Rapid loss of sea-ice this summer
Eric Swanson
today's New York Times. Here's the link:
http://www.nytimes.com/2007/08/10/science/earth/10arctic.html
As the sea-ice extent declines, it's thickness also decreases. I
think it's likely that the thickness will decline so much that there
will be the chance of a mechanical failure, even before the extent
could actually reaches zero. The result could look much like the
breakup of the Larson B ice shelf along the Antarctic Peninsula, which
was sudden and spectacular .
Last summer, there was the formation of a large polynya which formed
just to the north of Alaska. Hers's a discussion of last year's sea-
ice cycle:
http://nsidc.org/news/press/2006_seaiceminimum/20060816_arcticseaicenews.html
That polynya may have been the result of a large tropical cyclone,
which moved out of the tropics and then tracked over Alaska and the
Arctic. As the sea-ice extent and thickness declines further, one
might reasonably expect that other such storms could trigger a
shattering of the remaining sea-ice, as the tropical cyclones tend to
occur at about the same time as the minimum extent of the Arctic sea-
ice.
As I understand it, there has never been a period in the history of
civilization in which there was no sea-ice over the Arctic. I'll
leave it to the experts to tell us just what things will be like once
the sea-ice extent has declined to zero, after which there won't be
any multi-year ice in the following winter. Given that there is a
positive feedback associated with the difference between the albedo of
sea-ice and that of open ocean, it's plausible that multi-year sea-ice
might not reappear in succeeding years.
E. S.
William M Connolley
On Fri, 10 Aug 2007, Eric Swanson wrote:
> As the sea-ice extent declines, it's thickness also decreases. I
> think it's likely that the thickness will decline so much that there
> will be the chance of a mechanical failure, even before the extent
> could actually reaches zero. The result could look much like the
> breakup of the Larson B ice shelf along the Antarctic Peninsula, which
> was sudden and spectacular .
This is unlikely. Sea ice has essentially no strength in tension anyway.
-W.
William M Connolley | w...@bas.ac.uk | http://www.antarctica.ac.uk/met/wmc/
Climate Modeller, British Antarctic Survey | 07985 935400
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Fergus
thinning N. of Greenland and Ellesmere; I've mentioned this on RC, but
nobody seems to have noticed. Are we in a position where we can expect
the entire ice sheet to detach from all land links? What implications,
if any, might this have?
:)
Michael Tobis
may be similar but the mechanics are very different, which in a sense
is the same point William was making.
Sea ice is essentially a film formed from and floating on the ocean.
Its mechanical properties are complex, but around the edges it behaves
more like a viscous fluid than like a solid. Whether it is adjacent to
land or not does not matter.
The geometry of ice shelves, which are mechanically part of
gravity-driven glacial flow, is much more crucial.
The main physical issue about sea ice (leaving aside biology and
chemistry where you'll have to ask someone else) is albedo feedback.
mt
Tom Adams
what kind of impact that will have on the Greenland ice shelf.
On Aug 10, 11:40 am, "Michael Tobis" <mto...@gmail.com> wrote:
> Essentially none; this is sea ice, not an ice shelf; the compositions
> may be similar but the mechanics are very different, which in a sense
> is the same point William was making.
>
> Sea ice is essentially a film formed from and floating on the ocean.
> Its mechanical properties are complex, but around the edges it behaves
> more like a viscous fluid than like a solid. Whether it is adjacent to
> land or not does not matter.
>
> The geometry of ice shelves, which are mechanically part of
> gravity-driven glacial flow, is much more crucial.
>
> The main physical issue about sea ice (leaving aside biology and
> chemistry where you'll have to ask someone else) is albedo feedback.
>
> mt
>
> On 8/10/07, Fergus <f...@btinternet.com> wrote:
>
>
>
>
>
> > I'm interested to know what the precedent is for the indicated
> > thinning N. of Greenland and Ellesmere; I've mentioned this on RC, but
> > nobody seems to have noticed. Are we in a position where we can expect
> > the entire ice sheet to detach from all land links? What implications,
> > if any, might this have?
