Using the climate feedback response analysis method to quantify climate feedbacks in the middle atmosphere

Kuilman, Maartje Sanne; Zhang, Qiong; Cai, Ming; Wen, Qin

doi:https://doi.org/10.5194/acp-20-12409-2020

Articles | Volume 20, issue 21

https://doi.org/10.5194/acp-20-12409-2020

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

https://doi.org/10.5194/acp-20-12409-2020

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

Articles | Volume 20, issue 21

Research article

|

30 Oct 2020

Research article |

| 30 Oct 2020

Using the climate feedback response analysis method to quantify climate feedbacks in the middle atmosphere

Maartje Sanne Kuilman, Qiong Zhang, Ming Cai, and Qin Wen

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Final revised paper (published on 30 Oct 2020)
Preprint (discussion started on 05 Mar 2020)

Interactive discussion

Status: closed

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

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RC1: 'Review', Anonymous Referee #3, 09 Mar 2020
RC2: 'Better documentation, please!', Anonymous Referee #2, 01 Apr 2020
SC1: 'Responses to some of the comments of reviewer #3', Maartje Kuilman, 20 Apr 2020
SC2: 'Responses to Reviewer #2', Maartje Kuilman, 20 Apr 2020
SC3: 'Responses to Reviewer #3', Maartje Kuilman, 20 Apr 2020
AC1: 'Final Responses to Reviewer #3', Maartje Kuilman, 06 Jun 2020
AC2: 'Final Responses to Reviewer #2', Maartje Kuilman, 06 Jun 2020

Peer-review completion

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

AR by Maartje Kuilman on behalf of the Authors (06 Jun 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (17 Jun 2020) by Farahnaz Khosrawi

RR by Anonymous Referee #3 (29 Jun 2020)

Suggestions for revision or reasons for rejection

I am sorry to say that I still have reservations about the paper in
its present form. I am afraid that there are some rather fundamental
disagreements between the authors and the reviewer so that my comments
are rather general.

My major point is that the paper is still missing a clear message,
going beyond what is already known.

Yes, in a doubled CO2 climate, the direct radiative forcing of CO2 will
lead to a cooling in the upper stratosphere, but this is certainly
well known (e.g. WMO 2018).

The cooling in the upper stratosphere, by affecting upper
stratospheric ozone chemistry (but which ozone chemistry exactly, see
below), leads to an increase in ozone (referred to in the abstract as
"ozone feedback", which leads to an increase in short-wave heating
(i.e. yields a radiative feedback that generally mitigates this
cooling) -- I agree, but again, what is new here?

The abstract states that the "temperature response due to dynamical
feedbacks is small in global average", but I find it difficult to
understand which dynamical feedbacks are meant here -- perhaps
enhanced tropical upwelling in a 2xCO2 run?

Further, it is stated that the "temperature change in the lower
stratosphere is influenced by the water vapour feedback", but again,
the processes in question here remain unclear. I suggest to state at
least what the sign of the temperature change is (increase or
decrease?) and what "water vapour feedback" means (increase or
decrease of water vapour? chemical impact of water vapour on ozone or
radiative effects of water vapour?).

What remains is an evaluation of CFRAM as a tool to study climate
change. There could be new developments here, but if the focus were
on CFRAM than the nature of the paper would be much more
methodological that it is in its present form.

I see also remaining disagreements between the authors and the reviewer
judging from the reply to my comments.

The authors state "We are not speaking here about the changes in
O3-concentration due to the ozone hole, but rather changes in ozone
concentration that are resulting from changes in the CO2
concentration."

I did not talk about the "ozone hole" either, what I am talking about
is the upper stratospheric ozone loss, which is also chlorine
driven. And enhanced levels of stratospheric chlorine are around for
many decades to come. From reading the manuscript, I assume that Cl
was set to zero, or perhaps 0.6 ppb -- but I am not sure (see also
below). I think this issue could be at least briefly addressed (if
chlorine is not relevant for the present study it should be stated in
the paper). Other chemical effects could be due to changing N2O
levels. I think it is not a good idea to remove the reference to the
WMO ozone assessment (WMO 2018) entirely.

I stated in my previous review that "it should be clearly said that
the middle atmosphere is *not* in radiative equilibrium" -- in
response the authors changed the discussion, which clearly improved
the presentation of this aspect. However I find the sentence "In the
absence of eddy motions the zonal-mean temperature would relax to a
radiatively determined state" still misleading. This sounds a bit as
this were still a possible state of the atmosphere; note that
without "eddy motions", i.e. without atmospheric waves, in a radiative
equilibrium there are no heating or cooling terms, i.e. no transport
across isentropic surfaces, in other words no Brewer-Dobson
circulation. (And I think that throughout most of the troposphere,
outside of convection, the troposphere is not dynamically unstable).

