Sunday, August 30, 2015

36 Hockey Sticks (And Counting)

Thanks to commenter Jack Dale at Roy Spencer's blog, who gave this long and useful list of studies that find a hockey stick from reconstructions of paleoclimate data, compiled by Jim Milks of Seeing the Environmental Forest.

Milks has links to three dozen studies that find a hockey stick, as of 2013. Three dozen. (For links to each specific study, see Milks' post.)

Crowley 2000: Used both his own and Mann et al. (1999)’s hockey sticks to examine the cause of temperature changes over the past 1,000 years. Found that natural forcings could not explain twentieth century warming without the effect of greenhouse gases.

Huang, et al. 2000: Reconstructed global average temperatures since AD 1500 using temperature data from 616 boreholes from around the globe.

Bertrand et al. 2002: Reconstructed solar output, volcanic activity, land use changes, and greenhouse gas concentrations since AD 1000, then computed the expected temperature changes due to those forcings. Compared the computed temperature changes with two independent temperature reconstructions.

Esper et al. 2002: Reconstructed Northern Hemisphere temperatures between AD 800 and AD 2000 using tree ring chronologies.

Cronin et al. 2003: Reconstructed temperatures between 200 BC and AD 2000 around Chesapeake Bay, USA, using sediment core records.

Pollack and Smerdon 2004: Reconstructed global average temperatures since AD 1500 using temperature data from 695 boreholes from around the globe.

Esper et al. 2005: Compared and averaged five independent reconstructions of Northern Hemisphere temperatures from AD 1000 to AD 2000.

Moberg et al. 2005: Combined tree ring proxies with glacial ice cores, stalagmite, and lake sediment proxies to reconstruct Northern Hemisphere temperatures from AD 1 to AD 2000.

Oerlemans 2005: Reconstructed global temperatures from AD 1500 to AD 2000 using 169 glacial ice proxies from around the globe.
Rutherford, et al. 2005: Compared two multi-proxy temperature reconstructions and tested the results of each reconstruction for sensitivity to type of statistics used, proxy characteristics, seasonal variation, and geographic location. Concluded that the reconstructions were robust to various sources of error.

D’Arrigo et al. 2006: Reconstructed Northern Hemisphere temperatures between AD 700 and AD 2000 from multiple tree ring proxies using a new statistical technique called Regional Curve Standardization. Concluded that their new technique was superior to the older technique used by previous reconstructions.

Osborn and Briffa 2006: Used 14 regional temperature reconstructions between AD 800 and AD 2000 to compare spatial extent of changes in Northern Hemisphere temperatures. Found that twentieth century warming was more widespread than any other temperature change of the past 1,200 years.

Hegerl et al. 2007: Combined borehole temperatures and tree ring proxies to reconstruct Northern Hemisphere temperatures over the past 1,450 years. Introduced a new calibration technique between proxy temperatures and instrumental temperatures.

Juckes et al. 2007: Combined multiple older reconstructions into a meta-analysis. Also used existing proxies to calculate a new Northern Hemisphere temperature reconstruction.

Wahl and Ammann 2007: Used the tree ring proxies, glacial proxies, and borehole proxies used by Mann et al. (1998, 1999) to recalculate Northern Hemisphere temperatures since AD 800. Refuted the McIntyre and McKitrick criticisms and showed that those criticisms were based on flawed statistical techniques.

Wilson, et al. 2007: Reconstructed Northern Hemisphere temperatures from AD 1750 to AD 2000 using tree ring proxies that did not show a divergence problem after AD 1960.

Mann et al. 2008: Reconstructed global temperatures between AD 200 and AD 2000 using 1,209 independent proxies ranging from tree rings to boreholes to sediment cores to stalagmite cores to Greenland and Antarctic ice cores.

Kaufman, et al. 2009: Used tree rings, lake sediment cores, and glacial ice cores to reconstruct Arctic temperatures between 1 BC and 2000 AD.

von Storch et al. 2009: Tested three different temperature reconstruction techniques to show that the Composite plus Scaling method was better than the other two methods.

