Response to CENR Comments for SAP 1.2 Prospectus

June 27, 2007

Reviewers

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

NSF
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°C”

The document is now heavily referenced.

NOAA
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:

NSF

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
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

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 (National Academy of Sciences Press, 2007  This report and others lays out the strategic concerns that are relevant.