Michael Mann, one of the country’s leading climatologists, has coauthored a major new review and analysis of climate science since the 2007 IPCC report.  Mann, Director of Pennsylvania State University’s Earth System Science Center, is much attacked by the anti-scientific disinformers because of his work on the paleoclimate “hockey stick” reconstructions of temperature over the past couple of millennia.  Contrary to what the disinformers continue to say, however, the hockey stick was essentially vindicated by the National Academy of Sciences (see NAS Report and RealClimate.org).

Since some of his email exchanges were made public by the recent illegal hack of documents from the University of East Anglia, he has also distributed a response to various members of the media and bloggers, which I reprint in full below.

Misrepresentation of these emails is so common that the Washington Post issued one of the fastest retractions/corrections in its history.  I had blogged on their November 25 op-ed “Climate of Denial” here — The newspaper that publishes George Will (and Sarah Palin) editorializes: “Many — including us — find global warming deniers’ claims irresponsible.” Well, one day later, they “clarified” one of their assertions about Mann (see here).  So this should be a cautionary tale to the media to go to the primary source before simply repeating what others have said.

Before reprinting Mann’s comments on the key emails, let me focus on what is far more important — the science.  As the UK’s Met Office, NERC and the Royal Society recently wrote, “even since the 2007 IPCC Assessment the evidence for dangerous, long-term and potentially irreversible climate change has strengthened.” Now we have the detailed scientific basis for such statements.

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Mann is a coauthor of “The Copenhagen Diagnosis,” in which the 26 leading climate researchers document “the key findings in climate change science since the publication of the landmark Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report in 2007.”  They “conclude that several important aspects of climate change are occurring at the high end or even beyond the expectations of only a few years ago”:

Without significant mitigation, the report says global mean warming could reach as high as 7 degrees Celsius by 2100.

And that plausible worst case scenario would cause unimaginable harm — including to this country (see UK Met Office: Catastrophic climate change, 13-18°F over most of U.S. and 27°F in the Arctic, could happen in 50 years, but “we do have time to stop it if we cut greenhouse gas emissions soon”).  And yes, that scenario is quite different from the simple analysis of what happens if the nation and the world just keep on our current emissions path.  We’ve known that end-of-century catastrophe for a while (see “M.I.T. doubles its 2095 warming projection to 10°F — with 866 ppm and Arctic warming of 20°F“).

None of this will be a surprise to those who follow the scientific literature or read CP.  Here are “the most significant recent climate change findings”:

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Surging greenhouse gas emissions: Global carbon dioxide emissions from fossil fuels in 2008 were nearly 40% higher than those in 1990. Even if global emission rates are stabilized at present –day levels, just 20 more years of emissions would give a 25% probability that warming exceeds 2oC. Even with zero emissions after 2030. Every year of delayed action increase the chances of exceeding 2oC warming.

Recent global temperatures demonstrate human-based warming: Over the past 25 years temperatures have increased at a rate of 0.190C per decade, in every good agreement with predictions based on greenhouse gas increases. Even over the past ten years, despite a decrease in solar forcing, the trend continues to be one of warming. Natural, short- term fluctuations are occurring as usual but there have been no significant changes in the underlying warming trend.

Acceleration of melting of ice-sheets, glaciers and ice-caps: A wide array of satellite and ice measurements now demonstrate beyond doubt that both the Greenland and Antarctic ice-sheets are losing mass at an increasing rate. Melting of glaciers and ice-caps in other parts of the world has also accelerated since 1990.

Rapid Arctic sea-ice decline: Summer-time melting of Arctic sea-ice has accelerated far beyond the expectations of climate models. This area of sea-ice melt during 2007-2009 was about 40% greater than the average prediction from IPCC AR4 climate models.

Current sea-level rise underestimates: Satellites show great global average sea-level rise (3.4 mm/yr over the past 15 years) to be 80% above past IPCC predictions. This acceleration in sea-level rise is consistent with a doubling in contribution from melting of glaciers, ice caps and the Greenland and West-Antarctic ice-sheets.

Sea-level prediction revised: By 2100, global sea-level is likely to rise at least twice as much as projected by Working Group 1 of the IPCC AR4, for unmitigated emissions it may well exceed 1 meter. The upper limit has been estimated as – 2 meters sea-level rise by 2100. Sea-level will continue to rise for centuries after global temperature have been stabilized and several meters of sea level rise must be expected over the next few centuries.

