No climate-related stories over the past few years have attracted the level of mainstream coverage as those involving personal e-mails of prominent climate scientists that were hacked from a mail server at the Climatic Research Unit (CRU), University of East Anglia in the United Kingdom (see Yale Forum article).

These e-mails provide plenty to criticize, but the most widely-publicized quotes often are taken out of context to falsely imply a conspiracy of sorts to hide declining temperatures and a lack of recent warming. A close reading of the e-mails in question reveals a more nuanced picture, with scientists struggling with how to explain uncertainties in complex systems in a world of 60-second sound-bytes and the certainty of blistering condemnations by those ideologically opposed to accepting scientific evidence of anthropogenic warming.

Some of the attitudes shown toward skeptics raise very troubling questions, and there is a clear tendency toward circling the proverbial wagons when anyone in the group is criticized. But nothing in the e-mails significantly calls into question the fundamentals underlying scientific understanding of the climate system. Still to be determined is whether the public at large, and the elected officials representing them, will come to that same conclusion on their own.

The scandal broke after 12 years of e-mails were released on climate skeptic blogs after what may have either been hacking by parties unknown or a leak from someone at East Anglia. Authorities are looking into those issues. Only a small portion of CRU Director Phil Jones’ e-mails were released, and those that appear to have been selected for being most likely to cause embarrassment. Given the sheer volume of e-mails over a 12-year period that have now undergone extensive scrutiny (including a useful keyword search tool), it’s almost surprising that there is so little actually there. That said, five major issues that have been seized upon in the e-mails bear review:

  • Scientist Kevin Trenberth’s remarks on scientists’ inability to account for lack of warming;
  • Phil Jones’ comment on using a “trick” to “hide the decline”;
  • Encouraging editors of Climate Research to resign after the publication of Soon and Baliunas (2003);
  • Discussions among scientists surrounding efforts to avoid citing two skeptical papers (Kalnay and Cai (2003) and McKitrick and Michaels (2004)) in the IPCC Fourth Assessment Report; and
  • Perhaps most damning, comments by Jones encouraging others to delete e-mails to avoid releasing them to freedom of information requests from climate skeptics.

Trenberth: ‘We can’t account for the lack of warming’

Kevin Trenberth is a well-respected and prominent climate scientist who heads the Climate Analysis Section at the National Center for Atmospheric Research, in Boulder, Co. In an e-mail to Jones and others, he remarked:

Hi all
Well I have my own article on where the heck is global warming …

Trenberth, K. E., 2009: An imperative for climate change planning: tracking Earth’s global energy. Current Opinion in Environmental Sustainability, 1, 19-27.
The fact is that we can’t account for the lack of warming at the moment and it is a travesty that we can’t [Emphasis added]. The CERES data published in the August BAMS 09 supplement on 2008 shows there should be even more warming: but the data are surely wrong. Our observing system is inadequate. That said there is a LOT of nonsense about the PDO. People like CPC are tracking PDO on a monthly basis but it is highly correlated with ENSO. Most of what they are seeing is the change in ENSO not real PDO. It surely isn’t decadal. The PDO is already reversing with the switch to El Niño. The PDO index became positive in September for first time since Sept 2007.

Publishing an article on something is hardly a good way to hide it, so it is somewhat enigmatic to see this particular quote lambasted so often. Indeed, his paper discusses in detail the limitations of scientists’ ability to account for heat flows in the climate system. He generally agrees with the attribution of unusually cool 2008 temperature to La Niña (though it’s worth noting that 2008 was only cool relative to the rest of the decade):

The global mean temperature in 2008 was the lowest since about 2000 … Given that there is continual heating of the planet, referred to as radiative forcing, by accelerating increases of carbon dioxide and other greenhouses due to human activities, why isn’t the temperature continuing to go up? The stock answer is that natural variability plays a key role and there was a major La Niña event early in 2008 that led to the month of January having the lowest anomaly in global temperature since 2000. While this is true, it is an incomplete explanation.

