|Werner et al., present a new climate field reconstruction for the terrestrial Arctic (>60N) based on ~50 annually-resolved temperature sensitive record. The reconstruction is created using an extended version of the age-uncertain BARCAST methodology presented in Werner and Tingley, 2015, which enables the authors to reconstruct the climate field while accounting for age uncertainty in the uncertain layer counted records (from ice cores and varved sediment). The result is a probabilistic CFR that extends back through the Common. This represents a major advance, both scientifically, as this is the longest and most data-rich CFR yet developed for the Arctic, and methodologically, as this is the first full-fledged CFR that I’m aware of that rigorously incorporates age uncertainty. These are both major scientific publications that warrant publication in Climate of the Past.|
Although the focus of the article is the methodology and presentation of the reconstruction, the authors explore some of the features of the new reconstruction, including the predominant trends, and the relative warmth and coldness of decadal and century scale variability in past intervals.
I also reviewed the initial submission of the manuscript, and am happy to see that the authors have addressed my primary concerns with the original product, and the revised paper is considerably improved.
One item that I continue to be confused about is the temporal duration of the reconstruction (much to the authors’ frustration, I believe). The authors say that “the gridded reconstruction is limited to the time after 750 CE”, and otherwise imply that the field reconstruction begins in 750, however other times they simply say that “the analysis is limited to the time after 750 CE”, and they also show reconstructed trends, spatially, for the period from 1-1850 CE in figure 6a. After twice reviewing the manuscript, and two responses from the authors, my current suspicion is that spatial reconstruction covers the period from 1-2002, however is not robust before 750, and they urge caution when interpreting it, only examining it themselves when looking at long term trends (and urging caution). This is fine, it just needs to be well (and consistently explained). Also, if I’m correct, will the full 1-2002 interval be included in the reconstructed data fields? My opinion is that they should be, with caution urged anywhere the data are hosted.
I have a few specific comments that can be easily addressed below, but this is an exciting study and a well-written paper. After the minor issues discussed above are resolved, I suggest that it be published in Climate of the Past.
More specific questions:
1. Data: I was glad to see the data availability section said that all the input data and code would be available – does this mean the input proxy data, including age ensembles, as well as the instrumental target developed as part of the paper will be available? The link is not currently active, but I hope this is the case as those data, as well as the full ensemble output, are extremely valuable for the community.
2. Figure axis labels are inconsistently handled, in terms of the orientation, and the common variable (units) structure. Several of the axis labels have what code names rather than common names.
3. The definition of the MCA used several places in the manuscript (920–1060 CE) is narrower than normal, to coincide with the warmest 140 years in the reconstruction. Additionally, the authors refer to a “late” Roman Warm Period in the 4th and 5th centuries. I’d encourage the authors to not feel obliged to identify the observed warm periods with these more classical and general names, and explicitly discuss the difference between the observed warm periods and the more general concepts.
4. The abstract says 44 records, and the conclusion says 54 records.
I attached detailed comments in a marked version of the manuscript.