The Global Warming Scam: Texts and Commentary

by John Pittman

Historical Perspective of Why Yamal Matters

I can say conclusively that the hacked emails are just blips of information that will have absolutely no impact whatsoever on the push to get policymakers to back the science,” said Anne Kelly, the policy director at Ceres, a sustainable business network whose members include PepsiCo, American Airlines and Bloomberg. Already the damage control is starting. The Monbiot is a classic. “”But do these revelations justify the sceptics’ claims that this is “the final nail in the coffin” of global warming theory?(8,9) Not at all. They damage the credibility of three or four scientists. They raise questions about the integrity of one or perhaps two out of several hundred lines of evidence. To bury manmade climate change, a far wider conspiracy would have to be revealed””.

This poor thinking and straw man/red herring mix needs to be challenged each time it is repeated. The first is just nonsense. I have spent three days and still have 80 more pages to read and study, after this long post, and this is just a partial list per the posters. Since this was a partial list per the posters, and no one has had time to analyze the impact, using an absolute term (absolutely no) that it will have no impact after a few short days, means that it is not about science at all. Though that statement of no impact may end up being true, it means that they have concluded the science doesn’t matter, because these blips of information show that the deck was stacked, and impartial science was evaded, purposedly. If the statement by Kelly is true, each person should contact their representatives and complain about being misled that this was about science and not greed, by PepsiCo and others, in pursuit of tax dollars, or cap and trade dollars.

The Monbiot is a classic due to the misleading by using facts to ignore the argument. The first point is that the basic global warming theory is based on sound physics. Little argument on basic facts. It is the magnitude that is important. Second, it ignores the historical development of the IPCC’s work, which we will examine below. The credibility damage of three or four scientists is also misleading. These are not just any scientists. No, these are the ones for whom it will be shown they took the AGW meme from “influencing global climate” to “global climate change is the greatest threat facing mankind.” Expect others to soon follow trying to downplay what occurred. This development, from just an influence to a catastrophe, will be detailed, and it will show that there will probably be a long line of misleading apologists in the near future. Next are a straw man and a red herring. It started with global warming theory and it highlights “one or perhaps two out of several hundred lines of evidence”. The hundreds of lines of evidence concern warming, not AGW. In paper after paper measuring the change, AGW is cited as the cause. But the papers have nothing to do with proving AGW, they only document the changes. Yes, it has been getting warmer since the Little Ice Age. Typical “bait and switch”. Few are arguing about all the lines of evidence showing that is getting warmer. The real argument concerns present temperature, past temperature, climate sensitivity and climate predictions (projections). To understand what the furor is about one has to go back to the SAR.

The story starts with the first CRU FOI text file Alleged CRU Email – 857677215.txt. Selected quotes below. I have cut out repetitive email, etc. I have also reformatted some for space requirements. This has the possibility of introducing small errors. I highly recommend that persons go to the originals that can be searched with “larch” and “sensitivity.”

The time is 1997. MBH has not been published and the IPCC has published the second assessment (SAR). The first email shows that the SAR has unresolved issues dealing with past climate resolution. It is a proposal. Issues that should be familiar with all critics of the post MBH98 IPCC work. At the time of the SAR, Lamb’s Central England temperatures have the longest, most detailed, and best resolution for millennial scale reconstructions. It has a problem. It conclusively shows a warmer medieval warm period than the current period. In the first text, familiar concerns about forcings and strong climatic signals come into play. The SAR has a fatal problem for the alarmists of the IPCC. It cannot support the AGW call to arms. It basically has to say, we believe that the current warm period is influenced by man (it does not support being alarmed). The TAR WG1 in commenting on the SAR had this to say “the report concluded that the ability to quantify the human influence on global climate was limited.” Not exactly a war cry that can be expected to unite a world addicted to cheap carbon based energy. This is the SAR Chapter 8 Summary p 412 “these results indicate that the observed trend in global mean temperature over the past 100 years is unlikely to be entirely natural in origin. More importantly, there is evidence of an emerging pattern of climate response to forcings by greenhouse gases and sulphate aerosols in the observed climate record. Taken together, these results point towards a human influence on global climate.” The quotes below indicate why Yamal and Taimyr were considerd important and what was thought would be learned from the research.

From: Eugene Vaganov evag

To: k.briffa

Subject: from Vaganov

Date: Thu, 6 Mar 97 14:40:15 +0000 (KRS)

The specific objectives of this proposal are the development of two supra-long (each spanning 6-9000 years up to present) continuous larch ring-width chronologies at two distant each other high-latitude locations of Siberia (Yamal and Taimyr peninsulas). Ring-width chronologies developed from coniferous trees growing at the polar timberline in Siberia contain a very strong climatic signal, mainly summer air temperatures. With these chronologies high-resolution continuous and quantitative reconstruction of summer temperatures will be made.

3.2 OBJECTIVES This research will make a major contribution to our knoweledge of high-resolution climate variability at high latitudes of Western and Middle Siberia throughout the Holocene using the unique potential of tree-ring data. The specific objectives of this proposal are as follows:

– to develop two supra-long (each spanning 6-9000 years up to present) continuous ring-width larch chronologies at two high-latitude locations of Siberia; – using these tree-ring chronologies, to make a multi-millennial high-resolution continuous and quantitative reconstruction of summer temperatures;

– to analyse spatio-temporal patterns of temperature variability at these locations over a range of timescales (annual, decadal, multi-decadal and centennial) and their connections with various forcing factors and other annual resolution records being developed elsewhere in the Arctic and Subarctic.

3.3. BACKGROUND Reconstruction and analysis of natural climatic changes through the whole Holocene at high latitudes are of great importance as climatic conditions, especially air temperature, are most variable and sensitive to various forcing functions (Budyko, 1980; Jones and Kelly, 1983; Intergovernmental Panel on Climate Change, 1990). However, there are a minute quantity of long, precisely-dated and high-resolution proxy climatic series for these regions.

