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Report of the International Panel set up by the University of East Anglia to 

examine the research of the Climatic Research Unit.

Introduction 

1. The Panel was set up by the University in consultation with the Royal Society 

to assess the integrity of the research published by the Climatic Research Unit 

in the light of various external assertions. The Unit is a very small academic 

entity within the School of Environmental Sciences. It has three full time and 

one part time academic staff members and about a dozen research associates, 

PhD students and support staff. The essence of the criticism that the Panel was 

asked to address was that climatic data had been dishonestly selected, 

manipulated and/or presented to arrive at pre-determined conclusions that 

were not compatible with a fair interpretation of the original data. The 

members of the Panel are listed in Appendix A at the end of this report. 

2. The Panel was not concerned with the question of whether the conclusions of 

the published research were correct. Rather it was asked to come to a view on 

the integrity of the Unit’s research and whether as far as could be determined 

the conclusions represented an honest and scientifically justified interpretation 

of the data. The Panel worked by examining representative publications by 

members of the Unit and subsequently by making two visits to the University 

and interviewing and questioning members of the Unit. Not all the panel were 

present on both occasions but two members were present on both occasions to 

maintain continuity. About fifteen person/days were spent at the University 

discussing the Unit’s work. 

3. The eleven representative publications that the Panel considered in detail are 

listed in Appendix B. The papers cover a period of more than twenty years and 

were selected on the advice of the Royal Society. All had been published in 

international scientific journals and had been through a process of peer review. 

CRU agreed that they were a fair sample of the work of the Unit. The Panel 

was also free to ask for any other material that it wished and did so. 

Individuals on the panel asked for and reviewed other CRU research materials. 

4. The Panel’s work began with a detailed reading of the published work. Every 

paper was read by a minimum of three Panel members at least one of whom 

was familiar with the general area to which the paper related. At least one of 

the other two was a generalist with no special climate science expertise but 

with experience of some of the general techniques and methods employed in 

the work. Most of the members of the Panel read all the publications. The 

publications provided a platform from which to gain a deeper understanding of 

the Unit’s research and enabled the Panel to probe particular questions in more 

detail. 
 

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5. Broadly the work of the Unit falls into two parts: 

• Construction and interpretation of tree ring chronologies extending 

over some thousands of years with a view to gaining information about 

past climates: 

• Studies of temperatures over the last few hundred years from direct 

observations. 

Dendroclimatology 

1. Tree growth is sensitive to very many factors including climate. By piecing 

together growth records from different trees, living or dead, it is possible to 

determine the temporal variation of growth patterns going back many 

hundreds of years. The dendroclimatological work at CRU seeks to go beyond 

this and to extract from the dated growth patterns the local and regional history 

of temperature variations. The Unit does virtually no primary data acquisition 

but has used data from published archives and has collaborated with people 

who have collected data. 

2. The main effort of the dendroclimalogists at CRU is in developing ways to 

extract climate information from networks of tree ring data. The data sets are 

large and are influenced by many factors of which temperature is only one. 

This means that the effects of long term temperature variations are masked by 

other more dominant short term influences and have to be extracted by 

statistical techniques. The Unit approaches this task with an independent 

mindset and awareness of the interplay of biological and physical processes 

underlying the signals that they are trying to detect. 

3. Although inappropriate statistical tools with the potential for producing 

misleading results have been used by some other groups, presumably by 

accident rather than design, in the CRU papers that we examined we did not 

come across any inappropriate usage although the methods they used may not 

have been the best for the purpose. It is not clear, however, that better methods 

would have produced significantly different results. The published work also 

contains many cautions about the limitations of the data and their 

interpretation. 

4. Chronologies (transposed composites of raw tree data) are always work in 

progress. They are subject to change when additional trees are added; new 

ways of data cleaning may arise (e.g. homogeneity adjustments), new 

measurement methods are used (e.g. of measuring ring density), new statistical 

methods for treating the data may be developed (e.g. new ways of allowing for 

biological growth trends). 