Frank et al. 2010: A brief history of proxy temperature reconstructions, as well as analysis of the main questions remaining in temperature reconstructions.

Kellerhals et al. 2010: Used ammonium concentration in a glacial ice core to reconstruct tropical South American temperatures over the past 1,600 years.

Ljungqvist 2010: Reconstructed extra-tropical Northern Hemisphere temperatures from AD 1 to AD 2000 using historical records, sediment cores, tree rings, and stalagmites.

Thibodeau et al. 2010: Reconstructed temperatures at the bottom of the Gulf of St. Lawrence since AD 1000 via sediment cores.

Tingley and Huybers 2010a, 2010b: Used a Bayesian approach to reconstruct North American temperatures.

Büntgen et al. 2011: Used tree ring proxies to reconstruct Central European temperatures between 500 BC and AD 2000.

Kemp et al. 2011: Reconstructed sea levels off North Carolina, USA from 100 BC to AD 2000 using sediment cores. They also showed that sea levels changed with global temperature for at least the past millennium.

Kinnard et al. 2011: Used multiple proxies to reconstruct late summer Arctic sea ice between AD 561 and AD 1995, using instrumental data to extend their record to AD 2000.

Martin-Chivelet et al. 2011: Reconstructed temperatures in the Iberian Peninsula from 2000 BC to AD 2000 using stalagmites.
Spielhagen et al. 2011: Reconstructed marine temperatures in the Fram Strait from 100 BC to AD 2000 using sediment cores.

Esper et al. 2012: Used tree ring proxies to reconstruct Northern Scandinavian temperatures 100 BC to AD 2000. May have solved the post-AD 1960 tree ring divergence problem.

Ljungqvist et al. 2012: Used a network of 120 tree ring proxies, ice core proxies, pollen records, sediment cores, and historical documents to reconstruct Northern Hemisphere temperatures between AD 800 and AD 2000, with emphasis on proxies recording the Medieval Warm Period.

Melvin et al. 2012: Reanalyzed tree ring data for the Torneträsk region of northern Sweden.

Abram et al. 2013: Reconstructed snow melt records and temperatures in the Antarctic Peninsula since AD 1000 using ice core records.

Marcott, et al. 2013: Reconstructed global temperatures over the past 11,000 years using sediment cores. Data ended at AD 1940.

PAGES 2k Consortium 2013: Used multiple proxies (tree rings, sediment cores, ice cores, stalagmites, pollen, etc) to reconstruct regional and global temperatures since AD 1.

Rhodes et al. 2013: Used proxy and instrumental records to reconstruct global temperatures from AD 1753 to AD 2011.

Again, this is hardly surprising. What would be surprising is if any studies found something other than a hockey stick.

As Jim wrote,
The proper response to someone who asserts that the Hockey Stick has been falsified is to ask "Which one?" 
Thanks Jim.

--
Added -- and more:

Y Zhang et al. 2014: "Millennial minimum temperature variations in the Qilian Mountains, China: evidence from tree rings," Climate of the Past, 10, 1763–1778, 2014.

Shi et al. 2015: "A multi-proxy reconstruction of spatial and temporal variations in Asian summer temperatures over the last millennium," Climate Change, August 2015, Volume 131, Issue 4, pp 663-676. [PDF]

Thursday, August 27, 2015

US Gun Violence: So Bad, All That's Left Is a Joke


Via the Washington Post. Economist link here.

At least someone is trying to keep track. It looks like a full-time job.

Mark Steyn's Expert Comes Up Short

Mark Steyn is back, looking for money to pay a lawyer. And pushing opinions instead of science.

Awhile back Steyn quoted a Jonathan Jones, Lecturer in Physics at Oxford University, about Mann's work. So I wrote to Dr. Jones asking for more details. Despite Jones' bluster, what I found wasn't very convincing.

