Carbon Monitoring System Flux Net Biosphere Exchange 2020 (CMS-Flux NBE 2020)

Liu, Junjie; Baskaran, Latha; Bowman, Kevin; Schimel, David; Bloom, A. Anthony; Parazoo, Nicholas C.; Oda, Tomohiro; Carroll, Dustin; Menemenlis, Dimitris; Joiner, Joanna; Commane, Roisin; Daube, Bruce; Gatti, Lucianna V.; McKain, Kathryn; Miller, John; Stephens, Britton B.; Sweeney, Colm; Wofsy, Steven

doi:https://doi.org/10.5194/essd-13-299-2021

Articles | Volume 13, issue 2

https://doi.org/10.5194/essd-13-299-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/essd-13-299-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 13, issue 2

Data description paper

|

10 Feb 2021

Data description paper |

| 10 Feb 2021

Carbon Monitoring System Flux Net Biosphere Exchange 2020 (CMS-Flux NBE 2020)

Junjie Liu, Latha Baskaran, Kevin Bowman, David Schimel, A. Anthony Bloom, Nicholas C. Parazoo, Tomohiro Oda, Dustin Carroll, Dimitris Menemenlis, Joanna Joiner, Roisin Commane, Bruce Daube, Lucianna V. Gatti, Kathryn McKain, John Miller, Britton B. Stephens, Colm Sweeney, and Steven Wofsy

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Final revised paper (published on 10 Feb 2021)
Preprint (discussion started on 07 Jul 2020)
Supplement to the preprint

Interactive discussion

Status: closed

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

- Printer-friendly version

- Supplement

RC1: 'Concerns about the completeness of the dataset', Julia Marshall, 28 Jul 2020
- AC1: 'Response to reviewer 1', Junjie Liu, 02 Sep 2020
RC2: 'referee report on CMS-Flux NBE 2020', Anonymous Referee #2, 07 Aug 2020
- AC2: 'Response to reviewer 2', Junjie Liu, 02 Sep 2020

Peer-review completion

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

AR by Junjie Liu on behalf of the Authors (30 Sep 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (07 Oct 2020) by David Carlson

RR by Julia Marshall (02 Dec 2020)

Suggestions for revision or reasons for rejection

I’m happy to see that the authors have taken up many of the reviewer suggestions. In particular, the comparison to the NOAA background sites in Figure 12 proved to be quite interesting. What is going on in the Southern Hemisphere from 2013 onward? This is really surprising, and seems hard to explain, especially as the agreement was rather good prior to 2013. It’s a pity that the fluxes for the TransCom ocean regions weren’t compared to those from the other global inversions used for comparison in Figure 8 to try to get to the root of the problem. Is there some change in the quality of the GOSAT data that could explain this, and is it fair to conclude that the OCO-2-based inversion (from 2015) does not provide fluxes consistent with the surface stations in the Southern Hemisphere?

In the very first sentence of the paper it is stated that “satellite observations provide an important complement to global aggregated fluxes and inversions based on surface CO2 observations, especially over the tropics and the Southern Hemisphere where conventional surface CO2 observations are sparse”. This suggests that the OCO-2 optimized fluxes might be more believable in this region, but the comparison to independent measurements (surface sites and ATOM-1, in Figures 12 and 10 respectively) does not support this.

In light of this I would argue that the conclusions have to be softened somewhat. The authors state that “the estimated posterior flux uncertainty agrees with the expected uncertainty in the posterior fluxes based on the comparison to aircraft CO2 observations”. (Should the “posterior fluxes” be “posterior concentrations” here maybe? I wasn’t sure.) At the same time they acknowledge that the RMSE/RMSE_MC ratio is well over one for some regions when compared to aircraft data, most notably over the Atlantic during ATOM-2, over the Southern Ocean during ATOM-1, and at high latitude during HIPPO-4. These cases are further studied in the supplement, and the new comparison to surface stations suggest that something is pretty systematically off in the Southern Hemisphere. As such, I think that the suggestion that the aircraft measurements suggest a good agreement and appropriate uncertainties needs some caveats.

I understand that the partitioning into GPP has been left out of this paper, which I described as a lack of completeness in my first review. I do wonder about the GPP reported in Figure S4 though: it seems that the partitioning was indeed carried out and partially discussed, but not included in the dataset release. Or does this figure show the FLUXSAT-GPP product? The caption and the reference to the figure in the text do not make it clear. In the end the decision about whether the dataset is complete or has arbitrarily been split to result in more publications is an editorial one.

