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What do the 'Climategate' hacked CRU emails tell us?

What the science says...

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Several investigations have cleared scientists of any wrongdoing in the media-hyped email incident.

Climate Myth...

Climategate CRU emails suggest conspiracy

“[T]he 1079 emails and 72 documents seem indeed evidence of a scandal involving most of the most prominent scientists pushing the man-made warming theory - a scandal that is one of the greatest in modern science. […] emails suggesting conspiracy, collusion in exaggerating warming data, possibly illegal destruction of embarrassing information, organised resistance to disclosure, manipulation of data, private admissions of flaws in their public claims and much more.” (Andrew Bolt, Herald Sun)

At a glance

What do you do if you cannot overturn well-established scientific theories by fair means? In the case of climate science deniers, you cheat. You play foul.

This is exactly what happened in November 2009. Sometime earlier, the email server at the Climatic Research Unit, University of East Anglia, was hacked (an illegal act in itself). A huge number of emails were stolen, sifted through and a selection was made available for download on a Russian server. The timing of the release was unsurprising, for early the following month the COP15 Climate Summit was due to be held in Copenhagen.

Selectively quoting parts of an email message removes all context. One of the most widely-quoted sentences, that will do nicely as an example, was as follows:

"I've just completed Mike's Nature trick of adding in the real temps to each series for the last 20 years (ie from 1981 onwards) and from 1961 for Keith's to hide the decline."

Those fanatically promoting this conspiracy theory encouraged people to take such sentences at face value. The implication that was intended to be the take-home in this case was that climate scientists were covering up declining temperatures. However – and serial misinformers have a long track-record in this kind of thing - it means nothing of the sort. The people in that email were not talking about measured temperatures. Let's take a look at the context to find out what it really meant.

"Mike's Nature trick" referred to a technique described in a 1998 Nature paper, presenting a 600 year-long global temperature reconstruction by Michael Mann and colleagues. Michael is a palaeoclimate specialist who has for many years used tree-ring growth patterns in ancient wood to reconstruct conditions at the time those rings formed. The basic idea is that in cold, dry years, trees grow more slowly so their rings are relatively narrow and densely-spaced. In warm wet years, it's the opposite.

The "trick" is the technique of plotting recent instrumental data (i.e. weather observations) alongside the reconstructed tree-ring data for the time they overlap. It's a good way of checking if the reconstructed tree-ring data are representative and meaningful. They're no good for anything if they are not.

So, what does the “decline” refer to? It's also known as the 'divergence problem', a point on the timeline beyond which the reconstructed tree-ring data stop being representative and meaningful. This is a well-known issue in certain tree-ring datasets from specific places. What happens is that when plotted against instrumental temperature data, the reconstructed tree-ring data fall away – decline - below the instrumental data. This is a recent phenomenon that only showed up after about 1960. Prior to that, it hadn't been a problem.

Climate scientists started discussing the decline in the literature as long ago as 1995 – by which time they had many years of data showing that, where present, it stood out like a sore thumb. It seems to have been caused by an apparent loss in temperature-sensitivity with respect to certain species of trees growing in certain areas. Something had changed, making affected datasets unrepresentative of actual conditions.

All that ado about nothing. Just how much taxpayer's money was wasted on all the public inquiries that followed is anyone's guess. None were necessary. All you need to remember is that when it comes to climate science deniers, the difference between fair means and foul is at best blurred and more usually non-existent.

Please use this form to provide feedback about this new "At a glance" section. Read a more technical version below or dig deeper via the tabs above!

Further details

In November 2009, the servers at the University of East Anglia in Britain were illegally hacked and emails were stolen. When a selection of emails between climate scientists were published on the internet, a few suggestive quotes were seized upon by many claiming global warming was all just a conspiracy. A number of independent enquiries have investigated the conduct of the scientists involved in the emails. All have cleared the scientists of any wrong doing:

