IPCC WGI THIRD ASSESSMENT REPORT – (TAR)
GOVERNMENT/EXPERT REVIEW – APRIL-JUNE 2000
COLLATED EXPERT COMMENTS 
 GENERAL

General Comments
I have noticed that each chapter contains in one way or another a summary of the previous report or the progress made since then. I would encourage to have this part istitutionalized for all the chapters with emphasis on the progress  made since last report.
Guido Visconti, Università Degli Studi dell' Aquila, Italy, (Exp.)

General Comments
This reviewed draft of the Third Assessment Report of the IPCC Working Group I describing the state of the art climate change, is now quite satisfactory to me.  I have read again chapters 1, 2, 3, 4 and 5 completely with interest and thoroughly. I believe that in this moment I have no more contributions to the review.
I hope this little effort of myself will not be detrimental for the entire work.
Dr. Nadia Gamboa, Pontificia Universidad Catolica del Peru, (Exp.)

General Comments
I commend the authors for their tremendous effort in reviewing a large and wide-ranging topic. I feel the improvements over the SAR are numerous.   This is especially true for the treatment of the West Antarctic ice sheet, the particular expertise from which I review this draft report. The improvements in this latest draft are also significant and it is clear that my comments on the last revision were taken seriously.  Most of my concerns have been adequately incorporated.  I feel there some ways to correct and improve the current revision.  

My primary concern is with the misuse of a particular non-peer-reviewed report: Spouge and Vaughan (2000).  One misuse is the assignation of “majority” to a view of the report participants that I believe will be read to imply a majority view of the community.  This occurs not only in Chapter 11, but also in the Summary for Policymakers and in the Technical Summary.  The second misuse is in a quantitative statement of collapse probability made in Chapter 11 that has already been extracted by the media--a tragic violation of a document not yet intended for the public.  I state my objections more specifically below.
Robert Bindschadler, NASA Goddard Space Flight Center, USA, (Exp.)

General Comments
A recurrent criticism by the "Global Warming Naysayers" is that satelliteand radiosonde temperature observations of the troposphere show little orno warming in the last two decades in contrast to the surface temperaturedata showing a clear warming trend. (The latter are also challenged withthe "heat island" argument.)  Though some helpful corrections have beenmade to the data sets (since the SAR) from the MSU and radiosondes, thesetwo independent data sets still show remarkable agreement while stillsignificantly differing from the best available surface temperature data.This is striking in  figure 2.12.  It is also disturbing in that the modelresults are not convincingly consistent with this data.

The issue is mentioned in the Summary for Policymakers, the TechnicalSummary, and in Chapter 2.  The text addresses this difference byreference.  Recent corrections to both the radiosonde data and the MSU datasets have helped narrow the previous gap somewhat but the possibleexplanation for attribution of the remaining differences (volcaniceruptions, spatial coverage differences and ozone) however, is weak anddoes not directly address the troubling fact that the corrected radiosondeand satellite data are still remarkably well correlated, yet independentdata sets that differ from the surface observations and the model results.It would be better to say more up front about the weakness of theexplanation (or give a better one) than to give  the critics the invitationto draw attention to this point to discredit the report.   It may be thatthere should be a difference and the models haven't got it right yet.
 Arthur G. Alexiou, IOC/UNESCO, France, (Exp)

General Comments
I checked the revised version of the manuscript. My earlier corrections to the text are included.  I do not have any additional suggestions on its improvement.
Dr. Simon O. Krichak, Tel Aviv University, Israel, (Exp.)

General Comments
Fully reviewed Chapters 1, 2 and Summary for Policymakers, partly reviewed  chapters 3, 4, 5, 6, 9 and 10. Helpful is the executive summary for each chapter.  All chapters were improved since the first draft. Most of the remarks for the  first draft have been considered, however not all has been improved. For 
several figures in different chapters several curves can not or only hardly be  distinguished due to the black and white presentation of the copies. But these  problems will disappear when presenting the curves in different colours in the  original publication later. 
Heinz-Jürgen Ahlgrimm, FAL, Germany, (Exp.)