Tree rings as a proxy indicator of the past climatic conditions are of special interest as they allow to reconstruct climatic parameters with seasonal and annual resolution for many hundred and thousand years, to provide an exact absolute and relative dating of the tree-ring data, to establish high-frequency climate changes (from interannual to centennial timescales) with high confidence, to obtain dendroclimatic information practically for every site where trees grow at present or grew in the past.

Ring-width chronologies developed from coniferous trees growing at the polar timberline in moderate-continental and continental regions of Siberia contain a very strong climatic signal, mainly summer air temperatures of tree growth year (Graybill and Shiyatov, 1992; Briffa, Jones, Schweingruber, Shiyatov and Cook, 1995; Hantemirov, 1995; Vaganov, Shiyatov and Mazepa, 1996). The explained variance over the calibration and verification periods is highest reported in the literature to date (65-70%) and it allows to make a quantitative reconstructions of summer temperatures. These chronologies and temperature reconstructions will be the first to be so long, reliable, annually-resolved and precisely-dated with known reliability across the whole of northern Hemisphere. These reconstructions will allow to compare and contrast the details of temperature changes at the moderate-continental region of Yamal Peninsula with the continental region of Taimyr Peninsula and allow modern and predicted temperature patterns to be compared with variability patterns of pre-industrial era.

– The Climatic Research Unit of the University of East Anglia, Norwich, Great Britain is one of the world’s leading research organisation specialising in the study of climate change: climate history, current climates, projected changes and impacts. Dr. K.R.Briffa, Senior Research Associate at the Climatic Research Unit, has considerable experience in climatology and with the use of statistical methods of climate analyses and dendroclimatic reconstruction, especially with regard to large-spatial-scale reconstructions of climate patterns and published many articles on the theoretical and practical aspects of dendrochronology and dendroclimatology, and on use of paleoclimate data for understanding current and possible future climates.

Dr K.R.Briffa (Climatic Research Unit) will be the responsible scientist on the proposed project and he will take part in analysing growth-climate relationships, developing statistical models of tree growth, extracting climatic signal, reconstructing and analysing climatic conditions of the remote past.

The Russian laboratories together with the Climatic Research Unit of the University of East Anglia during 1997-1999 will be analysing the material obtained (standardization of individual series, development of mean chronologies, studying growth-climate relationships, developing statistical models of tree growth, extracting climatic signal, reconstructing and analysing climatic conditions of the remote past). This work will be finished at the end of 1999.

Along comes MBH98, and the MWP has disappeared. Better than that, the large variance of temperatures which would preclude getting excited even if warming was being caused by manmade greenhouse gases, have disappeared as well. The IPCC was so impressed, the paleo-graphs exploded across the third report (TAR). The furor climaxes with Mann being declared Time’s Man of the Year. Now the IPCC has a war cry. Temperatures have not been this hot for ten thousand years or more. It has to be manmade, and we must do something. It will be important to remember this chronology when the effects of recent revelations are discussed. It will be important to remember this is about the shaft, not the blade of the hockey stick. It will be important to remember that even back in 1997 that dendrochronology and dendroclimatology, use paleoclimate data for understanding current and possible future climates.

With the TAR, the UN realizes that they finally have a shot at getting something they always wanted. The legitimacy to tax, and disperse monies. For decades the UN had been thwarted by such countries as the United States that refused to give self funding authority to the UN. They refuse to give up their veto powers. Now comes a long an issue so large it cannot be ignored and selfish, sovereignty issues cannot be allowed to derail the salvation of the world. With the different systems, monies, etc, there has to be a brokerage for all the monies, regulations, and the day to day accounting that would be entailed to change the way humans obtain the largest fraction of energy used for civilization. And a model is proposed. The cap and trade that had worked for acid rain would provide a market mechanism that could be traded, accounted, and most basically, monies could be kept as a service charge. For governments it provided a way to access huge monies, take a small, basically hidden tax, and be justified on the basis of saving the world. However, the cap and trade has a problem. The acid rain (SO2) cap and trade worked because there were cheap alternatives. For a small increase in equipment costs, acid could be scrubbed. For a small increase in costs, cleaner fuel could be used. Something came along that took attention away from the fact that the SO2 model was inappropriate for GHG’s. The miserable record from the Kyoto Agreement proves that cap and trade, with offsets, works little, if at all, and more importantly, does cost a lot. That something was Al Gore’s “An Inconvenient Truth.” So begins the PR blitz that changes the policy scene to a media fest.

But there is a problem. After getting an argument that could be used to bring reluctant nations such as the United States, two researchers release a paper that destroys the poster boy “Hockey Stick.” Up to and beyond the 4AR, the self-named “Team” fights to save the Hockey stick. Even worse, their efforts expand to include the Briffa Yamal use. The Wegman and North reports demolish the use of certain chronologies and methodology of MBH98. Further negative developments include a court decision that the PR side, “An Inconvenient Truth” is propaganda. The basis for immediate and wide ranging action, and its most visible PR tool, is being derailed. At this point, I think an editorial comment is appropriate. After reading the selected emails that I used for this post, it appears that the Process is at fault and not Dr. Briffa. His recent statement of working on these dendro problems is reflected in the emails. He never stopped working on the science. Later when we start exploring just how important the MWP is, we find the pursuit of consensus ran rough shod over the science; and since Dr. Briffa was doing science, he and his work were simply not put in the best light. IMO. It is also apparent that from the beginning, a castle mentality was enforced from Dr. Mann especially that exists to this day as far as can be told, and unfortunately it does affect the claim of impartial science.

But there is another chronology that shows the “hockey stick.” It is the Yamal series, and it is latched on to in order to justify a claim of independent support for the hockey stick. It starts showing up in study after study. Fast forward to right before the release of the emails. It has taken the place of the discredited series and papers based on MBH. But, the persons, and now even more professionals are dissecting the Yamal, and Taimyr, and finding problems. So we will look at the history of the “hockey stick” controversy from the Yamal perspective tying it in with the overall development of the TAR and 4AR. The next quote outlines the fertilization question that became an issue with the MBH Wegman and North papers.

