A - Do you agree that according to the global temperature record used by the IPCC, the rates of global warming from 1860-1880, 1910-1940 and 1975-1998 were identical?
An initial point to make is that in the responses to these questions I've assumed that when you talk about the global temperature record, you mean the record that combines the estimates from land regions with those from the marine regions of the world. CRU produces the land component, with the Met Office Hadley Centre producing the marine component.
Temperature data for the period 1860-1880 are more uncertain, because of sparser coverage, than for later periods in the 20th Century. The 1860-1880 period is also only 21 years in length. As for the two periods 1910-40 and 1975-1998 the warming rates are not statistically significantly different (see numbers below).
I have also included the trend over the period 1975 to 2009, which has a very similar trend to the period 1975-1998.
So, in answer to the question, the warming rates for all 4 periods are similar and not statistically significantly different from each other.
Here are the trends and significances for each period:
Period Length Trend
(Degrees C per decade) Significance
1860-1880 21 0.163 Yes
1910-1940 31 0.15 Yes
1975-1998 24 0.166 Yes
1975-2009 35 0.161 YesB - Do you agree that from 1995 to the present there has been no statistically-significant global warming
Yes, but only just. I also calculated the trend for the period 1995 to 2009. This trend (0.12C per decade) is positive, but not significant at the 95% significance level. The positive trend is quite close to the significance level. Achieving statistical significance in scientific terms is much more likely for longer periods, and much less likely for shorter periods.C - Do you agree that from January 2002 to the present there has been statistically significant global cooling?
No. This period is even shorter than 1995-2009. The trend this time is negative (-0.12C per decade), but this trend is not statistically significant.D - Do you agree that natural influences could have contributed significantly to the global warming observed from 1975-1998, and, if so, please could you specify each natural influence and express its radiative forcing over the period in Watts per square metre.
This area is slightly outside my area of expertise. When considering changes over this period we need to consider all possible factors (so human and natural influences as well as natural internal variability of the climate system). Natural influences (from volcanoes and the Sun) over this period could have contributed to the change over this period. Volcanic influences from the two large eruptions (El Chichon in 1982 and Pinatubo in 1991) would exert a negative influence. Solar influence was about flat over this period. Combining only these two natural influences, therefore, we might have expected some cooling over this period.E - How confident are you that warming has taken place and that humans are mainly responsible?
I'm 100% confident that the climate has warmed. As to the second question, I would go along with IPCC Chapter 9 - there's evidence that most of the warming since the 1950s is due to human activity.F - Sceptics of anthropogenic global warming (AGW) suggest that the official surface record paints a different story from the actual station records. To restore trust, should we start again with new quality control on input data in total transparency?
First, I am assuming again that you are referring to the surface record from both land and marine regions of the world, although in this answer as you specifically say "station" records, I will emphasise the land regions.
There is more than one "official" surface temperature record, based on actual land station records. There is the one we have developed in CRU, but there are also the series developed at NCDC and GISS. Although we all use very similar station datasets, we each employ different ways of assessing the quality of the individual series and different ways of developing gridded products. The GISS data and their program are freely available for people to experiment with. The agreement between the three series is very good.
Large numbers of the CRU e-mails were posted on the web
Given the web-based availability of the Global Historical Climatology Network (GHCN), which is used by both NCDC and GISS, anyone else can develop their own global temperature record from land stations.
Through the Met Office we have released (as of 29 January 2010) 80% of the station data that enters the CRU analysis (CRUTEM3).
The graphic in the link below shows that the global land temperature series from these 80% of stations (red line) replicates the analysis based on all 100% of stations (black line).http://www.metoffice.gov.uk/climatechan ... raphic.GIF
The locations of the 80% of stations are shown on the next link in red. The stations we have yet to get agreement to release are shown in grey.http://www.metoffice.gov.uk/climatechan ... ations.GIF
I accept that some have had their trust in science shaken and this needs the Met Office to release more of the data beyond the 80% released so far. Before all the furore broke we had begun discussions with the Met Office for an updated set of station temperatures. With any new station dataset we will make sure we will be able to release all the station temperature data and give source details for all the series.G - There is a debate over whether the Medieval Warm Period (MWP) was global or not. If it were to be conclusively shown that it was a global phenomenon, would you accept that this would undermine the premise that mean surface atmospheric temperatures during the latter part of the 20th Century were unprecedented?
