[Vision2020] Arctic Sea Ice "An Icy Retreat, " Dirk Notz, Max-Planck-Institute for Meteorology

[Ted Moffett]

I don't waste my time with "Watts Up With That's" pseudo-scientific bias,
unless to point out scientific errors promoted by Anthony Watts. There is
far too much credible climate science from professional climate scientists
to consume my limited time...

Actually, given the science behind measuring Arctic sea ice thickness and/or
volume, some of which has already been posted to Vision2020, I thought Notz
somewhat misstated the science regarding current ability to make estimations
of sea ice volume, as is indicated from the climate science references given
lower down in this post.

But regardless, from my reading of his text, to paraphrase, he stated that
we know there is considerably more thin Arctic sea ice than in previous
decades, which can melt and reform quickly, therefore more extreme seasonal
changes in the sea ice extent are possible, as water and ice conditions
respond to cold or warm temperatures, and other variables (wind, ocean
currents).  However, to make an accurate estimate of total ice volume
requires more precise measurements (my wording), which apparently will be
possible with the new satellite Cryosat 2 Notz mentioned.

>From the following Vision2020 post, science is presented on the
skepticalscience.com website given, that indicates estimations of Arctic sea
ice volume; the graph from Polar Ice Center, for example:

http://mailman.fsr.com/pipermail/vision2020/2010-June/070583.html

http://www.skepticalscience.com/Has-Arctic-sea-ice-returned-to-normal.html

Quote below from website immediately above:

Sea ice extent gives us a reasonable indication of the amount of Arctic sea
ice but does have its limitations. Extent tells us about the state of the
sea ice at the ocean's surface, not what's happening below. A better metric
for the total amount of sea ice is, well, the actual total amount of sea
ice, measured by sea ice volume. Satellite radar altimetry (Giles
2008<http://www.agu.org/pubs/crossref/2008/2008GL035710.shtml>)
and satellite laser altimetry (Kwok
2009<http://www.agu.org/pubs/crossref/2009/2009JC005312.shtml>)
find that Arctic sea ice has been thinning, even in 2008 and 2009 when sea
ice extent showed a slight recovery from the 2007 minimum. So while some
claimed Arctic sea ice was recovering after 2007, the total volume of Arctic
Sea ice through 2008 and 2009 were the lowest on record (Maslowski
2010<http://soa.arcus.org/sites/soa.arcus.org/files/sessions/1-1-advances-understanding-arctic-system-components/pdf/1-1-7-maslowski-wieslaw.pdf>,
Tschudi 2010<http://soa.arcus.org/abstracts/trends-and-patterns-sea-ice-age-distributions-within-arctic-basin-and-their-implications-c>).

----------------------------

More scientific information on measuring Arctic sea ice thickness was
presented in the following Vision2020 post:
http://mailman.fsr.com/pipermail/vision2020/2010-June/070680.html

Quoting the Vision2020 post above:

In fact, satellites can provide data important in measuring Arctic sea ice
thickness, which is revealed in the following article, unless I
misunderstand (some of the scientific terminology used I do not understand),
which discusses data from ICEsat and GRACE satellites, and "ice thickness
calculations":

http://www.csr.utexas.edu/grace/GSTM/b4.html

*Session: B.4.a - Theme: GRACE & the Arctic*
*Title: Average and interannual dynamic topography from altimetry and the
GRACE mean geoid *
*First Author*: Ron Kwok
*Presenter*: Ron Kwok
*Co-Authors*: J. Morison

*Abstract*: We present our first estimates of the dynamic topography of the
Arctic Ocean derived from ICESat and EGM2008. EGM2008 has benefited from the
latest GRACE based satellite-only solutions, but is mixed with altimetric
estimates to the best of our knowledge. In ICESat processing, we retrieve
the ice and sea surface heights (ISH, SSH) by separating the elevation
returns from Arctic sea ice and open water. Differencing the ISH with the
local SSH gives the sea ice freeboard used in ice thickness calculations.
The sparsely sampled SSHs within the ice cover are used to estimate dynamic
topography – less than a few percent of the area of ice cover is open water.
An accurate geoid is clearly useful in minimizing the uncertainties in our
derived quantities at all length scales. We show the contributions of GRACE
data in improving the Arctic Gravity Project geoid (ArcGP-geoid) - what
looks to be long wavelength anomalies across the Arctic Basin are not longer
present. The resulting dynamic topography shows the expected relief but the
interpretation of the fields of interannual variability remains. There are
residuals in the field that may be due to uncertainties in EGM2008.
------------------------------------------
Vision2020 Post: Ted Moffett

