Great resource on various MWP proxy reconstructions

A commenter here a couple of months ago posted a link to a truly great resource of paleoclimate proxy reconstructions covering various time periods all including the time of the Medieval Warm Period, or MWP.

The MWP was a time of generally warmer temperatures in the North Atlantic region lasting from roughly 950AD to 1250AD. It was once thought to have been global in extent and perhaps as warm as or warmer than today. Notably, the 1990 IPCC report contained a rough, manually drawn schematic of global temperatures over the last 1100 years that placed the MWP well above the current global anomaly:

But science progresses, and that crude educated guess has since been replaced with a multitude of scientific studies based on all kinds of climate proxies, from pollen in lake sediment to layers of calcium carbonate in limestone caves. These studies indicate that the medieval warm period was not globally synchronous and was not warmer than today. It remains one of the most common denialists talking points, even if it is of questionable relevance when it comes to what the future likely holds.

So it is with tremendous, unintended irony that, via CO2 [Psuedo] Science, a local denialist drops a truly great resource for illustrating the current state of the science around this issue at our feet.

This web resource can be found here and is a repository of graphics of temperature reconstructions, together with references to the studies they came from, all scattered across an image of our blue planet. So in one spot we have 43 paleoclimate studies visually associated with the area studied.

But what's so ironic? Well, far from supportting the desired fiction of a globally synchronous MWP, it makes it completely clear that this was not the case. These studies surely do show warm periods, and most show warm periods in medieval times. But they are not synchronized at all.

A few examples will show what I mean. Now remember, this is supposed to show that all over the planet it was nice and warm between ~950AD and 1250AD.

I think you get the idea. Now, to be sure there are some studies showing a nice ~950AD to ~1250AD warming, notably in the North Atlantic area. But this is supposed to be evidence that the MWP was everywhere! According to their own citations, it was not.

What I did above may look like cherry picking, and technically it is, but in my defense I am just going through the bowlful they provided. These are their cherries, but when we actually look, they are mostly just pits.

More like this

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For those as easily confused as I, the 950-1250AD MWP interval is 760-1060 in years-before-present.

The fact that warming can take place even when CO2 levels are low is supposed to make us less worried when CO2 levels are high?

Can these people keep two thoughts in their heads simultaneously or is that asking way too much?

By Gingerbaker (not verified) on 06 Apr 2010 #permalink

Gingerbaker, the idea behind a lot of denial is that CO2 causing warming is only a hypothesis or vague suspicion, based on the simultaneous rise of CO2 and temperatures *and nothing else*.

They never feel they have to explain why the actual physical properties of CO2 would allow an increase in atmospheric concentration (few deny the measurements that show this) together with a complete absence of any warming (which would be a puzzling thing to have happen, based on what we can see happens when you put CO2 in an infrared spectrometer).

Just out of curiosity, have you done anything similar with temperature data for the past 40 years? My bet is, you would see the same thing.

Want to take that bet?

Dave X: "For those as easily confused as I, the 950-1250AD MWP interval is 760-1060 in years-before-present."

I believe that where past events are dated Before Present (BP), present actually means 1 January 1950. Or so says Wikipedia:

So 950-1250 AD is 1000-700 BP.

Posting this here in response to Earthling's comments an this thread… as I took so long in composing it coby locked the thread before I could post it :-( Coby please feel free to move or delete it.

Earthling presents some citations (though the link to CO2Science at the bottom of his link is telling and the false claims at the top are gratuitous).

First paper on the link is Cook et al. Which mandas discusses at #25 above ("Similar to the NH, this SH expression of the MWP is not homogeneous in time. Rather, it is composed of two periods of generally above-average warmth, A.D. 1137â1177 and 1210â1260, that are punctuated by years of below-average temperatures and a middle period that is near average" and "Of equal interest in the reconstruction is the sharp and sustained cold period in the A.D. 993â1091 interval")

Nunn's book is a new one on me. I've not read it and will give the quotes given from Earthling's link the scepticism they deserve.

Newton et al. Is closer to the mark. Though as noted by Abram et al (Oscillations in the southern extent of the Indo-Pacific Warm Pool during the mid-Holocene (2009) Quaternary Science Reviews Volume 28, Issues 25-26) "The Indo-Pacific Warm Pool (IPWP) is thought to play a key role in the propagation and amplification of climate changes through its influence on the global distribution of heat and water vapour." So it should be unsurprising that major climate anomalies both northern & southern will be reflected. Interestingly Newton's single core show marked differences to Oppo et al's multi-core proxies using updated coring technology (see below).

