Drivers of multi-century trends in the atmospheric CO<sub>2</sub> mean annual cycle in a prognostic ESM

Liptak, Jessica; Keppel-Aleks, Gretchen; Lindsay, Keith

doi:https://doi.org/10.5194/bg-14-1383-2017

Articles | Volume 14, issue 6

https://doi.org/10.5194/bg-14-1383-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/bg-14-1383-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 14, issue 6

Research article

|

20 Mar 2017

Research article |

| 20 Mar 2017

Drivers of multi-century trends in the atmospheric CO₂ mean annual cycle in a prognostic ESM

Jessica Liptak, Gretchen Keppel-Aleks, and Keith Lindsay

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Final revised paper (published on 20 Mar 2017)
Preprint (discussion started on 05 Apr 2016)

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Status: closed

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

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RC1: 'Multicentury trends in CO2', Anonymous Referee #1, 17 Jun 2016
- AC1: 'Responses to Reviewer 1', Jessica Liptak, 08 Aug 2016
RC2: 'Review of "Drives of Multicentury Trends in the atmospheric CO2 mean annual cycle in a prognostic ESM"', Anonymous Referee #2, 11 Jul 2016
- AC2: 'Responses to Reviewer 2', Jessica Liptak, 08 Aug 2016

Peer-review completion

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

ED: Reconsider after major revisions (09 Sep 2016) by Laurent Bopp

AR by Jessica Liptak on behalf of the Authors (21 Oct 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (04 Nov 2016) by Laurent Bopp

RR by Anonymous Referee #2 (11 Jan 2017)

Suggestions for revision or reasons for rejection

I thank the author for their detailed responses to my comments. They made a substantial effort to account for most of the concerns i raised with thorough responses and the needed clarifications in the text for a better understanding of the paper objectives and methodology (in particular the pulse response approach).

The description of the context of the study has been significantly improved (especially with respect to recent publications) with a refinement of the focus of the paper; the objectives are now less on the understanding of the drivers of the atmospheric CO2 amplitude increase but more on how this observational constraint could be used with a couple carbon - climate model and how the driver of the CO2 amplitude increase may change in the 2300 time horizon.

Although i still believe that current model structure (related to CESM1 version that is used) limits the biogeochemical conclusions that could be drawn for the horizon 2100 - 2300 (lack of permafrost, dynamic vegetation and ecosystem management (crops)), the paper can bring some interesting methodological/theoretical contributions to the existing literature around the valorisation of the atmospheric CO2 amplitude changes. With this context in mind i would encourage the author to slightly improve the text to emphasize especially in the discussion on the methodological aspects and to draw further recommendations for other ESM modeling groups with respect to « how to use the constraint from atmospheric CO2 amplitude growth".

Finally as a little remark it seems to me that the discussion on the Water Use Efficiency, although welcome, should be more precise. The authors conclude that from a simulation without radiative forcing (but including CO2 fertilization effects), soil water content increases by 1% on average and suggest improved WUE by vegetation. This seems not so obvious as changes in precipitation, relative humidity, … complicate the relation and they probably have the model output to diagnose the effective WUE or even the intrinsic one.

Note also that the discussion contains now only one sub-section « 4.1 » which seems strange.

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ED: Publish subject to minor revisions (Editor review) (16 Jan 2017) by Laurent Bopp

AR by Jessica Liptak on behalf of the Authors (10 Feb 2017) Author's response Manuscript

ED: Publish as is (21 Feb 2017) by Laurent Bopp

AR by Jessica Liptak on behalf of the Authors (27 Feb 2017)

Short summary

We analyzed the evolution of the atmospheric CO₂ mean annual cycle simulated during 1950–2300 under three scenarios designed to separate the effects of climate change, CO₂ fertilization, and land use change. CO₂ fertilization in boreal and temperate ecosystems drove mean annual cycle amplification over the NH midlatitudes during 1950–2300. Boreal and Arctic climate change drove high-latitude amplification before 2200, after which CO₂ fertilization contributed nearly equally to amplification.

Drivers of multi-century trends in the atmospheric CO2 mean annual cycle in a prognostic ESM

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Drivers of multi-century trends in the atmospheric CO₂ mean annual cycle in a prognostic ESM