Arguments
The Medieval Warm(ish) Period In Pictures
Posted on 10 July 2011 by Rob Painting
The Medieval Warm Period (MWP) is a subject of "skeptic" focus, primarily because it was a time of natural warming. It took place from about 950-1250 AD, and, as opposed to today's warming which is global in extent and due to human activities, the MWP was mainly a northern hemisphere phenomenon and smaller in scale. Indeed, the advance of North American glaciers during the MWP is in stark contrast to what is happening in North America today.
The MWP in global maps
Mann (2009) was an analysis of a large set of climate/temperature proxies (ice cores, tree rings, cave mineral deposits, sediments, etc.) covering the MWP. See below:
Figure 1: Reconstructed surface temperature anomaly for Medieval Warm Period (950 to 1250 A.D.), relative to the 1961–1990 reference period. Gray areas indicate regions where adequate temperature data are unavailable.
It's clear from the map that only limited areas of the world were warmer during the MWP than the 1961–1990 reference period, Greenland in particular. Much of the rest of the planet, especially the oceans, were cooler. And take note of the cooler North American west coast, which is consistent with the glacier advance there during the MWP. Obviously, the Earth has continued to warm even further since the 1961–1990 period, so the difference in temperature between the MWP shown in the reconstruction and today is even greater.
Climate Models and the MWP
The climate proxies suggest a rather different distrubition of heat and rainfall than today. So the question arises: based on the current well-understood climate system, can ocean-atmosphere processes produce temperature patterns like the MWP? For answers we turn to climate models.
The cool central and eastern Pacific suggested by Mann 2009 explain some of planet-wide climate features observed in the MWP, but they fail to explain other aspects, such as as a more positive North Atlantic Oscillation (NAO), and increased rainfall in parts of Asia.
Graham (2010) used the NCAR climate model and, based on findings from other modelling studies and proxy evidence for a warmer Western Pacific Ocean, found that by forcing the simulation to have a slightly warmer Indian and Western Pacific Ocean relative to other ocean basins, the model results match the climate suggested by the proxies.
Below are the comparisons between the climate model control runs (a pre-industrial baseline) and the simulations including a warmer Indian-Western Pacific Ocean, for the northern hemisphere (boreal) winter (figure 2 and 3)
Figure 2: Differences in December–March temperature between the Indian Ocean Warm Pool (25) and control simulations (°C, color; values are Sea surface temperature over ocean and 2-m temperature over land).Lined contour interval is 0.5°C between 30°N and 30°S and 1°C elsewhere. From Graham 2010.
Figure 3: Differences in December–March precipitation (expressed as fraction of Control simulation, color) and Sea level Pressure (difference, hPa) for the Indian Ocean Warm Pool simulation. SLP contour interval is 1.0 hPa except 0.25 hPa in the region 30°S–40°N and 25°E–100°E where the finer interval highlights temperature-driven low pressure around continental periphery of northern Indian Ocean. From Graham 2010.
The warm Indian-Western Pacific Ocean, combined with the cool Central and Eastern tropical Pacific reveals a good match with the paleoclimate proxies shown in the Mann 2009 reconstruction, namely:
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The NAO becomes more positive (A in figure 2 and 3), matching proxies of Atlantic sea surface temperature and sea ice distribution. This due to an atmospheric teleconnection (two connected atmospheric processes separated by large distances) between the NAO and warming over the Indian Ocean.
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Seasonal dryness in northeast Africa (B in Figure 3 )
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And wetter conditions in India, Southeast Asia and China(C in figure 3)
A mechanism for such warming of the Indian and western Pacific Oceans has not been found, nor do the climate model simulations resolve all the patterns suggested by the proxies (such as warming of the British Isles); however, these findings represent another small step forward in piecing together the puzzle of the MWP, and also support the interpretation of the proxy data in Mann 2009.
Science marches on while skeptics don't
The MWP was very unlike warming today; the growing North American glaciers during the MWP being somewhat of a giveaway. The MWP only affected warming in a handful of regions, with Greenland being especially warm (Figure 1), whereas much of the Earth was actually cooler than the late 20th century. By comparison; today virtually every glacier and ice sheet on the planet is in rapid retreat.