>>On Mon, 3 Nov 1997, Keith Briffa wrote:

>> I have been agonising for months that these results are not some

>> statistical artifact of the analysis method but we can’t see how. For just

>> two species (spruce in the western U.S. Great Basin area and larch in

>> eastern Siberia) we can push the method far enough to get an indication of

>> much longer term growth changes ( from about 1400) and the results confirm

>> a late 20th century apparent fertilization! The method requires

>> standardizing (localized mean subtraction and standard deviation division)

>> by species/age band so we reconstruct relative (e.g. per cent change) only .

>> We have experimented with integrating the different signals in basal area

>> and density(after extracting intra ring ring width and density data where

>> available) within a ‘flat mass’ measure which shows a general late 20th

>> century increase – but whether this incorporates a defensible relative

>> waiting on the different components (and what the relative carbon

>> components are) is debatable. We now need to make some horrible simplistic

>> assumptions about absolute carbon in these (relatively small) components of

>> the total biomass carbon pool and imlpications for terrestrial and total

>> carbon fluxes over the last few hundred years – and beyond! Without these

>> implications we will have difficulty convincing Nature that this work is

>> mega important.

The next quote outlines some of the objections skeptics have had of the use of paleoclimatic data. The email to Briffa indicate that the tree line and most favorable conditions were 5000-1700BC, and there is no evidence of the polar timberline moving northward for the past century (about 1897). This does not support the claim that CWP is special in terms of most favorable conditions for tree growth.

From: Rashit Hantemirov rashit

To: Keith Briffa k.briffa

Subject: Short report on progress in Yamal work Date: Fri, 9 Oct 1998 19:17:12 +0500

Reply-to: Rashit Hantemirov rashit

Dear Keith, ………….

According to reconstructions most favorable conditions for tree growth have been marked during 5000-1700 BC. At that time position of tree line was far northward of recent one. [Unfortunately, region of our research don’t include the whole
area where trees grew during the Holocene. We can maintain that
before 1700 BC tree line was northward of our research area. We
have only 3 dated remnants of trees from Yuribey River sampled
by our colleagues (70 km to the north from recent polar tree
line) that grew during 4200-4016 and 3330-2986 BC.] …..During last 3600 years most of reconstructed indices have been varying not so very significant. Tree line has been shifting within 3-5 km near recent one. Low abundance of trees has been fixed during 1410-1250 BC and 500-350 BC. Relatively high number of trees has been noted during 750-1450 AD. There are no evidences of moving polar timberline to the north during last century.

The next quote supports the previous posts of Why Yamal Matters. In this email sensitivity, Bayesian criteria, and other items are discussed. By the time of the 4AR, this approach with millenial reconstructions are used to justify the claim that only with CO2 forcings can models replicate the CWP. But there will remain a problem that McIntyre, McKitrick, and others continue to explore to this day, and was shown in the Wegman report. The high resolution reconstructions needed for claiming very likely, and that most of the warming of the latter part of the 20th century are not truly independent. In a seemingly prescient way, Wegman outlines how the team is writing with each other, reviewing each others papers, and the recent email released show that they were gaming the system against those who were not in their group, according to what I will show below, releases in blogs, and in newspapers across the world. It casts a bad light on those involved. For the innocent, there is an old saying “One should not complain of fleas, when sleeping with dogs.”

From: Bryson Bates bryson

To: Barrie Pittock barrie.pittock

Subject: Re: uncertainties guidance paper

Date: Mon, 14 Dec 1998 18:58:01 +0800 (WST)

Cc: “‘econf.part2’”


> 6. Regarding para. 67, I am more concerned about the “best” or “central”

> estimate for climate sensitivity of 2.5 deg.C for 2xCO2 than about the

> range. Several lines of evidence (paleo-evidence, fitting models to the

> last 100 years, the distribution of improved model results) all suggest

> that the “best estimate” for this increasingly dated and artificial

> notion should be raised from 2.5 to nearer 3.5. This would be

> controversial, but I believe it would also be giving the best advice

> possible. Whatever you believe is the correct number, the level of

> concern such a change would raise is in itself evidence for the

>importance of central estimates in the climate change debate.
This could be investigated and quantified in a Bayesian framework.

> 7. I share Martin Manning’s problems with the use of the term “Bayesian”

> and equating it with “subjective”. Personally I think this paper should

> avoid such specialist technical terms if possible, especially if there

> is disagreement about what they mean!

Yes: Bayesian methods provide a means of combining prior (expert) knowledge with data to quantify the posterior distribution. The prior knowledge may be based on the results of previous experiments and need not be subjective. Another point is that formal application of Bayesian methods usually leads to problems that are analytically intractable. The recent development of Markov chain Monte Carlo methods has largely overcome this.

The next one is one of those unbelievable ones that needs to be included to understand some of the apologists comments. In 1999, they did not work on the assumption that the scenarios were realistic. More importantly, they did not, or at least Dave did not have full confidence in climate system model projections of confidence. The important part for this post is the appraising of problems, certainties, etc. were considered. This will preclude apologists (or should) trying to claim later that somehow the effects of models, paleo reconstructions, and their effects somehow were not considered when we start dissecting the effect of MBH and Yamal.

From: Dave Schimel schimel

To: Shrikant Jagtap sjagtap Subject: RE: CO2

Date: Mon, 17 May 1999 09:21:35 -0600 (MDT)

Cc: franci <franci, Benjamin Felzer <felzer, Mike Hulme <m.hulme, schimel, wigley, kittel, nanr, Mike MacCracke mmaccrac

I want to make one thing really clear. We ARE NOT supposed to be working with the assumption that these scenarios are realistic. They are scenarios-internally consistent (or so we thought) what-if storylines. You are in fact out of line to assume that these are in some sense realistic-this is in direct contradiction to the guidance on scenarios provided by the synthesis team.

If you want to do ‘realistic CO2 effects studies, you must do sensitivity analyses bracketing possible trajectories. We do not and cannot and must not prejudge what realistic CO2 trajectories are, as they are ultimatley a political decision (except in the sense that reserves and resources provide an upper bound).
‘Advice’ will be based on a mix of different approaches that must reflect the fact that we do not have high coinfidence in GHG projections nor full confidence in climate system model projections of consequences.