He goes on to note that:

In particular, what are the physical processes? From an energy standpoint, there should be an explanation that accounts for where the radiative forcing has gone. Was it compensated for temporarily by changes in clouds or aerosols, or other changes in atmospheric circulation that allowed more radiation to escape to space? Was it because a lot of heat went into melting Arctic sea ice or parts of Greenland and Antarctica, and other glaciers? Was it because the heat was buried in the ocean and sequestered, perhaps well below the surface? Was it because the La Niña led to a change in tropical ocean currents and rearranged the configuration of ocean heat? Perhaps all of these things are going on?

But surely we have an adequate system to track whether this is the case or not, don’t we? Well, it seems that the answer is no, we do not. But we should! Given that global warming is unequivocally happening … then adapting to the climate change is an imperative. To plan for and cope with effects of climate change requires information on what is happening and why, whether observed changes are likely to continue or are a transient, how they affect regional climates and the possible impacts.

It is not a sufficient explanation to say that a cool year is due to natural variability … There must be a physical explanation, whether natural or anthropogenic. [Emphasis added]

It is quite clear from this context that Trenberth is not questioning the link between anthropogenic greenhouse gas emissions and warming, or even suggesting that recent temperatures are unusual in the context of short-term natural variability. Rather, he is bemoaning scientist’s inability to effectively model and monitor the energy flows associated with this short-term variability. Indeed, it should come as no great surprise to students of climate science that our understanding of short-term climate variability is quite limited, and it is telling that this brouhaha accompanied Trenberth’s single cherry-picked sentence rather than his more nuanced publication on the subject.

‘Mike’s Nature trick … to hide the decline’

This particular phrase has probably gotten more attention than any other contained in the hacked e-mails. Stripped of its context, it seems to confirm what skeptics have always feared: that scientists are cooking the proverbial temperature books to artificially inflate warming and hide any evidence of declining global temperatures. The full e-mail that contains the phrase is:

Dear Ray, Mike and Malcolm,
Once Tim’s got a diagram here we’ll send that either later today or first thing tomorrow.
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) amd [sic] from 1961 for Keith’s to hide the decline. Mike’s series got the annual land and marine values while the other two got April-Sept for NH land N of 20N. The latter two are real for 1999, while the estimate for 1999 for NH combined is +0.44C wrt 61-90. The Global estimate for 1999 with data through Oct is +0.35C cf. 0.57 for 1998. Thanks for the comments, Ray.

Something immediately stands out that should put to rest fears that climatologists are conspiring to hide recent cooling: namely the reference to the real temps line — “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) amd [sic] from 1961 for Keith’s to hide the decline” [emphasis added].

Indeed, using “real temps” to hide a decline in recent temperature makes no sense at all.

To understand the context of this quote, realize that the scientists here aren’t talking about recent global temperatures from thermometers at all. Rather, the e-mail is discussing the creation of a diagram showing a proxy reconstruction of northern hemispheric temperatures over the past 1,000 years based on tree rings. Jones is essentially replacing the data from tree rings post-1960 with real global temperature data from thermometers worldwide; temperature data, it is worth noting, that is independently validated by satellite measurements.

Still, it might seem odd to arbitrarily discard declining proxy data in favor of thermometer data known to be accurate for the recent past. It is quite reasonable to ask how, if tree ring proxies are not reliable for the past 40 years, can they possibly be used to reconstruct temperature over the past 1,000 years?

It is true that there is considerable uncertainty associated with tree ring proxies, and scientists can reliably reconstruct global temperature records for the past 600 years using non-tree ring proxy data. However, tree ring width is strongly correlated with temperature over the past 200 years or so for which there are instrumental records, and there is reason to believe that the decrease in tree ring width post-1960 is caused by something other than declining temperatures (since the temperatures where these trees are located are, by and large, not declining).