There is much debate over whether the Medieval Warm Period was global in extent or not. The MWP is most clearly expressed in parts of North America, the North Atlantic and Europe and parts of Asia. For it to be global in extent the MWP would need to be seen clearly in more records from the tropical regions and the Southern Hemisphere. There are very few palaeoclimatic records for these latter two regions.
Of course, if the MWP was shown to be global in extent and as warm or warmer than today (based on an equivalent coverage over the NH and SH) then obviously the late-20th century warmth would not be unprecedented. On the other hand, if the MWP was global, but was less warm that today, then current warmth would be unprecedented.
We know from the instrumental temperature record that the two hemispheres do not always follow one another. We cannot, therefore, make the assumption that temperatures in the global average will be similar to those in the northern hemisphere.H - If you agree that there were similar periods of warming since 1850 to the current period, and that the MWP is under debate, what factors convince you that recent warming has been largely man-made?
The fact that we can't explain the warming from the 1950s by solar and volcanic forcing - see my answer to your question D.I - Would it be reasonable looking at the same scientific evidence to take the view that recent warming is not predominantly manmade?
No - see again my answer to D.J - Are there lessons to be learned for society or scientists about the way we see uncertainty and risk?
Yes - as stated by Sir John Beddington - the government chief scientist. And this doesn't just apply to climate science.K - How much faith do you have - and should we have - in the Yamal tree ring data from Siberia? Should we trust the science behind the palaeoclimate record?
First, we would all accept that palaeoclimatic data are considerably less certain than the instrumental data. However, we must use what data are available in order to look at the last 1,000 years.
I believe that our current interpretation of the Yamal tree-ring data in Siberia is sound. Yamal is just one series that enters some of the millennial long reconstructions that are available.
My colleague Keith Briffa has responded to suggestions that there is something amiss with the Yamal tree-ring data. Here is his response:http://www.cru.uea.ac.uk/cru/people/briffa/yamal2009/L - Can you confirm that the IPCC rules were changed so lead authors could add references to any scientific paper which did not meet the 16 December 2005 deadline but was in press on 24 July 2006, so long as it was published in 2006? If this is the case, who made the decision and why?
This is a question for the IPCC.M - What advice did you seek in handling FOI requests?
The university's policy and guidelines on FOI and the Environmental Information Regulations are on our website and the information policy and compliance manager (IPCM) takes responsibility for co-ordinating responses to requests within that framework. We also have colleagues in each unit and faculty who are trained in FOI to help in gathering information and assessing any possible exceptions or exemptions.
I worked with those colleagues and the IPCM to handle the requests with responses going from the IPCM. He also liaises with the Information Commissioner's Office where necessary and did so on several occasions in relation to requests made to CRU. Where appropriate he also consulted with other colleagues in the university on specific issues.N - When scientists say "the debate on climate change is over", what exactly do they mean - and what don't they mean?
It would be supposition on my behalf to know whether all scientists who say the debate is over are saying that for the same reason. I don't believe the vast majority of climate scientists think this. This is not my view. There is still much that needs to be undertaken to reduce uncertainties, not just for the future, but for the instrumental (and especially the palaeoclimatic) past as well.O - Can you tell us about your working life over the past decades in climate science. Paint a picture about the debate with your allies and scientific rivals etc.
I have been at CRU since November 1976. Up until 1994, my working life was almost totally in research. Since 1994, I have become more involved in teaching and student supervision both at the postgraduate and undergraduate level. I became a Professor in 1998 and the director of the Climatic Research Unit in 2004 (I was joint director from 1998).
I am most well known for being involved in the publication of a series of papers (from 1982 to 2006) that have developed a gridded dataset of land-based temperature records. These are only a part of the work I do, as I have been involved in about 270 peer-reviewed publications on many different aspects of climate research.
