Global Carbon Budget 2018

Le Quéré, Corinne; Andrew, Robbie M.; Friedlingstein, Pierre; Sitch, Stephen; Hauck, Judith; Pongratz, Julia; Pickers, Penelope A.; Korsbakken, Jan Ivar; Peters, Glen P.; Canadell, Josep G.; Arneth, Almut; Arora, Vivek K.; Barbero, Leticia; Bastos, Ana; Bopp, Laurent; Chevallier, Frédéric; Chini, Louise P.; Ciais, Philippe; Doney, Scott C.; Gkritzalis, Thanos; Goll, Daniel S.; Harris, Ian; Haverd, Vanessa; Hoffman, Forrest M.; Hoppema, Mario; Houghton, Richard A.; Hurtt, George; Ilyina, Tatiana; Jain, Atul K.; Johannessen, Truls; Jones, Chris D.; Kato, Etsushi; Keeling, Ralph F.; Goldewijk, Kees Klein; Landschützer, Peter; Lefèvre, Nathalie; Lienert, Sebastian; Liu, Zhu; Lombardozzi, Danica; Metzl, Nicolas; Munro, David R.; Nabel, Julia E. M. S.; Nakaoka, Shin-ichiro; Neill, Craig; Olsen, Are; Ono, Tsueno; Patra, Prabir; Peregon, Anna; Peters, Wouter; Peylin, Philippe; Pfeil, Benjamin; Pierrot, Denis; Poulter, Benjamin; Rehder, Gregor; Resplandy, Laure; Robertson, Eddy; Rocher, Matthias; Rödenbeck, Christian; Schuster, Ute; Schwinger, Jörg; Séférian, Roland; Skjelvan, Ingunn; Steinhoff, Tobias; Sutton, Adrienne; Tans, Pieter P.; Tian, Hanqin; Tilbrook, Bronte; Tubiello, Francesco N.; van der Laan-Luijkx, Ingrid T.; van der Werf, Guido R.; Viovy, Nicolas; Walker, Anthony P.; Wiltshire, Andrew J.; Wright, Rebecca; Zaehle, Sönke; Zheng, Bo

doi:https://doi.org/10.5194/essd-10-2141-2018

ESSD | Articles | Volume 10, issue 4

Earth Syst. Sci. Data, 10, 2141–2194, 2018
https://doi.org/10.5194/essd-10-2141-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

ESSD | Articles | Volume 10, issue 4

05 Dec 2018

Global Carbon Budget 2018

Corinne Le Quéré et al.

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Final revised paper (published on 05 Dec 2018)
Preprint (discussion started on 04 Oct 2018)

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AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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EC1: 'Editor comment', David Carlson, 04 Oct 2018

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AR: Author's response | RR: Referee report | ED: Editor decision

AR by Corinne Le Quere on behalf of the Authors (04 Oct 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (04 Oct 2018) by David Carlson

RR by Anonymous Referee #1 (15 Oct 2018)

RR by Albertus J. (Han) Dolman (15 Oct 2018)

Suggestions for revision or reasons for rejection

This the 13-th version of the global Carbon Budget. As is other version the authors are to be applauded for putting this all together. In general the paper is again well written, concise and transparent.

I have a few minor comments.

Page 13 line 8. I am not familiar with Holt Winters smoothing, and the text of “exponential smoothing with multiplicative seasonality “ does not really brings further understanding. Can the authors say in understandable language why Holt Winters is chosen and what it effectively does?

Page 17/18 lines 30-1. Is this an improvement? Has the impact of using this resolution been quantified somewhere?

Page 21 Line 19. Strictly what you call here uncertainty is climatic variability.

Page 23 lines 15-27. I like this metric very much, but the description of it is rather dense. Maybe have a look, reformulate and make the text a little less dense.

Page 26 line 27-28. Why is only the land sink adjusted and not the ocean sink as well?

Page 28 line 29. It would help the reader if a final sentence stating that given the uncertainty in the balance of these two processes the choice was not to include these emissions.

