Wednesday, March 28, 2012


date: Fri Jul 11 17:27:35 2008
from: Keith Briffa <>
subject: Re: URGENT: Review of Nature manuscript 2008-05-04767A

things have been very hectic for me and I am sorry it has taken some time to do this . I
have really had to study it and several associated papers before coming to this conclusion.
My overall opinion is reject. There is little I believe that is significant here , and a
lot of implied significance and absence of clear interpretation of the results. There is
also a "new" approach to processing data hidden in the supplementary material but this is
not relevant to the substance of the paper as the later processing negates the need to use
it in the end anyway. The following section may be copied to the authors but I prefer to
remain anonymous .
I appreciate your offer to copy this review into the system for me - as I am really
overloaded with stuff, I accept. Please acknowledge receipt
thanks again
Comments to be passed to the authors on

Non-uniform interhemispheric temperature trends over the past 550 years

By R. Duncan et al

The basic message proposed by the authors in this manuscript is that the Northern
Hemisphere mean annual temperature varies, largely out of phase, with annual average
Southern Hemisphere temperatures on a characteristic timescale of about 30-60 years. One
might query whether this is saying much of interest, but the authors couch this result in
the context of statements about the roles of natural versus anthropogenically driven
inter-hemispheric temperature differences. If the paper was to provide insight into the
specific role of tropospheric aerosols and the validity of the way they have been included
in IPCC AR4 models to achieve greater consistency between observed temperatures and forced
GCM model experiments then this would provide a strong case for publication. However, I do
not feel that the manuscript does anything like this . Nor does the manuscript really
confirm that an understanding of the workings of the IPO or AMO are critical for
understanding and modelling future climate changes to any greater degree than was already
understood on the basis of instrumental analyses or model experiments.

The primary mode of instrumental temperature variability across both the North and South
Hemispheres over the 20^th century, comprises the 3-stage wide-scale warming illustrated in
Figures 1 and 2 of Parker et al. (2007). Understanding of regional and decadal-scale
differences in temperature changes over land and ocean and between North and South are
relevant for framing uncertainties in attribution studies and projections of likely warming
rates, their significance on decadal scales should not be overstated. For example, the
variance explained by the AMO and IPO in large-scale analyses of instrumental temperature
variability in the 20^th century is on the order of a few per cent (e.g. Parker et al.,
2007). This paper is not able to advance our understanding of the causes or even quantify
the changing amplitude of the IPO or AMO or the net effect of their combined influence over

Looking at the new data the authors present, it is not clear to me that the evidence for
out of phase cycling between the Northern Hemisphere reconstructions and the New Zealand
reconstructions is particularly strong or constant over the whole length of the series. Any
(even white-noise) bandpass filtered data series , when superimposed, would show periods of
in phase and out of phase behaviour. The series shown by the authors are out of phase
sometimes and not at others. We can deduce little about the past behaviour of the IPO or
AMO for either circumstance.

The characterisation of the dominant multi-decadal patterns of variability of the so-called
IPO varies in spatial signature and temporal importance depending on whether SST or NMAT
data are used as the basis data set (e.g. see Figure 3 of Parker et al., 2007 quoted by
authors). Regardless of which are used the relationships between New Zealand temperature
variations and temperatures in other parts of the Southern Hemisphere, associated with
changing IPO status are complex (and possibly seasonally dependent). This suggests that
using New Zealand as a surrogate for mean Southern Hemisphere temperatures on the decadal
timescale, may be unfounded.

The authors imply that their data are being used to imply details of contrasting
temperature trends between the northern and southern hemispheres and that these data are
the only data available to compare against the northern hemisphere average data. While it
is true that instrumental data show the AMO and IPO to be negatively correlated with New
Zealand temperatures, temperatures in other areas of the Southern Hemisphere are not. The
authors do not present a formal phase analysis or, for that matter, compare their New
Zealand bandpassed data with those from temperature series representing other regions of
the Southern Hemisphere that do exist (in South America, Tasmania and even New Zealand i.e.
as published by Cook and colleagues). The work by Cook has specifically pointed out a
characteristic peak in the variance spectrum at around 30-60 years in Tasmanian temperature
and he carried out an analysis of its changing significance through time using singular
spectrum analysis. A similar detailed formal comparison of the covariance between the
various available Southern Hemisphere data (and the Northern Hemisphere data) seems
justified. Personally, I consider the plots of the Wavelet spectra shown in Supplementary
Figure 1 of little value in this regard.

It is true that Figure 2 of the manuscript, at first sight, appears to show an intriguing,
even compelling, correlation between the series representing the sum of the IPO and AMO and
the Northern Hemisphere/New Zealand temperature difference (specifically Figure 2c).
However, previous analyses of instrumental data show New Zealand temperatures to be
negatively correlated with each of (and so also the sum of ) the IPO and AMO. As these
modes describe contrasting temperatures in the North and South Hemispheres it is to be
expected that the Northern Hemisphere minus New Zealand temperature ( or estimated
temperature fitted against it) will correlate positively .

In summary I just can not see that there is enough new information or new insight provided
in this manuscript to support publication.
At 11:33 08/07/2008, you wrote:

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Dear Professor Briffa
I am writing in reference to the manuscript by Dr Duncan and co-authors entitled
Non-uniform interhemispheric temperature trends over the past 550 years.. It has now
been a number of weeks since we sent this manuscript to you for your comments, but we
have not yet received your review. Your comments on this manuscript are valued; however,
it is of the utmost importance that we receive them as soon as possible to prevent any
further delay in making a decision on this manuscript.
You can view the manuscript and complete the review form by clicking on the link below:
Alternatively, if it would be more convenient, you may send your review directly to me
by return email. In this case, please highlight which comments are confidential and
which should be passed on to the authors.
General information for peer-reviewers is at
We look forward to receiving your comments very soon.
Yours sincerely
Faye Fornasier
This email has been sent through the NPG Manuscript Tracking System NY-610A-NPG&MTS

Professor Keith Briffa,
Climatic Research Unit
University of East Anglia
Norwich, NR4 7TJ, U.K.

Phone: +44-1603-593909
Fax: +44-1603-507784

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