The next email is posted to show that if these are not authentic, it should be easy to prove. In this discussion, problems are outlined; and I love the response, pick a value. Kinda like pic-a-flic climate sensitivity. But this is apparently one of those expert conversations that would require a lot of expertise to say that the response was inappropriate. Just what one would expect in emails among professionals with a difficult subject.

From: David Viner d.viner

To: m.hulme, s.raper

Subject: Fwd: Re: Climate Sensitivity

Date: Tue, 18 May 1999 11:48:40 +0100

The climate sensitivity of HadCM2…..pick a value between 2.5 and 4.1K


>Envelope-to: f046

>Date: Tue, 18 May 1999 11:27:48 +0100 (BST)

>From: T Johns tcjohns

>Subject: Re: Climate Sensitivity

>To: d.viner

>Cc: tcjohns



>Hi David,


>I have just got back from leave today – sorry for the lack of response

>to your emails.


>On climate sensitivity, the equilibrium sensitivity in HadCM2 was difficult

>to get a definitive answer for initially as the conventional slab experiment

>was unstable, so we estimated it from part of a transient coupled run

>instead. We quoted 2.5 K in the original Nature paper. Recently we

>have done a HadAM2 slab experiment (modified sea ice and slab ocean physics)

>which indicated 4.1 K rather than 2.5 as an equilibrium value. This is

>quoted in a paper submitted as a CMIP study. The HadAM3 conventional

>slab experiment gave the 3.3 K figure I think. The HadCM2 discrepancy

>indicates the perils of this yardstick; other research here suggests that

>the effective climate sensitivity does respond to climate change feedbacks

>in transient experiments (with HadCM2 particularly). The early 2.5 K

>estimate has been revised upwards based on a long coupled run of HadCM2 to

>be closer to the 3.3 K we got from HadCM3 equilibrium slab experiments.


>Comparing transient temperature responses to similar time-varying forcing

>may be a better indication of real sensitivity, but so long as we quote

>single climate sensitivity numbers I fear that there is scope for confusion.




Now that we have established that the emails appear to be real, and that the work supports the development of combining reconstructions for model sensitivity as was written in TAR and 4AR, we go to the heart of the issue. The next email is in 2001. In it is the discussion of the claim that the MWP is not as warm as the CWP. T.L. Delworth has some insightful questions. In order to understand that the MBH98 did not immediately turn the SAR and proxies over, this is a mustread. It also shows that the proxy reconstructions and models go hand in hand. This is a point the apologists will want to ignore. I have included just the parts that support that ongoing discussions of models and contentions about the MWP wrt CWP were occurring. Obviously, a draft of a letter to be published may be historically interesting, but the final letter should be the one read, and considered. It would be inappropriate to argue its (draft) merits.

From: “Thomas L. Delworth” td

To: “Michael E. Mann” mann

Subject: Re: letter to Science

Date: Thu, 01 Mar 2001 08:19:45 -0500

Cc: tom, hpollack, mhughes, rbradley, p.jones, k.briffa
Dear Mike et al,

I offer the following comments on your letter for your consideration.

It seems to me there are 2 primary issues to address: (A) what does proxy evidence say about whether the Medieval Warm period was global (B) what do we know about potential mechanisms for the Medieval Warm period (i) evidence for a forced phenomenon (ii) evidence for internal variability. Issue (A) is currently dealt with in your sections (1) and (2). One point that could be perhaps conveyed more clearly is the necessity of using the spatial information conveyed in (multi) proxy reconstructions, rather than overly interpreting sets of local proxy evidence. I felt this point could have been stressed more, and is one which the casual reader may not appreciate. Issue (B, Bi) is in your section (3). I suggest a more explicit mention of conclusions with regard to the Medieval Warm period in recent work on this topic. The first statement in this section doesn’t provide (I don’t think) explicit evidence to back itself up. The sentence starting “These results …” could be more explicit about what those studies show with respect to the Medieval Warm period, in addition to the more general statement about the partitioning between forced and internal variability. A reader could ask “Ok, if 50% of the variability is explained by volcanic and solar forcing, that doesn’t exclude the other 50% playing a strong role for events such as the Medieval Warming.” Such a question could be dealt with in advance by stating what role these studies suggest for radiative forcing in the Medieval Warm period.


(1) I agree with the overall message you are conveying, but might choose somewhat differing wording in a place or two. The statement is made “(1) It cannot reasonably be argued that the Middle Ages were as warm as the 20th century at global or hemispheric scales.” This might be a bit strong … I would think one can have a reasoned discussion on this topic. Perhaps something like “We strongly disagree with the assertion that the Middle Ages were as warm as the 20th century at global or hemispheric scales.”

Tom Delworth


pps I previously provided to Tom correlations between the THC and global/hemispheric temperature based on a 900 year run of our R30 coupled model. These correlations were relatively low (0.27), but probably significant. The applicability of those correlations to the issue of the Medieval Warming may not be strong. If the Medieval Warming is a multi-century event, then I should really be looking at the correlations of low frequency (>50 years) filtered model output from a run of several millenia duration. Thus, the 900 year run may not be applicable. I will revisit this topic using a multi-millenial R15 coupled run, but probably won’t have any results today. I don’t think that would change the essential conclusions, however. I recall that experiments with the R15 model in which the THC was substantially weakened through the addition of fresh water to the North Atlantic provided strong regional temperature anomalies, but their global expression was small. These experiments are being repeated with the higher resolution model. In light of these issues, I suggest that the focus be not so much on saying the THC cannot be responsible for the Medieval Warming, but rather on saying (1) there is strong evidence for a substantial role of radiative forcing, and (2) the burden is on the author to provide evidence for the role of the THC.


