The Medieval Warm Period in the Arctic

Since the IPCC AR5 is again making news in talking about the Medieval Warm Period, this review from Craig Idso at seems appropriate. -Anthony

Medieval Warm Period (Arctic) — Summary

This review begins with the study of Dahl-Jensen et al. (1998), who used temperature measurements from two Greenland Ice Sheet boreholes to reconstruct the temperature history of this portion of the earth over the past 50,000 years. Their data indicated that after the termination of the glacial period, temperatures steadily rose to a maximum of 2.5°C warmer than at present during the Holocene Climatic Optimum (4,000 to 7,000 years ago). The Medieval Warm Period (MWP) and Little Ice Age (LIA) were also observed in the record, with temperatures 1°C warmer and 0.5-0.7°C cooler than at the time of their writing, respectively. After the Little Ice Age, they report that temperatures once again rose, but that they had “decreased during the last decades,” thereby indicating that the MWP in this part of the Arctic was significantly warmer than it was just before the turn of the century.

Wagner and Melles (2001) also worked on Greenland, where they extracted a 3.5-m-long sediment core from a lake (Raffels So) on an island (Raffles O) located just off Liverpool Land on the east coast of Greenland, which they analyzed for a number of properties related to the past presence of seabirds there, obtaining a 10,000-year record that tells much about the region’s climatic history. Key to the study were biogeochemical data, which, in the words of the two researchers, reflect “variations in seabird breeding colonies in the catchment which influence nutrient and cadmium supply to the lake.”

These data revealed sharp increases in the values of the parameters they represented between about 1100 and 700 years before present (BP), indicative of the summer presence of significant numbers of seabirds during that “medieval warm period,” as Wagner and Melles described it, which had been preceded by a several-hundred-year period (the Dark Ages Cold Period) with little to no bird presence. And after that “medieval warm period,” their data suggested another absence of birds during what they called “a subsequent Little Ice Age,” which they said was “the coldest period since the early Holocene in East Greenland.”

The Raffels So data also showed signs of a resettlement of seabirds during the last century, as indicated by an increase of organic matter in the lake sediment and confirmed by bird counts. However, values of the most recent measurements of seabird numbers were not as great as those inferred for the earlier Medieval Warm Period, which result indicates that higher temperatures prevailed during much of the period from 1100 to 700 years BP than those that had been observed over the most recent hundred years.

A third Greenland study was conducted by Kaplan et al. (2002), who derived a climatic history of the Holocene by analyzing the physical-chemical properties of sediments obtained from a small lake in the southern sector of Greenland. This work revealed that the interval from 6000 to 3000 years BP was marked by warmth and stability, but that the climate cooled thereafter until its culmination in the Little Ice Age. From 1300-900 years BP, however, there was a partial amelioration during the Medieval Warm Period, which was associated with an approximate 1.5°C rise in temperature.

In a non-Greenland Arctic study, Jiang et al. (2002) analyzed diatom assemblages from a high-resolution core extracted from the seabed of the north Icelandic shelf, which led to their reconstruction of a 4600-year history of summer sea surface temperature at that location. Starting from a maximum value of about 8.1°C at 4400 years BP, the climate was found to have cooled fitfully for about 1700 years and then more consistently over the final 2700 years of the record. The most dramatic departure from this long-term decline was centered on about 850 years BP, during the Medieval Warm Period, when the temperature rose by more than 1°C above the line describing the long-term downward trend to effect an almost complete recovery from the colder temperatures of the Dark Ages Cold Period, after which temperatures continued their descent into the Little Ice Age, ending with a final most recent value of approximately 6.3°C. Hence, their data clearly showed that the Medieval Warm Period in this part of the Arctic was significantly warmer than it is there now.

Moving on, Moore et al. (2001) analyzed sediment cores from Donard Lake, Baffin Island, Canada, producing a 1240-year record of average summer temperatures for this Arctic region. Over the entire period from AD 750-1990, temperatures averaged 2.9°C. However, anomalously warm decades with summer temperatures as high as 4°C occurred around AD 1000 and 1100, while at the beginning of the 13th century, Donard Lake witnessed “one of the largest climatic transitions in over a millennium,” as “average summer temperatures rose rapidly by nearly 2°C from 1195-1220 AD, ending in the warmest decade in the record” with temperatures near 4.5°C.

