June 27, 2007

**Response to CENR Comments for SAP 1.2 Prospectus**

**[Reviewers]{.underline}**

**NSF**

Marta Cehelsky

Executive Secretary

NSTC Committee on Science and

Senior Adviser, Office of the Director

National Science Foundation

703-292-8003

mcehelsk@nsf.gov

**NOAA**

Mary Glackin

Acting Assistant Administrator for Weather Services/Director, National
Weather Service

NOAA / DOC

301-713-1632

mary.glackin@noaa.gov

**ONR**

Patricia L. Gruber

Director of Research

Office of Naval Research

703-588-2904

patricia.gruber@navy.mil

**[General Comments]{.underline}**

[NSF]{.underline}

The final Prospectus should include proper citations to the cited
literature. In fact, there is not a single literature citation in this
entire Prospectus. Even for an internal document, that is inappropriate,
given the widespread use of statements of findings. An example, of a
text that clearly needs a citation if this section from page 2 paragraph
1:

"Some paleoclimate indicators are easy to read and understand. For
example, grass-covered dunes of the Sand Hills of northwestern Nebraska
document formerly more-arid conditions. Similarly, the unique glacial
erosional and depositional features found in New York, Cleveland, and
the northern New England states which now lack glaciers, demonstrate the
existence of a previous cold ice age. Evidence of the colder
temperatures of this ice age is still preserved in the Greenland ice
sheet. The depths of the ice sheet in Greenland have not finished
warming from that ice age, with warmer ice both above and below a cold
zone in the middle of the ice sheet, and analyses of that temperature
profile show that ice-age cooling in central Greenland was more than
20^o^C"

The document is now heavily referenced.

[NOAA]{.underline}

The prospectus should make more reference to findings in the fourth IPCC
Report, in order to better ground the context of the SAP.

Multiple references to AR4 have been added.

The revised draft does not adequately respond to the public comments, in
reference to the approach for addressing the key questions in section
1.3.

A significant amount of text has been added to address this.

**[Specific Comments:]{.underline}**

[NSF]{.underline}

On page 5, first full paragraph, the sentence \"\... will raise global
sea level by 7m\...\" should be modified to read \"\...would raise \...
7m if it were to melt completely.\"

'Will' has been changed to 'would' in several instances as per this
review. However we note that previous CCSP reviewers have requested that
our original use of 'would' be changed to 'will' in many instances. We
have used our discretion in each instance to reflect the distinction
between conditional and demonstrated events.

The brief section encompassed by lines 5:33-6:2 addresses consequences
of arctic climate change on future Arctic ecosystems, permafrost,
decomposition, rivers, global climate, and more. This consideration of
the future consequences of future climate changes is either:

\(1\) out of place in this report, or

\(2\) superficial reference to an integral component of this assessment
that is ignored even to lacking any citations to relevant literature.

In the first case, the above-referenced lines should be deleted, as
being out of place in this Prospectus and without supporting
documentation. In the second case, a substantive discussion needs to be
provided.

We feel that section should be kept in the prospectus and we have
elaborated and modified the tone from consequences to how paleo data
provides the déjà vu of what we can expect in the future. The landscape
instability (especially coastal permafrost), changing hydrology, and CO2
aspects of this section are extremely relevant. and we would be
negligent not to include an assessment of what we know about past
change. For example, there is no data to suggest that arctic clathrates
degassed during the last interglacial -- submerged areas of the
continental shelf remained frozen and today many parts of the sea bed
have temperatures of -4 deg C even after 10kys of submergence. During
warmer periods of the past, the forest have moved north of the Brooks
Range and across the arctic such movements of vegetation would have had
large impacts on albedo.

[NOAA]{.underline}

p\. 5, line 6: The reference to the Greenland ice sheet melting gives a
wrong impression and is unduly alarmist. Yes mathematically, if the
Greenland ice sheet melted, it would raise sea level by 7 meters. But is
this realistic and what is the time scale? As noted in IPCC AR4,
complete melting is considered possible. We suggest noting, instead,
that the IPCC Report suggests a sea level rise of 0.3-0.8 m by 2300. .
Table SPM-3 of the Summary for Policymakers of Working Group 1, Fourth
Assessment Report (2007) has in the sea-level-rise column "Model-based
range excluding future rapid dynamical changes in ice flow". And on p.
14-15 of that document, important text says :