A few details:

l 214: WACCMs chemical model is associated here with CO2 changes?
What is the CO2 chemistry in WACCM? Or is it transport and changing
CO2 emissions that are relevant here?

l. 224: I think you need more documentation here on the WACCM run. I
see pre-industrial CO2 and doubled CO2 (also SSTs are
mentioned), but a lot of other fields are unclear;
e.g. stratospheric chlorine, N2O, CH4. Aerosol loading? Are
these compounds (and the entire setup) based on
"pre-industrial"? Could tropospheric ozone be relevant
(different between the runs). Perhaps you could use a
citation, where all the assumptions of the WACCM run are
described? Note that when you use pre-industrial with (just)
CO2 doubled, these doubled CO2 runs do not describe a future

l 745-748: You state "Ozone plays a major role in the chemical and
radiative budget of the middle atmosphere. The ozone
distribution in the mesosphere is maintained by a balance
between transport processes and various catalytic cycles
involving nitrogen oxides, HOx and Clx radicals." Which
transport processes with an impact on ozone are you referring
to here?

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RR by Anonymous Referee #2 (03 Jul 2020)

Suggestions for revision or reasons for rejection

\section{General comments}

The paper is now much clearer but there are still minor revisions necessary, especially concerning atmospheric chemistry.

\section{Specific comments}

Section 2.2, line 214ff: It is still not clear if the radiatively and chemically active gases CH$_4$ and N$_2$O (sometimes called well-mixed greenhouse gases) are kept at preindustrial levels in all scenarios at the surface (include in Table 1). It should be also
mentioned that there are no CFCs in the atmosphere (I hope this is the case, otherwise major revision necessary).
Are the boundary conditions for all anthropogenic emissions
kept constant in all scenarios? The remark on inconsistencies in SST in the reply should be included in the text.

Line 305ff: It is not a good idea to use the same letters for different physical quantities (power flux and heating rate). Also the
constant 'g' is not defined (gravitational acceleration?).

Line 669: Cite the original references also here, they are in the reference list.

Line 708: Only non-orographic gravity waves are modulated by convection. Please rearrange paragraph.

Line 745ff: please rewrite: HOx dominates ozone destruction in the mesosphere and lower stratosphere, NOx and Clx in the middle and upper stratosphere.
Insert in line 754 "due to the strong temperature dependence of the Chapman reaction O+O$_3$". In the preindustrial stratosphere are no
aircraft NOx-emissions and no CFCs (line 755). Cl should be only from CH$_3$Cl (forest fires etc.) This is misleading here.

Line 773ff: Please rewrite and include something like the following: If O/O$_3$ is shifted to lower values due to cooling the catalytic
ozone destruction cycles are slower since the reactions of the radicals (NO$_2$, OH, HO$_2$, ClO) with O are the rate limiting steps.

Line 783: Why? This is secondary if the scenarios are consistent. There are a lot of textbooks and review papers on stratospheric and mesospheric chemistry.

Line 788: This is very special and only relevant in case of perturbations by solar particles at solar maximum conditions.
Chlorine should be low (in total < 0.6ppbv).

Line 928: This sentence is a mess. Focus on temperature dependence of reaction rates.

Line 944ff: This is uncertain, please include remark or leave out here.

\section{Technical corrections}

Table 1: use subscripts.

Line 710: Typo

Line 736: Subscripts

line 749: Typo, also include 'e.g.' in citation.

References: Several entries are incomplete, e.g. page numbers and/or DOI missing. Line 1121: incomplete journal name.

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ED: Reconsider after major revisions (07 Jul 2020) by Farahnaz Khosrawi

AR by Maartje Kuilman on behalf of the Authors (17 Aug 2020) Author's response Manuscript

ED: Publish subject to minor revisions (review by editor) (26 Aug 2020) by Farahnaz Khosrawi

AR by Maartje Kuilman on behalf of the Authors (01 Sep 2020) Author's response Manuscript

ED: Publish as is (07 Sep 2020) by Farahnaz Khosrawi

AR by Maartje Kuilman on behalf of the Authors (13 Sep 2020) Manuscript

Short summary

In this study, we quantify the temperature changes in the middle atmosphere due to different feedback processes using the climate feedback response analysis method. We have found that the change due to the increase in CO₂ alone cools the middle atmosphere. The combined effect of the different feedbacks causes the atmosphere to cool less. The ozone feedback is the most important feedback process, while the cloud, water vapour and albedo feedback play only a minor role.