This rapid warming of the 13th century was followed by a period of extended warmth that lasted until an abrupt cooling event occurred around 1375, which made the following decade one of the coldest in the record. This event signaled the onset of the Little Ice Age, which lasted for 400 years, until a gradual warming trend began around 1800, which was followed by a dramatic cooling event in 1900 that brought temperatures back to levels similar to those of the Little Ice Age. This cold regime lasted until about 1950, whereupon temperatures warmed for about two decades but then tended downwards again, all the way to the end of the record in 1990. Thus, in this part of the Arctic, the Medieval Warm Period was also warmer than it is there currently.

The following year, Grudd et al. (2002) assembled tree-ring widths from 880 living, dead, and subfossil northern Swedish pines into a continuous and precisely dated chronology covering the period 5407 BC to AD 1997. The strong association between these data and summer (June-August) mean temperatures of the last 129 years of the period then enabled them to produce a 7400-year history of summer mean temperature for northern Swedish Lapland. The most dependable portion of this record, based upon the number of trees that were sampled, consisted of the last two millennia, which Grudd et al. said “display features of century-timescale climatic variation known from other proxy and historical sources, including a warm ‘Roman’ period in the first centuries AD and a generally cold ‘Dark Ages’ climate from about AD 500 to about AD 900.” They also noted that “the warm period around AD 1000 may correspond to a so-called ‘Mediaeval Warm Period,’ known from a variety of historical sources and other proxy records.” Last of all, they stated that “the climatic deterioration in the twelfth century can be regarded as the starting point of a prolonged cold period that continued to the first decade of the twentieth century,” which “Little Ice Age,” in their words, is also “known from instrumental, historical and proxy records.” Going back even further in time, the tree-ring record displays several more of these relatively warmer and colder periods. And in a telling commentary on current climate-alarmist claims, they report that “the relatively warm conditions of the late twentieth century do not exceed those reconstructed for several earlier time intervals.” In fact, the warmth of many of the earlier warm intervals significantly exceeded the warmth of the late 20th century.

Seppa and Birks (2002) used a recently developed pollen-climate reconstruction model and a new pollen stratigraphy from Toskaljavri – a tree-line lake in the continental sector of northern Fenoscandia (located just above 69°N latitude) – to derive quantitative estimates of annual precipitation and July mean temperature. And as they described it, their reconstructions “agree with the traditional concept of a ‘Medieval Warm Period’ (MWP) and ‘Little Ice Age’ in the North Atlantic region (Dansgaard et al., 1975) and in northern Fennoscandia (Korhola et al., 2000).” In addition, they reported there was “a clear correlation between [their] MWP reconstruction and several records from Greenland ice cores,” and that “comparisons of a smoothed July temperature record from Toskaljavri with measured borehole temperatures of the GRIP and Dye 3 ice cores (Dahl-Jensen et al., 1998) and the ð18O record from the Crete ice core (Dansgaard et al., 1975) show the strong similarity in timing of the MWP between the records.” Last of all, they noted that “July temperature values during the Medieval Warm Period (ca. 1400-1000 cal yr B.P.) were ca. 0.8°C higher than at present,” where present means the last six decades of the 20th century.

Noting that temperature changes in high latitudes are (1) sensitive indicators of global temperature changes, and that they can (2) serve as a basis for verifying climate model calculations, Naurzbaev et al. (2002) developed a 2,427-year proxy temperature history for the part of the Taimyr Peninsula of northern Russia that lies between 70°30′ and 72°28′ North latitude, based on a study of ring-widths of living and preserved larch trees, while further noting that “it has been established that the main driver of tree-ring variability at the polar timber-line [where they conducted their study] is temperature (Vaganov et al., 1996; Briffa et al., 1998; Schweingruber and Briffa, 1996).” And in doing so, they found that “the warmest periods over the last two millennia in this region were clearly in the third [Roman Warm Period], tenth to twelfth [Medieval Warm Period] and during the twentieth [Current Warm Period] centuries.”