  1. In February 2010, the Pennsylvania State University released an Inquiry Report that investigated any 'Climategate' emails involving Dr Michael Mann, a Professor of Penn State's Department of Meteorology. They found that "there exists no credible evidence that Dr. Mann had or has ever engaged in, or participated in, directly or indirectly, any actions with an intent to suppress or to falsify data". On "Mike's Nature trick", they concluded "The so-called “trick”1 was nothing more than a statistical method used to bring two or more different kinds of data sets together in a legitimate fashion by a technique that has been reviewed by a broad array of peers in the field."
  2. In March 2010, the UK government's House of Commons Science and Technology Committee published a report finding that the criticisms of the Climatic Research Unit (CRU) were misplaced and that CRU’s "Professor Jones’s actions were in line with common practice in the climate science community".
  3. In April 2010, the University of East Anglia set up an international Scientific Assessment Panel, in consultation with the Royal Society and chaired by Professor Ron Oxburgh. The Report of the International Panel assessed the integrity of the research published by the CRU and found "no evidence of any deliberate scientific malpractice in any of the work of the Climatic Research Unit".
  4. In June 2010, the Pennsylvania State University published their Final Investigation Report, determining "there is no substance to the allegation against Dr. Michael E. Mann".
  5. In July 2010, the University of East Anglia published the Independent Climate Change Email Review report. They examined the emails to assess whether manipulation or suppression of data occurred and concluded that "we find that their rigour and honesty as scientists are not in doubt."
  6. In July 2010, the US Environmental Protection Agency investigated the emails and "found this was simply a candid discussion of scientists working through issues that arise in compiling and presenting large complex data sets."
  7. In September 2010, the UK Government responded to the House of Commons Science and Technology Committee report, chaired by Sir Muir Russell. On the issue of releasing data, they found "In the instance of the CRU, the scientists were not legally allowed to give out the data". On the issue of attempting to corrupt the peer-review process, they found "The evidence that we have seen does not suggest that Professor Jones was trying to subvert the peer review process. Academics should not be criticised for making informal comments on academic papers".
  8. In February 2011, the Department of Commerce Inspector General conducted an independent review of the emails and found "no evidence in the CRU emails that NOAA inappropriately manipulated data".
  9. In August 2011, the National Science Foundation concluded "Finding no research misconduct or other matter raised by the various regulations and laws discussed above, this case is closed".

Just as there are many independent lines of evidence that humans are causing global warming, similarly a number of independent investigations have found no evidence of falsification or conspiracy by climate scientists.

Note: Updated on July 8, 2023 to correctly name CRU as the Climatic Research Unit.

Last updated on 8 July 2023 by John Mason. View Archives

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The House of Commons report on the emails stolen from CRU has vindicated Phil Jones -- he has "no case to answer":

The focus on Professor Jones and CRU has been largely misplaced. On the accusations relating to Professor Jones's refusal to share raw data and computer codes, we consider that his actions were in line with common practice in the climate science community. We have suggested that the community consider becoming more transparent by publishing raw data and detailed methodologies. On accusations relating to Freedom of Information, we consider that much of the responsibility should lie with UEA, not CRU.

In addition, insofar as we have been able to consider accusations of dishonesty--for example, Professor Jones's alleged attempt to "hide the decline"--we consider that there is no case to answer. Within our limited inquiry and the evidence we took, the scientific reputation of Professor Jones and CRU remains intact. We have found no reason in this unfortunate episode to challenge the scientific consensus as expressed by Professor Beddington, that "global warming is happening [and] that it is induced by human activity"

Official statement from Climatic Research Unit (CRU)

In an interview with Andrew Freeman, historian Spencer Weart puts Climategate and the global warming skeptic phenomenon in perspective:

"...we've never before seen a set of people accuse an entire community of scientists of deliberate deception and other professional malfeasance. Even the tobacco companies never tried to slander legitimate cancer researchers."

George Monbiot reveals the most damaging email in The Knights Carbonic. Here is an excerpt, revealing the depth of the climate conspiracy:

"Then began the most hazardous task of all: our attempt to control the instrumental record. Securing the consent of the scientific establishment was a simple matter. But thermometers had by then become widely available, and amateur meteorologists were making their own readings. We needed to show a steady rise as industrialisation proceeded, but some of these unfortunates had other ideas. The global co-option of police and coroners required unprecedented resources, but so far we have been able to cover our tracks.
Our co-option of the physical world has been just as successful. The thinning of the Arctic ice cap was a masterstroke. The ring of secret nuclear power stations around the Arctic Circle, attached to giant immersion heaters, remains undetected, as do the space-based lasers dissolving the world’s glaciers.
Altering the migratory and reproductive patterns of the world’s wildlife has proved more challenging. Though we have now asserted control over the world’s biologists, there is no accounting for the unauthorised observations of farmers, gardeners, bird-watchers and other troublemakers. We have therefore been forced to drive migrating birds, fish and insects into higher latitudes, and to release several million tonnes of plant pheromones every year to accelerate flowering and fruiting. None of this is cheap, and ever more public money, secretly diverted from national accounts by compliant governments, is required to sustain it."