General Comment
(Please note that he is complaining to sonone called Tom Spence and not the TSU. He was not one of our designated reviewers) TSU note.
My overall GENERAL COMMENT, on the whole of IPCC TAR, is that the time given to reviewers is woefully insufficient. Your E-mail request was sent to me on April 24, 2000, and asked for a reply by May 8. Even with the "special-favor, personal extension" that you have given me till today, this is much shorter than the time allowed by Nature or Science for reviewing a single paper, let alone that customary for specialist journals. Given the purported importance of the massive document we are discussing, the time given for reviewers' input is totally inadequate.

I have discussed this point, as well as some of the following ones, with Andre Berger last Friday and with Jean Jouzel yesterday, during visits scheduled a long time ago to their respective labs. They agree with me in a general way, but I am cc'ing them on this msg., just in case they wish to clarify their viewpoints, to the extent that they differ from what is explicitly stated herein.
Michael Ghil, UCLA, USA, (Exp.)

General Comments
In general, the manuscripts are technologically complete and thorough in demonstrating what is known (and not known) about the state of the climate and climate change issues today. There are parts that focus on only the changes since the second assessment, which is appropriate. 

In light of the second assessment which concluded that “....the balance of the evidence suggests a discernable human influence on global climate....”, the balance of the evidence suggests that the findings of the third assessment will be just as strong or stronger. I believe that sentiment is too strong given the uncertainties and gaps that still exist in our knowledge regarding climate change issues. Nonetheless, the real argument may yet be the extent to which the current climate changes are naturally forced versus anthropogenically forced. Given what we know today, and the uncertainties in properly assessing climate and measuring change, I would have to lean toward the former being far more prevalent (see comments below on chapter 1).
Anthony R. Lupo,University of Missouri , USA, (Exp.)

General Comments
1. Great job by all authors!
2. A general subject index for all chapters would be helpful.
3. An index of works cited in the whole TAR would also be very useful.
Paul D. Farrar, USA(Exp.)

General Comments
The idea that climate without human intervention can only undergo “natural variability”, and that “climate change” can only result from human activity is false and fallacious. It is in conflict with all that we know of evolution and geology. It is simply wrong to assume that “ climate change” automatically implies human influence on the climate.
This fallacy is embraced by the Framework Convention on Climate Change, but the IPCC (Footnote to “Summary for Policymakers. Page 1) claim that they are prepared to accept “natural variability” as “climate change”. They are, however, unwilling to accept the truth, which is that climate can change without human intervention. 

This fallacy renders worthless several conclusions of the Report, notably, that  “there has been a discernible human influence on the climate”. The surface temperature rise, however “unprecedented” could be “natural”, and the entire Chapter  12 “Detection of Climate Change and Attribution of Causes”  should be rejected as based on a false premise.

An additional fallacy adopted by the IPCC is the claim that it is possible to “attribute”  cause and effect from a correlation.  Science can  assign probability levels of  the likelihood of a cause and effect relationship, but it can never attribute a cause and effect relationship with certainty.  This Report does not assign any quantitative probability levels to correlations.

The statistical treatment of data, and of model simulation is inadequate throughout the Report. The conventional use of 95% confidence limits for estimates is followed only for surface temperatures, but ignored elsewhere, where a single standard deviation (60% confidence) is preferred, or no indication of the level of confidence is stated. For example, in Figure 2.11 (Chapter 2, page 101) showing ocean heat, error bars are only one standard error. They should be doubled.

Linear regression is used throughout the Report without the necessary checks for linearity and autocorrelation corrections.

Models are particularly lacking in adequate statistical information of uncertainty or correlation. It is just not good enough to use qualitative and subjective estimates of “consistency”. “Goodness of fit” should be quantified. Projections from carbon cycle and climate models never have the necessary uncertainty information, and are therefore wholly unreliable.

I would like to suggest that the whole Report is checked over by a specialist in the statistical treatment of data and of  correlation procedures with a view to more scientific and  uniform treatment of data, and the overall provision of the standard quantitative measures of correlation and accuracy.

