Eamon,

Mann's graph had an R2 near zero, making it worthless. He must have known this, it's the primary validation measure, yet he presented his graph as if it was good evidence.

The point about bristlecones was that they're unsuitable for temperature reconstructions - they shouldn't have been used at all, instead Mann gave them greater weight than all other proxies. This is particularly strange as the bristlecone data was restricted to just one area of the US.

Marco,

I didn't know about the two instances of 20th c. freezing of the Baltic Sea. Thanks for pointing that out. At the same time, my point stands : Seina and Palosuo (1996) say that the maximum extent of the Baltic Sea ice-cover has been on a decreasing trend for several centuries, which is consistent with warming temperatures over that period.

Concerning confidence levels, Mann's graph showed a cooling trend from the 1600's at the very least (where the confidence ranges are tighter).

Marco: "And yes, the other reconstructions broadly agree with Mann's initial analysis", "

They don't seem to. These are taken just from the IPCC 2007 report :

A. Moberg, D.M. Sonechkin, K. Holmgren, N.M. Datsenko and W. Karlén (2005) - shows warming from late 16th century.
J. Esper, E.R. Cook, and F.H. Schweingruber (2002) - shows warming from early 17th century.
S. Huang (2004) - shows warming from late 17th century.
Crowley and Lowery (2000) - shows warming from mid 17th century.

And don't forget the world-wide study of 979 borehole temperature reconstructions, further documenting this warming : http://www.geo.lsa.umich.edu/climate/core.html .

Mr. Hassan,

The writers of the CFI report may not be the most careful researchers. I found the following error after within 5 minutes, which I should probably pass on.

The summary of the CFI findings say that that about 8% of the '700' aren't even scientists. I downloaded the spreadsheet with the per-person evaluation ( the document can be found at http://www.centerforinquiry.net/uploads/attachments/Data_Set_for_web_vie... ), and checked the first person listed with a 'yes' in the 'not a scientist?' column, and that was Dr. Randy Cerveny at Arizona U. In the spreadsheet, his entries for "related to climate change?" and "peer reviewed publications (climate related)?" are blank (no). Under "climate scientist" it says "maybe". For "argument" it says "we just don't know".

I was able confirm within a few minutes Dr. Cerveny's academic credentials as a scientist, the fact that he has published papers on climate science in peer-reviewed journals, and that he was an AGW sceptic. The information is right there on the University of Arizona's departmental web-pages, and was incredibly easy to find. Even a simple search on Google Scholar using his name provides pages of papers he’s published in the top peer-reviewed publications.

Almost every entry in the spreadsheet about Dr. Cerveny is wrong, and will have impacted the six stats in the summary in a direction that would have made them more damaging, or as damaging as such a toothless report that doesn’t approach the scientific issues can be.

How hard can the CFI have looked in order for them to write "we just don't know"? It sounds like they are slightly exasperated, as if they had had a difficult time determining whether he had anything to say about AGW, or was even a scientist (conclusion: no!), yet the slightest effort at research would have let them know that almost every entry they made about him is wrong.

I can envisage sloppy research letting slip by someone who is incorrectly listed as being a scientist , or someone who has false given scientific credentials, and to mistakenly mark them as a scientist, but to mark someone down as ‘not a scientist’ who’s effortlessly verifiable as a peer-reviewed climate scientist seems a more difficult mistake to make.

To be fair, I only checked the name, and it happened to catch an error. I'm guessing that the report is broadly correct that many of the dissenters are not climate scientists (35% are, according to the report), but that most are scientists, and a few come from other backgrounds. This is interesting information, but hardly a blow against the scientific case opposing AGW, which the report fails to address.

To Mehdi Hasan:

Thanks for your elitist attitude. Who would have ever guessed that "being published" magically confers the capacity to understand the peer reviewed literature of others. Tell this to Canadian scientists Stephen McIntyre and Ross McKitrick (neither of whom is a "climate scientist") whose work ultimately discredited the highly touted and peer reviewed "Hocky Stick" graph.