>
> > :)
>
> > On Aug 10, 2:26 pm, William M Connolley <w...@bas.ac.uk> wrote:
> > > On Fri, 10 Aug 2007, Eric Swanson wrote:
> > > > As the sea-ice extent declines, it's thickness also decreases. I
> > > > think it's likely that the thickness will decline so much that there
> > > > will be the chance of a mechanical failure, even before the extent
> > > > could actually reaches zero. The result could look much like the
> > > > breakup of the Larson B ice shelf along the Antarctic Peninsula, which
> > > > was sudden and spectacular .
>
> > > This is unlikely. Sea ice has essentially no strength in tension anyway.
>
> > > -W.
>
> > > William M Connolley | w...@bas.ac.uk |http://www.antarctica.ac.uk/met/wmc/
> > > Climate Modeller, British Antarctic Survey |07985 935400
>
> > > --
> > > This message (and any attachments) is for the recipient only. NERC is subject
> > > to the Freedom of Information Act 2000 and the contents of this email and any
> > > reply you make may be disclosed by NERC unless it is exempt from release under
> > > the Act. Any material supplied to NERC may be stored in an electronic
> > > records management system.- Hide quoted text -
>
> - Show quoted text -
Michael Tobis
significant ice shelves around Greenland.
Wikipedia says ice shelves are on Ellesmere Island and Antarctica,
though it makes no claim that the list is exhaustive. Remarkably, the
ice shelves around Ellesmere, which is pretty darned far north, are in
rapid retreat, which will presumably cause a speedup of Ellesmere
glaciers.
http://en.wikipedia.org/wiki/Ellesmere_Island
http://en.wikipedia.org/wiki/Ice_shelf
mt
Eric Swanson
Eric Swanson wrote:
> There's an article about this year's rapid loss of Arctic sea-ice in
> today's New York Times. Here's the link:
>
> http://www.nytimes.com/2007/08/10/science/earth/10arctic.html
As one might expect, there is a thread today on Real Climate about the
article:
http://www.realclimate.org/index.php/archives/2007/08/arctic-sea-ice-watch/
E. S.
Eric Swanson
William M Connolley wrote:
> On Fri, 10 Aug 2007, Eric Swanson wrote:
> > As the sea-ice extent declines, it's thickness also decreases. I
> > think it's likely that the thickness will decline so much that there
> > will be the chance of a mechanical failure, even before the extent
> > could actually reaches zero. The result could look much like the
> > breakup of the Larson B ice shelf along the Antarctic Peninsula, which
> > was sudden and spectacular .
>
> This is unlikely. Sea ice has essentially no strength in tension anyway.
Looking about, I found some references to various models for sea-ice
strength, i.e., rheology. An early modeling approach by Hibler used a
viscous-plastic assumption, which has been used by some ocean model
builders. There appear to be other models based on an elastic
assumption, such as this one:
David M. Holland, "A 1-D elastic-plastic sea-ice model solved with an
implicit Eulerian-Lagrangian method", Ocean Modelling Volume 17, Issue
1, 2007, Pages 1-27
Either way, it would seem that the resistance to motion would be
greater for thicker multi-year ice than for first year ice. It's the
potential for an increase in motion that I think would be important.
To begin with, if the sea-ice is no longer bound to fast ice along the
coast lines, surely it would move faster. Here's a model study
which uses an elastic-plastic model:
http://efdl.cims.nyu.edu/publications/summer_students/mazover_landfast_05.pdf
I think their point about the permanence of landfast ice is important,
since we know it exists and isn't easily dislodged. This suggests
that the tensile strength of sea-ice away from the coast may also be
important.
E. S.
William M Connolley
The common model used in GCMs is viscous plastic (or more primitive). Or the
more modern elastic-viscous-plastic, which is supposedly scientifically
equivalent (look up Hunke). Elastic-plastic is rather different and certainly
not used in GCMs.
On the resistance to motion, is doesnt matter a great deal how thick it is,
in the sense that acceleration can usually be neglected. But clearly it affects
its resistance to compression or shear (but the pure tensile strength remains
negligible).
