Decadal Ocean Heat Redistribution Since the Late 1990s and Its Association with Key Climate Modes
Round 1
Reviewer 1 Report
Review of “Decadal ocean heat redistribution since the late 1990s and its association with key climate modes
Overall:
Understanding the flows of energy through Earth’s climate system is critical to understanding and projecting climate variability and changes. The ocean is the largest heat reservoir within this system and therefore the changes in heat storage there has a significant impact. Over the recent period between 1998 and 2013 there as a slowdown in the global mean surface warming trend that has been subject to significant debate. In this work, the authors apply a novel and improved ocean heat content data set to analyze the changes in OHC over the ~50 year record with a specific focus on the differences between the SWS period and the previous reference period (1982-1997). The results with the novel OHC data set indicate a rich spatial pattern of OHC indicating that a significant redistribution of energy occurred within the global ocean during the SWS period. Moreover, the study argues that the redistribution of energy within the ocean resulted from natural variability (not a forced response) and investigated the potential contributions from known modes of oceanic variability (ENSO, PDO, and AMO). This paper argues that no one known mode of decadal OHC variability explains that pattern of OHC redistribution within the global ocean. Rather, some combination of modes is required account for the OHC redistribution during the SWS.
This is a well written paper that makes a significant contribution to our understanding of the SWS period. I recommend publication after minor revisions.
Major Comments:
-It is stated in section 2 that the concept of “influencing radii” would be discussion. I cannot find any such discussion in section 3.1 Please include a paragraph discussing the important considerations as this concept appear critical to the arguments that are being made about the enhancements of the new data product (IAP).
-The IAP data set is critical to the results shown in this paper. In fact, the author’s arguments and justification for why previous reports are incorrect is based upon this data set. It is important that the discussion of the IAP data set and a justification for the validity and accuracy of the data set be provided in the paper. In my view, the description provided is incomplete and needs to be bolstered with quantitative arguments where possible. Why should I trust the IAP data? How good is it?
Minor Comments:
Line 14: “1990” should be “1990s”
Line 43: remove “a” before “statistical”
Line 48: “of” should be “for”
Line 57: remove word “because”
Line 64: should be a period, not a comma, after measurements
Line 73: “rising” should be “raising”
Line 80: remove “And” and capitalize “Also,”
Line 105: add “the” before “tropical”
Line 165: remove “in details”
Line 179: I recommend using the word “variability” instead of “variabilities”
Line 213: There appear to be words missing from this statement.
Line 220: add “the” between “in literature”
Line 229: change “attached” to “shown”
Line 287-289: revise sentence beginning with “However, as discussed…”, it is not clear.
Line 392: “The” should be “the”
Line 395: “shows” should be “show”
Line 408: “debated” should be “debate”
Line 420: “viable” does not seem to be the best word choice here, try “notable” or “important”
Author Response
Reviewer 1
Comments and Suggestions for Authors
Review of “Decadal ocean heat redistribution since the late 1990s and its association with key climate modes
Overall:
Understanding the flows of energy through Earth’s climate system is critical to understanding and projecting climate variability and changes. The ocean is the largest heat reservoir within this system and therefore the changes in heat storage there has a significant impact. Over the recent period between 1998 and 2013 there as a slowdown in the global mean surface warming trend that has been subject to significant debate. In this work, the authors apply a novel and improved ocean heat content data set to analyze the changes in OHC over the ~50 year record with a specific focus on the differences between the SWS period and the previous reference period (1982-1997). The results with the novel OHC data set indicate a rich spatial pattern of OHC indicating that a significant redistribution of energy occurred within the global ocean during the SWS period. Moreover, the study argues that the redistribution of energy within the ocean resulted from natural variability (not a forced response) and investigated the potential contributions from known modes of oceanic variability (ENSO, PDO, and AMO). This paper argues that no one known mode of decadal OHC variability explains that pattern of OHC redistribution within the global ocean. Rather, some combination of modes is required account for the OHC redistribution during the SWS.
This is a well written paper that makes a significant contribution to our understanding of the SWS period. I recommend publication after minor revisions.
Rely: Thanks for the evaluation.
Major Comments:
-It is stated in section 2 that the concept of “influencing radii” would be discussion. I cannot find any such discussion in section 3.1 Please include a paragraph discussing the important considerations as this concept appear critical to the arguments that are being made about the enhancements of the new data product (IAP).
Rely: Thanks. We have re-wording the related discussions in section 3.1. The influence of “influencing radii” was discussed in the paragraph starting at line 287.
-The IAP data set is critical to the results shown in this paper. In fact, the author’s arguments and justification for why previous reports are incorrect is based upon this data set. It is important that the discussion of the IAP data set and a justification for the validity and accuracy of the data set be provided in the paper. In my view, the description provided is incomplete and needs to be bolstered with quantitative arguments where possible. Why should I trust the IAP data? How good is it?
Rely: Thanks. More explanations were provided. (1). The authors had two separate papers on developing and evaluating IAP data products (Cheng&Zhu 2016, Cheng et al. 2017). Many quantitative evaluations were provided to validate IAP data. (2). A separate study by Wang et al. 2017 comprehensively compares IAP, EN4 and Ishii data, showing the evidence of the “conservative error” in EN4 and Ishii data.
Therefore, justification for the validity and accuracy of IAP data is based on a rich body of published literatures, and this study just provides the key concept and links to the “hiatus” debate.