Steyn quoted Jones:
The Hockey Stick is obviously wrong. Everybody knows it is obviously wrong. Climategate 2011 shows that even many of its most outspoken public defenders know it is obviously wrong. And yet it goes on being published and defended year after year.

Do I expect you to publicly denounce the Hockey Stick as obvious drivel? Well yes, that's what you should do. It is the job of scientists of integrity to expose pathological science... It is a litmus test of whether climate scientists are prepared to stand up against the bullying defenders of pathology in their midst.
As I showed here, the hockey stick is, in fact, an elementary result of basic scientific reasoning. So I was curious about the surety of Jones' conclusions, given that I couldn't recall any papers by him on the subject.

On August 11th, I wrote to Jones:
Why do [you] hold this view? Why is it "obviously wrong?" The hockey stick has been reproduced several times now, some using independent mathematical techniques
and I gave him links to Tingley and Huybers, Marcott et al, and PAGES 2k.

Jones replied:
The quotation Mr Steyn is using can be found in context at http://www.bishop-hill.net/blog/2011/12/2/tim-barnett-on-the-hockey-stick.html#comment16080991.

I’m afraid that I am somewhat confused by your question, as your suggested conclusion does not follow from your premises.  However I will do my best to answer.

First please note that my comments which you quote apply specifically to the Mann hockey sticks, MBH98 and MBH99.  The methods underlying these reconstructions have been comprehensively debunked, most famously by Steve McIntyre; if you are unfamiliar with the story then I suggest “The Hockey Stick Illusion” by Andrew Montford as an excellent primer.  Even if one accepts the underlying method of multiproxy reconstruction with effective selection of individual proxies by correlation (and like most people outside the small world of people doing such reconstructions I don't) the inclusion of "proxies" known not to be reliable temperature proxies (e.g. bristlecone pines and contaminated lake sediment series) and the use of inappropriate mathematical techniques (mostly famously decentred PCA in MBH98) renders the reconstructions useless.

These papers are methodologically bogus, and would remain methodologically bogus even if other papers were to reach similar conclusions.  In so far as such papers rely on the same bogus methods then their conclusions are equally invalid; conversely papers which reach similar conclusions by different means have nothing to say in support of the bogus methods of MBH.

You mention three particular reconstructions, none of which provide any support for the methods in the MBH papers.

The Marcott 2013 multi-proxy reconstruction is most famous for the dramatic uptick which occurs at the end of the reconstruction.  However it is now well known that this uptick is not robust, and is almost certainly an artefact.  It is notable that this uptick does not occur in Marcott’s thesis, and I understand that the authors no longer defend this portion of the reconstruction.  Once this uptick is removed there is nothing much to see unless you are advocating splicing temperature data onto proxy data.

The Pages2K 2013 reconstruction suffers from many of the same problems as the MBH reconstructions, with many datasets in common, including contaminated lake sediments and bristlecone tree ring series known to be unsuitable.  Famously some of the series are used "upside down": this is a common error in papers which use selection by correlation, and a clear indication of why the method shouldn't be used.  The paper adds little or nothing to the debate on MBH.

The Tingley and Huybers story is a long and complex one, and I am not sure quite which paper you are referring to, but many of their papers have used notorious “proxies” such as Mann’s PC1, the Yamal lone tree, and the most famous of the upside down contaminated lake sediment series, Tiljander's data as used by Mann.  The mathematical techniques used are not as different as you suggest, and any similarities in outcome largely reflect the inclusion of the same inappropriate proxies.  Once again it adds little or nothing to the debate.