Minor typographical/grammar comments (some for the second time…):

L19: Researc -> Research

L32: remove “the” before “NASA’s”

L148: its -> their (fluxes is plural)

L152: CARDAMOM -> The CARDAMOM

L154: following a similar Bayesian approach used -> following a Bayesian approach similar to that used

L227 & L230: the variability of annual total -> the variability of the annual total

L229: of OCO-2 -> of the OCO-2

L563: over Southern -> over the Southern

L564: The posterior CO2 -> The posterior CO2 concentrations

Figure 8: Australia is missing an “l”.
In the supplement:

Figure S5: Is this just for surface fluxes at every grid point over land? Or only for the sensitivity to NBE? I’m surprised that the ocean has no influence at all, otherwise. Also: for this and the following plots, I guess that it should be clarified that the sensitivity of “posterior CO2 concentrations” is meant, and the adjoint is “carried out over” such-and-such a time period.

Figure S6: over Pacific -> over the Pacific

Figure S7: see comment to S6. Also: why not put the titles at the top, as in S6?

S8-S10: See caption comments for S5.

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ED: Publish subject to minor revisions (review by editor) (06 Dec 2020) by David Carlson

AR by Junjie Liu on behalf of the Authors (08 Dec 2020) Author's response Manuscript

ED: Publish subject to minor revisions (review by editor) (20 Dec 2020) by David Carlson

Page 19, lines 493-494: Author cite Friedlingstein 2019 for the most recent GCB but their summary in these lines misses two source terms of the global carbon budget. Technically I think we would call annual growth in atmospheric CO2 concentrations the 'net' of sources and sinks, not the 'sum'.

Page 20, lines 505-506: Authors change units here (from GtC to %) but they have not quoted GCB correctly. For decade 2009-2018, GCB has ocean sink at 2.5 +/- 0.6 GtC yr-1 and land sink at 3.2 +/- 0.6 GtC yr-1. Land significantly greater than ocean in GCB while these authors have ocean greater than land. Something wrong somewhere. Reader can not accept (line 507) that these numbers fit within uncertainty of GCB numbers.

Authors here refer to GCP (Global Carbon Project?)? Friedlingstein 2019 refers to GCB: global carbon budget. Neither Friedlingstein 2019 nor Friedlingstein 2020 make any mention of NBE. This section (4.1) needs complete rewrite: use correct terms, adopt consistent units (GtC or %) but not both, line 507 conflicts with line 516-517. NBE as defined here does not match terms from GCB. What happened to cement? Do these authors adopt the same +/- 1 sigma as GCB? ESSD readers who might take an interest in this product will very likely know GCB in good detail to detect deficiencies here.

Line 552 - TER not defined. Not defined until line 712.

Line 733: Authors refer to GCP when they mean GCB. Fix all of these errors! GCP 2019 not a valid citation, Friedlingstein 2019 is.

Line 738 to 746, illogical. Continental US (CONUS) and state-level of CONUS have very good observational data (ground and aircraft). Therefore, observational basis of CO2 emission for these particular regions (authors do NOT go to state level) will likely always prove more reliable (less uncertain) than satellite xCO2. Unreliable estimates of NBE, no matter how well distributed over CONUS, will never prove more reliable than obs here. But validation here can add credibility to xCO2 inversions elsewhere? Authors current paragraph implies that because NBE varies a lot regionally or seasonally, it will prove useful here. Not likely. 1.5 C target (hopeful) comes from UNFCCC CoP21 Paris Agreement, not from IPCC AR6. IPCC AR6 never cited here.

Supplement consists entirely of figures, with some redundancy to main text. Because Copernicus does not archive supplements, this supplement needs to go on the JPL site or these 11 figures need to go in the Appendix.

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AR by Junjie Liu on behalf of the Authors (21 Dec 2020) Author's response Manuscript

ED: Publish as is (23 Dec 2020) by David Carlson

AR by Junjie Liu on behalf of the Authors (29 Dec 2020) Manuscript

Short summary

On average, the terrestrial biosphere carbon sink is equivalent to ~ 20 % of fossil fuel emissions. Understanding where and why the terrestrial biosphere absorbs carbon from the atmosphere is pivotal to any mitigation policy. Here we present a regionally resolved satellite-constrained net biosphere exchange (NBE) dataset with corresponding uncertainties between 2010–2018: CMS-Flux NBE 2020. The dataset provides a unique perspective on monitoring regional contributions to the CO₂ growth rate.