“Michael E. Mann” wrote:

> Dear Colleagues,


> Below is a draft of a short letter to Science that Tom Crowley and I

> have put together, after discussing w/ Phil, Ray, and Malcolm. We

> feel that a reply to Broecker’s recent “Perspectives” piece is

> warranted to correct several misconceptions that Wally unfortunately

> chose to perpetuate


> Thanks in advance for your feedback,


> mike

> _________________________________________
> Medieval Warming Redux

In a recent “Perspectives” opinion piece, W. Broecker suggests that the “hockey stick” reconstruction of climate change over the past 1000 years – with extreme warming only in the late 20th century – is incorrect, and that the so-called “Medieval Warm Period” was at least as warm as the 20th century and due to oscillations in the thermohaline circulation. To reach this conclusion, Dr. Broecker rejects traditional empirical “proxy” climate indicators of past climate (e.g. tree ring, ice core, coral, and long historical documentary records) that are the foundation of a number of hemispheric reconstructions, as well as our current best physical understanding of the factors controlling climate at century-to-millennial timescales. We disagree with Broecker on several major points: (1) It cannot reasonably be argued that the Middle Ages were as warm as the 20th century at global or hemispheric scales. Although regional warmth during the Middle Ages may have sometimes been significantly greater than present, four different hemispheric-scale reconstructions (Jones, Mann, Briffa, Crowley) have been completed for the last 1000 years — all of them showing warmth in the Middle Ages that is either no warmer or significantly less than mid-20th century warmth. This is because it has been known for a quarter of a century that the timing of warmth during the Middle Ages was significantly different in different regions (Lamb, Dansgaard, Hughes). Failure to take this observation into account can lead to serious errors in the inference of hemispheric temperature trends


Our conclusion is also supported by measurements from tropical glaciers indicating an unprecedented level of recent warming with respect to the last 1,000-2,000 years (Thompson). (2) High-resolution proxy climate records which form the foundation of recent hemispheric temperature reconstructions are far more reliable indicators of century-to-millennial scale climate variability than is implied by Broecker. The potential limitations in interpreting long-term climate change from proxy indicators such as tree rings, have been long recognized by dendroclimatologists (e.g., Cook “segment curse” paper) and are almost always taken into account in framing interpretations of long-term trends. For example, Mann et al (1999) verified that a significant subset of multiple-millennial length tree ring and ice core proxy climate indicators used to reconstruct the trend over the past millennium passed rigorous statistical tests for fidelity at the millennial timescale, and that the basic attributes of the hemispheric reconstruction using more recent non-tree ring proxies available over the past few centuries yielded essentially the same result as that based on both tree ring and non-tree ring based information (Mann et al, Earth Interactions, 2000). Several independent reconstructions (Jones et al and Crowley and Lowery ), using a wide variety of proxy climate indicators and different statistical approaches, yield similar hemispheric temperature trends. Even the centennial-scale changes within the so-called “Little Ice Age” of the 15th-19th centuries are largely in agreement. Furthermore these centennial changes have been shown to be in “agreement”, rather than “in opposition” (as argued by Broecker) with evidence from alpine glacial advances

(4) It is not justifiable to argue that changes in the thermohaline circulation cause significant hemispheric or global changes in temperature. Although changes in the conveyor play a major role in the Atlantic Basin, to a first approximation changes in ocean circulation simply redistribute heat on the planet without significantly raising global temperature, or even hemispheric temperature. This conclusion is born out by very low correlations between warmth in the Greenland sector and the hemispheric indices over the last 1000 years (Crowley footnote ref.), a low correlation that is shared by coupled model experiments (Delworth citation)? In fact, sediment core data from the subtropical North Atlantic often cited as indicative of a distinct “Medieval Warm Period” and “Little Ice Age” (Keigwin Sargasso Sea), has recently been shown to be more consistent with changes in the North Atlantic Oscillation (Keigwin and Pickart), implying a zero sum pattern of regionally alternating warm and cold superimposed on far more modest hemispheric variations over the past 1000 years. This pattern itself may be forced, rather than internal in nature, and would explain the limited evidence for more dramatic cold and warm periods in regions such as Europe (see Mann, Sci Perspective, 2000). The above arguments lead us to conclude that, although the conveyor may be changing, radiative forcing perturbations were primarily responsible for centennial-millennial changes in the last 1000 years, with attendant implications for interpretation of earlier Holocene oscillations (e.g, Denton and Karlen). Furthermore, the weight of evidence indicates that the late 20th century hemispheric warming is significantly greater than the Middle Ages.

Michael E. Mann

Thomas J. Crowley


> Professor Michael E. Mann


Thomas L. Delworth

GFDL/NOAA e-mail: td

The next email (truncated) shows that the last few hundred to a thousand years are most relevant to potential future changes. In this email, it is wished that people read the IPCC. Agreed, especially how the models and reconstructions were used to attribute climate change. But most interesting is that there are concerns about the uncertainties about the reconstructions. This precedes M&M papers. The correspondence shows Mann’s concern with 2C millennial trends, and his opinion that such are not supported. Another note, is the comment of only 4 useful sites for reconstructions over the past thousand years. Most important is that this is 2001, and T.R. Karl states that “”we really need to show how the data prior to 1600 stands up. Some contend there are only 4 good sites in the first part of the record.”” It is ironic that Dr. Mann states “”But the claims we make (e.g. the anomalousness of recent warmth) are guided by the substantial uncertainties in the reconstructions, which of course take into account uncertainty due to increasingly sparse information back in time, and I have yet to see any legitimate argument that our reconstruction (or Phils, Toms, Keiths, etc.) is “wrong” within the context of the diagnosed uncertainties.”” This became one of the contentions of M&M. Further, the NAS report (North) concluded that reconstructions past about 1600 were too uncertain to be used conclusively. The opposite of Dr. Mann’s claim June 2001. Another quote shows that at this time the “hockey stick” is the basis for comparison and considered the final arbitrator “”It avoids the issue that the recent temperature increase is outside any estimates of natural variability without any forcings. What else is the warming due to? On p 14, it does not sum up the forcings and make a clear statement about the total. Nowhere does it say that the recent warming has to be because of an increase in heating.”” There is a lot of information in this email. I have not truncated it much. This is because this is an important time period, and the email links the historical events, and highlights their context. The “hockey stick” has won at this point. It was the measuring stick and was used in the TAR in an “unprecedented” manner.