Another amusing parody is Newtongate: the final nail in the coffin of Renaissance and Enlightenment ‘thinking’ which scrutinizes the private correspondance of Isaac Newton to cast doubt on Newtonian physics and integral calculus.

MediaMatters examines many of the claims coming out of "Climategate", exposing how the emails have been distorted and misrepresented.


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Comments 76 to 81 out of 81:

  1. What has become obvious to me is that all denialist arguments boil down to "It's a Hoax". Whatever the argument that a denialist is throwing out, it is something that the climate science community has already heard and refuted. The authors of the IPCC reports have also heard all of these arguments before. Therefore, the only way to continue to be a denier is to believe that the vast majority of scientists studying climate are wrong, or involved in the most elaborate international hoax in the history of the world. Clearly these views are irrational, and require a strong prediliction to deny climate changed usually based on ideology.

  2. Hilarious. ignore what they did and focus on the fact that a Board "cleared them".

    About as persuasive as when the police review board clears a police officer for shooting people without proper cause.

    the hockey stick and climate gate emails are scandalous. they cherry picked the series they wanted, deleted embarrassing data, and sticky taped it all together to produce the most compelling picture they could.

    it singlehandedly did more to undermine climate science than anything else.

    and we see no acknowledgement. No contrition. Just this whitewalling garbage that "they were cleared".


    and you wonder why people have doubts?


    [DB]  Repeated sloganeering snipped.

  3. Hi,

    in your article above you portray Climategate as follows: "Focusing on a few suggestive emails, taken out of context ..."

    After some minutes of googling I came across this article from the renowned british newspaper "The Telegraph" (in case someone doesn't know: the weekly version of "The Daily Telegraph"): LINK

    Citation: "There are three threads in particular in the leaked documents which have sent a shock wave through informed observers across the world. Perhaps the most obvious is the highly disturbing series of emails which show how Dr Jones and his colleagues have for years been discussing the devious tactics whereby they could avoid releasing their data to outsiders under freedom of information laws."

    The article also says that this scandal goes right to the heart of the IPCC: "Professor Philip Jones, the CRU's director, is in charge of the two key sets of data used by the IPCC to draw up its reports."

    The problem is that these pictures given differ so geatly that there is only one explanation: One side must be lying like a trooper.

    If the author of the article, columnist Christopher Booker, and the colleagues he is referring to, are all lying, he and them must have made up their accusations, that means the emails and the years of deceit do not exist, it is all invented. Or he misread the emails, he and his colleagues are just stupid. Or, on the other hand, climate alarmists are defending their cause by playing down a terrible scandal. Everyone shall decide for their own, which is more probable.

    The start page I read here was quite good and you made some interesting points I eventually will investigate on further. But here, talking about Climategate I once more come to the conclusion that Skeptics sometimes aren't quite that skeptic at all but love to trust in what authorities proclaim, without checking the facts.


    [DB] Shortened and activated URL.

  4. Booker is not a reliable source. The mining/fossil fuel stooge S. McIntyre years ago launched a harassment campaign by asking multiple followers to file FOI requests, directed against scientists whose work he disliked. Because they knew that the requests were not a good faith effort, the recipients were reluctant to release information, which unfortunately escalated to whole thing in a away that then became easy to exploit for the bad faith actors. It can certainly be said that Jones and others could have handled this better, and that was one of the conclusions of the investigation. Whomever can be perfect all the time when faced with bad faith attacks can throw the first stone.


  5. It is worth noting that the Telegraph is a Murdoch paper and, like all other tentacles of the Murdoch's empire, used to foster its boss' ideology. In any circumstance, I would give it only the credence it deserves. 

