Geoengineering as a design problem

Kravitz, Ben; MacMartin, Douglas G.; Wang, Hailong; Rasch, Philip J.

doi:https://doi.org/10.5194/esd-7-469-2016

Articles | Volume 7, issue 2

https://doi.org/10.5194/esd-7-469-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/esd-7-469-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 7, issue 2

Research article

|

24 May 2016

Research article |

| 24 May 2016

Geoengineering as a design problem

Ben Kravitz, Douglas G. MacMartin, Hailong Wang, and Philip J. Rasch

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Final revised paper (published on 24 May 2016)
Preprint (discussion started on 08 Sep 2015)

Interactive discussion

Status: closed

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

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- Supplement

RC C554: 'Review of Geoengineering as a Design Problem', Anonymous Referee #1, 16 Sep 2015
- AC C748: 'Response to reviewer #1', Ben Kravitz, 03 Nov 2015
RC C624: 'anonymous review', Anonymous Referee #2, 06 Oct 2015
- AC C749: 'Response to reviewer #2', Ben Kravitz, 03 Nov 2015

Peer-review completion

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

AR by Ben Kravitz on behalf of the Authors (03 Nov 2015) Author's response Manuscript

ED: Referee Nomination & Report Request started (18 Nov 2015) by Hermann Held

RR by Anonymous Referee #1 (01 Dec 2015)

RR by Anonymous Referee #2 (11 Jan 2016)

Suggestions for revision or reasons for rejection

I think that the manuscript has considerably improved through the revision. And I only have a few further concerns specified below.

The authors now discuss more carefully the implications of their proposed control strategy for actually geoengineering the climate. This is in particular true for the introduction. I’m still not fully happy of the discussion in the final section. The authors still state that they had “demonstrated the ability to simultaneously manage multiple climate criteria using the common approach of changing solar irradiance”. The common approach is to reduce solar irradiance. In one of the examples (2x2 with the CESM) it is clearly shown that the design goals can’t be reached by reducing solar irradiance. Why not stating this very clearly instead of vaguely saying that “accomplishing the objectives with physically achievable mechanisms […] introduces additional complications”. In particular as it is stated in the introduction now, that “it may not be possible to achieve all objectives due to physical constraints”, it is nice to come back to this statement in the conclusions with an example.

I had suggested to remove Fig. 1 because I thought it is a banality that more or less reducing the irradiance would reduce the global temperature more or less. As the authors have argued against it I looked at Fig. 1 a bit more carefully than in the first review. I agree now that the Figure is interesting but in a very different sense which I think needs further discussion. I would have guessed that a smaller reduction of solar irradiance (as in the middle panel compare to the top panel) should increase the temperature almost globally. While a reduction seems to be simulated in some areas (like Northern Africa or the North Atlantic) in other regions (e.g. polar regions and tropical oceans) the opposite is simulated. Am I missing something, here? If there is no error in my thinking or the figures I’d consider this an interesting example for non-linearity which would render the optimization difficult even with just one control parameter.

I’m still not totally happy with the use of the references to Kalidindi et al. (2014), Ferraro et al. (2014), and Niemeier et al. (2013). It sounds now like there was a consensus that different SRM methods would produce only regionally different responses. However, the latter two papers specifically argue also for global differences, even if one may consider them relatively small.

Apparently also the other reviewer doesn’t feel fully comfortable with reviewing the large part of the paper (Section 3) dealing with the design of the feedback strategy which albeit may seem the central part of this manuscript. It may hence be advisable to search for a specialist in this area for such a review.

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ED: Publish subject to minor revisions (review by Editor) (17 Mar 2016) by Hermann Held

AR by Ben Kravitz on behalf of the Authors (18 Mar 2016) Author's response Manuscript

ED: Publish as is (10 May 2016) by Hermann Held

AR by Ben Kravitz on behalf of the Authors (10 May 2016)

Short summary

Most simulations of solar geoengineering prescribe a particular strategy and evaluate its modeled effects. Here we first choose example climate objectives and then design a strategy to meet those objectives in climate models. We show that certain objectives can be met simultaneously even in the presence of uncertainty, and the strategy for meeting those objectives can be ported to other models. This is part of a broader illustration of how uncertainties in solar geoengineering can be managed.