I apologise that this reply is not particularly detailed, but I am currently very busy with the fallout from admissions and examining.  If you want to read more about the deficiencies of the reconstructions above I suggest you take a look at McIntyre’s site, climateaudit.org, although you may find that the posts there swiftly become rather technical unless you have a strong mathematical background.
This is clearly just a lot of hand-waving -- not sure if Steyn and his readers are familar with that scientific slang -- so I followed up to Jones:
Of course I know about McIntyre & McKitrick, but I haven't seen many experts take it very seriously, especially after Wahl and Amman (2007):

"Robustness of the Mann, Bradley, Hughes reconstruction of Northern Hemisphere surface temperatures: Examination of criticisms based on the nature and processing of proxy climate evidence, Eugene R. Wahl and Caspar M. Ammann, Climatic Change, November 2007, Volume 85, Issue 1-2, pp 33-69
http://link.springer.com/article/10.1007%2Fs10584-006-9105-7

My point about the other reconstructions -- Marcott et al, PAGES 2k, and Tingley and Huybers -- is that, if independent analyses find essentially the same result at MBH, using different mathematical techniques, how can Mann et al be so badly wrong?
Jones' reply:
I'm afraid that I don't share your take on Wahl and Amman. In fact this paper largely establishes the correctness of the McIntyre and McKitrick criticisms. In particular I draw your attention to table 1S on page 63.

If you would like to read more about this it is explored in some detail in Montford's book.  Or, if you don't want to read the whole book, see "Caspar and the Jesus Paper" which you can find at http://bishophill.squarespace.com/blog/2008/8/11/caspar-and-the-jesus-paper.html

Your final question was answered in detail in my previous reply, so I am confused as to why you are asking it again.
I found it odd that a scientist would cite a blog. The difference between peer reviewed papers published in major journals and blog posts is -- or should be -- very obvious. (Yes, that holds for this blog as much as any other. Blog posts aren't science.) They simply aren't in the same league, and it is very rare, if ever, you will ever see a scientist cite a blog post.

So I asked Jones about his own work on the hockey stick.
Your criticisms of all these papers -- Marcott et al, PAGES 2k, Tingley & Huybers -- strike me as shallow. They are hand-waving.

Where are the peer reviewed papers showing them wrong?

Have you published any papers showing them wrong?

I'm a science journalist. I'm well aware that blogs can, and do, say anything, with few, if any, consequences for being wrong. So I prefer to work from the peer reviewed literature.
I never heard back from Dr. Jones.

Maybe asking about his own publications was a touchy subject for him. But blog-level thinking isn't good enough for professional scientists -- I can get that anywhere. The point of being a professional is to offer professional critiques. Jones did not do that. I don't see much, if any, merit in his replies.

I'm sure Steyn's readers will be impressed by whatever he writes and whomever he quotes. And Judith Curry will repeat them without question.

But as Jonathon Jones showed, at least, his criticism quoted by Steyn wasn't scientific, and wasn't impressive or convincing.

Steyn's readers got all hot and bothered by this post, but completely ignored the posts that showed how the hockey stick is an unsurprising consequence of basic physics.

I suspect most of them don't understand basic physics. Science simply isn't their interest. Instead, they are thrilled by rhetorical fluorishes and debate scoring, whether it's been the Second Iraq War or writing that sates their Islamophobia.

But as Neil deGrasse Tyson said, “The good thing about science is that it's true whether or not you believe in it.”

Monday, August 24, 2015

More on Latest Ocean Heat Data and Warming Acceleration

Following up on the previous post: the ocean heat content data for the 0-700 meter region shows a much clearer acceleration when using the full dataset going back to 1955 -- it comes to 0.009 W/m2/yr.

It's also notable how much less variation there is in the quarterly data since the Argo buoys took over the job in 2005. (Before Argo, ocean temperatures were measured with "expendable bathythermographs" (XBTs) thrown overboard from "ships of opportunity.")


New Ocean Heat Data Shows Global Warming is Accelerating

The second quarter numbers for ocean heat content (OHC) are in, and they again show large increases year-over-year.

Changes in ocean heat content are thought to be the best way to detect and measure a planetary energy imbalance, since the vast majority (about 93%) of the extra heat goes into the ocean, and because its huge heat capacity -- about 1,000 times that of the atmosphere -- means heat changes there are much less fickle than in the atmosphere. As oceanographer Greg Johnson of NOAA puts it, "global warming is ocean warming."