  6. "... there is only one explanation: One side must be lying like a trooper."

    That is a real logic failure there. I can think of at least two more explanations that would fit those criteria.

  7. There are some quotes from emails sent on September 9th 1999 which are frequently brought up by conspiracy theorists that don't seem to be discussed here. Forgive me if I have simply missed discussion of them. They regard the divergence of Keith Briffa's tree ring reconstruction from Mann and Jones.

    IPCC author Chris Folland writes "A proxy diagram of temperature change is a clear favourite for the Policy Makers summary. But the current diagram with the tree ring only data somewhat contradicts the multiproxy curve and dilutes the message rather significantly." 

    Briffa writes there is "pressure to present a nice tidy story as regards ‘apparent unprecedented warming in a thousand years or more in the proxy data…,’”

    Mann writes "Everyone in the room at IPCC was in agreement that this was a problem and a potential distraction/detraction from the reasonably consensus viewpoint we’d like to show w/ the Jones et al and Mann et al series"

    This has been used to suggest that the IPCC is after particular data to support a message which it will pressure scientists for, and the IPCC will ideally exlude data which 'dilutes' the message. I don't believe that but it's become a common talking point.


    [BL] The tendency for contrarians to take email quotes out of context is well known.

    Two additional myth rebuttals at SkS cover parts of this discussion, and reference material from Briffa:

    Climategate and the peer review process

    Were skeptic scientists kept out of the IPCC



  8. Thanks for the quick response.

    The article 'Were skeptic scientists kept out of the IPCC' shows evidence that the working group did not suppress contrarian papers but honestly critiqued them, hence it can be argued that they also honestly critiqued Briffa's tree ring data (and from what I know, they did indeed and there was a detailed discussion of Briffa's tree ring data in the report). But someone making the argument I laid out in the above post might still say the quotes, including apparently quite explicit ones from Briffa himself, are evidence of improper pressure to create consensus rather than uncertainty for the policy makers, even if in this case there was ultimately no impact on the results. As you say, I think there's a good chance the quotes are taken out of context like so much of the selective quoting done by 'Climategate' proponents, but if they have been I can't find any material showing how they have been taken out of context.

  9. Please note: the basic version of this rebuttal has been updated on Feb 14, 2023 and now includes an "at a glance“ section at the top. To learn more about these updates and how you can help with evaluating their effectiveness, please check out the accompanying blog post @

    Thanks - the Skeptical Science Team.

  10. Judith Curry recently did an interview on Jordan Peterson's podcast - and she still leans very heavily on Climategate. She made some points which I've not seen covered here - about emails where climate researchers were bullying editors into silencing critics - it would be good to have some of that rebutted here (just because Peterson's reach is huge).
    If you're not across it I'll suffer through listening to it again and will provide a summary - please let me know if you'd like me to do this.

  11. JonJC

    I'd like to listen to the suspect climate gate program. Do you have a link?

  12. JonJC @85 ,

    the Climategate biz is rather ancient history by now ~ but the science-denialists are desperatey short of ammunition . . . so they have to keep dredging it up (and they can never admit they got it wrong).

    My favorite discussion of it is by science journalist "Potholer54" , back in about 2010.   Google his youtube video titled "Climate Change - Those hacked e-mails".

    His video runs 9 minutes, and you will find it amusing as well !

    ( The issue has had no significant developments since since then.)

  13. JonJC, Eddie:

    I suspect that the video in question is the one recently discussed on the "It's the sun" thread. MA Rodger's comment provides a link to the Curry/Peterson part of the video, with a pithy comment about the quality of Curry's blatherings.

    I also suspect that there is nothing new in Curry/Peterson that isn't the result of a gross misrepresentation of the email contents. For the peer-review aspects, you should also read this SkS post on the subject:

    Climategate and the Peer-review Process

  14. The Climategate and Peer-review link I gave above is #95 on SkS's "Most Used Climate Myths". (This thread is # 17.)

    If you really want to read about corruption of the peer-review process, you should look at # 205 on the list: "How contrarians used pal review to publish contrarian papers". In the contrarians' world it is easy to imagine that the mainstream climate scientists are corrupting the process, because that's exactly what the contrarians are willing to do when they have control of a journal. Accuse your opponent of doing what you are doing...

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