Delay in action risks irreversible damage: Several vulnerable elements in the climate system (e.g. continental ice-sheets. Amazon rainforest, West African monsoon and others) could be pushed towards abrupt or irreversible change if warming continues in a business-as-usual way throughout this century. The risk of transgressing critical thresholds (“tipping points”) increase strongly with ongoing climate change. Thus waiting for higher levels of scientific certainty could mean that some tipping points will be crossed before they are recognized.

The turning point must come soon: If global warming is to be limited to a maximum of 2oC above pre-industrial values, global emissions need to peak between 2015 and 2020 and then decline rapidly. To stabilize climate, a decarbonized global society – with near-zero emissions of CO2 and other long-lived greenhouse gases – need to be reached well within this century. More specifically, the average annual per-capita emissions will have to shrink to well under 1 metric ton CO2 by 2050. This is 80-90% below the per-capita emissions in developed nations in 2000.

The time to act is now if not sooner.

Now back to Mann and the emails.

As noted, Mann has been a primary target of the disinformers because of the hockey stick.  Yet even more important than the fact that the original analysis was defensibly correct, is that the conclusions were correct [which could be true even if the analysis had flaws in it].  Is the planet now as hot (or hotter) than it has been in a millenium?  Try two millennia (see “Sorry deniers, hockey stick gets longer, stronger: Earth hotter now than in past 2,000 years“).  See also “Human-caused Arctic warming overtakes 2,000 years of natural cooling, ’seminal’ study finds.”  That’s why climatologist and one-time darling of the contrarians Ken Caldeira said last month, “To talk about global cooling at the end of the hottest decade the planet has experienced in many thousands of years is ridiculous.”

Now Mann is being attacked again, again primarily by those misrepresenting his work and what he has written.  You can find excellent explanations of many of those emails and the issues they raise at RealClimate (here).  Here are Mann’s comments on the hacked emails:

1. “I’ve just completed Mike’s Nature trick of adding in the real temps to each series for the last 20 years (i. e. from 1981 onwards) and from 1961 for Keith’s to hide the decline.” (from Phil Jones).

Phil Jones has publicly gone on record indicating that he was using the term “trick” in the sense often used by people, as in “bag of tricks”, or “a trick to solving this problem …”, or “trick of the trade”. In referring to our 1998 Nature article, he was pointing out simply the following: our proxy record ended in 1980 (when the proxy data set we were using terminates) so, it didn’t include the warming of the past two decades. In our Nature article we therefore also showed the post-1980 instrumental data that was then available through 1995, so that the reconstruction could be viewed in the context of recent instrumental temperatures. The separate curves for the reconstructed temperature series and for the instrumental data were clearly labeled.

The reference to “hide the decline” is referring to work that I am not directly associated with, but instead work by Keith Briffa and colleagues. The “decline” refers to a well-known decline in the response of only a certain type of tree-ring data (high-latitude tree-ring density measurements collected by Briffa and colleagues) to temperatures after about 1960. In their original article in Nature in 1998, Briffa and colleagues are very clear that the post-1960 data in their tree-ring dataset should not be used in reconstructing temperatures due to a problem known as the “divergence problem” where their tree-ring data decline in their response to warming temperatures after about 1960.  “Hide” was therefore a poor word choice, since the existence of this decline, and the reason not to use the post 1960 data because of it, was not only known, but was indeed the point emphasized in the original Briffa et al Nature article. There is a summary of that article available on this NOAA site:
http://www.ncdc.noaa.gov/ paleo/ globalwarming/ briffa.html
There have been many articles since then trying to understand the reason for this problem, which applies largely to only one very specific type of proxy data (tree-ring wood density data from higher latitudes).

As for my research in this area more generally, there was a study commissioned by the National Academies of Science back in 2006 to assess the validity of paleoclimate reconstructions in general, and my own work in specific. A summary of that report, and link to it, is available here:
http://www.realclimate.org/ index.php/ archives/ 2006/ 06/ national-academies-synthesis-report/

The New York Times (6/22/06), in an article about the report entitled  “Science Panel Backs Study on Warming Climate”  had the following things to say:

A controversial paper asserting that recent warming in the Northern Hemisphere was probably unrivaled for 1,000 years was endorsed today, with a few reservations, by a panel convened by the nation’s preeminent scientific body…At a news conference at the headquarters of the National Academies, several members of the panel reviewing the study said they saw no sign that its authors had intentionally chosen data sets or methods to get a desired result. “I saw nothing that spoke to me of any manipulation,” said one member, Peter Bloomfield, a statistics professor at North Carolina State University. He added that his impression was the study was “an honest attempt to construct a data analysis procedure.”