Your elitist atitude is a convenient cover for yet another way to summarily dismiss legimate disagreement with mainstream AGW science.

Marco, you said: "Then to your claim that Mann's graph shows that the 17th century was warmer than the early 20th century [..] Note the confidentiality range. "

The BBC on the hockey stick graph, back in 2004 :
"There are few more provocative symbols in the debate over global warming than the "hockey stick". The hockey stick was a term coined for a chart of temperature variation over the last 1,000 years, which suggested a recent sharp rise in temperature caused by human activities. The chart is relatively flat from the period AD 1000 to 1900, indicating that temperatures were relatively stable for this period of time. The flat part forms the stick's "shaft". But after 1900, temperatures appear to shoot up, forming the hockey stick's "blade". "
( http://news.bbc.co.uk/1/hi/3569604.stm )

The BBC, and most of the rest of the world's media, and most everyone I thought, agreed with the characterisaton of the graph I've given (although it's actually a gentle downward trend from AD1000 to 1900, not 'relatively flat' as the BBC described it). The 'hockey-stick' shape was what was shocking about it. The IPCC 2001 report had five or six times reproductions of the graph in it. I don't remember them telling the BBC or anyone that the 'hockey stick' interpretation was wrong - they were spreading it.

Marco:

I'm not sure what you're on about re: 'ogling', and no, your accusation to the contrary, no-one's telling me what to write. Please try to debate the issues ad rem, and not ad hominem..

re: hockey stick :

You say that the hockey stick pattern of 900-years steady slight cooling, followed by a 100-yr sharp warming is NOT present in the Mann's graph, because of the error bars or confidence ranges.

Here's the IPCC 2007 report, referring back to the hockey stick graph :

"For 900 years, this series exhibits multi-decadal fluctuations with amplitudes up to 0.3°C superimposed on a negative trend of 0.15°C, followed by an abrupt warming (~0.4°C) matching that observed in the instrumental data during the first half of the 20th century."

I should add that if one includes the second half of the 20th century portion of Mann's graph, his graph shows about 1.1 C warming after 1900. So the IPCC describes the graph as a 900-year cooling trend, followed by an abrupt warming period in the 20th century.

This agrees with my characterisation of the graph and the BBC's, and almost all others on both sides of the debate. It necessarily follows that my assertion, which you challenged, is correct: Mann's graph showed higher temperatures in the 17th and 18th century than at the beginning of the 20th century.

Re: the start date for warming in those two temperature reconstructions you query :

I stand by the dates I estimated from those graphs.
For Moberg, I said late 17th c., you said 1700: not a big difference. I checked again and the warming from the trough begins one or two decades before 1700.
For Esper, you're counting warming as starting after the early 18th c. cold dip, but that was a brief pause in the longer-term warming going on since about 1700.

Re: the RealClimate article that you seem to believe debunks Loehle's temperature reconstruction :

The article raises some minor dating and data issues which were addressed in Loehle's correction. Otherwise the article is mostly an (interesting) critique of the problems in paleoclimate reconstructions in general.

It does also criticise Loehle's choice of proxies, - it dismisses all 18 of Loehle's choices as being unsuitable, but as has been pointed out, 8 of these were also used in the 11-proxy study done by Moberg et al 2005 (included in IPCC 2007 report).

So RealClimate calls Loehle's choice of proxies unacceptable, but at the same time he praised the Moberg paper, which used 8 of the same proxies in its 11 proxy report.

Mann's RealClimate website doesn't really seem to be engaged in a genuine scientific debate - it may in fact be helping to occlude the truth here.

( The article also contains some unusual errors, as has been noted, eg. dismissing one of the proxies, it writes : "Loehle #12 (Calvo et al, 2002) is also off by 50 years, but since it doesn’t start until 1440 CE, its presence in this collection is surprising in any case.". The Calvo temperature reconstruction is from ocean cores, and actually goes back thousands of years, not just to 1440. This might just be a mistake and not deliberate, but it hasn't been corrected. )

a.m.r.