From: Phil Jones p.jones

To: “Michael E. Mann” <mann, Thomas R Karl Thomas.R.Karl

Subject: Re: NRC report on climate change

Date: Tue, 12 Jun 2001 08:46:36 +0100

Cc: trenbert,”Michael E. Mann” <mann, rbradley Crowley <tom, mhughes, Folland Chris ckfolland
< x-flowed>

Dear All,

I’d just like to echo all the points made by Mike and Kevin. The logic behind saying that there isn’t enough paleo data before 1600 yet there may have been even early millennia which experienced warming of almost 2 C per millennium escapes me. As Kevin points out they have mixed up all the various factors that force climate on interannual to intermillennial timescales. One of the main points of IPCC is to synthesize the science, with particular reference to potential future changes. Changes in the distant past (glacial and deglaciation) are of less relevance to the 21st century because of differences in boundary conditions. The last few hundred to a thousand years are clearly more important to the near future. At least from my quick reading there seems no explicit reference to changes in the thermohaline circulation. Perhaps the paleo people on this list need to redouble their efforts to empahasize the importance of the last few thousand years, stressing absolute dating, calibration and verification. Another issue that is mixed up in the report (apart from the forcing) is spatial scales. I will try and address these at the Chicago meeting. What are the 4 useful sites ? I just hope in the US that people read the full IPCC reports and the summaries, rather than this hastily cobbled together document. I also hope that Europeans don’t read it. It has already got some air time here and may get some more with Bush here this week. Issues like star wars and capital punishment were commented upon whilst I came to work. Kyoto wasn’t mentioned.



At 10:45 11/06/01 -0400, Michael E. Mann wrote:

Hi Tom,

Thanks for your message. I know how hard you worked to make the report as balanced as possible, and realize this experience must have been a bit frustrating for you, after all the careful and hard work you and Chris put into our IPCC chapter. While the idea that the limited panel involved in the NAS report can provide an improved or more objective assessment of the science relative to IPCC seems, of course, ridiculous to a lot of us. But I’m very thankful you were on the panel. Needless to say, my criticism below is in no way directed towards you, but rather some of the other panel members whom I think did a real injustice to the science.

Having seen the list of authors and reviewers of the report, I think I have a pretty good idea what the source of a good deal of that skepticism is and I think much of it is spurious and unfair. There are legitimate caveats and uncertainties–I think we’ve been very honest about these in our publication, and we (as Phil, Keith, and others) are working earnestly to improve the reconstructions. But the claims we make (e.g. the anomalousness of recent warmth) are guided by the substantial uncertainties in the reconstructions, which of course take into account uncertainty due to increasingly sparse information back in time, and I have yet to see any legitimate argument that our reconstruction (or Phils, Toms, Keiths, etc.) is “wrong” within the context of the diagnosed uncertainties. Unfortunately, much of the criticsm that has been advanced recently is knee-jerk and unsubstantiated, particularly with regard to dendroclimatological issues (which Malcolm and Keith can comment on best). Much of this has to do w/ a lack of understanding of tree ring information (to be honest Tom, I didn’t see one name in the list of authors or reviewers of the NAS report whom I think is qualified to comment on dendroclimatological climate reconstruction and its strengths and weaknesses, and that is a real problem. In such a vaccum it is easy, for example, for Wally to wave around some highly non-standard, un peer-reviewed tree-ring analysis that he has been promoting (which Ed Cook himself, a co-author on this, admits makes use of a questionable standardization approach), in an attempt to dismiss all other climate reconstructions which use tree ring information. The criticism that there are only “4 useful sites” for reconstructing climate over the past 1000 years is especially irksome and ignorant. Does Tom C. agree that there are only 4 meaningful records that contribute to his reconstruction? Does Phil, or Keith? Where does that number come from? The same source as R.L.’s GHG sensitivity factor of 1.0 (i.e., the ether) I suspect.

The discussion of paleo in the report (which I realize you had very limited control over) is disturbingly misleading and flawed to many of us who actually work in this area. There are throwaway statements about millennial trends of 2 C in global temperatures being typical during the early Holocene that have no basis in fact. They are again probably based on this increasingly disturbing notion that Arctic ice core borehole thermometry or other ice core information tells us anything at all about the hemisphere let alone globe. A small number of scientists are really misleading the scientific community in this regard. How odd that the panel was happy to claim that there were millennial periods with 2 degree C warming in global temperature during the holocene (for which there is no reliable empirical evidence whatsoever) and yet focuses its skepticism on much more detailed and careful assessments of the most recent millennium. I think you can see why some of us are frustrated by this type of inconsistency, and suspect some degree of bias or agenda at work. There was a clear bias in the panel in the promotion of ice cores (which sample a very limited portion of the globe and are very questionable in their ability to say *anything* about hemispheric or global temperature variations). I am disturbed by this because the NAS report shouldn’t have been promoting a particular specific area of funding. It seems to have.

Finally, with regard to one of the primary supposed discrepancies in the paleo record of the past 1000 years, temperature reconstructions from boreholes vs. other proxies, I’ll be presenting some results in Chicago which I think you’ll all find quite elucidating. Turns out there is no discrepancy after all. More on that soon. I’ll also try to confront both the “real” and “imagined” sources of uncertainty and bias in paleoreconstructions in my presentation there, and we should all be able to have a very healthy discussion of this.

I really think that there was a bias in this panel which cannot be considered representative of the community as a whole. So I vote that we not over-react. I’m anxious to see Lindzen, Broecker, or Mike Wallace publish a peer-reviewed critical analysis of proxy data over the past 1000 years. Until that day, I take their comments w/ a shaker of salt…

> At 09:41 AM 6/11/01 -0400, Thomas R Karl wrote:

I agree with most of your points. It was a very interesting Panel. I should emphasize however, that the Paleo record (at least the last 1000 years) has many critics, and we really need to show how the data prior to 1600 stands up. Some contend there are only 4 good sites in the first part of the record. I am not sure of this, perhaps Mike and others will explain this in Chicago.

