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Faster
than previously thought.
"Despite all of this, Levermann cautions that the results should not be over-interpreted in an alarmist way, since whatever change may be occurring, it is certainly not expected to happen all at once."
I'll give you at tip Mr Levermann, it's much worse than you think.
There we go us being "Alarmist " again!
--Kevin
Hester
Scientists confirm their fears about West Antarctica — that it’s inherently unstable
2
October, 2015
It
may be the biggest climate change story of the last two years.
In
2014, several research groups suggested that the oceanfront glaciers
in the Amundsen Sea region of West Antarctica may have reached a
point of “unstoppable”
retreat due
to warm ocean waters melting them from below. There’s a great
deal at stake — West Antarctica is estimated to contain enough ice
to raise global sea levels by 3.3 meters, or well over 10 feet, were
it all to melt.
The
urgency may now increase further in light of just
published research suggesting
that destabilization of the Amundsen sea’s glaciers would
indeed undermine the entirety of West Antarctica, as has long been
feared.
In
a new
study published
Monday in the Proceedings of the National Academy of Sciences,
Johannes Feldmann and Anders Levermann of the Potsdam Institute for
Climate Impact Research use a sophisticated climate model to study
what will happen if these glaciers are, indeed, fully
destabilized. And in essence, they find that the process of
retreat doesn’t end with the region currently up against the ocean.
“We
showed that there is actually nothing that stops it,” said
Levermann. “There are troughs and channels and all this stuff,
there’s a lot of topography that actually has the potential to slow
down or stop the instability, but it doesn’t.”
Or
as the paper puts it: “The result of this study is an if–then
statement, saying that if the Amundsen Sea Sector is destabilized,
then the entire marine part of West Antarctica will be discharged
into the ocean.”
West
Antarctica can actually be considered the smallest of
three planetary
ice sheets —
Greenland contains some 6 meters (20 feet) of potential sea level
rise, and East Antarctica is the most vast of all, at nearly
60 meters, or 200 feet.
However,
West Antarctica is currently believed to be the most vulnerable to
rapid, large scale change, due to the fact that the Amundsen
Sea’s glaciers are rooted on a seabed that slopes downward as
you move further inland, in some places plunging a mile or more below
sea level. The region’s largest glacier, the gigantic
Thwaites, is bigger than Pennsylvania and over a mile in total
thickness in places — and may be the single most vulnerable point.
Indeed,
Antarctic scientists have expressed
a strong consensus that
they need to conduct a lot more research in this very remote area as
soon as possible, to determine how fast the change could happen.
The
current study was not an example of — and cannot replace — this
difficult fieldwork. Rather, the researchers used a complex ice
sheet model that simulated the entire West Antarctic ice sheet, as
well as the Antarctic peninsula and some of East Antarctica. They
then simulated what they termed a 20 to 200 year “perturbation”
to the region, in the form of increased rates of melt similar to what
is believed may have already happened. “Our modeled sea-level
contribution from the perturbed region lies well within the range of
observations,” they say.
With
a 60 year or greater perturbation, the model — which, the
researchers caution, is only “a single realization of an ice-sheet
model that applies approximations to the ice dynamics” — then
produced a retreat that continues even without continuance of the
perturbation. That is, after all, precisely what has been feared —
that the region has an inherent “marine ice sheet instability,”
as researchers put it.
“If
you have a situation where the bedrock is declining when you go
inland, that means that wherever the grounding line is, it is thicker
the further it is inland,” explains Levermann. “Which means the
[ice] flux is bigger the further you go inland. Which means you lose
more ice the further you go inland, which is the vicious cycle.”
Levermann confirmed, by email, that this in effect means that there
is an “inherent” instability to West Antarctica, based on his new
research.
Here’s
a visualization of what is happening with West Antarctica, and how a
“marine ice sheet instability” works:
The
critical issue here is, of course, the speed at which this could all
occur. The new study’s simulations show the loss of West
Antarctica playing out over thousands of years. But many scientists
worry that at least some of the change could happen faster.
