Granger causality from changes in level of atmospheric CO<sub>2</sub> to global surface temperature and the El Niño–Southern Oscillation, and a candidate mechanism in global photosynthesis

Leggett, L. M. W.; Ball, D. A.

doi:https://doi.org/10.5194/acp-15-11571-2015

Articles | Volume 15, issue 20

https://doi.org/10.5194/acp-15-11571-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/acp-15-11571-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 15, issue 20

Research article

|

21 Oct 2015

Research article |

| 21 Oct 2015

Granger causality from changes in level of atmospheric CO₂ to global surface temperature and the El Niño–Southern Oscillation, and a candidate mechanism in global photosynthesis

L. M. W. Leggett and D. A. Ball

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Final revised paper (published on 21 Oct 2015)
Supplement to the final revised paper
Preprint (discussion started on 21 Nov 2014)
Supplement to the preprint

Interactive discussion

Status: closed

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

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- Supplement

RC C10403: 'Comments on “First and second derivative atmospheric CO2, global surface temperature and ENSO” By L. Leggett and D. Ball', Anonymous Referee #1, 22 Dec 2014
RC C11720: 'Bringing the first review stage to a conclusion', Rob MacKenzie, 31 Jan 2015
AC C12527: 'Interactive comment', Mark Leggett, 06 Mar 2015
AC C12956: 'Author response', Mark Leggett, 08 Apr 2015
AC C12957: 'Manuscript', Mark Leggett, 08 Apr 2015

Peer-review completion

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

AR by Mark Leggett on behalf of the Authors (08 Apr 2015) Author's response Manuscript

ED: Referee Nomination & Report Request started (29 Apr 2015) by Rob MacKenzie

RR by Anonymous Referee #1 (07 May 2015)

ED: Reconsider after major revisions (07 May 2015) by Rob MacKenzie

AR by Mark Leggett on behalf of the Authors (16 Jun 2015)

ED: Referee Nomination & Report Request started (16 Jun 2015) by Rob MacKenzie

RR by Anonymous Referee #1 (16 Jul 2015)

Suggestions for revision or reasons for rejection

This is, yet again, virtually a new paper, but much the best of the three. It is generally clearly written and presents what seems to me to be some very interesting evidence. I think that their findings are likely to be robust to any reasonable changes of technique and, as such, deserve consideration.

In particular, in the matter of series smoothing which I raised previously, they claim (in the supplement) to show that their results are not affected by this. I am still not entirely convinced that the difference between seasonal adjustment (which removes specifically seasonal frequencies) and moving average smoothing (which attenuates all higher frequencies) is fully appreciated. But never mind, I think that they have made their point on this, that their transformations do not materially affect their findings. They correctly point out that transformations of stationary series cannot induce spurious correlations between unrelated series, even if they could mask existing correlations.

Evidence of a significant relation between temperature and growth in CO2 concentration would appear to be of considerable importance to the AGW debate. If long-term global warming really does require continuously accelerating growth in CO2, that fact immediately throws light on the current "pause", and also dramatically changes the prospects for the next 50-100 years. Of course, at the moment this is just a data regularity, and the lack of any established geophysical theory to explain it is a problem. One could suggest that there are regulatory mechanisms in play that respond as a negative feedback, but it would help to know what these are. These authors are aware of the issue and they suggest a role for the biosphere, the known fact of faster photosynthesis in the presence of higher CO2 concentrations. They claim some statistical support for a role for NDVI. Section 4.4 still seems to me a bit weak and speculative (and could be deleted from the paper without loss) but this evidence, such as it is, maybe is worth mentioning.

While by no means perfect, the paper could help to stimulate further research on these important questions. If I have one comment they might be asked act on, it relates to their third paragraph on page 21. Comment 9 of my last report pointed out that this test result is a logical implication of their findings on integration order, not a new finding. They have ignored this comment; they should point out clearly that correlations between stationary and nonstationary series are not well defined.

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RR by Anonymous Referee #3 (28 Aug 2015)

ED: Reconsider after minor revisions (Editor review) (31 Aug 2015) by Rob MacKenzie

AR by Mark Leggett on behalf of the Authors (13 Sep 2015) Author's response Manuscript

ED: Publish subject to technical corrections (30 Sep 2015) by Rob MacKenzie

AR by Mark Leggett on behalf of the Authors (07 Oct 2015) Manuscript

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Short summary

The previously expected linear relationship between atmospheric CO2 and climate variables including temperature is showing an increasing mismatch. This paper nonetheless provides fresh and possibly definitive support for a major relationship between CO2 and climate. Granger causality analysis provides evidence that change in level not level of CO2 primarily influences both global temperature and the El Niño–Southern Oscillation. The results may contribute to the prediction of future climate.

Granger causality from changes in level of atmospheric CO2 to global surface temperature and the El Niño–Southern Oscillation, and a candidate mechanism in global photosynthesis

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Interactive discussion

Peer-review completion

Granger causality from changes in level of atmospheric CO₂ to global surface temperature and the El Niño–Southern Oscillation, and a candidate mechanism in global photosynthesis