On 7/26/10, Paul Rumelhart <godshatter at yahoo.com> wrote:
>
>
> Why does he state that Arctic sea ice has become very thin while also
> stating that they haven't been able to measure sea ice thickness reliably in
> the past?
>
> Andrew Watts has a page up that shows many different graphs relating to sea
> ice in the arctic and antarctic: http://wattsupwiththat.com/sea-ice-page/
>
> Despite your misgivings about his blog, you'll find the graphs (which are
> updated when the source graphs update) to be worth watching.  There is even
> a web cam at the North Pole he links to.
>
> Paul
>
> Ted Moffett wrote:
>
>>
>> http://www.realclimate.org/index.php/archives/2010/07/an-icy-retreat/#more-4469
>>
>>
>>      An icy retreat
>>
>>
>>      26 July 2010 -
>>
>> Guest Commentary by Dirk Notz, MPI Hamburg <
>> http://www.mpimet.mpg.de/en/mitarbeiter/dirk-notz/>
>>
>> *Dirk Notz* is head of the research group “Sea ice in the Earth System” at
>> the Max-Planck-Institute for Meteorology in Hamburg.
>>
>> It’s almost routine by now: Every summer, many of those interested in
>> climate change check again and again the latest data on sea-ice evolution in
>> the Arctic. Such data are for example available on a daily basis from the US
>> National Snow and Ice Data Center <http://nsidc.org/arcticseaicenews/>.
>> And again and again in early summer the question arises whether the most
>> recent trend in sea-ice extent might lead to a new record minimum, with a
>> sea-ice cover that will be smaller than that in the record summer of 2007.
>>
>> However, before looking at the possible future evolution of Arctic sea ice
>> in more detail, it might be a good idea to briefly re-capitulate some events
>> of the previous winter, because some of those are quite relevant for the
>> current state of the sea-ice cover. The winter 2009/2010 will be remembered
>> by many people in Europe (and not only there) as particularly cold, with
>> lots of snow and ice. Not least because of the sustained cold, some began to
>> wonder if global warming indeed was real.
>>
>> Such questioning of global warming based on a regional cold period of
>> course neglects the crucial difference between weather and climate, with the
>> former being the only thing that we as individuals will ever be able to
>> experience first hand. A single regional cold spell has not a lot to do with
>> climate – let alone with global climate. This becomes quite obvious if one
>> instead considers the mean temperature of the entire globe during the last
>> 12 months: this period was, according to the GISS data, the warmest 12-month
>> period since the beginning of the records 130 years ago. Regarding sea ice,
>> it was particularly important that temperatures in parts of the Arctic were
>> well above average for most of the winter. This was directly experienced by
>> some members of our working group during a field experiment at the West
>> Coast of Greenland.
>>
>> The initial plan of this field experiment was to study the growth and
>> decay of sea ice in great detail throughout an entire winter. In particular,
>> we wanted to focus on the evolution of very young sea ice that had just
>> formed from open water. Therefore, we wanted to start our measurements just
>> before initial ice formation, which usually takes place in mid-November, at
>> least according to past experience of the local Greenlandic population.
>> Hence, we traveled to our measuring site close to the Greenlandic settlement
>> of Upernavik in early November to put out our measuring buoys. We were
>> hoping that ice formation would start shortly after we had put out the
>> instruments such that they were protected from storms and waves. However,
>> with temperatures that were often more than 10°C above the long-term mean,
>> sea ice was nowhere to be seen. Even in January, there were days on end with
>> above 0°C temperature and heavy rain fall. Finally, in February a stable ice
>> cover formed, which of course remained relatively thin and which hence had
>> melted completely by mid May.
>>
>> The fact that it was sometimes warmer at our measurement site at the West
>> Coast of Greenland than it was in Central Europe at the same time surprised
>> us quite a bit. However, some recent studies indicate that such a
>> distribution of relatively high temperature in parts of the Arctic and