I think you're making an unwarranted conclusion when you say that Wegman provided the data.

On the subject of dropping bristlecone data - if you look on google scholar you'll see it is still being used in climate circles. That doesn't seem like an invalidation.

On the subject of Mann's basic conclusions being wrong - even the North Report says:

"Presently available proxy evidence indicates that
temperatures at many, but not all, individual locations were higher during the past 25
years than during any period of comparable length since A.D. 900."

North goes on to say:

"The basic conclusion of the 1999 paper by Dr. Mann and his colleagues was that
the late 20th century warmth in the Northern Hemisphere was unprecedented during at
least the last 1,000 years. This conclusion has subsequently been supported by an array
of evidence that includes both additional large-scale surface temperature reconstructions
and pronounced changes in a variety of local proxy indicators, such as melting on icecaps
and the retreat of glaciers around the world, which in many cases appear to be
unprecedented during at least the last 2,000 years."

Both quotes at http://www.nationalacademies.org/images/testimony7-19-06.pdf

The other funny thing is this a.m.r. - North's report makes no mention of Bristlecones.

So, did you just imagine that? Did you also imagine the MWP then being comparable to '20th century temperatures' (And what a wide net the 20th century is temperature-wise!)

“The amazing thing about all this is that people who claim to be scientists are so willing to become so profoundly and righteously committed to a belief in something that, at best, is highly uncertain, and the reality of which will inevitably become apparent in the not too distant future. It appears that such persons somehow think that their own unshakable faith will determine that reality. It also seems clear that what they claim to fear so greatly is, perversely, what they actually so desperately hope for.”

-- from Global Warming, a Mass Mania by Walter Starck

In the comments:
"We discussed Moberg et al when it came out, and the problem there is the same as that highlighted above - how to you calibrate low-resolution data" (spelling error is Gavin's).

Oh, and the wavelet analysis indeed 'removes' most of the influence of the tree rings, but does more than just that. It *is* of importance to be able to use non-annually resolved proxies.
Ultimately, it was the novel approach that received most 'praise' when Moberg's article had just come out. On realclimate they did point to a few of the added problems: make a small mistake in the 'calibration period', and everything is way off.

bcronos, you make the same mistake as the investigator who decides that the forrest could not have been set on fire, because forrests have been catching fire for hundredthousands of years, even before there were humans...

> whose work ultimately discredited the highly touted and peer reviewed "Hocky Stick" graph.

That would be the same graph that has been independently verified on half a dozen or so separate occasions using a variety of different methodologies, yes? The graph is anything but discredited - simply repeating the party line does not make it true.

a.m.r., Let me add that John Theon was as much Jim Hansen's supervisor as my Head of Department is my supervisor: a paper shuffler who needs to check I follow the requirements of a University professor, and make sure I get the money I need to do my research. But unlike Theon and Hansen, I actually meet and discuss with my Head of Department.

This type of overhyping credentials is now a common theme in the world of the deniers (they certainly are not skeptics, as accepting this overhyping shows). Also look at the use of "UN IPCC expert reviewer" I mentioned earlier.

You remember almost completely correct, Dave. Gray had 97% rejected. Mostly because he simply wanted to change the science: if something was likely to be a result of human emissions, he demanded "likely" to be changed to "unlikely"...

JeffM had a beauty: "To Mehdi Hasan: Thanks for your elitist attitude...."

You can't win with the denialists. There was a great summary of how the denialists 'argue' their beliefs by Mercurious at http://larvatusprodeo.net/2009/08/01/the-rules/

(If a.m.r. can cobble unreadable crap together from dodgy websites then I can cobble quality stuff. Here it is:)

1) Nothing that was recorded by instruments such as weather-stations, ocean buoys or satellite data. Since all instruments are subject to error, we cannot use them to measure climate.