Richey et al. is again from a single core (note how many of those citing these kinds of papers (I'm not talking about you Earthling, but the likes of Vernon above who also cited this paper) are so vociferous about the perception that the likes of Mann et al. base their conclusions on 'single tree cores'. Unfortunately I couldn't find a link to the paper (Earthling where did you read it?) So can't comment directly. However I will note that the Gulf of Mexico is in the N. hemisphere and is part of the Atlantic Warm Pool so this study does not invalidate the idea that the MWP is a predominantly Northern and Atlantic phenomenon.

Oppo et al. again base their cores in the Indo Pacific so my comments about the Newton et al. paper are also germane here. Note again that although they do not completely disagree with Newton's findings there are significant differences between the two results. I'll also point out here that the IPWP is also in the N. hemisphere.

Keigwin's paper is about the Sargasso sea. In the North Atlantic. Again there is no link to the actual paper - Earthling you've read it what are the methods? (It is referenced by the, frankly, scarily titled Abrupt climate change and collapse of deep-sea ecosystems Yasuhara et al. (2008) PNAS 105 1556 - 1560 though.)

Grove & Switzur is based on the hypothesis that "Medieval Warm Period was preceded and followed by periods of moraine deposition associated with glacier expansion" which is fair enough though untested. Again the full paper is paywalled - Earthling where did you get your copy? It is referenced by Jones & Mann (2004) Reviews of Geophysics 42(2) "Simple interpretation of such information in terms of past surface air temperature and precipitation changes is, however, confounded by the delicate balance between local changes in melting and ice accumulation and the variable response timescale of glacial mass balance (which typically increases with the size of the glacier, potentially approaching century timescales for large mountain glaciers). In other words, glacial moraine evidence may be indicative of past climate variability, but it cannot, despite claims sometimes made to the contrary [e.g., Broecker, 2001], be uniquely interpreted in terms of specific past temperature or precipitation histories. Both increased winter precipitation (through greater accumulation) and lower summer temperatures (through decreased melting or ââablationââ) can lead to more positive glacial mass balances. While the response to climate forcing may be close to contemporaneous for small, fast moving glaciers, the inertia of large glaciers dictates that they respond to climate change relatively slowly, with delays of decades or occasionally centuries [Jo¨hanneson et al., 1989].

Finally Zhang is also paywalled. Earthling did you buy all these papers to read them? It is referenced by Ge et al. (2007) Int. J. Climatol. Who state "differences in the results of reconstructions exist even when people are using similar documents" and "the warming intensity in the Medieval Warm Period in China is so moderate when compared with the warmth in the 20th century" Again though, China is in the Northern Hemisphere.

In summary, whilst I don't want to appear "alarmist" and write these papers off I would say that the selection does not back up the claim made in post #175 that "There are too many studies to link to with strong evidence that the MWP was global and possibly the LIA as well." The breakdown of the location of the studies cited are as follows: 1 global (but possibly flawed); 2 North Atlantic and environs; 2 Indo-pacific Warm Pool (Effectively this is double counting, Oppo et al. state that the Newton et al. Core is "nearby" and uses it in their analysis); 1 China (just north of the IPWP) and one New Zealand that shows a very cold period slap bang in the middle of the MWP date range.

Coby wrote:
"Earthling, we've seen all that before. The problem is that all of those studies look at individual regions, there are no global reconstructions that indicate a pronounced MWP."
There evidently isn't enough grant money available to fund these studies, coby.
My thanks to Chris for spending his time debunking those in the link I posted, there are more.
Here's the Medieval Warm Period Project Interactive Map for you to take to pieces:
And a country by country MWP research list:
"Greeland's Medieval Warming Hotter Than Modern Temps: Bird Crap Nails MWP for Researchers"…
Last for today, but by no means least, a map of MWP studies that even the staunchest alarmists will have trouble debunking from his armchair.

By Earthling (not verified) on 30 Sep 2010 #permalink

Ok, question time.

E'ling: First, what do you believe is demonstrated by the interactive map--that there was a globally synchronous MWP? Something else? I need to know exactly what you're claiming here.

Second, did you read *any* of the studies--or maybe the abstracts of the articles listed. (I'm not going to unrealistically demand that you have read them all, just, you know, have at least taken a solid look.)

Third, what do you think a warmer Greenland means in terms of the MWP debate?

Fourth, it there was a global MWP, what is the implication for climate science?

And full disclosure: We had a massive discussion about the CO2 science site a few months back. Suffice it to say nobody was compelled to declare global warming a "myth". Even our dear Crakar later conceded there was no evidence for a global MWP.