Indeed, this phenomenon is well known as the “divergence problem” (pdf) in the dendroclimatology literature. Hundreds of peer-reviewed papers have been written on the subject. Prime suspects for the cause of divergence include reduced insolation (global dimming) as the result of aerosols; temperature-induced drought stress; or other anthropogenic factors that would cause the historical relationship between tree ring width and temperature to break down in recent years in the locations where they are being measured.

So by “hide the decline,” Jones was referring to obscuring the divergence problem in the resulting chart by replacing tree ring proxy data with global temperature data. This may be somewhat dubious in that it gives the impression that proxy reconstructions match the observed temperature record better than they otherwise would. However, it is likely that Jones sincerely concludes that the divergence problem is indeed an exogenous anomaly in the record, and that replacing the recent divergent proxy record with real temperatures for the recent past creates a more accurate impression of the real global temperature than leaving in the proxy reconstruction post-divergence. Hardly the stuff that conspiracies are made of.

As further proof that scientists make poor conspirators, they follow the lead of Trenberth (albeit anachronistically) in describing what they did in the peer reviewed literature. Indeed, Jones’ reference to “Mike’s Nature trick” refers to a Nature paper by Michael Mann (and others) where the real temperature record was appended to proxy data, and this process is described in detail in the supporting documentation. It is worth noting, however, that the Mann et al paper in question did not drop any divergent data, though other subsequent publications (including the IPCC assessment reports have described the reason for doing so and Briffa’s original paper on the subject was quite frank about divergence issues.*

There has also been a lot of focus on the use of the word “trick” as somehow indicating intentional malfeasance, but the term trick is commonly used to refer to clever mathematical operations in numerous papers and should not offhand imply bad faith.

‘Get editorial board members to resign’

Some climate scientists have an unfortunate habit of dismissing arguments on blogs and other media as not being worth responding to because they are not published in peer-reviewed journals.

While it is true that the signal-to-noise ratio for many discussions on the internet is painfully low, there are important arguments that have been raised by Canadian mathematician Steve McIntyre, among others, that cannot be dismissed offhand simply because they are not published in the peer-reviewed literature.

Furthermore, the constant refrain by climate scientists for skeptics to “put up or shut up” by publishing is undermined by their own comments in some of the e-mails that show some scientists putting in quite a bit of effort to try and ensure that papers they deem flawed are not published.

This is tricky ground, with no bright line, since many will argue that the point of peer review is to screen out papers with poor or flawed methodology, and that editors on their own must help in separating pure chaff from wheat. Furthermore, many scientists argue that a sound paper would stand up on its own merits, and some skeptical papers that make it through peer review are sometimes given a free pass by ideologically sympathetic editors.

It is hard to completely buy the notion that ideology impacts only one side, however, or that this particular group of climate scientists does not allow their own preconceptions to affect what papers they like and dislike. That is not to suggest that the opposite extreme is desirable, that every paper with any position on climate science should be published regardless of its methodological merits out of some misguided sense of equal opportunity. Indeed, it is clear that some journals like Energy & Environment have occasionally let their standards drop because papers fit their own ideology.

The most commonly referenced example of this in the e-mails involves an incident where the journal Climate Research published a paper by Soon and Baliunas (2003). Their paper re-examined past proxy records and argued that recent temperature were by no means unprecedented over the past millennium.

The paper was immediately assailed by Mann, Jones, and others who accused a skeptical editor, Chris de Freitas, of letting the paper through with insufficient review by experts in the field. In the ensuing drama (recounted by a former editor here), half the editorial board resigned. Among those who resigned is Hans von Storch, the Editor-in-Chief, who is definitely not up-tight with Mann or Jones. The journal later released an editorial stating that “[Climate Research] should have requested appropriate revisions of the manuscript prior to publication.” Further paleoclimatological research has not supported the arguments in Soon and Baliunas (2003), and in this particular case it seems that the outside pressure on Climate Research may not have been untoward.