Over the years at scientific meetings, I've met many people and had numerous discussions with them. I work with a number of different groups of people on different subjects, and some of these groups come together to undertake collaborative pieces of work. We have lively debates about the work we're doing together.P - The "Climategate" stolen emails were published in November. How has your life been since then?
My life has been awful since that time, but I have discussed this once (in the Sunday Times) and have no wish to go over it again. I am trying to continue my research and supervise the CRU staff and students who I am responsible for.Q - Let's talk about the e-mails now: In the e-mails you refer to a "trick" which your critics say suggests you conspired to trick the public? You also mentioned "hiding the decline" (in temperatures). Why did you say these things?
This remark has nothing to do with any "decline" in observed instrumental temperatures. The remark referred to a well-known observation, in a particular set of tree-ring data, that I had used in a figure to represent large-scale summer temperature changes over the last 600 years.
The phrase 'hide the decline' was shorthand for providing a composite representation of long-term temperature changes made up of recent instrumental data and earlier tree-ring based evidence, where it was absolutely necessary to remove the incorrect impression given by the tree rings that temperatures between about 1960 and 1999 (when the email was written) were not rising, as our instrumental data clearly showed they were.
This "divergence" is well known in the tree-ring literature and "trick" did not refer to any intention to deceive - but rather "a convenient way of achieving something", in this case joining the earlier valid part of the tree-ring record with the recent, more reliable instrumental record.
I was justified in curtailing the tree-ring reconstruction in the mid-20th Century because these particular data were not valid after that time - an issue which was later directly discussed in the 2007 IPCC AR4 Report.
The misinterpretation of the remark stems from its being quoted out of context. The 1999 WMO report wanted just the three curves, without the split between the proxy part of the reconstruction and the last few years of instrumental data that brought the series up to the end of 1999. Only one of the three curves was based solely on tree-ring data.
The e-mail was sent to a few colleagues pointing out their data was being used in the WMO Annual Statement in 1999. I was pointing out to them how the lines were physically drawn. This e-mail was not written for a general audience. If it had been I would have explained what I had done in much more detail.R - Why did you ask a colleague to delete all e-mails relating to the Fourth Assessment Report of the IPCC?
This was an e-mail sent out of frustration at one FOI request that was asking for the e-mail correspondence between the lead authors on chapter six of the Working Group One Report of the IPCC. This is one of the issues which the Independent Review will look at.S - The e-mails suggest you were trying to subvert the process of peer review and to influence editors in their decisions about which papers to publish. Do you accept that?
I do not accept that I was trying to subvert the peer-review process and unfairly influence editors in their decisions. I undertook all the reviews I made in good faith and sent them back to the editors. In some e-mails I questioned the peer-review process with respect to what I believed were poor papers that had appeared. Isn't this called freedom of speech? On some occasions I joined with others to submit a response to some of these papers. Since the beginning of 2005 I have reviewed 43 papers. I take my reviewing seriously and in 2006 I was given an editor's award from Geophysical Research Letters for conscientious and constructive reviewing.T - Where do you draw the line on the handling of data? What is at odds with acceptable scientific practice? Do you accept that you crossed the line?
This is a matter for the independent review.U - Now, on to the fallout from "Climategate", as it has become known. You had a leading role in a part of the IPCC, Working Group I. Do you accept that credibility in the IPCC has been damaged - partly as a result of your actions? Does the IPCC need reform to gain public trust?
Some have said that the credibility in the IPCC has been damaged, partly due to the misleading and selective release of particular e-mails. I wish people would spend as much time reading my scientific papers as they do reading my e-mails. The IPCC does need to reassure people about the quality of its assessments.V - If you have confidence in your science why didn't you come out fighting like the UK government's drugs adviser David Nutt when he was criticised?
I don't feel this question merits an answer.W - Finally, a personal question: Do you expect to return as director of the Climatic Research Unit? What is next for you?
This question is not for me to answer.