5. This is illustrated by the way CRU check chronologies against each other; this 

has led to corrections in chronologies produced by others. CRU is to be 

commended for continuously updating and reinterpreting their earlier 

chronologies. 
 

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6. With very noisy data sets a great deal of judgement has to be used. Decisions 

have to be made on whether to omit pieces of data that appear to be aberrant. 

These are all matters of experience and judgement. The potential for 

misleading results arising from selection bias is very great in this area. It is 

regrettable that so few professional statisticians have been involved in this 

work because it is fundamentally statistical. Under such circumstances there 

must be an obligation on researchers to document the judgemental decisions 

they have made so that the work can in principle be replicated by others. 

7. CRU accepts with hindsight that they should have devoted more attention in 

the past to archiving data and algorithms and recording exactly what they did. 

At the time the work was done, they had no idea that these data would assume 

the importance they have today and that the Unit would have to answer 

detailed inquiries on earlier work. CRU and, we are told, the tree ring 

community generally, are now adopting a much more rigorous approach to the 

archiving of chronologies and computer code. The difficulty in releasing 

program code is that to be understood by anyone else it needs time-consuming 

work on documentation, and this has not been a top priority. 

8. After reading publications and interviewing the senior staff of CRU in depth, 

we are satisfied that the CRU tree-ring work has been carried out with 

integrity, and that allegations of deliberate misrepresentation and unjustified 

selection of data are not valid. In the event CRU scientists were able to give 

convincing answers to our detailed questions about data choice, data handling 

and statistical methodology. The Unit freely admits that many data analyses 

they made in the past are superseded and they would not do things that way 

today. 

9. We have not exhaustively reviewed the external criticism of the 

dendroclimatological work, but it seems that some of these criticisms show a 

rather selective and uncharitable approach to information made available by 

CRU. They seem also to reflect a lack of awareness of the ongoing and 

dynamic nature of chronologies, and of the difficult circumstances under 

which university research is sometimes conducted. Funding and labour 

pressures and the need to publish have meant that pressing ahead with new 

work has been at the expense of what was regarded as non-essential record 

keeping. From our perspective it seems that the CRU sins were of omission 

rather than commission. Although we deplore the tone of much of the criticism 

that has been directed at CRU, we believe that this questioning of the methods 

and data used in dendroclimatology will ultimately have a beneficial effect and 

improve working practices 

Temperatures from Historical Instrumental Records 

1. The second main strand of work at CRU has been the collection and collation 

of instrumental land temperature records from all over the world and the 

construction of regional, hemispherical and global scale temperature records. 

These records are irregularly distributed in space and time. Modern records 

come largely from land-based meteorological stations but their geographical 

distribution is uneven and strongly biased in favour of the northern hemisphere 
 

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where most of the Earth’s land masses are located. Oceans cover two thirds of 

the Earth’s surface and away from the main shipping routes coverage is thin. 

For earlier centuries the record is much sparser. Deriving estimates of past 

temperatures on a global, hemispheric and regional scale from incomplete data 

sets is one of the problems faced by the Unit and in consequence an important 

current interest is the discovery of useable old temperature records from a 

variety of sources. 

2. In the latter part of the 20th century CRU pioneered the methods for taking into 

account a wide range of local influences that can make instrumental records 

from different locations hard to compare. These methods were very labour 

intensive and were somewhat subjective. Much of this work was supported by 

the US Department of Energy and was published with the details of station 

corrections several times a year. Since the 1980s the Unit has done no more of 

this work and have concentrated on the merging and interpretation of data 

series corrected by others. There have been various analyses of similar 

publicly available data sets by different international groups. Although there 

are some differences in fine detail that reflect the differences in the analytical 

methods used, the results are very similar. 

3. The Unit has devoted a great deal of effort to understanding how instrumental 

observations are best combined to derive the surface temperature on a variety 

of time and space scales. It has become apparent from a number of studies that 

there is elevation of the surface temperature in and around large cities and 

work is continuing to understand this fully. 

