CCSP Collated Comments Prospectus 1.2

NOAA Comments

General Overall Comment

Given, the natural link among the meridional overturning circulation change, the Greenland ice sheet variability and the increase of greenhouse gas is addressed in these two separate products (S&A Products 1.2 and 3.4 [1.3i, iii, iv]), the author teams need to coordinate closely.

General Comments

Since the title of this SAP is Past Climate Variability and Change in the Arctic and at High Latitudes, it would be helpful if the authors defined “Arctic” and “High Latitudes”.

Discussion among the attendees at the scoping meeting led to the decision to defer a definition of precisely how far south to extend the definition of ‘high latitudes’ until the writing teams began their work. This decision arose from the recognition that defining a hard boundary as to which records would or would not be considered based on latitude could potentially place undue restriction on records derived from specific sub-polar regions the inclusion of which will provide unique records. While ‘Arctic’ is generally accepted as meaning above 66° 33’N latitude, we wish to defer articulating a definition of ‘high latitude’ pending decisions on which records will be included in the synthesis and assessment product.

The document is a little “thin” on details. For example: Which paleo proxies provide the best opportunity for good records? Which physical (or other) variables will the paleo record allow the authors to investigate? What tools will they use to understand the cause and effect they intend to elucidate? How complete (or incomplete) is the paleo record as far as yielding information over the various regions that make up the Arctic, i.e., regional differentiation? Admittedly, some of this will come out of the assessment itself, but it would be nice to know upfront what the prospects for success are and where the emphases will be.

Paleo data are not only proxy records. Ice cores provide many direct measurements including atmospheric gas composition and gas isotopes, accumulation, aerosol and dust content of the atmosphere (including isotopic concentrations in dusts), sea salt loading, and records of unique events such as volcanic eruptions. Proxy records from ice cores include atmospheric temperature via stable isotopes, terrestrial productivity via entrapped pollen, and oceanic productivity from methane sulfonate. Additional records will include but not be limited to those derived from tree rings, pollen records, lake sediments, marine sediments, past permafrost records, surface exposure dating, and periglacial and other geomorphic features. Taken together, these records will provide a comprehensive picture of past climate regimes in the Arctic.

This is a study of the paleo record but one of the questions is: What will be the fate the Arctic sea ice cover in the 21st century? This implies that projections/predictions will be referred to, but there is no mention of this. It appears that events (e.g., warming episodes) in the paleo record will be the sole source of inferring changes in the future. Is this correct?

The paleo record integrates into the record of modern observation. To the extent that the paleo record of arctic sea ice cover can provide insight into future behaviors and/or provide some boundaries on these behaviors, this information will be elaborated in the SAP.

A similar comment applies to the question: How much warmer/colder, wetter/drier is it going to get in the next 100 years? Here the method will presumably be “Past warm periods provide analogs for future change”. If this is true, is there sufficient information in the paleo record?

Yes, there is sufficient information in the paleo record to provide insights and analogy for future change provided that the record considered extends far back enough to include prior warm periods that are analogous to the present.

In regard to the question What is the status of the Greenland Ice Sheet?, how does this relate to the Product 3.4 focus on this same phenomenon? Product 3.4 does mention that there is some overlap. There will have to be some coordination of approaches and/or results reported between these two assessments.

Please see remarks under ‘General Overall Comments’ above. We recognize the need to coordinate these two products.

The question What will be the rates of change? will, presumably, be addressed, also, by referring solely to the paleo record, but it is not made clear that the conditions (i.e., the forcings) that the Arctic will experience in the future have their counterpart in the paleo record.

This point is well taken. We fully appreciate that, although the paleo record clearly indicates that current temperatures in the Arctic are not unprecedented, the current rates of temperature change are unusually rapid. We anticipate that although the current rates of some changes are more rapid than has been seen in the past, the basic mechanisms that underlie these changes are fundamentally the same mechanisms as those which have operated in the past.

Recommend that the author list be expanded to cover more expertise.

The list of authors given in the prospectus represents only the lead authors for each of the questions. Lead authors will assemble writing teams with broad expertise to develop a record that draws on as many pertinent fields as possible. A need that was immediately recognized is the requirement for input from the field of paleobotany in order to incorporate information on the type and extent of prehistoric ecological systems. We anticipate that the final product will include a much broader information base than that represented by the makeup of the current team of lead authors.

Detailed Comments

Page 2, line 39-40: “… changes in sea ice will influence weather systems both in the Arctic and in the middle latitudes.”

Not only the weather systems but also the short term climate variability (from submonthly to interannual timescales, including ENSO, NAO, MJO, monsoons, etc.) are affected through complex interactions between the lower boundary forcing and internal dynamics. The potential impact of Arctic sea ice and Greenland ice sheet variability and change on the predictability of weather-climate system in the middle and subtropical latitudes, particularly over North America, could be large and should be on the synthesis and assessment list to support national weather-climate forecast improvement. Because of the vital importance and critical needs, an independent question arises:

“What is the potential impact of Arctic sea ice and Greenland ice sheet variability and change on the predictability of short-term climate and weather systems in middle and subtropical latitudes?”

