Tropical Pacific climate variability under solar geoengineering: impacts on ENSO extremes

Malik, Abdul; Nowack, Peer J.; Haigh, Joanna D.; Cao, Long; Atique, Luqman; Plancherel, Yves

doi:https://doi.org/10.5194/acp-20-15461-2020

Articles | Volume 20, issue 23

https://doi.org/10.5194/acp-20-15461-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-20-15461-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 20, issue 23

Research article

| Highlight paper

|

11 Dec 2020

Research article | Highlight paper |

| 11 Dec 2020

Tropical Pacific climate variability under solar geoengineering: impacts on ENSO extremes

Abdul Malik, Peer J. Nowack, Joanna D. Haigh, Long Cao, Luqman Atique, and Yves Plancherel

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Final revised paper (published on 11 Dec 2020)
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Preprint (discussion started on 07 Jan 2019)
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Interactive discussion

Status: closed

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

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RC1: 'Review of Malik et al.', Anonymous Referee #1, 15 Feb 2019
- AC1: 'Response to Referee 1', Abdul Malik, 29 Aug 2020
SC1: 'Does HadCM3L really have a good representation of ENSO?', Peter Irvine, 27 Mar 2019
- AC3: 'ENSO representation in HadCM3L', Abdul Malik, 29 Aug 2020
RC2: 'Major comments on the manuscript titled Tropical Pacific Climate Variability under Solar Geoengineering: Impacts on ENSO Extremes', Anonymous Referee #2, 27 Apr 2019
- AC2: 'Response to Referee 2', Abdul Malik, 29 Aug 2020

Peer-review completion

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

AR by Abdul Malik on behalf of the Authors (29 Aug 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (21 Sep 2020) by Timothy J. Dunkerton

RR by Anonymous Referee #1 (07 Oct 2020)

Suggestions for revision or reasons for rejection

This paper has been well revised and the authors are thanked for their effort. I only have minor comments below.

Add *a slight* in this sentence: “Overall there is a change in sign and reduction of MSSTG in 4×CO2 (~-111 %, 99 % cl) and only *a slight* decrease in G1 (~-9 %, 99 % cl) (Fig. S3, and Table S2).” (Section 3.1.4, page11, lines 17-19)

There are many instances where the authors state that the model can “reproduce” observed events. It would be better to replace “reproduce” (which sounds like an exact copy) with “reasonably simulate or capture”.

Regarding the definition of E-index and C-index, in the original definition by Takahashi et al. 2011, the first and second principal components PC1, PC2 are first normalized before calculating the E-Index, C-Index. Please ensure that this is mentioned. Takahashi et al. 2011 defined the E-Index and C-Index; Cai et al. 2018 applied these indices.

P10, L24-40: On definition of Westerly Wind Burst and Easterly Wind Burst. These winds are ought to be identified using daily wind data (e.g., in Hu and Fedorov 2016). If this is not the case, please reword, e.g., “although not explicitly diagnosed, WWB and EWB are contained respectively in the positive and negative values of this wind index.” Then please be careful with calling them WWBs and EWBs in the rest of the manuscript.

P15, L10-12: “Note that Wang et al. (2020) showed that extreme convective events can still happen even if the E-index is not greater than 5 mm day-1 (cf. 12 Figure 2 in Wang et al. 2020).” – E-index cannot be in the unit of mm/day.

P15, L24-41: On La Nina frequency change. The fact that there are no extreme La Nina events in 4xCO2 experiment is inconsistent with Cai et al. 2015. A remark on this is necessary to avoid confusion to description in L34-41 on G1.

P17, L3-23: Increased upper ocean stratification tends to enhance the Bjerknes feedback, likely through the coupling between the wind and thermocline. This is not yet diagnosed in this present analysis which instead represents the Bjerknes feedback solely on the coupling between SST and wind. The Bjerknes feedback has many components (e.g., Kim and Jin 2011), and some may increase and some may decrease under external forcing. It would be good to put a caveat like this in this paragraph.

The curve fitting in Fig. S1 (red curve) does not look a smooth parabolic.

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RR by Anonymous Referee #2 (07 Oct 2020)

ED: Publish as is (18 Oct 2020) by Timothy J. Dunkerton

AR by Abdul Malik on behalf of the Authors (28 Oct 2020) Author's response Manuscript

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Short summary

Solar geoengineering has been introduced to mitigate human-caused global warming by reflecting sunlight back into space. This research investigates the impact of solar geoengineering on the tropical Pacific climate. We find that solar geoengineering can compensate some of the greenhouse-induced changes in the tropical Pacific but not all. In particular, solar geoengineering will result in significant changes in rainfall, sea surface temperatures, and increased frequency of extreme ENSO events.