There is undue emphasis throughout on the importance of surface temperature trends measured by weather stations. Chapter 2 has 10 diagrams showing these data, but only one thoroughly confusing diagram (Figure 2.12) for other methods of global temperature measurement.  The fact that satellite and weather balloon measurements in the lower troposphere do not show a warming for the past 21 years suggests strongly that the surface data are influenced by proximity to human habitation, rather than by greenhouse warming. There is insufficient attention paid to the evidence that this is so, which is

•	A quadrupling of human population and increases in  human prosperity in the last century have led to a great increase in buildings, fuel consumption and vehicles in the vicinity of weather stations.
•	Weather stations do not take any precautions against these influences
•	Many remote weather stations do not show a warming
•	Much recent warming has been from a rise in the minimum temperature rather than the maximum
•	Recent warming took place mainly in cold climates, in winter, and at night
•	Two thirds of the weather stations operating in 1975, mainly rural, have been closed down
•	Many scientific studies have identified “urbanization” effects, but these have been underestimated, because “rural” stations are assumed to be free of such effects.
•	Vegetation growing around stations usually increases,  but is rarely reduced.
•	Airports have made a transition from  “rural” to “heat island”
•	Surface temperature compilations make inadequate corrections for urban effects

A human influence on climate  from these effects is highly likely. An influence from emissions of greenhouse gases is yet to be established.

The treatment of scenarios is confusing. There is only one  reference (in Chapter 13) to a document describing the SRES set of IPCC scenarios  and incomplete information is spread around several Chapters. There is a whole Chapter 13 on “Scenario Development” which does  mention the IPCC  SRES scenario as authored by Nakicenovic, and “under review” but gives no further details. . Several Chapters give model results from the obsolete IS92a scenario, thereby “selecting” it, in defiance of the IPCC claim that they do not favour one scenario over another. There is evidence in Chapter 4 (in Table 4.12a) that IS92a has been revised; the earlier version being referred to as “SAR” As IS92a made exaggerated assumptions of climate and social parameters for the years 1990 to 2000, this is to be welcomed, but these revisions presumably were not  used in the various reported models, and it seems that the revisions were only made for  1990-2000, whereas they should have been made throughout.

There are two different versions of the SRES scenarios in different Chapters. Chapter 4 has A1, A2, B1, B2 only, whereas the rest have A1B, A1T, A1F1, A2. B1 and B2.

The assumed atmospheric concentration figures for carbon dioxide  for the SRES scenarios were included in the First Draft, but have now been deleted. Presumably you are ashamed to admit such absurd figures. Figures for all the other gases are given in Chapter 4 including ridiculously exaggerated figures for future methane concentrations.

Chapter 13 needs to be rewritten to include explanatory material on  the IPCC scenarios.

The scenarios are merely the personal opinions of their creators, who seem uninterested in  procedures for checking whether any of the scenarios agree with past or future trends.
Recent  unwelcome changes in greenhouse gases are ignored. Carbon dioxide emissions from combustion of fossil fuels have fallen for the years 1997 and 1998. The rate of increase of  atmospheric methane has steadily decreased over the past 15 years, to a current value of zero, yet you persist in projecting increases.

The Report should be a review of published work, There is too high a proportion of references to papers that are “submitted”, “in the press”. or “in preparation”. Chapter 12 has 21% of such papers. How can you expect us to comment on material we cannot consult?

47 out of 91 models listed in Chapter 9 assume that carbon dioxide in the atmosphere is increasing at the rate of 1% a year when the measured rate of increase, for the past 33 years, has been 0.4% a year. The assumption of false figures in models in order to boost future projections is  fraudulent. What other figures are falsely exaggerated in the same way?

The use of questions as headings to paragraphs (particularly in the Summary for Policymakers and Chapter 2) is inappropriate for a supposedly scientific document, and gives the impression of a public relations exercise.
Vincent Gray, Climate Consultant, New Zealand, (Exp.)