This question could be the first paragraph of the first key issue in section 1.3 (line 36-42).

The text will be modified to refer to the impact of ice variability on the predictability of short-term climate and weather systems as indicated in this remark, but an attempt to elaborate on the impact that such variability may have had in the past is beyond the scope of resolution possible this S&A.

Page 3, lines 29-30: I would delete "continued retreat will potentially impact ecotourism as well." Why?
Page 5, line 7: Use the word “Stakeholders.” concur
Page 6, line 6: Use Kathleen, instead of Kathy. concur
Page 6, line 21: Insert Dr. David Verado. concur
Page 11, line 3: Leningrad, instead of Lenigrad. concur

DOE Comments

It would be useful to know what time scales 1.2 will span. The draft prospectus says beyond the historical period, but it’s not clear how far back in time they will go.

Similar to the line of reasoning arrived at during the scoping session on drawing hard limits on the geographical definition of ‘high latitudes’, the participants agreed that at the outset they would focus on a timescale for which meaningfully-resolved records exist, for which the role of orbital forcing would come into play, and for which good analogs for present conditions exist. There was general consensus that the timescale needs to be flexible enough to yield meaningful insights and not be artificially constrained by setting a limit which might exclude consideration of important analogs that lie outside such a limit. Having said this, it is likely that the record to be considered will extend back at least as far as the last full interglacial but will entrain much older portions of the record where doing so yields additional insights.

Page 1 Line 43: can you put numbers on 30 year trend in Arctic?

The authors declined to specify this because the spatial variability in the Arctic is high enough to make the use of an average number inappropriate in the prospectus.

Page 2 Line 44: Some of these are already occurring. Why is the draft prospectus talking in future tense.

The authors intend to utilize the record of past climate changes in the Arctic to both inform the current process of change and to provide a long-term context for it.

Page 3 Lines 9-15: How will the CCSP product address this, if at all? What is the relevance of this para to 1.2? Page 3, line 32 also refers to iceberg distribution and ‘thus shipping’.

Page 8: Final prospectus is scheduled for Dec 2006. IT will take at least a couple of months before FACA committee is approved. Page 9 timetable is not realistic.

The timetable will be amended to reflect FACA process time requirements, but the Agency Lead will seek to expedite the process.

There is a lack of reference to global coupled climate models. If the questions raised in 1.2 dealt with determining the range of variability based on the paleo record to provide a context of current changes in Arctic, based on past observational and proxy data, it’s fine to bypass dealing with climate projection results. But Question 1, Question 3, Question 4 need GCMs to answer. Question 1, Question 3, Question 4 are all to do with future… simply analyzing the past record won’t do. There is no mention of how these will be addressed using climate change projections.

The paragraphs under Question 1, do not deal with answering Question 1 per se. They deal with the impact of decreased sea ice cover. Either the question should be substituted to be the one that will be answered by the text, or the text should be altered to answer Question 1 ‘What will be the fate of the Arctic sea ice in the 21st century?’ This question can only be answered using climate change projections.

Similarly the paragraphs under Question 3, do not deal with answering Question 3 per se. They deal with the impact warming would have, and historical records. Either the question should be substituted to be the one that will be answered by the text, or the text should be altered to answer Question 3 ‘How much warmer/colder, wetter/drier is it going to get in the next 100 years?’ This question can only be answered using climate change projections.

Question 4 ‘What will be the rates of change?’ We’d need to refer to climate model results. But page 4, line 44 is how the report will answer this question, viz the report will summarize paleoclimatic data … filling those gaps’. I believe this will not provide the answer to Question 4. Either change question, or change text to answer question.

From these remarks we understand that by casting our key questions to address the future we have raised a question as to what role global climate models will play in this S&A. Since it is not the intent of the Lead Authors to entrain the results of such models to any great extent in S&A 1.2 we have rephrased the key questions as suggested by this reviewer.

How is 1.2 related to 3.4? 1.2 will look at Abrupt Climate Change in the Arctic; 3.4 deals solely with Abrupt Climate Change. So will both deal with Abrupt Climate Change. It is not clear where climate processes will be dealt, under 1.2 or 3.4? Given these assessment products in the same stage of evolution, there needs to be some cross-talk so redundancy is reduced.

Abrupt Climate Change in the Arctic is the sole focus of S&A Product 3.4. The focus of S&A Product 1.2 is the entire span of climate behaviors as documented in the paleoclimate record for the high latitudes. There is no intention to concentrate specifically or solely on rapid events alone. We recognize the need to coordinate activities between the two products in sections that make reference to the same events. Please see our remarks under ‘General Overall Comments’.