Fergus
greenland is also showing melt/glacier acceleration (okay, it's still
coastal, and a long way from the pack, so I'm nitpicking. I was also
along lines that William seems to have picked up on; given the dynamic
nature of the subsurface and the effect of wind on ice movement, if
the 'central pack' is no longer anchored to the land, even for a few
weeks, we might see all sorts of consequences; another Fram outflux of
pack ice; acceleration of the Beaufort gyre, or an enhancement of the
AO are all possible side-effects...
Respectfully.
On Aug 10, 4:40 pm, "Michael Tobis" <mto...@gmail.com> wrote:
> Essentially none; this is sea ice, not an ice shelf; the compositions
> may be similar but the mechanics are very different, which in a sense
> is the same point William was making.
>
> Sea ice is essentially a film formed from and floating on the ocean.
> Its mechanical properties are complex, but around the edges it behaves
> more like a viscous fluid than like a solid. Whether it is adjacent to
> land or not does not matter.
>
> The geometry of ice shelves, which are mechanically part of
> gravity-driven glacial flow, is much more crucial.
>
> The main physical issue about sea ice (leaving aside biology and
> chemistry where you'll have to ask someone else) is albedo feedback.
>
> mt
>
Eric Swanson
> On Fri, 10 Aug 2007, Eric Swanson wrote:
> >> This is unlikely. Sea ice has essentially no strength in tension anyway.
> > I think their point about the permanence of landfast ice is important,
> > since we know it exists and isn't easily dislodged. This suggests
> > that the tensile strength of sea-ice away from the coast may also be
> > important.
>
> The common model used in GCMs is viscous plastic (or more primitive). Or the
> more modern elastic-viscous-plastic, which is supposedly scientifically
> equivalent (look up Hunke). Elastic-plastic is rather different and certainly
> not used in GCMs.
>
> On the resistance to motion, is doesnt matter a great deal how thick it is,
> in the sense that acceleration can usually be neglected. But clearly it affects
> its resistance to compression or shear (but the pure tensile strength remains
> negligible).
Having been educated as a mechanical engineer, I learned a bit about
structures and stresses. I've also done a small bit of work with
fatigue failure. That said, I think it's obvious that ice does
exhibit tensile strength, all thought how that applies to sea-ice, I
can't yet say.
An obvious example is the fact that vehicles can and are driven over
frozen lakes. There are even people that hold races on the frozen
lakes. The weight of the vehicles produces a tensile load on the
lower surface of the ice. If, as you claim, "tensile strength remains
negligible", then the ice would fail and the vehicles would go to the
bottom of the lake. Furthermore, the ability of the ice to support a
load is a direct function of it's thickness.
>From my limited knowledge, I would expect that the sea-ice would be
anything but homogeneous. The thickness would be highly variable,
judging from some photographs I've seen taken from below the ice.
Under such conditions, the ice would fail at the weakest point, i.e.,
where it is thinnest. Using an average thickness would give a
confusing picture of what would actually be happening in a failure. I
would guess that tension failure might be similar to a fatigue failure
in a metal, which begins with small crack which slowly increases in
size, which, in effect, reduces the cross section of the material
subject to loading. In a fatigue failure, the apparent load based on
the initial dimensions is much below that which would have caused
failure before crack formation when a part is new. That does not
imply that there is no tensile strength.
If one has been in a lab and seen the failure of a material placed
under a controlled loading, one quickly notes the speed with which the
final failure occurs. The stress builds up as strain and when the
failure happens, there's a sudden release of the load. Such failures
can be very spectacular, such as the bridge failure in Minnesota last
week. I viewed a video of that collapse the other day. The camera
showed things looking quite normal, then, the center section dropped
into the water in a few seconds. Earthquakes are another example of
the effects of a stress buildup followed by failure, with spectacular
consequences.
Sea-ice dynamics may be analogous to that of earthquakes, in that the
stresses are spread over a large area, but the failures are local.
The appearance of leads and polynyas is said to be rather sudden. The
breakup of river ice and lake ice in spring can also be very sudden.
My point is that we are likely to see such a breakup of Arctic sea-ice
in some sudden fashion, as the extent and thickness continue to
decline. That's not to say the sea-ice would then instantly disappear
afterwards. The sea-ice could re-freeze into another continuous
sheet, if the temperatures were low enough. Or, the shattered sea-ice
could become more mobile, as apparently happened last year with the
large polynya to the north of Alaska.