General Comments
I would be happy to comment on the TAR. However, the deadline of 18 June mentioned in your letter makes it very difficult for me to realize your invitation. Anyway, I expressed some of my general thoughts on the matter in my earlier letter to Sir John Houghton. Besides, you can find a detailed presentation of my views on climate problems in any of my three recent monographs:
1)	“Multidimensional Global Change”, Wiley/Praxis, Chichester, 1998;
2)	“Climatic Effects of Aerosols and Clouds”, Springer/Praxis, Chichester, 1999;
3)	“Atmospheric Ozone Variability: Implications for Climate Change, Human Health and Ecosystems” (with C.A. Varotsos), Springer/Praxis, Chichester, 2000.
Prof.Dr. Kirill Ya. Kondratyev, Research Centre for Ecological Safety, Russia

General Comments
In the previous Expert Review, I noted that Chapter 2 (Observed Climate Variability and Change) was, in general, a very high quality product; I did not review other chapters at that time.

While it is still the best chapter in the WG1 document, I find that the quality of  Chapter 2 has declined some, with comments detailed below.  By extension, the rest of the document suffers greatly.  The Policymakers Summary contains several rhetorically alarming statements that are sure to misused in the hue and cry that will result from the leaking of this document at a critical time in the American election cycle.  Some of the SRES scenarios  are simply politically correct fantasies that are logically inconsistent. 

Ironically, the likely answer on the sensitivity of climate change has already been determined, unless IPCC wants to argue that the functional form of almost every climate model is wrong (I choose my words carefully here).  What no one knows is how technology will ultimately evolve.  But what we DO know is that any assumption of similar technology over the course of the next several centuries flies in the face of history.

Note that the Technical Summary and the SPM are reviewed after the Chapters.
Patrick  J. Michaels, University of  Virginia, USA, (Exp.)

General Comments
In order to facilitate the reading of the document which contains many abbreviations, we hope to add at the beginning (or at the end) of the report an alphabetical index table which contains all the nomenclature used in the report: for example: RCMs: Regional Climate Models, Etc ...
A. Mokssit and S. El Khatri, Meteorological Office, Morocco (Exp.)

General Comments
On expression of atmospheric abundance of trace gases such as greenhouse gases.

It would seem that the IPCC reports should strive for precision (and consistency) in expression of quantities and units.  Yet there is lack of both in the report, specifically with respect to abundance of greenhouse gases.  

In precise work it is now accepted that the quantity by which the local abundance of a gas is best expressed is the mixing ratio with respect to dry air.  This is a dimensionless quantity, so it is appropriate to use a unit such as ppm or ppb.  More specifically the mixing ratio is a mixing ratio by mole, so that ppb is shorthand for nmole per mole of dry air.  Cognizant international bodies such as IUPAC (the International Union of Pure and Applied Chemistry) deprecate any qualifier on the unit ppb, such as "ppbv"; rather it is the quantity, i.e., mixing ratio, that should be qualified, e.g., "volume mixing ratio is 1760 ppb", not "mixing ratio is 1760 ppbv"; one might hope that IPCC would strive to conform to recommendations of such an international union of national scientific societies.  Note also that the quantity of choice is mixing ratio by mole, and not by volume, although these are essentially identical (within the approximation of the ideal gas law), as it is generally the amount of material (moles) of the trace gas that is determined not its volume.

Note that the mixing ratio is NOT a concentration.  Strictly "concentration" refers to an amount of material (mass, moles) per volume.  Concentration of a trace gas that is well mixed in the atmosphere depends on temperature and pressure whereas mixing ratio does not.  It is for this reason that mixing ratio is preferred to concentration, although many investigators loosely use the terms synonymously.  IPCC should decide whether it wants to be precise and formal or informal, imprecise (and incorrect).  

Note also that for the well mixed greenhouse gases it is imperative (in precise work, such as would appear in a journal) to specify that the quantity being reported is mixing ratio relative to dry air.  Water vapor mixing ratio is highly variable and can be up to several percent; hence the need to refer all mixing ratios to dry air.

The document as it stands is inconsistent in terminology.  Mostly (perhaps even exclusively) the term "concentration" is used rather than mixing ratio.  The unit is sometimes given as ppm, ppb, ppt (parts per trillion), without qualifier (v), e.g., technical summary.  Sometimes the qualifier is retained, i.e., ppmv, ppbv (chapter 6, p 39, line 47, and elsewhere; chapter 14, page 8, lines 40-42 and elsewhere).   Attention should be paid also to captions and axis labels of figures (e.g., Figure 9.15, concentrations, ppbv; Tech Summary, Figure 18, concentrations, ppm) and to column heads of tables (Tech Sum, Table 1, ppm but ppbv, pptv).  