OHC for the top half of the ocean (0-2000 meters), measured by the Argo bouys in the last 10+ years, is now clearly accelerating. The year-over-year change for the 0-700 meter region is 1.1 W/m2, and 1.5 W/m2 for the 0-2000 meter region.

I divided the heat increases by the total area of the Earth, since almost all of the heat trapped by manmade greenhouse gases, across the entire planet, goes into the ocean.

For the 0-2000 meter region, a quadratic fit to the data is better than a linear fit, with an acceleration of 0.09 ± 0.03 (W/m2)/yr (statistical error, no autocorrelation):


Here, ZJ = 1 zettajoule = 1021 Joules.

A quadratic fit to these data keeps getting better and better relative to a linear fit:

Saturday, August 22, 2015

More About Generating Hockey Sticks

A little more about generating hockey sticks from the world's history of CO2 emissions....

As Hüsler and Sornette discuss here, the world's CO2 emissions were superexponential, up until around the middle of the 20th century when the population growth rate peaked. Before that, a realistic-looking model for the amount of CO2 in the atmosphere over the last millennia is


where t is time, going from 0 to 1, and C(t) is the atmospheric CO2 concentration at time t. (More on the exponent 2/3rds below.) This means C=1 at the start time t=0, which you can rescale to 280 ppm if you want, but I'll keep the function simple to make the conclusion clearer.

Then the forcing from that CO2 in the atmosphere is



and the change in temperature, which is proportional to the change in forcing, is

   



(I've dropped proportionality constants.) This is simple enough. I've plotted these functions to the right.

Again, I'm not interest in an exact match, only getting a realistic shape for the C(t) curve. (You can rescale everything by adding constants and multiplying constants, if you really want to get a good match to the observed values.)

The curve C(t) is superexponential -- it's increasing faster than an exponential function. The green line is the exponential fit to the C(t) data points using linear regression, and it can't keep up with the C(t) curve.

The brown line is the resulting temperature change -- a hockey stick. It's a straightforward consequence of the world's path on CO2 emissions and the basic physics.

Thus, it would be surprising if any of the paleoclimate studies gave anything other than a hockey stick.

Of course, the real world is messy with natural flucuations and nonlinearities and the like, so a hockey stick isn't guaranteed by the data. But it seems to me a hockey stick is the best, first guess. (I think it was John Wheeler who said you should never start a calculation until you know the answer, and this, plus a good intuition for the actual numbers, is the kind of thing he had in mind. Though few of us are John Wheelers, and this kind of argument shows up for me usually only in retrospect.)

--

In their paper, Hüsler and Sornette construct a very simple economic model that gives this superexponential for atmospheric CO2. They make some basic and plausible assumptions -- about population growth, the labor force, about the amount of capital, and about the progress of technology, and get a set of coupled differential equations they solve. A simple case give the exponent 2/3rds I used above. You can tweak that too, if you want. See their paper for details.

C(t) is no longer increasing superexponentially. It can't do that forever, in a real, finite world -- as Hüsler and Sornette write, such an increase eventually leads to "regime change" -- a fundamental change in an input function like population. Perhaps that's what the peak population growth rate in the 1960s was.

On the other hand, climate feedbacks are coming into play, so the temperature increase is hardly over yet. Really, it's just getting started.

Friday, August 21, 2015

The Thing Is, the Hockey Stick Isn't a Surprising Result

The other day I wrote that I doubted Steyn considered the work by other research groups that have found hockey sticks in the paleoclimate data, many using independent mathematical methods.

I still think that. Because, here's the thing: the hockey stick isn't a surprising result.

In fact, physics says it'd be far more surprising if the hockey stick wasn't true. And this is true regardless of any particularities of the proxy data -- it depends only on the track followed by atmospheric carbon dioxide, and the basic physics of global warming.