Page 32. The skill score on the DGVM’s is nice. But it would also be honest to say that the models perform poorly, specifically on important aspects of the carbon cycle. Even though, that is what they are used here for. Now the text is a bit too non-non-committal to my taste.

Page 36. Lines 4-10. Yes it is long known that the NH land fluxes are poorly resolved. In fact I would make the point that despite, say 10-15 years of active research, we still have not been able to resolve one of the main uncertainties/unknown in the inversions/continental scale carbon cycle.

Page 43. Lines 17-20 can be deleted. Has been stated before.

Page 45. The conclusion section is rather obsolete. I would suggest to close off the paper with the data availability section (5) and add, only if it has not been said before, some of the conclusion statements in the discussion. This would improve to my mind the overall readability of the document, that, it has been said before, is becoming quite long.

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RR by H. Damon Matthews (22 Oct 2018)

Suggestions for revision or reasons for rejection

This manuscript is a comprehensive and important update to the annual carbon budget, a dataset which has become one of the most important and widely used outputs in the field of climate science. The authors are to be congratulated on this sustained effort over time.

Given the breadth of the paper, I have restricted my comments to those areas where I have some reasonable level of expertise. My comments are fairly minor, but could improve the clarity of the manuscript in some places.

1) As a note on the use of 1870 as a reference year, the new IPCC 1.5°C Special Report seems to be defining “pre-industrial temperature” as the 1850-1900 average (rather than 1860-1880 as some have previously done) — this suggests that there may be utility in updating the reference year at some point to 1875 to represent the mid-point of the pre-industrial temperature range.

2) The difference between E_LU for DGVMs vs Book-keeping models in the recent decade is obviously striking (and well discussed), though I didn’t come away with any explanation for the mechanism behind this difference. Is there some change in LU patterns (used to drive DGVMs) that explains the increase from the previous decades? Or is this a reflection of some response to climate change? Some speculation could help here (even if that is all it is at this point).

3) Related to this:
- On page 18 (lines 19-20), note that DGVMs and BK models agree prior to the recent decade (but not for the most recent year / decade)
- On page 18, lines 11-12: Is this loss of additional sink capacity the same as the finding that some have shown that simulated LU emissions in models tend to increase as a function of increasing CO2, since CO2 fertilization acts equally in “agricultural” areas, and maintaining constant cropland/pasture areas in a model results in higher emissions when CO2 is higher compared to when it is lower. I think it is kind of the same process at work but I am not completely sure…

4) Section 3.2: It is worth clarifying here that the values chosen to reflect E_LU and S_LAND in the budgets for the recent decade and for 2017 reflect different (and not necessarily consistent) methods. i.e. E_LU is from Book-keeping models (which do not include lost sink capacity), whereas S_LAND is from DGVM (which does include lost since capacity). It would be worth justifying this choice (notably the choice of using the BK estimate of emissions rather than DGVMs) and noting the inconsistency more explicitly to avoid confusion comparing numbers between Tables 5 and 6.

5) In the 2018 emissions projections for China, US, EU and India, why not add red dots to Figure 5 (similar to the global value)? Also, it is striking to me that US emissions are anticipated to increase by 2.2%, which is a very large departure from the recent decreasing trend. It would be worth noting this on page 39 (lines 3-4).

6) Another potentially missing process (that is not mentioned here at all I don’t think) is the effect of terrestrial weathering. Of course this is a very small carbon flux, but some recent model studies suggest the possibility of small increases over the historical period (due to warming, increased mid/high latitude runoff, vegetation expansion …), which might account for some portion of the cumulative carbon imbalance shown here.

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ED: Reconsider after major revisions (24 Oct 2018) by David Carlson

AR by Corinne Le Quere on behalf of the Authors (19 Nov 2018) Author's response Manuscript

ED: Publish as is (19 Nov 2018) by David Carlson

AR by Corinne Le Quere on behalf of the Authors (20 Nov 2018) Author's response Manuscript

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Global Carbon Budget 2018

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