2) Nothing that has been corrected to account for the error of recording instruments. Any corrected data is a fudge. You must use only the raw data, which is previously disqualified under rule #1. Got that? OK, moving along…

3) Nothing that was produced by a computer model. We all know that you can’t trust computer models, and they have a terrible track record in any industrial, architectural, engineering, astronomical or medical context.

4) Nothing that was researched or published by a scientist. Such appeals to authority are invalid. We all know that scientists are just writing these papers to keep their grant money.

Then there are the corollaries:

A) Any previous errors in climate science are automatic proof that new data is also wrong. For example, if you produce results which show a reduction in ice coverage, or a warming of ocean temperatures, all I have to do is shout ‘Hockey Stick!’ and the new data is instantly dispelled.

B) So, before I will accept your new data, it must retrospectively correct any errors in past data, and erase them from the space-time continuum as though they never occurred. Furthermore, if you do manage to perform this feat, your data will be invalid because corrected data is disqualified under rule #2.

C) Al Gore is a big fat hypocrite and a liar and a fraud who jets around the world and has a big house and eats puppies for breakfast. And will you please stop the ad hominem attacks on Ian Plimer?

D) Will somebody, please, somewhere, anywhere, address the science in Ian Plimer’s book? I mean, surely that’s not too much to ask? By the way, anybody who addresses the science in Ian Plimer’s book is just a nit-picker who hasn’t addressed the main issue.

E) Please, spare me your conspiracy theories. It’s not my fault that AGW is a giant hoax perpetrated by Big Green to take over the world in a socialist plot. I’m just trying to uncover the truth here, with the assistance of a lot of commentators, media personalities, corporate executives and hired scientists who just happen to share similar political views to my own.

F) Your position is based on religious faith, not on the science. I can tell because you pay attention to the scientific instruments, the corrected data, the computer models and the writings of published scientists, instead of what I know, deep in my heart to be the truth: that AGW is a giant hoax and a fraud.

G) If you ever refuse to debate with me, that is proof that your position is untenable, you’re frightened of the truth and you don’t have the evidence. And, by the way, when will Burt Newton respond publicly to the claims that he’s a trans-gender vampire who was regenerated in a vat from a single hair of Vlad the Impaler? His silence on this issue is telling…

@bcronos,
If this is your best argument, I understand why you have so much trouble understanding the science of global climate change strongly supporting the influence of anthropogenic CO2 release as responsible for at least 50% of the warming since about 1970.

a.m.r.

Again, you supply lots of innuendo and arguments of a political nature, without ever really addressing anything of substance or laying out exactly what your position is.

The press release for the report you mention on the MBH graph is here: http://www8.nationalacademies.org/onpinews/newsitem.aspx?RecordID=11676

Given that they agree with the conclusions of the graph it not exactly damning, is it? It's largely seen as a vindication of the MBH work against critics who claimed that it was entirely spurious, and was the result of programming errors.

Here's an assessment of the report at realclimate: http://www.realclimate.org/index.php/archives/2006/06/national-academies...

As I stated before, the so-called "hockey stick" has been verified many times independently using different approaches - see eg. this easily available copy of the famous "spaghetti" graph: http://en.wikipedia.org/wiki/File:1000_Year_Temperature_Comparison.png

Simply launching smear attacks against the original "hockey stick" like it's a weak spot that'll cause the whole edifice to come crashing down is - frankly - absurd. Again, please spell out what precisely about AGW you dispute and why - eg. whether it is warming, the rate and extent of that warming, what forcings are principally responsible etc.

a.m.r.

You say: "And don't forget the world-wide study of 979 borehole temperature reconstructions, further documenting this warming : http://www.geo.lsa.umich.edu/climate/core.html ."