I'm sure that these ideas is not new and I will need to do some more
study to catch up with the present understanding. I do think that the
models could benefit from some representation of a threshold failure
mode based on thickness between elastic and viscous behavior. Whether
this sort of approach is presently included, I can't say. Time for
more reading...
Michael Tobis
Of course ice has some tensile strength; the question is whether that
is important in a given circumstance.
Consider the question of liquid water surface tension. It's a crucial
term in cloud microphysics. Cloud microphysics is important to
weather, and weather is important to ocean circulation, yet no
oceanographer (actually I know of a marginal exception, someone
looking at air entrainment into the ocean in surf, but his career is
in trouble because it has turned out that the problem he is pursuing
is unimportant) spends any attention on surface tension. It negligible
on the scales of interest.
It seems to turn out to be negligible in sea ice distribution
calculations. I have not seen this worked out, but likely it has been
done often enough. If William says the term is negligible then I
believe him. That certainly agrees with my qualitative understanding.
The present question seems to be whether the possibly unprecedented
opening near the Ellesmere or North Greenland Coast has large scale
geophysical implications. If that is the question your intuition
counts for less than the intuition of people working in the field.
BURDEN OF PROOF
It is not inconceivable that the conventional wisdom, here represented
by WIlliam with me as cheerleader, is wrong.
The same applies elsewhere in climate. Science cannot pursue every lay
person's intuitions, even every informed lay person's opinions, a
resource that our field is unusually blessed with in proportion to the
actual population of professional workers.
That's why burden of proof is on you to come up with a model (not
necessarily a computation, but necessarily something resembling a
testable hypothesis) where this matters.
Now, getting that noticed if you have such a model originating outside
the recognized research centers is another matter, and maybe science
is due for some criticism on that score.
As far as I know you and Fergus just have hunches, though.
IMPLICATIONS ON SMALLER SCALES
If there are smaller scale implications at the site is another
question. Maybe so.
I doubt if anyone has paid enough attention to those sites to have any
strong opinion. It is interesting. I wonder if there is any precedent,
and if not, what is actually going on up there.
Interestingly, it will be impossible to fund and mount a mission in
time to do an in situ check. Perhaps some fabulously wealthy cowboy
will do us the favor of getting some cameras and instruments to the
site and simultaneously loosening the institutional monopolies.
SCALING REVISITED
All of this reminds me how scaling and regimes are not generally
understood. It's a part of basic undergraduate mathematics to
meteorologists and oceanographers, and to a lesser extent to fluids
folk in general, but it isn't really part of even the mathematically
literate lexicon in general. We are so steeped in it that we forget
how alien it is to others. I heard nothing like it in engineering
school. Though in retrospect it is implicit everywhere in engineering,
as far as I know it is nowhere explicit.
Since this is fundamental to my critique of economics, it's a first
order important culture gap in my peculiar worldview. In short, I
suspect that the approximations on which conventional economics is
based are inappropriate on longer time scales. I have never seen
economics explicitly apply conventional scaling arguments either.
However, engineers have the advantage of real world tests. Either the
bridge stands up, or it falls down.
mt
William M Connolley
On Sat, 11 Aug 2007, Eric Swanson wrote:
> Having been educated as a mechanical engineer, I learned a bit about
> structures and stresses. I've also done a small bit of work with
> fatigue failure. That said, I think it's obvious that ice does
> exhibit tensile strength, all thought how that applies to sea-ice, I
> can't yet say.
Ice certainly has a tensile strength. Where it gets confusing (in terms of large
scales, model or reality) is that you shouldn't think of it as one floe; its
always an assembly of floes. Thats where both the "viscous" bit comes from, and
the zero tensile strength (actually I think you'd find that a homogenous solid
piece of ice 1m think has almost no tensile strength (measured by the wind
whether it had leads or not; the same ice, on scales of 1m, would be strong).