With respect to the second of these periods, they emphasize that “the warmth of the two centuries AD 1058-1157 and 950-1049 attests to the reality of relative mediaeval warmth in this region.” Their data also reveal three other important pieces of information: (1) the Roman and Medieval Warm Periods were both warmer than the Current Warm Period has been to date, (2) the “beginning of the end” of the Little Ice Age was somewhere in the vicinity of 1830, and (3) the Current Warm Period peaked somewhere in the vicinity of 1940.

All of these observations are at odds with what is portrayed in the thousand-year Northern Hemispheric hockeystick temperature history of Mann et al. (1998, 1999) and its thousand-year global extension developed by Mann and Jones (2003), wherein (1) the Current Warm Period is depicted as the warmest such era of the past two millennia, (2) recovery from the Little Ice Age does not begin until after 1910, and (3) the Current Warm Period experiences it highest temperatures in the latter part of the 20th century’s final decade.

Advancing two years closer to the present, Knudsen et al. (2004) documented climatic changes over the last 1200 years by means of high-resolution multi-proxy studies of benthic and planktonic foraminiferal assemblages, stable isotopes, and ice-rafted debris found in three sediment cores retrieved from the North Icelandic shelf. This work revealed that “the time period between 1200 and around 7-800 cal. (years) BP, including the Medieval Warm Period, was characterized by relatively high bottom and surface water temperatures,” after which “a general temperature decrease in the area marks the transition to … the Little Ice Age.” They also note that “minimum sea-surface temperatures were reached at around 350 cal. BP, when very cold conditions were indicated by several proxies.” Thereafter, they report that “a modern warming of surface waters … is not registered in the proxy data,” and that “there is no clear indication of warming of water masses in the area during the last decades,” even in sea surface temperatures measured over the period 1948-2002.

Fast-forwarding another two years,Grinsted et al. (2006) developed “a model of chemical fractionation in ice based on differing elution rates for pairs of ions … as a proxy for summer melt (1130-1990),” based on data obtained from a 121-meter-long ice core they extracted from the highest ice field in Svalbard (Lomonosovfonna: 78°51’53″N, 17°25’30″E), which was “validated against twentieth-century instrumental records and longer historical climate proxies.” This history indicated that “in the oldest part of the core (1130-1200), the washout indices [were] more than 4 times as high as those seen during the last century, indicating a high degree of runoff.” In addition, they said they had performed regular snow pit studies near the ice core site since 1997 (Virkkunen, 2004) and that “the very warm 2001 summer resulted in similar loss of ions and washout ratios as the earliest part of the core.” They then stated that “this suggests that the Medieval Warm Period in Svalbard summer conditions [was] as warm (or warmer) as present-day, consistent with the Northern Hemisphere temperature reconstruction of Moberg et al. (2005).” In addition, they concluded that “the degree of summer melt was significantly larger during the period 1130-1300 than in the 1990s,” which likewise suggests that a large portion of the Medieval Warm Period was significantly warmer than the peak warmth (1990s) of the Current Warm Period.

Moving ahead two more years, Besonen et al. (2008) derived thousand-year histories of varve thickness and sedimentation accumulation rate for Canada’s Lower Murray Lake (81°20’N, 69°30’W), which is typically covered for about eleven months of each year by ice that reaches a thickness of 1.5 to 2 meters at the end of each winter. With respect to these parameters, they write – citing seven other studies – that “field-work on other High Arctic lakes clearly indicates that sediment transport and varve thickness are related to temperatures during the short summer season that prevails in this region, and we have no reason to think that this is not the case for Lower Murray Lake.”

So what did they find? As the six scientists describe it, the story told by both the varve thickness and sediment accumulation rate histories of Lower Murray Lake is that “the twelfth and thirteenth centuries were relatively warm,” and in this regard we note their data indicate that Lower Murray Lake and its environs were often much warmer during this time period (AD 1080-1320) than they were at any point in the 20th century, which has also been shown to be the case for Donard Lake (66.25°N, 62°W) by Moore et al. (2001).