And it has a a rising trend that is not at odds with AGW at all, though this is clearer at http://www.ncdc.noaa.gov/paleo/borehole/core.html

Dave, Eamon

No, the report you cite is a different, later one. The one I cited upholds the criticisms of the hockey stick graph, and finds that Mann's conclusion of unprecedented 20th century temperatures in the last 1000 years is not justified by his work.

The later report that you cite doesn't challenge the Wegman report, but notes (based not on the hockey stick graph) that 20th century temperatures are unprecedented in the last 400 years.

This is quite different from what Mann said, and the 2007 IPCC report has at least been updated to reflect this.

The 2001 report (with the hockey stick graph) also said that the LIA was restricted to the northern hemisphere. Since 2001 there have been at least seven independent papers showing that, as thought previously, the LIA also occured in the southern hemisphere.

The hockey stick graph showed no warming in the 18th and 19th centuries, whereas it's well-known that we've been warming for at least 200 years.

Marco, the hockey stick graph has been discredited, and the IPCC no longer use it, or graphs showing similar results. They've replaced it with a 'spaghetti' multi-proxy graph, which shows the LIA quite clearly.

Ah, I did not realise you were talking about the Wegman report. In any event, here's the helpful graph showing the original MBH reconstruction, overlaid with the validated corrections from M&M:

http://www.realclimate.org/images/WA_RC_Figure1.jpg

Both reports came to the same conclusion - that some criticism was valid, but that it did not materially affect the result. The oft-repeated allegations that the shape of the reconstruction was spurious, fraudulent, or an artefact of the analytical process - none of these were supported by either report.

You seem to think that "discredited" means "incorporating a valid criticism and finding that the conclusion remains the same". This is the way science is supposed to work you know - working towards an improved understanding via peer reviewed publication? The valid criticisms of M+M had already been acknowledged, but their invalid criticisms, rhetoric and inferences had rightly been disregarded because it was unsupported and unsupportable. The corrected results are still the same - harping on about the existence of criticism, or the fact that reports upheld some criticism doesn't change that fact. The work has not been discredited, it has been upheld, improved and strengthened - and as Marco points out, look for the MBH line on the "spaghetti" graph to see that the original "hockey stick" is very much alive and well, and these days buttressed by lots of more recent independent work that reaffirms the original findings.

Sorry, a spelling mistake, where I wrote "Even Mann and Jones 2003 multi-proxy study shows warming starting in the early 18th century" - that should be early 19th century.

Eamon,

The investigative report into Mann's statistical analysis is informally called the Wegman report, which upheld McIntyre's and McKitrick's criticisms of Mann's work on the hockey stick graph.

The report that you mentioned, sometimes called the North report, doesn't really vindicate Mann as you seem to think it does, although it does say that Mann's basic conclusion that the 20th century has the highest temperatures of the last 1000 years is "plausible". (But this was widely speculated anyway - we knew we were roughly at similar temperatures to the Medieval Warm Period, perhaps even a bit warmer).

The lead writer of the report, North, was asked whether he agreed with the Wegman report, and the reply was yes. ie. even though Mann's basic conclusion may have been correct, he had used faulty methodology to arrive at it.

As Wegman pointed out, Wrong Method + Right Answer = Bad Science .

Also, I'd point out that the 'answer' contained in Mann's graph is not just the basic conclusion (that the end point is higher than any other point), but the entire shape of the graph itself, and in that case, it's Wrong Method + Wrong Answer = Bad Science .

The North report also says this :

"Large-scale surface temperature reconstructions yield a generally consistent picture of temperature trends during the preceding millennium, including relatively warm conditions centered around A.D. 1000 (identified by some as the “Medieval Warm Period”) and a relatively cold period (or “Little Ice Age”) centered around 1700. The existence of a Little Ice Age from roughly 1500 to 1850 is supported by a wide variety of evidence including ice cores, tree rings, borehole temperatures, glacier length records, and historical documents."

Almost all the proxy data shows warming taking place in the 18th and 19th centuries.
You can see this in the graph in the report's summary ( can be found here http://books.nap.edu/openbook.php?record_id=11676&page=2 ).