William M Connolley
On Sat, 11 Aug 2007, Michael Tobis wrote:
> It seems to turn out to be negligible in sea ice distribution
> calculations. I have not seen this worked out, but likely it has been
> done often enough. If William says the term is negligible then I
> believe him. That certainly agrees with my qualitative understanding.
The paper establishing the VP-type behaviour is a very early Hibler, something
like 1978. Averaging across floes is crucial, as is the large-scaleness.
For a time before, people tried to treat sea ice as elastic (which it is,
considered as a single flow) but this is completely intractable (you have to
keep histories).
Eric Swanson
William M Connolley wrote:
> On Sat, 11 Aug 2007, Eric Swanson wrote:
> > Having been educated as a mechanical engineer, I learned a bit about
> > structures and stresses. I've also done a small bit of work with
> > fatigue failure. That said, I think it's obvious that ice does
> > exhibit tensile strength, all thought how that applies to sea-ice, I
> > can't yet say.
>
> Ice certainly has a tensile strength. Where it gets confusing (in terms of large
> scales, model or reality) is that you shouldn't think of it as one floe; its
> always an assembly of floes. Thats where both the "viscous" bit comes from, and
> the zero tensile strength (actually I think you'd find that a homogenous solid
> piece of ice 1m think has almost no tensile strength (measured by the wind
> whether it had leads or not; the same ice, on scales of 1m, would be strong).
>
> -W.
Thanks. With a bit of googling, I found some reports on the subject,
including Hunke and Dukowicz, (1997), which I think you pointed to.
They do mention that the viscous approach includes the thickness of
the sea-ice in the calculations. Others have pointed out the low
tensile strength of ice, but that wasn't what I was trying to deal
with as much as the possible difference between first year and multi-
year ice in terms of motion. Using the viscous model, it would appear
obvious that the first year ice should tend to move about much more
easily than multi-year ice .
Other reading brought out the scale problem which Michael discussed.
The physical strength of the ice is a factor at micron levels, yet the
movement and stresses are evident over hundreds of kilometers. One
example given showed fractures in the ice cap which produced features
evident over nearly the whole extent of the ice field. Ice rafting
and pressure ridges change the character of the ice as well and are
more likely to be seen in multi-year ice compared with first year
ice. Michael should know that the scale of the model in terms of the
resolution (or grid spacing) would change the level of detail that
would be appropriate for the sea-ice model as well, since the
treatment of the sea-ice as an aggregate of individual floes probably
will not be appropriate when the average floe size is near that of the
grid size. I doubt that's yet a problem, BTW.
However, if the sea-ice becomes thinner as time goes on, the likely
result might be smaller floes, as storms and waves would tend to break
up the larger floes. That would make motion easier and might be
represented as a reduced viscosity. As it is, the model by Hibler is
said to use a viscosity that varied with the stress tensor. I do not
yet know whether that variation also includes ice thickness, but I
think it should. As noted by Hunke and Dukowicz, the viscosity used
in the VP models extend over several orders of magnitude, which is
part of their motivation in offering their improved model, since their
use of an elastic response speeds the computations considerably,
especially for short term transient situations.
Perhaps we will witness another strong storm moving across the Arctic
sea-ice this season, while the ice is near minimum. Such an event
could prove extremely interesting to the curious, since we wouldn't
need a model to see changes.
E. S.
Fergus
merely speculation of the most unscientific kind. I don't really
expect too much 'new' to happen to the main pack ice itself, unless
there is some evidence of stronger than usual interannual drift over
the coming years.
One reason that I suggested a possible strengthening of the AO was a
comparison with the Antarctic, where open water all around appears to
amplify the force of the internal circulation patterns and isolate
their effects from the surrounding areas to some extent. The present
situation is not likely to do that, but perhaps a semi-permanent
seasonal decoupling of the pack from the surrounding land areas will,
in future, produce a smaller, comparable effect during the Summer.
This would then have implications for North Atlantic and Continental
weather, and possibly thereby patterns of ocean circulation or
jetstream position.
Now that's speculation...
Steve Bloom
expectation is that after the initial summer sea ice loss it will reform in
the winter because winter air temps will remain damned cold. That reformed
ice will be thin stuff and very prone to disappearing quickly the following
summer, but still will be thick enough to allow the Arctic Ocean to retain
much of the heat gained via the summer open water.
