Thursday, February 20, 2014

The Medieval Warm Period in the IPCC 1AR

What was known about the "Medieval Warm Period" before Mann et al and others did their reconstruction work in the 1990s?

Not a whole lot. At least, not as portrayed in the IPCC's First Assessment Report.

A commenter writes,
Pardon me, but assuming Michael Mann and co-authors are correct...isn't Mann himself a contemporary example of a dogged contrarian overturning the long-held consensus regarding the so-called Medieval Warm Period postulated by Hubert Lamb and agreed to by like 97% or so(earlier) eminent climatologists? From the IPCC First Report (FAR) back into the history of science, the consensus seemed to be that the era about AD 1000 to AD 1300 was "warmer" (whatever that means) than the following "little ice age" between AD 1400 and AD 1800, and that "now" was again "warm". EVERYBODY tended to agree with Lamb and his acolytes....
which is similar to what Mark Steyn said on a recent Powerline podcast:
"Dr. Michael Mann created this thing called the hockey stick, which purposted to show that late 20th century temperatures are warmer than they've been in a millennium. I don't think that's true -- a lot of people don't think that's true.... To get that result he had to eliminate....

"His big contribution was eliminating this thing called the Medieval Warm Period, when they had vineyards in Greenland, for example. The Medieval Warm Period is something I learned about at school. It was followed by the Little Ice Age where they were skating on the Thames, and this kind of thing, He eliminated all that and showed a flat line from the year 900 to the year 1900, and I think that's a lot of hooey."
Is it hooey? I can't vouch for the quality of Steyn's science education, but that picture of the MWP is not what the IPCC wrote on their First Assessment Report in 1990. In the FAR Chapter 7, page 202, they gave the figure to the right.

Notice there isn't even a scale on the vertical axis (the IPCC calls it a "schematic diagram").

The text reads
"The period since the end of the last glaciation has been characterized by small changes in global average temperature with a range of probably less than 2°C (Figure 7.1), though it is still not clear whether all the fluctuations indicated were truly global....

The late tenth to early thirteenth centuries (about AD 950-1250) appear to have been exceptionally warm in western Europe, Iceland and Greenland (Alexandre 1987, Lamb, 1988) This period is known as the Medieval Climatic Optimum China was, however, cold at this time (mainly in winter) but South Japan was warm (Yoshino, 1978) This period of widespread warmth is notable in that there is no evidence that it was accompanied by an increase of greenhouse gases.
In other words, there wasn't a lot known then, and there were cold regions as well. They refer to only two papers, both of which pertain mostly to Europe.
So Mann et al didn't "eliminate" anything -- they provided illumination where before there was much darkness.

There just wasn't a lot known about the MCA (Medieval Climate Anomaly) before people started seriously collecting and understanding proxy data, and the theorists then started to analyze it.


J Melcher said...

I believe you mean to say that only archeology, anthropology, and geology had much to say about climate, in the the pre-instrumental era, until dogged contrarians such as Michael Mann introduced the concept of temperature estimation by statistical analysis of proxy data.
Again, not that Mann was wrong or that the anthropologists were wrong, but that the "consensus of science" -- as a general body of knowledge -- was revised with the publication of Dr Mann's "hockey stick".

David Appell said...

You have yet to prove there was a consensus before Mann (I think you said it was "97%").

It looks to me that there just wasn't much data in the time of Lamb.

dave said...

Bit inaccurate to say that Mann, Bradley and Hughes (MBH) overturned Lamb about the Medieval Warm Period: indeed in 1982 Lamb himself wrote that "China and Japan evidently missed this warm phase."

The IPCC First Assessment Report in 1990 did discuss a "Medieval Warm Period (which may not have been global)", but the Second Report of 1996 (SAR) cited Hughes & Diaz 1994 as questioning how widespread the warmth had been at any one time, so they could not "conclude that global temperatures in the Medieval Warm Period were comparable to the warm decades of the late 20th century." The SAR also showed a graph from Bradley & Jones 1993 which anticipates the broad conclusions of MBH98, albeit on a decadel scale and without showing the uncertainty.

Although MBH99 gets the 1,000 year "hockey stick" fame, it was anticipated by Jones et al. 1998 which covered the same period and showed a similar graph, although on a decadel scale without the uncertainty area. So, not really such a revolution, more an incremental refinement!

J Melcher said...

Dave, thanks for noting that Lamb's view on climate was not confined to the 1990 IPCC FAR. 1982 before that, and I intend to bring forward a piece of work from 1976. As I originally wrote, the model for which Lamb was merely one outspoken champion was "long-held" (also, widely held, and widely promulgated.)

Mann's work and views were and are quite different in tone and detail from Lamb's. Contrary, so to speak. And between 1990 and 2000 Mann's view, the view he championed, came to dominate. To argue that Mann has merely been, as our host says, " testing the edges of knowledge, where things are still not settled." is to deny, (so to speak) Mann the accomplishment and credit due him, his co-authors,and the "hockey stick". Mann was, and remains, a contrarian and progressive compared to the prior, prevailing, consensus; and those opposed to Mann's view are as fairly characterized as 'reactionary' as any follower of Adam Smith reacting to the propositions of Karl Marx. This is NOT to take sides in the dispute, it is to say that science does NOT happen in the absence of scienTISTS, nor does a new hypothesis arise as an un-caused consequence by some miraculous form of spontaneous generation. Mann created the consensus on climate that now prevails.