Finally one should perhaps note that although the Dobson Unit is widely employed as a measure of column burden, it is not universally known, and should definitely be defined on first use, e.g., Chapter 6, page 16, line 44.  
Stephen E. Schwartz, Brookhaven, USA (Exp)

Genaral style comment
I suggest that the first person plural ("we", "our") be avoided.  The pronoun is inevitably ambiguous:  Does it refer to the authors, the scientific community?  I give instances of suggested change in language.  I suggest do a search and replace as appropriate throughout.  
Stephen E. Schwartz, Brookhaven, USA (Exp)

General Comments
1. It is unfortunate the the recent version of TAR makes no reference to the ease which nitrous oxide emission may be reduced at the source, as described in references cited in my original comments. 
2. It is equally unfortunate that the TAR understates the current impact of nitrous oxide on global warming (now 13% that of carbon dioxide) by averaging data from pre-industrial times to the present.  Significant ncrease in atmospheric nitrous oxide began around 1960, when improved Haber-Bosch synthesis led to sharp increase of use of fertilizer nitrogen from 10 million metric tons in 1960 to 85 million tons today
Marshall Spector, University of Virginia, USA, (Exp.)  

General Comments

Executive Summary
This individual review paper focuses on IPCC's three most essential modelling and core parameter errors. The impacts on all modelling results would be so tremendous that if the TAR would be corrected for these errors, there would hardly be any more justification for it. So this paper addresses only few individual TAR fallacies, but focuses on the nondisclosed flawed science it is based on.

Solar impacts
Taking into account the impact of solar variability on global warming, best fit studies have revealed that solar forcing is amplified by at least a factor 4. By leaving out this 'Svensmark factor' and using an exaggerated aerosol cooling, IPCC maintains a CO2 doubling sensitivity of 2.5 °C that is about a factor 3 too high.

Carbon cycle
Our global Carbon Cycle Model reveals a half-life time of only 38 years for any CO2 excess. With present constant global CO2 emission until 2100, the temperature would only further increase by 0.15 °C. Scenario IS92a would end up with 571 ppm only. IPCC assumed that far more fossil reserves would be burnt than being available. Using a flawed eddy diffusion ocean model, the IPCC has grossly underestimated the future oceanic CO2 uptake. Hardly coping with biomass response, limited fossil reserves and using a factor 4 temperature sensitivity, all this leads to an IPCC exaggeration factor of about 6 in yr 2100. The usable fossil reserves of 1300 GtC burnt by 2090, merely cause 548 ppm – not even a doubling. The WRE 650, 750 and 1000 ppm scenarios, projected until 2300, are infeasible. Emission reduction is absolutely useless: the realistic temperature effect of Kyoto till 2050 will be only 0.02 °C.

Radiative forcing
The additional IR absorption (being evaluated here for CO2 doubling) is the energy source for global warming. HITRAN transmission spectra – the fringes being by no means saturated yet – can be used to compute this absorption, mostly occurring near ground. A simple radiative energy equilibrium model of the troposphere yields an IPCC-conforming radiative forcing which is here defined as the additional energy re-radiated to ground. Coping with water vapor overlap on the low frequency side of the 15 µm band, the clear sky CO2 forcing is considerably reduced to 1.9 W/m². With vapor feedback and for cloudy sky the equilibrium ground warming will be about 0.4 to 0.6 °C only – a factor 4 to 6 less than IPCC's 'best guess' for CO2 doubling.
The detailed paper titled "IPCC's most essential model errors" is in HTML, with 16 figures at http://www.microtech.com.au/daly/moderr.htm. I am a known contrarian (see John Daly's Website), and I suppose IPCC can hardly cope with my arguments. So as I basically do not consent with the TAR, please do not use my name within the listing of reviewers.
Peter Dietze, Germany, (Exp.)