Eric Swanson
Steve Bloom wrote:
> Eric, regarding a comment you made a couple of posts ago, IIRC the
> expectation is that after the initial summer sea ice loss it will reform in
> the winter because winter air temps will remain damned cold. That reformed
> ice will be thin stuff and very prone to disappearing quickly the following
> summer, but still will be thick enough to allow the Arctic Ocean to retain
> much of the heat gained via the summer open water.
Yes, I would most certainly expect that new sea-ice would form during
the cold and dark of winter.
But, once the so-called multi-year ice is gone, then the new, first
year sea-ice that would replace it would have different
characteristics overall. I was suggesting that the net effect would
be a tendency toward more rapid motion and/or breakup for the complete
mass of the ice cap. I think the multi-year sea-ice has provided a
bit of stability which will disappear once that thicker ice is gone.
And, once gone, we may find that it does not often return, depending,
of course on the variability in weather. As the Greenhouse Effect is
expected to continue to strengthen, we should expect that there will
come a time after which there will never be any multi-year sea-ice,
that is, all the sea-ice would be gone at the end of the summer melt
season every year.
This would be a threshold kind of event, i.e., one of those "tipping
points" frequently talked about these days. Given the rapid decline
in minimum sea-ice extent (or area) which we are seeing, it appears to
be something we can expect to witness in the very near future. Just
how near is anybody's guess.
E. S.
William M Connolley
On Sat, 11 Aug 2007, Eric Swanson wrote:
> the sea-ice in the calculations. Others have pointed out the low
> tensile strength of ice, but that wasn't what I was trying to deal
> with as much as the possible difference between first year and multi-
> year ice in terms of motion. Using the viscous model, it would appear
> obvious that the first year ice should tend to move about much more
> easily than multi-year ice .
Only because its thicker, and it depends on the motion. In converging motion,
yes, there will be less deformation. In diverging, the internal ice strength
makes little difference.
> includes ice thickness, but I think it should. As noted by Hunke and
> Dukowicz, the viscosity used in the VP models extend over several orders of
> magnitude, which is part of their motivation in offering their improved model,
> since their use of an elastic response speeds the computations considerably,
> especially for short term transient situations.
Yes, but don't forget that the E in H+D is only a computational trick, and the
scientific results are (nominally) identical.
Eric Swanson
unintentional prodding of others. The reports from the SHEBA
experiment have been especially enlightening. Here was one I found
the other day:
Richter-Menge, J. A., S. L. McNutt, J. E. Overland, and R. Kwok,
Relating arctic pack ice stress and deformation under winter
conditions, J. Geophys. Res., 107(C10), 8040, doi:
10.1029/2000JC000477, 2002.
The authors present a discussion of the stress and motion measurements
taken during SHEBA. One small point of interest to me was their map
of the track of the ship while stationed at the ice floe. They began
at (roughly) 75.8N, 144W, as seen in their Figure 2. This area was
chosen because it was within the "Perennial Ice Zone" as it was called
at the time. At roughly the minimum extent so far observed, say 21
September 2005, that location was covered by heavy ice, as seen here:
That year, the majority of high latitude open water was on the Russian
side. This year, with perhaps 6 more weeks of melting to be expected,
what do we see (besides lots of nice colors)?
http://iup.physik.uni-bremen.de:8084/amsr/arctic_AMSRE_nic.png
It appears to me like the original SHEBA site will be open water this
year. And, from Robert Grumbine's NCEP animation, there looks to be a
prominent flow of sea-ice thru the Fram Strait into the Greenland
Sea. These flows have been shown to continue into the winter months.
http://polar.ncep.noaa.gov/seaice/nh.html
I wouldn't be surprised to learn that there's another salinity anomaly
in the Greenland Sea later this year and into next year.
E. S.
Hank Roberts
> Wednesday, May 17, 2000
>
> Anchorage, Alaska -- Five adventurers -- including the aviation legend Dick Rutan -- were rescued from the North Pole > after their biplane broke through the ice and sank more than 13,000 feet to the bottom of the Arctic Ocean....