Both the climate proxies and the climate models imply that the MWP was a re-organization of the Earth's climate, and that much of this re-organization can be explained by oceanic patterns of warming and cooling, although what started all this rolling in the first place is still unknown.
So while some climate "skeptics" are stuck in a time loop, wilfully reliving their own version of Groundhog Day, science continues to move forward.
Where is the evidence about past sea surface temperatures in the Tropical Pacific?
The paper show that during the so-called MWP the Tropical Pacific was dominated by a persistent La Niña anomaly.
However, the only climate proxies for SST anomalies in the Tropical Pacific that I could find were in the following paper about the Central Pacific:
El Niño/Southern Oscillation and tropical Pacific climate during the last millennium
That shows an incomplete record of the SST anomalies in the central Pacific (NINO 3.4 area), showing that at least during the periods covered by the Palmyra Islands coral record, the NINO 3.4 zone was dominated by La Niña.
But in the Mann 2009 paper (from where the above map was taken) show a persistent La Niña over the entire MWP and also shows the NINO 3 area as a zone with reconstructed cool SST anomalies.
From what proxies did Mann obtained proxies that record the entire 1000 past years and from where obtained data about the entire NINO3 area, a zone where there are no islands?
I searched for studies showing this, and I just found the Palmyra Islands (incomplete) record for just the NINO3.4 area linked above.
I would like more info, both for having a better answer to the "skeptic" arguments about the MWP and for living in Peru, where the ENSO climate oscillation is the dominant force in the regional climate and weather behaviour
(after all, the name "El Niño" is a Peruvian one, referring to the Holy Baby (Jesus Christ) Christmas holiday that is when typically an ENSO event peaks)
I noticed the same thing and I am sure Mr. Painting will address this issue.
Mann 2009 uses a Climate Field Reconstruction (CFR) method. This method involves analysing proxies and instrumental records for spatio-temporal covariance patterns during periods when sufficient data is available, then applying those patterns to build past maps when and where there is no physical data.
SSTs at any given gridpoint would be reconstructed by reference to proxies (land or ocean, near or far) with an established covariance relationship.
The other notable issue seems to be the sparsity of southern hemisphere proxies, so most multi-proxy reconstructions are heavily weighted to the northern hemisphere which should bias reconstructions toward warming.
There is still lots of new research coming out all the time. Already in 2010-11 a plethora of new papers have hit the journals. My general sense is that, as more data comes to light the hockey stick is going to start to straighten back out to something more resembling Mann's 99 work. And that is going to be a real stick in the craw of the denier set.
From Peru - "However, the only climate proxies for SST anomalies in the Tropical Pacific that I could find were in the following paper about the Central Pacific"
The supplementary information for Mann (2009) is here. It details the CFR method outlined by pauls, and note the data and codes provided.
From Peru-" From what proxies did Mann obtained proxies that record the entire 1000 past years and from where obtained data about the entire NINO3 area, a zone where there are no islands?"
There are few proxies for the tropical Pacific, Palmyra coral, Galapagos coral, and Californian and South American marine sediments, but given the locations of the two indexes are you proposing some new, as yet unobserved, flavour of ENSO? There was a bit of scientific 'how's your father' over whether the Pacific SST's were warm or cold up until recent years, but the general concensus now is that a La Nina-like background state prevailed in the MWP. El Nino and La Nina still happened, but the background state was cool like La Nina.
A cool tropical eastern-central Pacific (La Nina-like) validates the paleoclimate proxies for rainfall elsewhere on Earth during the MWP, in contrast to a warm eastern-central Pacific (El Nino-like) which doesn't. For example: the centuries-long megadrought, of the (now) southern United States, during most of the MWP is only observed in climate modeling when the tropical Pacific is in a cool La Nina-like background state. Combining the La Nina-like Pacific with the warm Atlantic (evidenced by the strong positive NAO) matches the distribution of drought and wet areas in North America during the MWP.
