ronne Ice Shelf adjacent to a rapidly warming Weddell Sea during January of 2010. A new study has found warm water upwelling from the Circumpolar Deep Water is rapidly approaching this massive ice shelf. Loss of Filchner-Ronne and its inland buttressed glaciers would result in 10 feet of sea level rise. Image source: Commons.)
For
a study this week confirmed that Antarctica is now seeing a yearly
loss of ice equal to one half the volume of Mt Everest every single
year. A rate of loss triple that seen just ten years ago. An
acceleration that, should it continue, means a much more immediate
threat to coastal regions from sea level rise than current IPCC
projections now estimate.
Shoaling
of the Circumpolar Deep Water
The
source of this warm water comes from a deep-running current that
encircles all of Antarctica. Called the Circumpolar Deep Water, this
current runs along the outside margin of the continental shelf.
Lately, the current has been both warming and rising up the
boundaries of the continental zone. And this combined action is
rapidly bringing Antarctica’s great ice sheets under increasing
threat of more rapid melt.
According
to a
new study led by Sunke Schmidtko, this deep water current has
been warming at a rate of 0.1 degrees Celsius per decade since 1975.
Even before this period of more rapid deep water warming, the current
was already warmer than the continental shelf waters near
Antarctica’s great glaciers. With the added warming, the
Circumpolar Deep Water boasts temperatures in the range of 33 to 35
degrees Fahrenheit — enough heat to melt any glacier it contacts
quite rapidly.
Out
in the deep ocean waters beyond the continental shelf zone
surrounding Antarctica, the now warmer waters of this current can do
little to effect the great ice sheets. Here Sunke’s study
identifies the crux of the problem — the waters of the Circumpolar
Deep Water are surging up over the continental shelf margins to
contact Antarctica’s sea fronting glaciers and ice shelves with
increasing frequency.
In
some cases, these warm waters have risen by more than 300 feet up the
continental shelf margins and come into direct contact with Antarctic
ice — causing it to rapidly melt. This process is most visible in
the Amundsen Sea where an entire flank of West Antarctica is now
found to be undergoing irreversible collapse. The great Pine Island
Glacier, the Thwaites Glacier and many of its tributaries altogether
composing enough ice to raise sea levels by 4 feet are now at the
start of their last days. All due to an encroachment of warm water
rising up from the abyss.
(Antarctic rivers of ice. Rising and warming waters from the Circumpolar Deep Water along continental margins have been increasingly coming into contact with ice shelf and glacier fronts that float upon or face the surrounding seas. The result has been much higher volumes of melt water contributions than expected from Antarctica. Image source:University of California.)
But
the warm water rise is not just isolated to the Amundsen Sea. For
Sunke also found that the warm water margin in the Weddell Sea on the
opposite flank of West Antarctica was also rapidly on the rise. From
1980 to 2010, this warm water zone had risen from a depth of about
2100 feet to less than 1100 feet. A rapid advance toward another
massive concentration of West Antarctic ice.
The
impacts of a continued rise of this kind can best be described as
chilling.
Sunke
notes in an interview with National
Geographic:
If
this shoaling rate continues, there is a very high likelihood that
the warm water will reach the Filchner Ronne Ice Shelf, with
consequences which are huge.
Filchner
Ronne, like the great Pine Island Glacier, has been calving larger
and larger ice bergs during recent years. Should warm waters also
destabilize this vast ice shelf another 1.5 feet of sea level rise
would be locked in due to its direct loss. Including the massive
inland glaciers that Filchner Ronne buttresses against a seaward
surge, much larger than the ones near the Amundsen sea, would add a
total of 10 feet worth of additional sea level rise.
Together,
these destabilized zones would unleash much of West Antartica and
some of Central Antartica, resulting in as much as 14 feet of sea
level rise over a 100 to 200 year timeframe. This does not include
Greenland, which is also undergoing rapid destabilization, nor does
it include East Antarctica — which may also soon come under threat
due to the encroachment of warm waters rising from the depths.
Are
IPCC Projected Rates of Sea Level Rise Too Conservative?
The
destabilization of glaciers along the Amundsen sea, the imminent
threat to the Filchner Ronne Ice Shelf, and the less immediate but
still troubling threat to East Antarctica’s glaciers, together with
a rapidly destabilizing Greenland Ice Sheet, calls into question
whether current IPCC predictions for sea level rise before 2100 are
still vlid.
IPCC
projects a rise in seas of 1-3 feet by the end of this Century. But
much of that rise is projected to come from thermal expansion of the
world’s oceans — not from ice sheet melt in Antarctica and
Greenland. Current rates of sea level rise of 3.3 milimeters each
year would be enough to hit 1 foot of sea level rise by the end of
this Century. However, just adding in the melting of the Filchner
Ronne — a single large ice shelf — over the same period would add
4.4 milimeters a year. Add in a two century loss of the Amundsen
glaciers — Pine Island and Thwaites — and we easily exceed the
three foot mark by 2100.
Notably,
this does not include the also increasingly rapid loss of ice coming
from Greenland, the potential for mid century additions from East
Antarctica, or lesser but still important additions from the world’s
other melting glaciers.
Such
more rapid losses to ice sheets may well reflect the realities of
previous climates. At current CO2e levels of 481 ppm (400 ppm CO2 +
Methane and other human greenhouse gas additions) global sea levels
were as much as 75-120 feet higher than they are today. Predicted
greenhouse gas levels of 550 to 600 ppm CO2e by the middle of this
century (Breaking 550 ppm CO2 alone by 2050 to 2060) are enough to
set in place conditions that would eventually melt all the ice on
Earth and raise sea levels by more than 200 feet. For there was no
time in the past 55 million years when large ice sheets existed under
atmospheric CO2 concentrations exceeding 550 parts per million.
Glaciologist
Eric Rignot has been warning for years that the IPCC sea level rise
estimates may well be too conservative. And it seems that recent
trends may well bear his warnings out. If so, the consequences to
millions of people living along the world’s coastlines are stark
and significant. For the world, it appears we face the increasing
likelihood of a near-term inland mass-migration of people and
property. A stunning set of losses and tragedy starting now and
ongoing through many decades and centuries to come.
Links:
No comments:
Post a Comment
Note: only a member of this blog may post a comment.