“We
know very little about the new world we are entering of rapid retreat
into deep basins,” said Sridhar
Anandakrishnan,
a glaciologist at Penn State University who has conducted research
atop Thwaites glacier and reviewed the study for the Post, by email.
“There
are likely processes there that we haven’t fully accounted for. For
example, as the grounding line shifts farther back, the ice front may
start to fracture and fail — something we don’t see today because
we don’t have any deep grounding lines to study and use as
analogies.”
When
asked how fast he thought all of this could unfold, Levermann
underscores that we simply don’t know. “And by we don’t
know, I mean, we don’t know,” he says. “I don’t want to
say it’s quicker, but it’s much more likely that it’s faster
than these thousands of years, than [that] it’s slower.” He
points out that based on reconstructions of the planet’s past,
there are reasons to think sea levels can rise fairly rapidly.
The
study therefore concludes that:
The currently observed retreat in West Antarctica hence might mark the beginning of a millennial period of self-sustained ice discharge from West Antarctica and require long-term global adaptation of coastal protection, such as the building or rebuilding or raising of dykes, the construction of seawalls, or the realization of land fills in the hinterland.
Given
the significance of the findings, the Post asked several other
Antarctic experts to comment on the work.
Anandakrishnan,
who was concerned that sea level rise could happen even faster than
in the study, nonetheless called the work a “fascinating
study that shows the tipping points in the stability of the whole
West Antarctic Ice Sheet (not just Thwaites or Pine Island, as some
previous studies have shown)” by email. “The retreat of Thwaites
continues past any ‘local’ ups and downs in its bed, and affects
the glaciers that flow into the Ross Ice Shelf and into the Filchner
Ronne Ice Shelf.” (You can see these regions on the map above.)
Jonathan
Bamber, a glaciologist at the University of Bristol in the UK, also
praised the study, calling the model “sophisticated” and adding,
“It make take millennia for a full collapse but once it’s started
we’re fully committed to multiple metres of sea level rise. How
quickly we reach this point of no return, and how rapidly it
proceeds, are sensitive to certain model details but what is clear is
that the next few decades will determine whether the WAIS is just
endangered or on its path to extinction.”
What’s
striking is that even though we are now having this discussion about
possible destabilization of West Antarctica, scientists are still not
fully sure about what has caused the phenomenon. One suspicion,
however, is that the warming of the climate as a whole has changed
wind patterns around Antarctica which, in turn, has also changed
ocean patterns — allowing warmer water to reach the bases of mostly
submerged glaciers that hold back the gigantic volumes of inland ice.
There
is some concern that similar processes may also play out in
submarine based glaciers of East Antarctica —
although so far, scientists have not identified a part of the
Antarctic continent that is both as vulnerable, and also experiencing
as rapid change, as West Antarctica.
Despite
all of this, Levermann cautions that the results should not be
over-interpreted in an alarmist way, since whatever change may be
occurring, it is certainly not expected to happen all at
once.
“No
one has to be afraid of
sea level rise,” he says. “One should be worriedabout
sea level rise. It is not a threat to people, it’s a threat to
things, and land, and cultural heritage.”
It
won’t take much to cause the entire West Antarctic Ice Sheet to
collapse—and once it starts, it won’t stop. In the last year, a
slew of papers has highlighted the vulnerability of the ice sheet
covering the western half of the continent, suggesting that its
downfall is inevitable—and probably already underway. Now, a new
model shows just how this juggernaut could unfold. A relatively small
amount of melting over a few decades, the authors say, will
inexorably lead to the destabilization of the entire ice sheet and
the rise of global sea levels by as much as 3 meters
Predictably other sources are the climate change denying Daily Mail and Telegraph.
Antarctica gaining more ice than losing – NASA
Antarctica has been accumulating more ice than it’s been losing in recent decades, a new study by NASA has revealed, challenging existing theories on climate change and rises in sea levels.
It comes on the same day as this - 
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