Suggest you have a read of Graham (2010) provided in the post. The point of this post was to highlight that the Mann (2009) proxy data are consistent with climate model simulations, and modern-day observations of global circulations. The La Nina drying of the southern US is a feature still observed today.
From Peru-"I would like more info, both for having a better answer to the "skeptic" arguments about the MWP"
May pay to ask them why North American glaciers were advancing during the MWP too. I can point you to a few other recent studies if you're interested.
From Peru-"and for living in Peru, where the ENSO climate oscillation is the dominant force in the regional climate and weather behaviour"
Long-term, most models indicate an El Nino-like background state for the tropical Pacific. Again that doesn't mean more El Nino's, just the background warming resembles the El Nino state. This will be bad for the Peruvian fishing industry if it occurs, and Amazonian drought too.
That's why I found pretty strange to take 300 years and compare it against a much shorter period full of climatic developments. I found pretty oxymoronic the act of comparing a pluri-centennial period against a shorter one in order to say that those three centuries were "all quiet in the western front" relative to a shorter quickly-changing abnormal reference [I see some acknowledgment of inadequacy in the coloring in Figure 1, chosen to deemphasize values close to those in the base period -and probably, huge radius too-]
The comparisons are important as they can reveal changes which have occurred in the past century (not just 30 years) with those that have occurred in the past. In order to show that today's warming is unprecedented, it has be larger in magnititude and more rapid than previous episodes.
In addition to the questionable sea surface temperatures, other work has shown significant warming in Russia compared to Figure 1 above.
http://hal.archives-ouvertes.fr/docs/00/29/81/68/PDF/cpd-3-1-2007.pdf
http://www.baikalscience.org/?cat=12
Russia also experienced the MWP at different times, earlier in the West, later in the east, with temperatures warmer than the present by 1C or more.
http://www.pages-igbp.org/products/abstracts/solomina.pdf
[DB] "The MWP has been acknowledged as the last period of globally warm temperatures"
Citation? As it stands, a nonsensical statement.
Your link to Baikal Science confirms Mann's analysis. The areas it identifies as having significantly warmd during the MWP (Taymir and Putoran, are also labelled in Figure 1 above as having warmed. The area of the Ural Mountains discussed in your link to Demezhko are also represented as having warmed in figure 1. As you're currently 0-2 I'm not going to bother with your link to Solomina.
Rob, I'm downloading the article by Mann, Zhang, Rutherford et al, and the supporting online material and I'm finding -correct me if I'm wrong- that a few proxies were used, that grey masks indicates regions were 1961-1990 data is insufficient to draw climatic normals -not insufficient proxy data, what didn't mean there were aplenty-, regions without hatching didn't pass validation, and the whole set was got using computer modeling. I suppose that when I read and analyze the article and dataset -at the best of my capacity- I'll be able to find what role played the proxies other than getting low-frequency components of the signals to reconstruct.
I know it's nice to look at a world map and confirm happy Vikings in Iceland and Greenland and turbulent Mongols and Tartars in the seek of better pastures. It looks like reassurance. It's not so nice that the reconstruction for the Little Ice Age in the same work is showing also not cooling Iceland and southern Greenland. In my opinion variability in times of slow changing technologies is what makes your living impossible. Then, what's the use of a 12-generation anomaly?
What I've seen so far makes me think that not much more imprecision would have come from using 1941-1970 normals. What would have let us comparing MCA, LIA and nowadays AGW. There'll always be the layman approach to the driven conclusions. That shouldn't drive anybody to choose inappropriate base periods.
It was not as warm, and temperatures in many, many areas were cooler. The warming was far from global, or equally distributed in either space or time. Hence, your statement is only remotely close to true if you use a running 200 year average to compute temperatures, and even then temperatures were still markedly lower than those of the last ten years in particular.Not remotely true. Look at the literature instead of just making stuff up.There is no need to show that today's warming is unprecedented. That it will inevitably be unprecedented, whether or not it is now, is the second important point, but the main point is that the cause of today's warming is unprecedented. It is being caused by the understandable and predicted effect of CO2, and it will be close to irreversible in human time frames if we take things too far.