This is just too funny.

"Last for today, but by no means least, a map of MWP studies that even the staunchest alarmists will have trouble debunking from his armchair."

The link is the 'Great Resource' that is the subject of this post.

Despite our host Coby's request that Earthling reads it, it seems our esteemed correspondent has neglected to in his haste to continue the argument.

What more needs to be said?

By the way, I wasn't debunking those earlier links Earthling. I'm sure they are all correct (with the possible exception of the Grove paper). I just don't think they mean what you think they mean. I am reminded of Inigo Montoya for some reason.

Also, I'd really like to know how you got hold of the paywalled papers. I'm always on the lookout for ways to get hold of research without having to bother the author for a pdf.

With scant and inconclusive research in the area of a global MWP, the research that has been carried out is enough to suggest that it could have been global and there's no conclusive research to prove that it wasn't.
Basically, we have a dilemma, "a problem offering at least two solutions or possibilities, of which none is practically acceptable."

By Earthling (not verified) on 30 Sep 2010 #permalink

here's no conclusive research to prove that [the MWP] wasn't global.

This is an argument?

What's the conention now--the MWP *might* have been global, so AGW is disproven?

Earthling's comment sounds eerily like those of avid religionists: "You can't disprove there's a god! Hence, there is one".

"What's the conention now--the MWP *might* have been global, so AGW is disproven?"
No, "conention" at all, skip, AGW remains as unproven as it is proven.

By Earthling (not verified) on 01 Oct 2010 #permalink

Marco wrote:
"Earthling's comment sounds eerily like those of avid religionists: "You can't disprove there's a god! Hence, there is one"."
Earthling is an Atheist, so that's your first assumption scuppered.
I also believe planet Earth is a globe and that it has been spinning around for a few billion years, so you can't peg me as a flat Earther or creationist.

How about trying to convince me that the MWP wasn't global?

By Earthling (not verified) on 01 Oct 2010 #permalink

Earthling is an Atheist . . . so you can't peg me as a flat Earther or creationist.

How about trying to convince me that the MWP wasn't global?

I am almost without words.

How about trying to convince me there is no God?

Skippy, the topic is the MWP or had you forgotten already?

By Earthling (not verified) on 01 Oct 2010 #permalink

You genuinely do not understand the analogy, or the point, do you?

Allow me to ask the question differently:

Do you believe you *could* disprove the existence of God--not that I'm asking you now--*if* you were inclined? In this hypothetical state of affairs, would it be acceptable for me to ask that you disprove it--God's existence, that is?

This is not about the existence of God per se, but what is and is not reasonable argumentation.

By the way, Earth,

Can you disprove the existence of the proof that there was no MWP?

Ha! You *cannot* disprove that this proof exists, which proves the MWP did not exist!

You probably don't understand the point of what I just wrote, do you?

Earthling doesn't understand analogies, apparently.

"How about trying to convince me that the MWP wasn't global?" is the same question as "How about trying to convince me that god does not exist?

The data is out there, it is in the link Coby provides. Of course, the people who provided all that data try to convince you otherwise, but to do so they just show you graphs WITHOUT doing any scientific analysis of those graphs. It really is the same as religionists, although they point to the bible or the quran as 'evidence' without noting the blatant contradictions in those documents.

I'll leave you all bowing to your god, Coby.

By Earthling (not verified) on 01 Oct 2010 #permalink


Famous last words.

Although I wonder: Can any of us really prove that *Coby* exists?

Not meaning to predjudice the investigation into my alledged existence with this comment, but I thought Earthling's promised departure might be a good time to recall how he entered this discussion:

"There are too many studies to link to with strong evidence that the MWP was global"

He of course never offered any specific study of these "many" and his links from CO2 Science were the standard fare of regional reconstructions showing warm periods of varying length, degree and timeframes: in other words, no globally synchronous MWP.

His parting assertion is much different:

With scant and inconclusive research in the area of a global MWP, the research that has been carried out is enough to suggest that it could have been global and there's no conclusive research to prove that it wasn't.

I'd say he deserves a pat on the head for accidentally learning something as he makes his way out...

Besides this Voice from the Heavens, I am also satisfied that i cannot *disprove* your existence. From that it follows you must exist.

just to clarify my last comment, Earthling still has it wrong, I just thought we should note his substantial retreat...

Nice watching the rhetoric go from "there was no MWP" to "it was only regional in the Atlantic" to now "it was only the NH."

Your point?

Actually, skip, Vernon is waving a strawman around.

Actually just point out a little history Marco. Now history is a strawman?

Actually Vernon, it's not changed.