4. Like the work on tree rings this work is strongly dependent on statistical 

analysis and our comments are essentially the same. Although there are 

certainly different ways of handling the data, some of which might be 

superior, as far as we can judge the methods which CRU has employed are fair 

and satisfactory. Particular attention was given to records that seemed 

anomalous and to establishing whether the anomaly was an artefact or the 

result of some natural process. There was also the challenge of dealing with 

gaps in otherwise high quality data series. In detailed discussion with the 

researchers we found them to be objective and dispassionate in their view of 

the data and their results, and there was no hint of tailoring results to a 

particular agenda. Their sole aim was to establish as robust a record of 

temperatures in recent centuries as possible. All of the published work was 

accompanied by detailed descriptions of uncertainties and accompanied by 

appropriate caveats. The same was true in face to face discussions. 

5. We believe that CRU did a public service of great value by carrying out much 

time-consuming meticulous work on temperature records at a time when it was 

unfashionable and attracted the interest of a rather small section of the 

scientific community. CRU has been among the leaders in international efforts 

to determining the overall uncertainty in the derived temperature records and 

where work is best focussed to improve them. 
 

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6. The Unit has demonstrated that at a global and hemispheric scale temperature 

results are surprisingly insensitive to adjustments made to the data and the 

number of series included. 

7. Recent public discussion of climate change and summaries and 

popularizations of the work of CRU and others often contain oversimplifications that omit serious discussion of uncertainties emphasized by the 

original authors. For example, CRU publications repeatedly emphasize the 

discrepancy between instrumental and tree-based proxy reconstructions of 

temperature during the late 20th century, but presentations of this work by the 

IPCC and others have sometimes neglected to highlight this issue. While we 

find this regrettable, we could find no such fault with the peer-reviewed papers 

we examined 

Conclusions 

1. We saw no evidence of any deliberate scientific malpractice in any of the work 

of the Climatic Research Unit and had it been there we believe that it is likely 

that we would have detected it. Rather we found a small group of dedicated if 

slightly disorganised researchers who were ill-prepared for being the focus of 

public attention. As with many small research groups their internal procedures 

were rather informal. 

2. We cannot help remarking that it is very surprising that research in an area that 

depends so heavily on statistical methods has not been carried out in close 

collaboration with professional statisticians. Indeed there would be mutual 

benefit if there were closer collaboration and interaction between CRU and a 

much wider scientific group outside the relatively small international circle of 

temperature specialists. 

3. It was not the immediate concern of the Panel, but we observed that there were 

important and unresolved questions that related to the availability of 

environmental data sets. It was pointed out that since UK government adopted 

a policy that resulted in charging for access to data sets collected by 

government agencies, other countries have followed suit impeding the flow of 

processed and raw data to and between researchers. This is unfortunate and 

seems inconsistent with policies of open access to data promoted elsewhere in 

government. 

4. A host of important unresolved questions also arises from the application of 

Freedom of Information legislation in an academic context. We agree with the 

CRU view that the authority for releasing unpublished raw data to third parties 

should stay with those who collected it. 

Submitted to the University 12 April 2010 
 

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Addendum to report, 19 April 2010 

For the avoidance of misunderstanding in the light of various press stories, it is 

important to be clear that the neither the panel report nor the press briefing intended to 

imply that any research group in the field of climate change had been deliberately 

misleading in any of their analyses or intentionally exaggerated their findings. 

Rather, the aim was to draw attention to the complexity of statistics in this field, and 

the need to use the best possible methods. 
 

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APPENDIX A 

PANEL MEMBERSHIP 

Chair: Prof Ron Oxburgh FRS (Lord Oxburgh of Liverpool) 

Prof Huw Davies, ETH Zürich 

Prof Kerry Emanuel, Massachusetts Institute of Technology 

Prof Lisa Graumlich, University of Arizona. 

Prof David Hand FBA, Imperial College, London. 

Prof Herbert Huppert FRS, University of Cambridge 

Prof Michael Kelly FRS, University of Cambridge
 

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APPENDIX B 

Peer-reviewed publications for assessment. 