2. “Perhaps we’ll do a simple update to the Yamal post. As we all know, this isn’t about truth at all, its about plausibly deniable accusations.” (from me)

This refers to a particular tree-ring reconstruction of Keith Briffa’s. These tree-ring data are just one of numerous tree-ring records used t
o reconstruct past climate.  Briffa and collaborators were criticized (unfairly in the view of many of my colleagues and me) by a contrarian climate change website based on what we felt to be a misrepresentation of their work.  A further discussion can be found on the site “RealClimate.org” that I co-founded and help run. It is quite clear from the context of my comments that what I was saying was that the attacks against Briffa and colleagues were not about truth but instead about making plausibly deniable accusations against him and his colleagues.

We attempted to correct the misrepresentations of Keith’s work in the “RealClimate article mentioned above, and we invited him and his co-author Tim Osborn to participate actively in responding to any issues raised in the comment thread of the article which he did.

3. “Can you delete any emails 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 email Gene and get him to do the same? I don’t have his new email address. We will be getting Caspar to do likewise.” (from Phil Jones)

This was simply an email that was sent to me, and can in no way be taken to indicate approval of, let alone compliance with, the request. I did not delete any such email correspondences.

4. “I think we have to stop considering Climate Research as a legitimate peer-reviewed journal. Perhaps we should encourage our colleagues in the climate research community to no longer submit to, or cite papers in, this journal” (from me)

This comment was in response to a very specific incident regarding a paper by Soon and Baliunas published in the journal “Climate Research”. An editor of the journal, with rather contrarian views on climate change, appeared to several of us to be gaming the system to let through papers that clearly did not meet the standards of quality for the journal. The chief editor (Hans von Storch), and half of the editorial board, resigned in protest of the publication of the paper, after the publisher refused to allow von Storch the opportunity to write an editorial about how the peer review process had failed in this instance.

Please see e.g. this post at RealClimate:
http://www.realclimate.org/ index.php/ archives/ 2009/ 11/ the-cru-hack-context/
(3rd bullet item–see the various links, which lead to letters from chief editor Von Storch, and an article by the journalist Chris Mooney about the incident).

Scientists all choose journals in which we publish and we all recommend to each other and our students which journals they should publish in. People are free to publish wherever they can and are free to recommend some journals over others. For an example of this behavior in daily life, people make choices and recommendations all the time in their purchasing habits. It is highly unusual for a chief editor and half of an editorial board to resign and that indicates a journal in turmoil that should possibly be avoided. Similarly, authors are allowed to cite any papers they want, although usually the editor will note incorrect or insufficient citing.

I support the publication of “skeptical” papers that meet the basic standards of scientific quality and merit. I myself have published scientific work that has been considered by some as representing a skeptical point of view on matters relating to climate change  (for example, my work demonstrating the importance of natural oscillations of the climate on multidecadal timescales).  Skepticism in the truest scientific sense of the word is good and is indeed essential to science.  Skepticism should not be confused, however, with contrarianism that does not meet the basic standards of scientific inquiry.

5 “‘It would be nice to try to contain the putative “MWP” (from me)

In this email, I was discussing the importance of extending paleoclimate reconstructions far enough back in time that we could determine the onset and duration of the putative “Medieval Warm Period”. Since this describes an interval in time, it has to have both a beginning and end. But reconstructions that only go back 1000 years, as most reconstructions did at the time, didn’t reach far enough back to isolate the beginning of this period, i.e. they are not long enough to “contain” the interval in question. In more recent work, such as the IPCC Fourth Assessment Report published in 2007, the paleoclimate reconstructions stretch nearly 2000 years back in time, which is indeed far enough back in time to “contain” or “isolate” this period in time.

I think it very useful and worthwhile for scientists to explain the science and to explain any misrepresentations of what they have said or written (see Let’s look at one of the illegally hacked emails in more detail — the one by NCAR’s Kevin Trenberth on “where the heck is global warming?”).  I will continue to write about both.

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