What is most entertaining about you, of all people, clinging to the MWP as yet another excuse to deny the physics behind climate science is the fact that there is no known or imaginable major source for warming in the MWP. This implies that such a cause was relatively small. This in turn points to a very, very high climate sensitivity as opposed to the foolishly low values to which you are so dearly wedded. That is the only way that the MWP could have been "as warm as today."
If you believe in the MWP, then you must refute your need to cling to climate sensitivity predictions below 3˚C per doubling.
Am I misreading Figure 1. It looks as if Mann was saying that the two Russian areas were cooling by 1+C rather than warmer by 1+C. If Mann is stating that they were warming, then I agree.
Sphaerica,
Some evidence, in addition to those precedented in my previous post, showing a global MWP.
http://ruby.fgcu.edu/courses/twimberley/EnviroPhilo/CookPalmer.pdf
http://www.clas.ufl.edu/users/rrusso/gly6932/Oppo_etal_Nature09.pdf
http://www.leif.org/EOS/2009JD012603.pdf
Rob, why somebody would analyse "the Medieval Warming Period" and "the Litle Ice Age" if not for comparison with actual developments? If the adjectives "Western European" or "Northern Atlantic" were added, that would be a horse of a different colour. Why a warming period in human history has no paired higher global temperature to show? So, there must be some preconceptions the researchers are trying to address, for instance, that the actual warming period can't be compared with the so-called MWP. Then, baselines are important, otherwise, why they use anomalies instead of instrumental temperatures? If we have to be sensitive to change, be sure we are sensitized using a proper base. In a post that is addressing general publics that is no minor an issue. On the other hands, when a thing is an important subject for analysis and not a bit of a stretch, one should easily find other works with other base temperatures.
Summarizing: MWP, LIA and actual AGW could be "easily" shown in contrast against a "normal" base, showing some misleading local warming and cooling for the first two what has clearly nothing to do with actual developments. Don't we have it? Well, such things happen when one allows [-snipped inflammatory comment] to dictate one's syllabus.
First, did you actually look at the papers you linked to? The last, Kellerhals et al, shows current temps substantially higher than the MWP.
The first, Cook, shows the MWP to be a fractionally present bump not much greater than other temps in the period, and also much lower than current temps.
So what exactly are you trying to prove?
And even if you found 3 proxy studies that show what you want, you're missing both points. The first is that that is mere cherry picking. A careful analysis of the data shows that warming that is supposedly the MWP is not contemporaneous... one study shows a peak in 1100, another 1300, another 950. It's also not nearly uniform around the globe. While one study shows a warm period here, another location at that same time shows cooling.
There is no doubt that there was a MCA, but there is no evidence that it was global, substantial evidence that it was not, and substantial evidence (as you have so kindly provided yourself) that temperatures even regionally did not match those of modern times.
Beyond this, you missed the other main points, which are first that whether there was a MWP or not, it does not change the radiative physics which clearly show we are causing greenhouse gas warming now, and if there was a MWP, and it was as warm as temperatures are now, then climate sensitivity is high and your constant admonishment that you are sure that climate sensitivity is likely to be below 2C goes out the window.
So you comment without actually reading the post? How can global temperature anomalies be similar to modern-day when North American glaciers were growing in the MWP?, and when the central and eastern tropical Pacific was much cooler than the 1961-1990 reference period?
Good points. And let us not forget this:
Comparison of temperature reconstructions, re-centered to match CRUTEM NH land record (based on each reconstruction's period of overlap).
[Source]
Notive how all the proxies show the MWP as being warmer than today?
[DB] Factually incorrect. See Martín-Chivelet et al.
[DB] Interested parties may see also Koch and Clague 2011 wherein they show that that several glaciers in western North America and elsewhere in the world advanced during Medieval time and that some of these glaciers achieved extents similar to those at the peak of the Little Ice Age, a very cold period many hundreds of years later.
More discussion on this here.
The reason for the advancement of the glaciers is not certain. There are proxies from NA that show during the MWP the precip was extensively higher than present. That would cause the advancement of glaceriers even if the temperature was warmer.