As he would tell you.

Rightly or wrongly.

David Appell said...

J Melcher: Did Lamb's research go beyond Europe?

Where is the evidence of a "consensus" during his time?

David Appell said...

Mann created the consensus on climate that now prevails.

No, he didn't, though he's played a role of course. There were many scientists before him.

You have some strange ideas.

J Melcher said...

My idea is that Mann's "hockey stick" as promoted in the IPCC TAR remains the consensus that prevails among the majority of those who "like science" or may be practicing scientists (but not climatologist). That stick shows (rightly or wrongly) the recent decades are "unprecedented" in climate history of the last 600 to 1000 years. Mann is lead author of the paper that first presented the image.

Mann's view is a radical refinement of prior views.

What's strange?

J Melcher said...

The evidence of consensus is the regard other scientists, editors, and publishers vested in Hubert Lamb to communicate "the" theory of climate to the public, policy makers, and to other scientists of other disciplines. The Lamb view is the consensus view in much the same way that, right now, the Neil Degrasse Tyson view about the definition of planets and the status of Pluto is the consensus of astronmers on the question. Not without dispute, but settled.

Tyson, of course, was, during the debate about Pluto, another of the "dogged contrarians" you refuse to admit exist in science. Now, having won, he champions the consensus view against reactionaries ("Pluto is SO a planet) and weirdos ("There are still hidden planets out past the thing called Pluto.")

I am working on the formal proof about when and why Lamb was the climate champion of the era 1960-2000. Were I not taking care and time, the proof would contain sloppy holes I'm confident you would dispute.

dave said...

Oh dear, J Melcher, you seem to have this fantasy that only Lamb and Mann contributed to paleoclimate studies. The concept of temperature estimation by statistical analysis of proxy data wasn't introduced by Mann, in 1929 Wilmot H. Bradley used annual varves in lake beds to detect climate cycles, in 1936 Douglass used tree rings and in 1962 Fritts developed accurate use of tree rings. In 1991 Bradley and others set out proposals for reconstructing the climate of the past 2,000 years. At this stage Mann was still studying theoretical condensed matter physics, but you seem to think he influenced the field before he even began studying it!

As for Lamb's tentative non-quantitative view being "long held", it was essentially based on Central England in 1965, and by 1982 he was proposing that the Medieval Warm Period was not world-wide. A view shared by other scientists, hence the caveats in the 1990 IPCC First Assessment Report. In other words, the consensus by 1990 was that the Medieval Warm Period was not global, and this was given detailed quantitative confirmation by Hughes & Diaz in 1994.

J Melcher said...

Hi Dave,

Please note that the MWP is not the be-all and end-all of the Lamb viewpoint. (Or MCA, if you prefer the Orwellian newspeak. I don't object.)

Lamb also championed the consensus on the so-called "Little Ice Age" -- quite explicitly holding THAT to be a world-wide trend.

The climate and stability of that climate during the period from AD 1400 to circa 1950 was understood one way by Lamb and his contemporaries; and that view persisted into the early 1990's at the time of the IPCC FAR. (Despite the "contrarians" Douglas, Bradley and Fritts that you cite, whom I happily acknowledge -- the point being our host Mr Appell has claimed that so such contrarians exist, and I argue otherwise.) It was Mann and the MHB98 paper that overturned the "Lamb consensus" regarding climate cycles.

Mann will himself tell you so.

dave said...

Hi J Melcher, so now you're randomly calling all the pioneers of paleoclimatology "contrarians".... that effectively supports David Appell's view that there was no consensus in the early years!

Don't see where "our host Mr Appell has claimed that so such contrarians exist", the clear point is that "There just wasn't a lot known about the MCA (Medieval Climate Anomaly) before people started seriously collecting and understanding proxy data, and the theorists then started to analyze it."

My point is that such analysis of proxy data goes back to Fritts, the idea of a worldwide MCA (or MWP) was already in question by 1982, and thoroughly disputed by Hughes & Diaz in 1994. So no consensus then.

The MBH98 paper didn't even cover the MCA, and it came to similar results to Bradley & Jones 1993 so was reaffirming the developing consensus. Jones et al. 1998 did cover the MCA, with similar results to the subsequent MBH99 so no overturning of consensus there.

As for what Mann would tell you, his book includes a chapter "Signals in the Noise" with a section on The Medieval Warm Period discussing the widespread misrepresentation of Lamb's seminal work. He notes how researchers in the early 1990s found that the warmth wasn't synchronous across regions, and cites as an example Hughes & Diaz. Which is where we came in...

J Melcher said...

Hi Dave,

Thanks for engaging.