Regards, To
>> Kevin

Trenberth wrote:>>

>> > FYI

>> > Some comments on the NRC/NAS report on the IPCC and global warming >
>> > Kevin Trenberth 6/7/2001

While the report overall is an endorsement of the IPCC report and the process, it has a lot of “buts” in it, and the overall tone is to somewhat downplay the problem. It does not focus on policy relevant issues. The report was done in a very hurried fashion and perhaps as a result, there are several factual errors or misstatements and there are errors of omission. My impression is that it tends to overstate the caveats and need for questioning of results and understate the certainties and likelihoods. 1. In dealing with natural variability, there are two aspects that are mixed in this report. There is natural variability of climate that is tied to external forcings, such as variations in the sun, volcanoes, and the orbital variations of the Earth around the sun. The latter is the driver for the major ice ages and interglacials. The second kind of natural variability is that internal to the climate system arising from interactions between the atmosphere and ocean, such as El Nino, for instance. This variability occurs even in an unchanging climate. In the section dealing with this and in the summary, both kinds of variability are discussed as if they are the second kind. Glacial to interglacial differences are discussed without any mention of the known causes and as if these can happen without a cause. This is misleading at best. A consequence is that there is no clear statement that the recent warming is outside the realm of natural variability – and that a cause is needed. And the cause is human induced changes in the atmospheric composition. 2. The report does not clearly address issues in attribution of recent climate change to human activities. At the end of p 3 in the summary it makes an equivocal statement. It avoids the issue that the recent temperature increase is outside any estimates of natural variability without any forcings. What else is the warming due to? On p 14, it does not sum up the forcings and make a clear statement about the total. Nowhere does it say that the recent warming has to be because of an increase in heating. This reasoning also put limits on how large aerosol cooling can be. On p 17, the ambiguity over the term “natural forcing” is used to say that a causal link can not be unequivocally established. It does not mention estimates of variability from the paleo record and how well they agree (or not) with model estimates. It does not note on p 17 that many models show the signal of greenhouse gas effects emerging from the noise of natural variability about 1980. The attribution statement is weak.


>> > —————

>> > Kevin E. Trenberth e-mail: trenbert


> Professor Michael E. Mann

Prof. Phil Jones

Next is a very truncated email. The part that is interesting is the coupling of reconstructions with modeling. Except for special cases, further examples are not necessary to show that proxy data and models were used as it is indicated in the IPCC reports.

From: “Michael E. Mann” mann

To: Hans von Storch Hans.von.Storch

Subject: Re: EOS report

Date: Tue, 03 Jul 2001 15:04:58 -0400

Cc: “Michael E. Mann” <mann, Julie Jones <jones, Julia Cole <jcole, rbradley, jto, weber, wanner, tom crowley <tom, k.briffa, Martin Widmann Martin.Widmann

>>>If you mean ‘forward modelling’, by what I term upscaling, this is done

>>>in exactly the same way as most other climate reconstructions,

>>>i.e. calibrating proxy data against climate data using linear multivariate

>>>statistical methods (in this case I use CCA), so has the same errors

>>>inherent in it as other reconstructions where proxy data has been

>>>calibrated against large-scale climate, or climate indices.


>>>If your idea is that such large-scale climate reconstructions may have

>>>additional uncertainties compared to local empirical models, where proxy

>>>data are calibrated against local climate records, I agree that this is

>>>so – but I think this applies to all such non-local reconstructions, so

>>>should maybe go in the paragraph which discusses reconstructions of

>>>regional climate variability to keep things consistent.







>>>Dr. Julie M. Jones

The next is a lengthy email concerning support of the MWP and different proxy reconstructions. The reading makes it obvious that the amplitude does matter (the shaft not the blade). It also appears that Dr. Mann’s concern is the support for the IPCC. Without a doubt it shows that for Dr. Mann’s part, weakening of the claim of warmest in the millennia was to be contested. The exchanges also indicate that there are potentially serious problems with reconstructions back a thousand years. It also reveals that these scientists are serious about their work. There are so many great quotes here; I think this one will be popular. Dr. Briffa definitely is not backing down about the science. One showing why it is so important that the MWP and shaft stay as in MBH is this quote “…we felt justified in concentrating on one issue; that of the importance of the method of scaling and its effect on apparent “absolute” reconstruction levels. In our draft, we went on to say that this was crucial for issues of simple model sensitivity studies and climate detection, citing the work of Tom Crowley and Myles Allen….” Another great quote is “We can, of course, argue about what this means for the pre-1400 part of your reconstruction, when only 1 EOF was reconstructed…” Another showing that Dr. Briffa is determined “Finally, we have to say that we do not feel constrained in what we say to the media or write in the scientific or popular press, by what the sceptics will say or do with our results. We can only strive to do our best and address the issues honestly. Some “sceptics” have their own dishonest agenda – we have no doubt of that. If you believe that I, or Tim, have any other objective but to be open and honest about the uncertainties in the climate change debate, then I am disappointed in you also.” But the quote for the Yamal debate is this one: “One very important additional point that Malcolm makes in his message is that conservative estimates of uncertainties, appropriate additional caveats, etc. were indeed all provided in MBH99, and I have always been careful to interpret our results in the context of these uncertainties and caveats. IPCC ’2001 was careful to do so to, and based its conclusions within the context of the uncertainties (hence the choice of the conservative term “likely” in describing the apparently unprecedented nature of late 20th century warmth) and, moreover, on the collective results of many independent reconstructions. Briffa & Osborn would have you believe that IPCC ’2001′s conclusions in this regard rested on MBH99 alone. Frankly, Keith and Tim, I believe that is unfair to the IPCC, whether or not one cares about being fair to MBH or not.” This is the bone of contention that if reconstructions are not independent but that reconstructions based on Yamal, strip bark etc, are flawed, then the shaft no longer is a shaft and that infamous quote in 4AR that one cannot get the CWP without using CO2 is unsupportable. The science ends up going back to the SAR where it was determined that man was influencing the climate, not causing catastrophic destruction.

One quote that deserves special emphasis is this one:

All of our attempts, so far, to estimate hemisphere-scale temperatures for the period around 1000 years ago are based on far fewer data than any of us would like. None of the datasets used so far has anything like the geographical distribution that experience with recent centuries indicates we need, and no-one has yet found a convincing way of validating the lower-frequency components of them against independent data. As Ed wrote, in the tree-ring records that form the backbone of most of the published estimates, the problem of poor replication near the beginnings of records is particularly acute, and ubiquitous. I would suggest that this problem probably cuts in closer to 1600 than 1400 in the several published series. Therefore, I accept that everything we are doing is preliminary, and should be treated with considerable caution.