[DB] Citations please. Unsupported claims carry little weight.
Precipitation increases do not necessarily translate into glacier advances. The mass balance between increased depositions in the accumulation zone have to outweigh losses in the ablation zone for glaciers to advance. Warming typically increases the size of the ablation zone and decreases that of the accumulation zone resulting in glaciers pulling back from their terminal moraines.
Koch etal talks about the increased precipitation in the Western Conus.
Here is a paper that has been cited 70 times about temperatures during the MWP:
Global Warming: A Geological Perspective
High precipitation plus warm temperatures = glacial advance? Not what Kirkbride and Dugmore 2008 found in Iceland:
medieval glacier advances between the 9th and 13th centuries are firmly identified for the first time in Iceland. This challenges the view of a prolonged Medieval Warm Period and supports fragmentary historical data that indicate significant medieval episodes of cooler and wetter conditions in Iceland. -- emphasis added
Koch 2008 is also a good short summary on this question:
an advance of Llewellyn Glacier, which drains the northeast sector of the Juneau Icefield, at the time of the Medieval Warm Period, cannot be reconciled with temperatures similar to those of today. This evidence suggests that temperatures were significantly lower than at present during the Medieval Warm Period, calling into question the existence of prolonged warmth at that time. We conclude that the Medieval Warm Period is at best an ill-defined term that encompasses a number of possibly unrelated climate anomalies. -- emphasis added
Good one. From 1999, the primary evidence presented for MWP temperatures dates from 1966:
Graph is modified from Keigwin, L. D., 1966, The Little Ice Age and Medieval Warming Period in the Sargasso Sea: Science, v. 274, p. 1504 - 1508.
Nothing much has changed in dating technology since the '60s. Or at least what little I remember of the '60s.
I dn't have access to the full paper, Kirkbride and Dugmore. Note tho, that the glaciers did not peak at the same approx time. With that in mind, remember how small Iceland is.
I will also point out that the proxy data from the Sargosa Sea presented in my link does not match the reanalysis from the Mann paper ref fig 1.
Woods hole was pretty excited about this, and to my knowledge, this temp study of the Sarasota Sea has never been disputed till now.
I don't understand how Dr. Mann missed this.
Woods Hole discussion of Sarasota Sea proxy data
But actual evidence shows that the waters now entering the Arctic Ocean from the Atlantic Ocean are the warmest they've been in the last 2,000 years.
Yet another MWP "Silver Bullet" (an underwater hockey stick, no less).
Time for another Coors Lite...
Wow, wow! It looked a bad copy of [- snip unnecessary disease references; some people around here actually have those problems -]
Do I need to recite a creed to get clearance? It's difficult to me; I'm Postheist. But called to do it, and as my only objection is using the verb "believe", I say: I believe in an ongoing AGW that is endangering the biosphere in such a degree that an obstinate keeping of those trends in the eighties during a couple of centuries will provoke events of dire consequences in a global scale.
That said, if you can avoid spotting a denier in disguise in every criticism you'll hear from me, you may explain for me what is the "it" in your "I think if you're wanting someone to rail against it should be Hubert Lamb?". I found that in English people tend to get cocky before talking clear.
Additionally, as you should have realised from the start, I'm not saying that the so-called MWP wasn't just a regional development. I'm saying that Figure 1 can be misinterpreted as showing a cooling average because it's contrasted against a warm period. That is not bona fide, the same way that is not bonafide your innuendos of me being a climatard just because I don't agree automatically with what is shown here. Your belligerent summoning for me to have all the backing information of Mann, Zhang, Rutherford et al read and analyzed together with a search for alternative renders for that period, in less of 24 hours, in a working day, is not bonafide too.
All these proxies show a distinct MWP, although the timing varies due to the proxies used.