You say you "Don't see where 'our host Mr Appell has claimed that so such contrarians exist'," so I infer you missed our host's post here:

The URL containing the title containing the claim that no "contrarians" exist in science.

Mr Appell has phrases his hypothesis rigorously and well, because it is falsifiable. A claim of the sort "all rocks sink in water" is a problem, because while on can demonstrate that THIS rock sinks and THAT rock sinks and ANOTHER rock sinks, one can't really PROVE that all rocks sink until one runs completely out of the universe of rocks. But a phrasing such as "no rocks float" can be falsified. "Well, marble sinks, and granite sinks, and limestone sinks, but, oh hey, PUMICE floats. Proof-- that the hypothesis was wrong!" Scientific laws are therefore generally formed in this fashion. NO energy can be created or destroyed. No change in motion results except from an outside force. No temperatures below -273 degrees Centigrade can be obtained. Mr Appell says "NO dogged contrarians" exist in science. I have cited Copernicus, Alvarez, and Mann himself as example proof to the contrary. But we keep winding up discussing the prior consensus of climate science and the theory of a warm period in the middle ages. *sigh*.

The MBH98 original "hockey stick" paper made two "contrarian" claims compared to prior work. (Work I attribute to Lamb, but Lamb really is a stand in for the views of all prior scientists in the same way Aristotle stands in for the paradigm of "motion" that existed before Newton. ) Mann and the MBH paper used a novel method to calibrate proxy data to temperature anomalies in increments of 0.1 degree Centigrade. (A much more precise claim than prior workers claimed.) And the shaft of the "hockey stick" indicated a much more stable temperature profile for the past 600 years (AD 1400 to circa 2000) than prior workers (who waved there hands over variations in a few, full, un-fractionated and unspecified number of degrees Centigrade.)

The paper was "contrary" to prior work by design and in response to the incentives he perceived in his discipline. As Dr Mann just recently posted:

" The way to get ahead in science is not to reinforce what is already known (i.e. "climate change is real, caused by us, and a threat"), but to expand the horizons of our knowledge (e.g. "how will climate change influence the El Nino phenomenon? Or hurricane activity?). That's how you get research grants, papers in Nature and Science and leading technical journals, etc. There is little if any incentive for a scientist to simply reaffirm what is already known. ...
The incentives are to prove the conventional wisdom wrong, or at least add a new twist or detail to the prevailing scientific understanding. "

Mann set out as a contrarian, doggedly pursued his goal, won the battle, overturned the IPCC FAR "graph" and substituted his own "hockey stick" in the IPCC TAR, and is now defending the paradigm and consensus he has built against attacks from the reactionaries (holding on the prior view) and the kooks (avant garde outsiders with little regard for either the old or current prevailing opinion.

dave said...

Hi J Melcher, your argument fails as the post you link to isn't just about contrarians, it's about the specific claim that "Science advances through dogged contrarians testing the "settled science".

The FAR words show clearly that the MWP wasn't "settled science", it was already questioned how much it was purely a regional effect, a question raised more than a decade before the MBH papers.

This polarised idea that MBH overturned the MWP/LIA is also incorrect: MBH99 explicitly "supports the notion of relatively warm hemispheric conditions earlier in the millennium, while cooling following the 14th century could be viewed as the onset of the Little Ice Age".

David Appell said...

J Melcher wrote:
Work I attribute to Lamb, but Lamb really is a stand in for the views of all prior scientists

How convenient! No need to prove a consensus, just cite one scientist and then claim that -- somehow -- he represents all of them. Problem solved!

This is why, J Melcher, I'm not debating you anymore.

J Melcher said...

Hi David,

You haven't really been debating me, previously.

Your claim is three part. (A) Steyn is silly (for claiming that science advances via the efforts of contrarians, because (B) there is no crying in baseball and no contrarians in science, and (C) (after being alerted to Mann's success in science, in promulgating a view "contrary" to what had gone before (to wit, the MWP) that in fact Mann has NOT succeeded in overcoming the previous paradigm because (c-1) Lamb wasn't the sole author of such a paradigm and (c-2) Lamb & others didn't evaluate climate with the precision of Mann and new others so Mann can't be said to have been contrary to a measurement that hadn't been made and (c-3) the MWP is really the MCA and the LIA isn't worth talking about and dammit Melcher you aren't following the script!

It seems to me you are so busy attacking Steyn you don't see how I have defended Mann -- against you and against my own reactionary inclinations.

It's your blog. And frankly the review of Lamb's life's work is worthy of a full post on another site (and my talents are not, after all up to reducing the case to my intended 500 words.)

I'll send you the link when it's up.

David Appell said...

J Melcher: Thanks for reading my blog, and your comments.

netspaced said...

You say there is no scale on the FAR diagram showing the MWP and the LIA. The accompanying text reads:
"The period since the end of the last glaciation has been characterized by small changes in global average temperature with a range of probably less than 2°C (Figure 7.1)..." and, sure enough, the diagram does have a scale - degrees centigrade.

Nice one, Dave.

David Appell said...

"Scale" means numbers, not units.