On his blog, Steyn wrote:


I don't doubt that Steyn looked at some of the other hockey stick papers, waved his hands and wrote some words about them -- the usual junk about Yamal proxies and upside down proxy arrays and the like. In other words, a lot of gossip and hearsay that can be found on many denier blogs over the years.

Steyn hasn't made a scientific argument about the hockey stick yet. Gossip, hearsay and (especially) blog posts aren't science. Science is what you find in the peer reviewed literature -- careful detailed work that is reviewed by experts. We're supposed to think that a blogger known mostly for his Islamophobia somehow disproved and dismissed all the independent mathematical work by Ammann and Wahl, Tingley and Huybers (and again in 2013), Marcott et al, and PAGES 2k -- the latter a huge, comprehensive paper written by over six dozen scientists?

That Steyn saw some simple thing that all these experts missed and was able to dismiss all the work and expertise in a few pages of a self-published book? And overthrew basic physics? Not. Bloody. Likely.

As I wrote, the hockey stick result is obvious, since it's based on some simple observations and simple physics:

1) The emissions of manmade CO2 increased faster than exponential after the start of the Industrial Revolution -- it was a "superexponential" increase:


This isn't surprising -- human population itself has been on a superexponential increase since 1000 A.D., so energy use has been as well. So have the other prominent greenhouse gases: methane and nitrous oxide concentrations in the atmosphere.

2) Global temperatrure change is proportional to changes in radiative forcing. And for the levels of CO2 we're at, the change in radiative forcing is logarithmic with CO2 concentration.

The logarithm of a superexponential function is an exponential function. So basic physics says the increase in temperature after the Industrial Revolution should be something like an exponential -- something like the hockey stick graph.

For methane and nitrous oxide, the numbers are worse, because their radiative forcing doesn't vary as the logarithm of their atmospheric concentration, but as the square root of their concentration (see Table 1 here). And the square root of a superexponential function is a superexponential function.

Of course, you still have to collect the proxy data and calibrate it and work through all the complicated mathematics to find what the actual temperature variation over the last X millennia is.

Human population, and atmospheric CO2, have decelerated to just exponential growth only in recent decades. As Hüsler and Sornette concluded:


So the hockey stick isn't a surprising result. And you won't find that in a book that's really just intended as nothing more than a big F-You.

NOAA's Temperatures Setting All Kinds of Records

NOAA came out with their number for the global mean surface temperature for July: +0.81°C. It is, which is almost a given anymore, the warmest July in their records, which start in 1880.

All kind of records are being broken lately. Here are the ranks of the individual months, each since 1880, for the last year and a half:


For a new NOAA record for the year, the last five months of 2015 need to average +0.60°C -- when the first seven months have averaged +0.85°C. With the El Nino in full steam, it's looking very likely (to almost certain) that 2015 is going to be the warmest year on record, and by a sizeable margin.

Wednesday, August 19, 2015

Mark Steyn Says He Quoted the Phil Jones Email Correctly

Mark Steyn says he didn't doctor an email to Mann in his vanity publication.

Fair enough. I'll believe him. My bad. My apologies.

Tony Heller Exposed, you seem to have botched this. My fault for believing you without checking.

I wonder then, how Judith Curry got the idea Steyn did doctor the email, because she definitely doctored it in her post.

I've written to her to ask.

Steyn thinks I should buy a copy of his book. Really, he does, for $15.46. Me, a poor freelancer scratching the floor for grains of wheat.

I'm happy to read a complimentary copy, and attempt to place a review -- here, if no one is interested -- but no, this isn't a book I'm going to buy from him. Or from Amazon -- I cancelled my account there last weekend, after the NY Times expose on their abysmal working conditions.

PS: I wonder if Steyn has examined any of the other evidence for the hockey stick, some derived with independent mathematical techniques. Like Marcott et al Science 2013, PAGES 2k, or Tingley and Huybers.

I expect he hasn't. If not, why not?

The New Term for "Geoengineering"

"Climate Intervention."

