"John Hall" wrote in message ...

If the amount of Arctic sea ice is reducing in JANUARY, even if it turns
out to be only for a day or two, that seems remarkable and really brings
it home just how far global warming has gone.
======================

This is for extent, which AIUI is more liable to error, as a parameter
rather than area but interesting nonetheless. But if you look at the NSIDC
extent chart at:

http://nsidc.org/arcticseaicenews/

you'll see that there was a also a brief net melt in November 2016 and
certainly a stall if not a technical dip in December and again in
mid-January.

What seems to be concerning the experts more than the relatively low current
area/extent values is that a substantial proportion of the arctic ice is
thin; while this will certainly still contribute to the area/extent values
as if it were traditional thicker ice, it will also be easier to melt out
once the spring/summer thaw starts in earnest. So arctic ice _volume_ is
potentially a more interesting parameter, though one tricky to estimate and
not updated publicly on a daily basis AFAIK. So it will be interesting to
see the PIOMAS end-January volume estimate when it hopefully gets released
in around a week's time.

On 29/01/2017 08:54, JohnD wrote:
"John Hall" wrote in message ...

If the amount of Arctic sea ice is reducing in JANUARY, even if it turns
out to be only for a day or two, that seems remarkable and really brings
it home just how far global warming has gone.
======================

This is for extent, which AIUI is more liable to error, as a parameter
rather than area but interesting nonetheless. But if you look at the
NSIDC extent chart at:

http://nsidc.org/arcticseaicenews/

you'll see that there was a also a brief net melt in November 2016 and
certainly a stall if not a technical dip in December and again in
mid-January.

What seems to be concerning the experts more than the relatively low
current area/extent values is that a substantial proportion of the
arctic ice is thin; while this will certainly still contribute to the
area/extent values as if it were traditional thicker ice, it will also
be easier to melt out once the spring/summer thaw starts in earnest. So
arctic ice _volume_ is potentially a more interesting parameter, though
one tricky to estimate and not updated publicly on a daily basis AFAIK.
So it will be interesting to see the PIOMAS end-January volume estimate
when it hopefully gets released in around a week's time.

The local retired polar oceanographer, living near me, seems to be most
concerned about the lack of multiyear ice in the Arctic, ie lack of
structural integrity.

The lack of Antarctic sea-ice area is before Larsen C breaks off

"N_Cook" wrote in message news
The lack of Antarctic sea-ice area is before Larsen C breaks off

Are you sure that the ice-shelf areas contribute to the overall sea ice
figures? My impression was that they didn't - I guess on the basis that are
(largely?) grounded ice fed by glaciers rather than floating sea ice. I
thought that the 'land' area boundaries of Antarctica on the extent maps
actually included the ice shelves. But ICBW and I'm sure someone here must
know for sure.

On 29/01/2017 09:24, JohnD wrote:
"N_Cook" wrote in message news
The lack of Antarctic sea-ice area is before Larsen C breaks off

Are you sure that the ice-shelf areas contribute to the overall sea ice
figures? My impression was that they didn't - I guess on the basis that
are (largely?) grounded ice fed by glaciers rather than floating sea
ice. I thought that the 'land' area boundaries of Antarctica on the
extent maps actually included the ice shelves. But ICBW and I'm sure
someone here must know for sure.

I've no knowledge on that, this is just my halfpennyworth. If the ice is
over seawater and when it breaks off it forms an ice-berg, then classed
as sea-ice I would have thought.
Penetrating radar has long since defined the boundary of the land.

"N_Cook" wrote in message news
I've no knowledge on that, this is just my halfpennyworth. If the ice is
over seawater and when it breaks off it forms an ice-berg, then classed
as sea-ice I would have thought.
Penetrating radar has long since defined the boundary of the land.
================

Yes, certainly, the true land boundary of the Antarctica is well known. But
that's not to say that the ice-shelves are not added to the land boundary
for the purpose of the sea ice maps.

Take a look for example at the extent of the Ross ice shelf, as per:

https://en.wikipedia.org/wiki/Ross_Ice_Shelf

Then compare that to the current NSIDC map.

The Ross sea ice looks to have very largely gone, yet there's no suggestion
AFAIK that the Ross ice shelf is actively melting. So it's presumably still
all there, yet not showing up on the NSIDC map.

And the introductory notes to sea ice at eg:

https://nsidc.org/cryosphere/seaice/index.html

make a major distinction between sea ice and land-derived ice, eg:

'Sea ice is simply frozen ocean water. It forms, grows, and melts in the
ocean. In contrast, icebergs, glaciers, ice sheets, and ice shelves all
originate on land. '

'The most basic difference is that sea ice forms from salty ocean water,
whereas icebergs, glaciers, and lake ice form from fresh water or snow. Sea
ice grows, forms, and melts strictly in the ocean. Glaciers are considered
land ice, and icebergs are chunks of ice that break off of glaciers and fall
into the ocean.' (Though this para doesn't specifically mention ice shelves,
AIUI the shelves are made from glacier ice and so aren't sea-ice by
definition.)