This is hardly the cry that will instill confidence in sacrificing modern civilization, but this is 2002 and that is the public claim. If anything shows through in these posts is that there is a whole lot less consensus and certainty than what they are telling policy makers. Now that critics are showing that the concerns of Dr. Briffa and others are legitimate, public revelation that this was already known will be a decided sore point that skeptics with an axe to grind will probably make good and often use. Remember this is the TAR with the claim of “the unprecedented late 20th century warming’ being used to drive policy. And, of course, with “An Inconvenient Truth”, it became the rallying cry for the necessity of remaking the modern industrial world.

But where do we go if Yamal and MBH are so flawed? We go back to the SAR. The statement accepting everything is preliminary and should be treated with caution was not given to the policy makers and the public. This statement becomes problematic when one considers what is just over the time horizon: McIntyre and McKitrick. If it is known that the tree rings form the backbone for the hemispheric temperature estimates exist with uncertainties and should be treated with considerable caution, then why was there such a negative reaction when M&M confirmed their suspicions voiced in this email? In hindsight, the “moving on” that the “Team” has been labeled with by McIntyre appears to be valid description. The problem is that while claiming that “peer reviewed” is the gold standard, the truth shown in the emails is that they gamed the system. From WSJ to WUWT, the gaming has been documented. So on the one hand, they will fight M&M by criticizing E&E, all the while trying to prevent a discussion in the peer reviewed literature that they knew from this email to be potentially, if not certainly, valid!

From: Keith Briffa k.briffa

To: “Michael E. Mann” <mann, p.jones, tcrowley, rbradley, mhughes, drdendro, rkerr, bhanson

Subject: Re: Briffa & Osborn piece

Date: Fri Apr 5 17:17:55 2002

Cc: Tim Osborn t.osborn

Dear Mike, (and interested colleagues)

Given the list of people to whom you have chosen to circulate your message(s), we thought we should make a short, somewhat formal, response here. I am happy to reserve my informal response until we are face to face! We did not respond earlier because we had more pressing tasks to deal with. This is not the place to go into a long or over-detailed response to all of your comments but a few brief remarks might help to clear up a couple of misconceptions. You consider our commentary on Ed and Jan’s paper “more flawed than even the paper itself” on the basis that scaling the relationship between full Northern Hemisphere and extratropical Northern Hemisphere is *much* more problematic than even any of the seasonal issues we discuss. In fact we did not do this. The curve labelled Mann99 in our figure was, in fact, based on the average of only the land areas, north of 20 degrees N, extracted from your spatially-resolved reconstructions. We then scaled it by calibration against the instrumental annual temperatures from the same region. This is, just as you stress in your comments on the Esper et al. paper, what should have been done. We think that this single point addresses virtually of all your concerns. We can, of course, argue about what this means for the pre-1400 part of your reconstruction, when only 1 EOF was reconstructed, but the essential message is that we did our best to exclude the tropics (and the oceans too!) from your series so that it could more readily be compared with the other records. The fact that we have used only the extra-tropical land from your data is not clear from the text, so we can see why you may not have appreciated this, but we think you will concede that this fact negates much of what you say and that we acted “more correctly” than you realised. Blame *Science* for being so mean with their space allocation if you want! Remember that this was an unrefereed piece and we felt justified in concentrating on one issue; that of the importance of the method of scaling and its effect on apparent “absolute” reconstruction levels. In our draft, we went on to say that this was crucial for issues of simple model sensitivity studies and climate detection, citing the work of Tom Crowley and Myles Allen, but this fell foul of the editor’s knife. You also express concerns about the calibration of Esper et al. (e.g., you say “if the authors had instead used the actual (unsmoothed) instrumental record for the extratropical northern hemisphere to scale their record, their reconstruction would be much closer to MBH99″). This point is wholly consistent with our discussion in the perspective piece, and indeed we show that in absolute terms the records are closer when Esper et al. is calibrated using unsmoothed data but since the variance is also reduced, the significance of the differences may be just as high. Finally, we have to say that we do not feel constrained in what we say to the media or write in the scientific or popular press, by what the sceptics will say or do with our results. We can only strive to do our best and address the issues honestly. Some “sceptics” have their own dishonest agenda – we have no doubt of that. If you believe that I, or Tim, have any other objective but to be open and honest about the uncertainties in the climate change debate, then I am disappointed in you also.

Best regards

Keith (and Tim)

At 12:39 PM 3/22/02 -0500, Michael E. Mann wrote:

Keith and Tim,

Sadly, your piece on the Esper et al paper is more flawed than even the paper itself. Ed, the AP release that appeared in the papers was even worse. Apparently you allowed yourself to be quoted saying things that are inconsistent with what you told me you had said. You three all should have known better. Keith and Tim: Arguing you can scale the relationship between full Northern Hemisphere and extratropical Northern Hemisphere is *much* more problematic than even any of the seasonal issues you discuss, and this isn’t even touched on in your piece. The evidence of course continues to mount (e.g., Hendy et al, Science, a couple weeks ago) that the tropical SST in the past centuries varied far more less in past centuries. Hendy et al specifically point out that there is little evidence of an LIA in the tropics in the data. The internal inconsistency here is remarkably ironic. The tropics play a very important part in our reconstruction, with half of the surface temperature estimate coming from latitudes below 30N. You know this, and in my opinion you have knowingly misrepresented our work in your piece. This will be all be straightened out in due course. In the meantime, there is a lot of damage control that needs to be done and, in my opinion, you’ve done a disservice to the honest discussions we had all had in the past, because you’ve misrepresented the evidence. Many of us are very concerned with how Science dropped the ball as far as the review process on this paper was concerned. This never should have been published in Science, for the reason’s I outlined before (and have attached for those of you who haven’t seen them). I have to wonder why the functioning of the review process broke down so overtly here,


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