At least, that's the term being used now by the National Research Council, as Marcia McNutt and Ken Caldiera talked about on a teleconference today regarding two recent NRC reports on the subject.


Why the change? Two reasons:

1) "geo" implies, they said, a focus on the Earth as a body, which is not where climate changes takes place.....

And more importantly....

2) "engineering" implies a project or process under precise control, with a definite outcome with little uncertainty, while "climate intervention" does not.

Intervention is more like a surgeon operating on you for cancer -- s/he and you would like the result to be something specific, something tailored, something definite -- but you both know, and so does everyone else, that it may not be. There is uncertainty.

It will be interesting to see if this nomenclature takes hold. It probably should. It would introduce a sense of uncertainty that the idea needs to convey, because it does carry a lot of uncertainties, especially for albedo modification ("solar radiation management"), which Ray Pierrehumert calls "batshit insane" "barking mad."

And yet I expect that in 20-30 years, the world -- or at least its major powers -- or at least one of them -- will be doing something like spraying aerosols into the stratosphere to reflect sunlight. Floridians are going to demand it, as climate change suddenly thumps them right in the forehead and their state begins to go underwater. It will become a presidential campaign issue. Scientists will point to their reports and warn of the dangers and uncertainties, and politicians will do it anyway. And most of the country, still as addicted to fossil fuels as ever, with Big Oil and Big Gas still buying politicians, thinking no deeper than did Freakonomics on the issue, will support it. Because it's easy.

That's what I expect.

--
By the way, Ray Pierrehumbert, of this "barking mad" article in Slate, was a co-author on these NRC reports.

Mark Steyn, Judith Curry Doctor a Climategate Email to Michael Mann

Correction 8/21: http://davidappell.blogspot.com/2015/08/mark-steyn-says-he-quoted-email-in-full.html

Note 8/21 9:40 am PDT: No response from Judith Curry. The doctored quote still appears on her blog.
--

Mark Steyn is doctoring words from Climategate emails. That's bad enough, but worse yet, Judith Curry is helping him.

This is shocking for being so obvious.

Here's what Steyn quoted in his vanity book "A Disgrace to the Profession," according to the angry, anonymous blogger Tony Heller Exposed. It is a supposed quote from Phil Jones to Michael Mann:
Keith [Briffa] didn’t mention in his Science piece but both of us think that you’re on very dodgy ground with this long-term decline in temperatures on the thousand-year timescale. It is better we put the caveats in ourselves than let others put them in for us.
Judith Curry repeated this quote here:

In fact, this isn't what the actual email says at all. It was, instead, the following -- I've highlighted in red what Steyn and Curry left out:
1) Keith didn't mention in his Science piece but both of us
    think that you're on very dodgy ground with this long-term
    decline in temperatures on the 1000 year timescale. What
    the real world has done over the last 6000 years and what
    it ought to have done given our understandding of Milankovic
    forcing are two very different things. I don't think the
    world was much warmer 6000 years ago - in a global sense
    compared to the average of the last 1000 years, but this is
    my opinion and I may change it given more evidence.
2) The errors don't include all the possible factors. Even
    though the tree-ring chronologies used have robust rbar
    statistics for the whole 1000 years ( ie they lose nothing
    because core numbers stay high throughout), they have lost
    low frequency because of standardization. We've all tried
    with RCS/very stiff splines/hardly any detrending to keep
    this to a minimum, but until we know it is minimal it is
    still worth mentioning.
It is better we ( I mean all of us
    here) put the caveats in ourselves than let others put them
    in for us.
That's right -- neither Steyn or Curry gave the actual quote, or put in ellipses for the part they left out. 

They also changed "1000 year" to "thousand year," and, more importantly, left out -- again, without ellipses -- the paranthetical phrase in the last sentence, "...(I mean all of us here)..." 

What they left out obviously changes the meaning and context of the quote they did give. Their quote is simply wrong, and worse, it's dishonest.