1. Brohan, P., Kennedy, J., Harris, I., Tett, S.F.B. and Jones, P.D., 2006: Uncertainty 

estimates in regional and global observed temperature changes: a new dataset from 

1850. J. Geophys. Res. 111, D12106. 

2. Briffa, K. R., F. H. Schweingruber, P. D. Jones, T. J. Osborn, S. G. Shiyatov, and E. 

A. Vaganov. 1998a. Reduced sensitivity of recent tree-growth to temperature at high 

northern latitudes. Nature 391:678-682. 

3. Briffa, K. R., F. H. Schweingruber, P. D. Jones, T. J. Osborn, I. C. Harris, S. G. 

Shiyatov, E. A. Vaganov, and H. Grudd, 1998b. Trees tell of past climates: but are 

they speaking less clearly today? Philosophical Transactions of the Royal Society of 

London Series B – Biological Sciences 353, 65-73. 

4. Briffa, K. R. 2000. Annual climate variability in the Holocene: interpreting the 

message of ancient trees. Quaternary Science Reviews 19, 87-105. 

5. Briffa, K.R., Osborn, T.J., Schweingruber, F.H., Harris, I.C., Jones, P.D., Shiyatov, 

S.G. and Vaganov, E.A., 2001: Low-frequency temperature variations from a 

northern tree-ring density network. J. Geophys. Res. 106, 2929-2941. 

6. Briffa, K. R., V. V. Shishov, T. M. Melvin, E. A. Vaganov, H. Grudd, R. M. 

Hantemirov, M. Eronen, and M. M. Naurzbaev. 2008. Trends in recent temperature 

and radial tree growth spanning 2000 years across northwest Eurasia. Philosophical 

Transactions of the Royal Society B-Biological Sciences 363, 2271-2284. 

7. Jones, P.D. and Moberg, A., 2003: Hemispheric and large-scale surface air 

temperature variations: An extensive revision and an update to 2001. J. Climate 16, 

206-223. 

8. Jones, P.D., Raper, S.C.B., Bradley, R.S., Diaz, H.F., Kelly, P.M. and Wigley, 

T.M.L., 1986a: Northern Hemisphere surface air temperature variations: 1851-1984. 

Journal of Climate and Applied Meteorology 25, 161-179. 

9. Jones, P.D., Raper, S.C.B. and Wigley, T.M.L., 1986b: Southern Hemisphere surface 

air temperature variations: 1851-1984. Journal of Climate and Applied Meteorology

25, 1213-1230. 

10. Jones, P.D., Groisman, P.Ya., Coughlan, M., Plummer, N., Wang, W-C. and Karl, 

T.R., 1990: Assessment of urbanization effects in time series of surface air 

temperature over land. Nature 347, 169-172. 

11. Jones, P.D., Lister, D.H. and Li, Q., 2008: Urbanization effects in large-scale 

temperature records, with an emphasis on China. Journal of Geophysical Research, 

113, D16122. 

 

 Supporting documentation 

 Briffa and Melvin (2009) which is online at 

 http://www.cru.uea.ac.uk/cru/people/briffa/yamal2009/
 

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 TR017 – Bradley, R.S., Kelly, P.M., Jones, P.D., Goodess, C.M. and Diaz, H.F., 1985: 

A Climatic Data Bank for Northern Hemisphere Land Areas, 1851-1980, U.S. Dept. 

of Energy, Carbon Dioxide Research Division, Technical Report TRO17, 335 pp. 

 TR022 – Jones, P.D., Raper, S.C.B., Santer, B.D., Cherry, B.S.G., Goodess, C.M., 

Kelly, P.M., Wigley, T.M.L., Bradley, R.S. and Diaz, H.F., 1985: A Grid Point 

Surface Air Temperature Data Set for the Northern Hemisphere, U.S. Dept. of 

Energy, Carbon Dioxide Research Division, Technical Report TRO22, 251 pp. 

 

 TR027 – Jones, P.D., Raper, S.C.B., Cherry, B.S.G., Goodess, C.M. and Wigley, 

T.M.L., 1986: A Grid Point Surface Air Temperature Data Set for the Southern 

Hemisphere, 1851-1984, U.S. Dept. of Energy, Carbon Dioxide Research Division, 

Technical Report TR027, 73 pp.