"Models used to date do not include uncertainties in climate-carbon
cycle feedback nor do they include the full effects of changes in ice
sheet flow, because a basis in published literature is lacking. The
projections include a contribution due to increased ice flow from
Greenland and Antarctica at the rates observed for 1993-2003, but these
flow rates could increase or decrease in the future. For example, if
this contribution were to grow linearly with global average temperature
change, the upper ranges of sea level rise for SRES scenarios shown in
Table SPM-3 would increase by 0.1 m to 0.2 m. Larger values cannot be
excluded, but understanding of these effects is too limited to assess
their likelihood or provide a best estimate or an upper bound for sea
level rise. {10.6}" Because the IPCC is highly explicit that the
numerical estimates given include only some sources of sea-level rise,
and represent "a best estimate or an upper bound for sea level rise" it
would be inappropriate to quote those numbers as actually being
projections of sea level rise.

The Report also states that if there continues to be a negative
area-wide accumulation on Greenland, major ice loss is on millennial
timescales. This timescale contrasts with temperature increases, sea ice
loss, and ecosystem impacts that will likely happen in the Arctic within
the next 50 years.\
. A comment on time scale has been added: "Rates of change are of
interest; models project centuries to millennia for major changes in the
ice sheet but lack key "fast" processes as documented in IPCC (2007);
any insights from the paleoclimatic record will be summarized in this
report."

Section 1.3: The paragraphs under the four questions do not lay out an
approximate approach or direction to answering the questions. The
paragraphs point out major changes that are occurring in the Arctic, but
their connection to paleo is weak with no examples. This was noted by
Jerry Elwood's comments and the responses to his comments are
inadequate.

We believe sufficient text has now been added to address these comments.

Here are a few connections that come to mind that the lead authors might
consider:

-   The wordings especially on page 2 (line 13, 39 and 40-42) would
    benefit from a clarification. Noted and modified.

-   The little ice age had several short cold events (and a few warm
    events). Is this "age" all due to random decadal variability plus a
    weak solar influence or is the difference between it and the 20th
    century a real centennial or longer climate feature?

-   Was the Medieval warm period centered on the Atlantic or was it
    Arctic wide?

-   Develop a complete documentation of the Holocene Optimum period. Was
    this primary Milankovich forcing or are feedbacks required?

-   Why is the climate of the Holocene so stable?

-   The abrupt climate changes came out of the major ice age periods
    with extensive ice sheet coverage. Is there any relationship to
    current ice free conditions?

-   The interglacials probably started with warmer temperature and CO2
    increases followed. How does this fit with the current conditions?

-   Is the Cenozoic greenhouse period the best analog for an ice free
    Arctic? Can we learn something from ice house conditions?

-   We would prefer a number of 3 deg C on page 2 line 36, rather than 5
    deg C. Yes on a seasonal and local basis you can find a 5 deg hot
    spot, but it is not valid to compare it to the global/annual
    average. 3 deg is closer to a regional Arctic/annual value, and is
    still much more than 0.74 deg, showing an Arctic amplification.
    Clarifying text added.

Suggestions noted.

[ONR]{.underline}

Section 1.2 of SAP 1.2 Prospectus seems overly amibtious. In particular,
the first paragraph on page 3 - \"paleoclimate records enable us to
define the range\....that are potential analogs of future conditions\".
I\'m skeptical that the data is sufficient to deliver on this. I\'d
recommend writing this paragraph as an approach rather than an
assertion.

The writing team should be ambitious. We believe there is a great deal
that can be said now with existing paleo data that needs to be written
and summarized.

Line 35, page 4. I don\'t think the prospectus should speculate on the
potential security/military implications of a loss of sea ice cover.
Presumably, these nations already have navy and coast guard capability
to operate in cold environments. I would prefer to replace the last two
sentences in this paragraph simply with: \"Changes in sea ice and
environmental conditions could impact commercial and military maritime
operations.\"

We feel that the comments in this section should stay in the report and
we have placed them into context by the NAS Report on the future of the
US Icebreaker Fleet ([[Polar Icebreakers in a Changing World: An
Assessment of U.S.
Needs]{.underline}](http://books.nap.edu/catalog/11753.html) (National
Academy of Sciences Press, 2007 This report and others lays out the
strategic concerns that are relevant.