>> relatively low temperature in Northern and Central Europe and parts of the
>> US might become somewhat more wide-spread in the future. While the Arctic
>> has always shown large internal variability that lead to large-scale shifts
>> in weather patterns, in the future the ongoing retreat of Arctic sea ice
>> might cause those weather patterns to occur more often that allow for
>> Northerly winds to bring cold air from the Arctic to the mid-latitudes.
>> Hence, it is quite possible that because of the retreat of Arctic sea ice,
>> some smaller parts of the Northern Hemisphere will experience pronounced
>> cold spells during winter every now and then. The mean temperature of the
>> Northern Hemisphere will nevertheless increase further, and the export of
>> cold air from the Arctic of course leads to warm anomalies there.
>>
>> But let’s return to the evolution of Arctic sea ice. Because of relatively
>> high temperatures, Arctic sea-ice extent remained well below the long-term
>> mean for most of the preceding winter. However, in March temperatures
>> suddenly dropped for a couple of weeks, in particular in parts of the
>> Barents Sea and in parts of the Beaufort Sea. This in turn lead to the
>> formation of a thin ice cover in these regions, which caused a marked
>> increase in observed sea-ice extent. For the measurement of this extent, it
>> doesn’t matter at all how thick the ice is: any ice, however thin,
>> contributes to sea-ice extent. Therefore, only considering a possible
>> “recovery” of just the /extent /of Arctic sea ice always remains somewhat
>> superficial, since sea-ice extent contains no information on the thickness
>> of the ice. A much more useful measure for the state of Arctic sea ice is
>> therefore the total sea-ice volume. However, for its estimation one
>> additionally requires information on the overall distribution of ice
>> thickness, which we have not been able to measure routinely in the past.
>> While this will hopefully change in the future because of the successful
>> launch of the Cryosat 2 satellite a couple of weeks ago, at the moment we
>> unfortunately must rely on judging the current state of the Arctic sea-ice
>> cover mostly by its extent.
>>
>> Because of the very low thickness of much of the Arctic sea ice, it wasn’t
>> too surprising that at the end of the winter, sea-ice extent decreased
>> rapidly. This rapid loss lead up to the lowest June sea-ice extent <
>> http://nsidc.org/arcticseaicenews/2010/070610.html>since the beginning of
>> reliable observations. After this rapid loss of the very thin ice that had
>> formed late in winter, the retreat slowed down substantially but the ice
>> extent remained well below the long-term mean. Currently, the ice covers an
>> area that is slightly larger than the extent in late July of the record year
>> 2007. However, this does not really allow for any reliable projections
>> regarding the future evolution of Arctic sea ice in the weeks to come.
>>
>> The reason for this is mostly that sea ice in the Arctic has become very
>> thin. Hence, in contrast to the much thicker ice of past decades, the ice
>> now reacts very quickly and very sensitively to the weather patterns <
>> http://nsidc.org/arcticseaicenews/2010/072010.html> that are predominant
>> during a certain summer. This currently limits the predictability of sea-ice
>> extent significantly. For example, in 2007 a relatively stable high-pressure
>> system formed above the Beaufort sea, towards the north of North America,
>> leading to rapid melting of sea ice there. If again such stable high
>> pressure system forms in the Arctic throughout the coming weeks, we might
>> well experience a sea-ice minimum that is below the record minimum as
>> observed in 2007. However, if the summer should turn out to be colder than
>> during the previous years, a sea-ice minimum similar to that observed in
>> 2009 would not be too surprising. Hence, at the moment all that remains is
>> to wait – and to check again and again the latest data of Arctic sea-ice
>> extent.
>>
>> --------------------------------------------------------
>>
>> Vision2020 Post: Ted Moffett
>>
>> ------------------------------------------------------------------------
>>
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