Rob, I've got the gridded data from climate normals 1961-1990 as an anomaly on a 1941-1970 base. This is the graphic -using a 250km radius-:
Now I have the problems of having two different grids and that those gridded data in Figure 1 are supposed to be plotted using a Matlab file. But I think that I'll finally manage to get a 5° grid for the image and to write a script to take gridded info from Figure 1 in order to develop a graphic that will approximately show what I am speaking form the very beginning. By eyeballing both images I could notice what I expected -what is dangerous itself: to expect- in comparison with Figure 1: even a bit warmer Iceland and Greenland, not so turbulent Mongols and Tartars, and about the "Figure 1" for LIA -Figure 2 in Mann et al- a confirmation of the reason for my city of birth to be established twice.
'Warmer weather is good for glaciers' should have an especially good run. Our current warming must therefore be the teaser for the upcoming fourth Ice Age, which is scheduled for worldwide release in July 2012.
Manny, Diego, and Sid - embark upon their greatest adventure after cataclysm sets an entire continent drift. Separated from the rest of the herd, they use an iceberg as a makeshift ship, which launches them on an epic seafaring quest. ... as they encounter exotic sea creatures, explore a brave new world, and battle ruthless pirates.
A proxy here, a proxy there; soon you're talkin' real data.
Another location analyzed: Cronin et al 2003, with comparison to the venerable Sargasso Sea data.
If the Chesapeake record for the period 450–1000 AD is viewed as a baseline for comparison to 19th and 20th century temperatures in lieu of pre-1000 AD atmospheric records, then the magnitude of recent Chesapeake temperature extremes are larger than those observed even during the relative warmth 1000–1500 years ago. Although this result may be partially due to greater sampling resolution in the last two centuries, it is nonetheless consistent with evidence from other studies suggesting that recent decadal climate variability in the North Atlantic region is extreme relative to long-term patterns and may be in part anthropogenic in origin. -- emphasis added
And there's that pesky consistency of the evidence again. I guess it's easy to object to one data point and pretend the rest don't exist.
We all know that there are places on earth that have not warmed as much as the rest of the earth. Continental USA is one of those places.
There are always various cold/hot spots. The evidence of a MWP over climatic times is quit evident. The extent of the warmth is what is in question.
We do know that the proxy data from the Sarasota sea shows that area has not warmed to the same level as during the MWP. Does this mean the whole world was as warm? I doubt it, and proxy data would not confirm this.
Do we know there were areas that were warmer than present temps?.....Yes, the proxy data confirms this as well.
[DB] BTW, it's usually called the Sargasso Sea.
Very well put, sir.
Figure 1 of this post provides just such context. It makes the 'MWP' look more like a couple of MWS (Medieval Warm Spots). Some credible warming along the SE coast of Greenland, the southern US and little else besides a couple of tepid patches of ocean. Surely you aren't saying that dull yellow 0.1-0.3 degree anomaly is the real thing?
And I'd still like to know what was driving the alledged MWP. I've yet to see a hypothesis for such. It's not enough to flap your arms and say "It's natural".
It is very obvious that the Saragasso Sea was warmer during this period than depicted on fig 1.
This does throw a large amount of uncertainty into the reanalysis presented.
[DB] "This does throw a large amount of uncertainty into the reanalysis presented."
Not on the basis of any information you have presented. Your link shows that the area of the Sargasso Sea was warmer at various periods of time than it was at the most recent data point in the graph - 385+ years prior to 1966.
Which is odd, given that Keigwin 1966 includes station data for the period 1924-1966, which are not shown in the source you provide. As constituted, the totality of the warming post-1880 is unrepresented.
Either way, you are still conflating a regional proxy into global effects.
[Source]
You were requesting information on glacial retreat. The first in from Schnidejoch in Central Europe, the second is from Glacier National Park in Montana, and the third is from the Greenland ice cores.
http://www.giub.unibe.ch/klimet/docs/climdyn_2007_grosjean_et_al.pdf
https://www.cfa.harvard.edu/~wsoon/RajeshKoushik10-d/MacGregoretal10-12900yrSwiftcurrentLakeGlacierNatlPark.pdf
ftp://ftp.ncdc.noaa.gov/pub/data/paleo/icecore/greenland/summit/gisp2/isotopes/gisp2_temp_accum_alley2000.txt