You missed out a word. G.l.o.b.a.l is the word in question.

Arguments about whether it was just the Atlantic or more widely across the NH are mere details compared to that. Unless someone's not told me about South America or Australia /NZ producing evidence of substantial SH warming in the same centuries. I recall reading about some SH warming at a different time, but none about simultaneous warming in both NH and SH.

Now history is a strawman?

Actually, Vern, the rhetorical question is itself yet another straw man. Precisely what is in question is your version of "history".

As Ad pointed out, no one has switched his story as to where there was a MWP--only whether it was globally synchronous. This was the "point" I was alluding to earlier.

Can you *document* your claimed changes in "the rhetoric"?

This thread is a very important one to read for anyone who wants to make claims about the so-called "MWP".

We have discussed this issue ad nauseum, and there are a number of resources available for anyone who wants to read up on it before making unsupportable claims. Funnily enough, the best resource is a denialist website, which published a map with linked papers and graphs which suppposedly proved the MWP was a globally synchronous phenomenon. The link is here:

What is funny about this is - just like all denialists - they have spectacularly failed to do their homework. If you actually read the papers and graphs, you will note that the MWP was NOT globally synchronous. In other words, the denialists once again failed to do any science, and linked to things they don't understand and have not analysed properly. They did a cursory analysis and THOUGHT from the title or abstract that it supported their viewpoint, when any real scientist could see otherwise. I guess that shows why real scientists are always preferred over amateurs with spreadsheets.

A more detailed analysis is contained above and on this thread:…

Happy science reading.

Adelaidy in 32,

Are you saying the MWP did in fact exist at some time in the NH? Was it seen in the entire hemishere or only in isolation? I only ask because the Hockey stick was a study of the NH and as far as i recall the temp line was pretty flat around then not sure what this means?

Mandas 34,

I have finally started reading Heaven and Earth (the weather makers is next) i am up to chapter 2 where he talks about the natural climate change of the past. He mentions the MWP and LIA and says they are global so i will make a note of the papers he references and let you know tomorrow so we can have a look at what they say.

Until then.


Thank you for that. Plimer huh? I can't wait for his pearls of wisdom to come driping from your fingers like saliva from my dog's mouth when I have food.

Your comment brought a smile to my face Mandas.

I am not doing this in an attempt to defend anyone or anything just simply supplying the papers he cites.

I have a question,

Coby states above that the NZ warmth was betwee 1200-1350AD now this is a level one study but there are 2 level 3 studies which he could have used and the dates for these are 900 to 1100 AD which fit a bit better to the dates 950 to 1250. Is there any reason why you could not use a level 3 study when just looking for periods of time?

Also how accurate are these dates? I would have thought depending on the proxy or methods used there must be some tolerance on the start and stop dates but none appear to have any, is there a reason for this?

You may use my metaphor if you wish (yes, I just made it up).

But sorry, I have no idea what you mean about Level 1/3 etc studies. I have heard about the concept in medicine, but not in other fields.

In regard to accuracy of dates, I would think it would depend on the proxy being used. Some would be highly accurate (perhaps within a couple of years), whereas others would be less so. But a proper study should show the error margin.


Page 63 plimer talks about the medievil warming (900-1300AD)

He states "it was far warmer than present and warming was wide spread" He cites Grove,J.M 1988: "The little ice age".

Reference to Nth America Broecker WS 2001 "Was the MWP global" science 291: 1497-1499

Finding it hard to see a reference for SH studies........he has one here where he states "A study of 6000 bore holes on all continents has shown that the temp in the MWP was warmer than today and fell by .2 to .7C during the LIA"

Huang, S., Pollack, H.N. and Shen, P.Y. 1997:Late quarternary temp changes seen in world wide continental heat flow measurements. geophysical research letters 24: 1947-1950

Why dont we start with that and i will look for some more. In regards to l1-3 studiesthe CO2science site gives you a explanation. There is a link here for explanation

From what i read L1 gives you temp period and magnitude L3 just gives you temp period.

found another,

"In Sth Africa a stalagmite from cave in the Makapansgat Valley showed a warm period from 1000 to 1300 AD"

Tyson, D., Karlen, W., Holmgren, K and Heiss G A 2000:The LIA and medieval warming in South Africa. Soth African Journal of Science 96:121-126.


I am sure you can find lots. Now, go to the link I provided above (which was originally your link by the way) and put them all together.

Yeah i knew it was my link, will have a look when i get time, i thought i would give you some as you have a better access to studies than most. You dont have to look at them, i thought since i started reading the book i should share the references with however is watching.