The Climate Research incident notwithstanding, other incidents in the e-mails do suggest a worrisome degree of collusion between some prominent scientists in marginalizing the views of skeptics with whom they disagree. This behavior on the part of scientists does not necessarily suggest that these skeptical papers were correct in their assertions by implication, or that climate scientists were somehow scrambling to defend a crumbling edifice as some skeptics suggest. Indeed, many of the papers that Jones et al objected to ended up being published by journals and even featured in the IPCC reports. Climate science is broad enough that no single group, however influential, can serve as inviolate gatekeepers of the peer reviewed literature.

‘Even if we have to redefine what the peer-review literature is’

Another e-mail message that has been distributed widely was a personal message sent from Phil Jones to Michael Mann where he remarks:

… The other paper by MM is just garbage – as you knew. De Freitas again. Pielke is also losing all credibility as well by replying to the mad Finn as well – frequently as I see it.
I can’t see either of these papers being in the next IPCC report. Kevin and I will keep them out somehow even if we have to redefine what the peer-review literature is ! [Emphasis added]

This e-mail refers to two papers, one by Kalnay and Cai (2003) in Nature and one by McKitrick and Michaels (2004) in Climate Research, both dealing with effects of land-use change on temperature measurements. Despite Jones’ dislike of the papers and his threat to keep them out of the IPCC Fourth Assessment Report, both papers were subsequently included in the Assessment, suggesting that no small group of scientists could be final arbiters of what is included in the IPCC reports.

‘Can you delete any e-mails …’

The University of East Anglia recently announced an independent investigation into the contents of the released e-mails to determine if any malfeasance had occurred, and Phil Jones has stepped down from his position as the head of the Climatic Research Unit pending the conclusion of the investigation. If anything contained in the e-mails has the potential to haunt Jones, it may be his suggestion to Keith Briffa, Michael Mann, and others that they should delete e-mail correspondences in order to avoid having to release them in response to Freedom of Information requests from climate skeptics associated with McIntyre’s Climate Audit blog:

Can you delete any e-mails you may have had with Keith re AR4?
Keith will do likewise. He’s not in at the moment – minor family crisis.

Can you also e-mail Gene and get him to do the same? I don’t have his new e-mail address.

We will be getting Caspar to do likewise.


While recipients of the e-mail say they did not act on the advice, recommending the destruction of material subject to a Freedom of Information (FOI) request may raise troubling questions under British law. While Jones and other climate scientists surely feel frustrated after being repeatedly bombarded with dozens of harassing FOI requests from skeptics, many of which they feel are motivated by political and not scientific concerns, the “delete” e-mail remark strikes many as inappropriate at best.

The Fallout

The release of the Climatic Research Unit e-mails is a blow to the reputation of many of the climate scientists involved, at least over the short run and perhaps among the public at large, if not necessarily among serious climatologists. They have been cast in a far different light from the general perception of scientists as impartial and impassionate.

Given the prominence of the scandal that has unfolded, it is unlikely that the whole affair will just fade away without anything changing. Indeed, there are growing calls for more openness and transparency in climate science research:  Climate scientists likely will have to accelerate efforts to be more open about their processes and data (though, to be fair, this is much further along than often thought).

It is unfortunate, if perhaps not surprising, that the quotes from the e-mails that have gotten the most publicity from skeptics and in some media strongly distort the views and actions of the scientists in question, contributing to a perception of collusion to manipulate the climate data itself.

Nothing contained in the e-mails, however, suggests that global temperature records are particularly inaccurate or, worse, that they have been manipulated to show greater warming. The  certainly troubling conduct exposed in some of the e-mails has little bearing on the fundamental science that strongly indicates that the world is warming and that anthropogenic emissions of greenhouse gases are the primary cause.

For the scientists involved and for many of their professional colleagues, that is the “bottom line.” Whethere the public and its elected and appointed policy leaders reach that same conclusion remains to be seen.

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* Editor’s Note: This paragraph was edited on 12/18 to clarify that the Mann et al 1998 study did not truncate the Briffa reconstruction.

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Zeke Hausfather

Zeke is an energy systems analyst and environmental economist with a strong interest in conservation and efficiency. He was previously the chief scientist at C3, an energy management and efficiency company,...