Now, if you will, please have a look at Mann's graph :
http://en.wikipedia.org/wiki/File:Hockey_stick_chart_ipcc_large.jpg

The warming in the 18th and 19th centuries is missing from Mann's graph, which shows temperatures still trending downwards until we enter the 20th century. This doesn't agree with the large body of evidence concerning the recent climate, as mentioned above in the North report that you cited.

For those interested in the latest Kerfuffle over 'Yamal tree rings' there's a scientific, but not complicated look at the issue at:

http://www.realclimate.org/index.php/archives/2009/09/hey-ya-mal/

JeffM : no problem, thank you for your kind words.

Dave:
Ritson's letter complaining about undisclosed data was written about 3 weeks after Ritson's request. (By the way, do compare that to Mann's refusal to divulge his data for years, despite persistent requests, until Congress stepped in.)

I can't find any more complaints after that August, from Ritson or anyone else, about Wegman not divulging data, so I suspect that the data was provided within a month or so of the request. If you have any evidence that the data wasn't made available, please let me know, I would be interested - certainly that would be wrong.

re: Waxman - a lying politician - what bearing does this have about the science? Al Gore, a politician, has spread many more lies in the 'other direction'. I seem to remember that his film 'An Inconvenient Truth' is barred from being used as teaching material in UK schools because it's so full of lies and exaggerations.

You say: "The North report found that the changes in methodology suggested by McIntrye et al would have had no measurable effect on the result. "

The North report found that the bristlecone proxy data, used by Mann, should be avoided in temperature reconstructions.

If we drop the bristlecone data and run Mann's analysis, then it's true that reconstructions using different PC methods give very similar results. The point is that leaving out the bristlecone data, as recommended by the North report, gives results that have one very significant feature - the Medieval Warm Period is graphed as being as warm as or warmer than the 20th century temperatures.

This means that Mann's basic conclusion (that 20th century temperatures are unprecendented in the last 1000 years) would not have been supported by his graph if he'd dropped the problematic proxy, as suggested by the North report.

Eamon,

Mann used a known problematical proxy (with a confounding CO2 covariance) that brought out the flaw in his unrecommended methodology, which was prone to distorting the shape of the graph, and gave that proxy the most prominent weight in his analysis. In doing so he produced a statistically close-to-meaningless graph that was good evidence for AGW.

Edward Wegman said, concerning the Wegman report : "The climate science community seemed unable to either refute McIntyre's claims or accept them. The situation was ripe for a third-party review of the types that we and Dr. North's NRC panel have done."

The Wegman committee's investigation found "the criticisms of MM03/05a/05b to be valid and compelling". ie. correct and important.

McIntyre and McKitrick had found that Mann's graph was based on statistical work with an R2 validation figure that was so low that the result was close to meaningless. Wahl and Amman's later paper in 'validation' of Mann's work also had a very low R2 figure.
Both papers did not publish their R2 figures.

So the 'hockey stick' is quantitatively and qualitatively wrong - it has a greatly diminished Medieval Warming Period (at least compared to numerous other reconstructions), more importantly the Little Ice Age is missing. The graph just shows steadily decreasing temperatures for 900 years and then a sharp jump up in the last 100 - it has very little relation to the actual data, as evidenced by the low R2 figure.

The science doesn't support the AGW hypothesis.

The IPCC is doing a great disservice to science and those scientists whose hard work it misrepresents, and to the people whom it is meant to serve.

There are many enviromental issues that should be concerning us. Targetting CO2 as the driver of the observed climate change, and a pollutant, is a mistake.

The reason they can challenge the climate change theses being put forth is that they are very challenge-worthy. If they were completely off piste in terms of evidence, their arguments would have no resonance. And this ridiculous terminological abuse of the worf "denier" to equate people who disagree with you seem like Nazis just makes people who are concerned with larger issues, including pollution, turn off. Al Gore is no meterologist either.