That's of course one of his high-tech composite canard aircraft, not
an old style over-and-under biplane.
By the way, anyone know if he had an American flag on board the
aircraft? Odds are it probably "flew" off laterally underwater rather
than going straight down, but I suppose those Russian submersible
operators _might_ find he'd beaten them to the bottom under the pole.
Zeke Hausfather
Himalayas next to the Tibetan border) last week watching CNN with a
bunch of Spaniards and Swiss folks. They were showing that rather
silly story about Russia planting a claim to the shelf extending under
the north pole, as well as some dubious estimates of mineral wealth
lying in wait under the ice ("hundreds of billions to trillions of
dollars" and "a quarter of the world's oil"). They than moved to
interview an "arctic explorer" with the tagline that not everyone was
in favor of developing the arctic's mineral resources.
The unnamed "arctic explorer" made the point that, perhaps, if our
actions are causing unprecedented ice melt in the arctic, than using
that ice melt as an opportunity to extract and consume more fossil
fuels might not be the best of ideas. It was met by a rather
enthusiastic round of applause from my European comrades.
Seriously, though, its a rather ironic example of a positive feedback,
and perhaps a sign that we are still largely blind to the problem when
it comes to substantive decisions.
sherr...@aapt.net.au
2.99 million km2 which is an impressive 25% below the previous record
low (http://arctic.atmos.uiuc.edu/cryosphere/).
Climate junkies may also enjoy the impressive movie of this years melt
provided at the same website (bandwidth warning - it is nearly 200Mb).
http://arctic.atmos.uiuc.edu/cryosphere/sea.ice.movie.2007.mov
Eric Swanson
the NSIDC. Note the difference between the "area" value calculated by
Bill Chapman for September 16, 2007 (2.92 million sq. km), and the
"extent" number given by the NSIDC (average for the month of September
was 4.28 million square kilometers or 1.65 million square miles).
Both are very much smaller than the previous records for each
variable.
http://nsidc.org/news/press/2007_seaiceminimum/20071001_pressrelease.html
There's an article by Andy Revkin in today's NYT about the remarkable
loss of sea-ice this year. Here's a link:
http://www.nytimes.com/2007/10/02/science/earth/02arct.html?hp
I like the photograph which accompanies the article, as it shows the
impact of the mirror like surface of the ocean at high zenith angles,
which has been something I've tried to point out for years. One can
also see the melt ponds which form on the surface of the sea-ice.
http://graphics8.nytimes.com/images/2007/10/02/science/02arct.xlarge1.jpg
When the story was first linked thru the main NYT home page with a
picture of the Arctic Ocean sea-ice cover near the minimum, but that
graphic is no longer available there. It may be seen in the
supplemental graphics, which are linked thru the "multimedia" box,
which is a FLASH player file.
There's also a story from the BBC about the large ice berg in the
Arctic, which broke off of the Ayles Ice Shelf in 2005. The map of
it's travels is interesting too:
http://news.bbc.co.uk/1/hi/sci/tech/7022192.stm
E.S.
----------------------------------------------------------------------------------------------
Eric Swanson
Eric Swanson wrote:
> The final tally for the yearly sea-ice decline has been released by
> the NSIDC. Note the difference between the "area" value calculated by
> Bill Chapman for September 16, 2007 (2.92 million sq. km), and the
> "extent" number given by the NSIDC (average for the month of September
> was 4.28 million square kilometers or 1.65 million square miles).
> Both are very much smaller than the previous records for each
> variable.
>
> http://nsidc.org/news/press/2007_seaiceminimum/20071001_pressrelease.html
There's an article which just appeared that discusses the situation in
the Arctic.
http://www.carbonequity.info/PDFs/Arctic.pdf
It's not peer reviewed, but there's lots of references, though many
are from news.
There's also an interesting graph in the section on sea-ice that
compares the decline
in sea-ice extent with IPCC model projections, attributed to Dr.
Asgeir Sorteberg,
Bjeknes Centre for Climate Research and University Center at Svalbard,
Norway.
Here's a link to the graph from the PDF file:
http://www.theoildrum.com/files/seaice07.gif
Of course, whether this steep decline continues or not will await the
future.
E. S.