Minor Comments:
Line 14: “1990” should be “1990s”
Rely: revised
Line 43: remove “a” before “statistical”
Rely: revised
Line 48: “of” should be “for”
Rely: revised
Line 57: remove word “because”
Rely: revised
Line 64: should be a period, not a comma, after measurements
Rely: revised
Line 73: “rising” should be “raising”
Rely: revised
Line 80: remove “And” and capitalize “Also,”
Rely: revised
Line 105: add “the” before “tropical”
Rely: revised
Line 165: remove “in details”
Rely: revised
Line 179: I recommend using the word “variability” instead of “variabilities”
Rely: revised
Line 213: There appear to be words missing from this statement.
Rely: sorry there is an error in this plot, we modified the plot and update the figure caption.
Line 220: add “the” between “in literature”
Rely: revised
Line 229: change “attached” to “shown”
Rely: revised
Line 287-289: revise sentence beginning with “However, as discussed…”, it is not clear.
Reply: This sentence was modified to “However, as discussed earlier in this paper and many other studies [9, 50, 77], the Southern Ocean was experiencing a significant warming since 1960 due mainly to the anthropogenic forcing, which was not related to the SWS.”
Line 392: “The” should be “the”
Reply: revised
Line 395: “shows” should be “show”
Reply: revised
Line 408: “debated” should be “debate”
Reply: revised
Line 420: “viable” does not seem to be the best word choice here, try “notable” or “important”
Reply: revised
Reviewer 2 Report
The paper proves that there is no global warming hiatus while there is Surface Warming Slowdown (SWS). Aspects of the heat redistribution associated with key climate modes are addressed but not in a conclusive fashion. It is not clear if this is due to the data or to the climate models or both.
Detailed comments:
line 13: SWS is acronym of "surface warming slowdown" not "surface warming hiatus" this is confusing to the reader until definition is given at line 97
line 21: replace "distinctive" with "distinct"
line 66: insert "been" between "there" and "a"
line 90: there is no Fig 1b
line 279: what is meaning of "attached 20 C isotherms"? Clarify
line 409: insert "of increase" after "rate"
line 416: move "is" from after "there" to before "there"
line 436: insert "it" between "relate" and "to"
line 448. replace "on" with "at".
Author Response
Reviewer 3
The paper proves that there is no global warming hiatus while there is Surface Warming Slowdown (SWS). Aspects of the heat redistribution associated with key climate modes are addressed but not in a conclusive fashion. It is not clear if this is due to the data or to the climate models or both.
Reply: Thanks! This excellent review comment was echoed by reviewer 2. Our response is the same as it is to reviewer 2.
Detailed comments:
line 13: SWS is acronym of "surface warming slowdown" not "surface warming hiatus" this is confusing to the reader until definition is given at line 97
Reply: The “surface warming hiatus” was changed to “surface warming slowdown”
line 21: replace "distinctive" with "distinct"
Reply: Done
line 66: insert "been" between "there" and "a"
Reply: Done
line 90: there is no Fig 1b
Reply: Changed to “Figure 1”
line 279: what is meaning of "attached 20 C isotherms"? Clarify
Reply: Sorry this is a mistaken, we removed this sentence.
line 409: insert "of increase" after "rate"
Reply: done
line 416: move "is" from after "there" to before "there"
Reply: done
line 436: insert "it" between "relate" and "to"
Reply: done
line 448. replace "on" with "at".
Reply: done
Reviewer 3 Report
Some comments:
Please decide whether to write "for 600-m" (line 270) or "at 600m" (line 228). I would prefer "at an altitude of 600 m".
How was Figure 3 created? What do these dotted lines mean (I understand what means “with observation distribution indicated by dots in the plots” (line 217-21810))?
I do not like the connection of the conclusions with the discussion (Chapter 4). It would be understandable to me if the discussion was first and then the conclusions arising from it. I got the impression that the authors were a bit afraid of clearly articulating the conclusions. I conclude that Chapter 4 should be divided into two.
Author Response
Reviewer 2
Comments and Suggestions for Authors
Some comments:
Please decide whether to write "for 600-m" (line 270) or "at 600m" (line 228). I would prefer "at an altitude of 600 m".
Reply: changed to “at the depth of 600 m”
How was Figure 3 created? What do these dotted lines mean (I understand what means “with observation distribution indicated by dots in the plots” (line 217-21810))?
Reply: Yes, thanks for the reminder. The dots are the observation distribution (purple dots for Aug.1971, grey dots for Aug. 1994). We clarify this in the figure caption.
I do not like the connection of the conclusions with the discussion (Chapter 4). It would be understandable to me if the discussion was first and then the conclusions arising from it. I got the impression that the authors were a bit afraid of clearly articulating the conclusions. I conclude that Chapter 4 should be divided into two.
Reply: Thanks! In the revised manuscript, we have separated Discussion with Conclusion. We end the manuscript with a Concluding Remarks discussion that contains two “take away points”. We appreciate the other comment the reviewer makes, about a seeming tentativeness about our conclusions. In fact, we are trying to be clear about what we can and cannot conclude. We hope our observations based on temperature measurements are useful to the community and specifically related to the most recent OHC trends and the impact on surface temperatures. But we are not able to conclusively explain the OHC patterns on any single oceanic mode. So, we want to be clear about that and we hope that this conclusion is useful to the scientific community.