Working concurrently on a floating platform in the middle of a small lake (Hjort So) on an 80-km-long by 10.5-km-wide island (Store Koldewey) just off the coast of Northeast Greenland, Wagner et al. (2008) recovered two sediment cores of 70 and 252 cm length, the incremental portions of which they analyzed for grain-size distribution, macrofossils, pollen, diatoms, total carbon, total organic carbon, and several other parameters, the sequences of which were dated by accelerator mass spectrometry, with radiocarbon ages translated into calendar years before present. This work revealed, as they describe it, an “increase of the productivity-indicating proxies around 1,500-1,000 cal year BP, corresponding with the medieval warming,” while adding that “after the medieval warming, renewed cooling is reflected in decreasing amounts of total organic carbon, total diatom abundance, and other organisms, and a higher abundance of oligotrophic to meso-oligotrophic diatom taxa.” And, as they continue, “this period, the Little Ice Age, was the culmination of cool conditions during the Holocene and is documented in many other records from East and Northeast Greenland, before the onset of the recent warming [that] started ca. 150 years ago.”

In addition to the obvious importance of their finding evidence for the Medieval Warm Period, the six researchers’ statement that the Little Ice Age was the culmination, or most extreme sub-set, of cool conditions during the Holocene, suggests that it would not be at all unusual for such a descent into extreme coolness to be followed by some extreme warming, which further suggests there is nothing unusual about the degree of subsequent warming experienced over the 20th century, especially in light of the fact that the earth has not yet achieved the degree of warmth that held sway over most of the planet throughout large portions of that prior high-temperature period.

One year later, based on the use of a novel biomarker (IP25), which they described as a mono-unsaturated highly-branched isoprenoid that is synthesized by sea ice diatoms that have been shown to be stable in sediments below Arctic sea ice, Vare et al. (2009) used this new climatic reconstruction tool – together with “proxy data obtained from analysis of other organic biomarkers, stable isotope composition of bulk organic matter, benthic foraminifera, particle size distributions and ratios of inorganic elements” – to develop a spring sea ice record for that part of the central Canadian Arctic Archipelago. And in doing so, they discovered evidence for a decrease in spring sea ice between approximately 1200 and 800 years before present (BP), which they associated with “the so-called Mediaeval Warm Period.”

Contemporaneously, Norgaard-Pedersen and Mikkelsen (2009), working with a sediment core retrieved in August 2006 from the deepest basin of Narsaq Sound in southern Greenland, analyzed several properties of the materials thus obtained from which they were able to infer various “glacio-marine environmental and climatic changes” that had occurred over the prior 8,000 years. This work revealed the existence of two periods (2.3-1.5 ka and 1.2-0.8 ka) that appeared to coincide roughly with the Roman and Medieval Warm Periods, while they identified the colder period that followed the Medieval Warm Period as the Little Ice Age and the colder period that preceded it as the Dark Ages Cold Period. And citing the works of Dahl-Jensen et al. (1998), Andresen et al. (2004), Jensen et al. (2004) and Lassen et al. (2004), the two Danish scientists said that the cold and warm periods identified in those researchers’ studies “appear to be more or less synchronous to the inferred cold and warm periods observed in the Narsaq Sound record,” providing ever more evidence for the reality of the naturally-occurring phenomenon that governs this millennial-scale oscillation of climate.

One year later, Vinther et al. (2010) analyzed 20 ice core records from 14 different sites, all of which stretched at least 200 years back in time, as well as near-surface air temperature data from 13 locations along the southern and western coasts of Greenland that covered approximately the same time interval (1784-2005), plus a similar temperature data set from northwest Iceland (said by the authors to be employed “in order to have some data indicative of climate east of the Greenland ice sheet”). This work demonstrated that winter ð18O was “the best proxy for Greenland temperatures.” And based on that determination and working with three longer ice core ð18O records (DYE-3, Crete and GRIP), they developed a temperature history that extended more than 1400 years back in time.

This history revealed, in the words of the seven scientists, that “temperatures during the warmest intervals of the Medieval Warm Period” – which they defined as occurring some 900 to 1300 years ago – “were as warm as or slightly warmer than present day Greenland temperatures.” As for what this result implies, they state that further warming of present day Greenland climate “will result in temperature conditions that are warmer than anything seen in the past 1400 years,” which, of course, has not happened yet. Furthermore, Vinther et al. readily acknowledge that the independent “GRIP borehole temperature inversion suggests that central Greenland temperatures are still somewhat below the high temperatures that existed during the Medieval Warm Period.”

About this same time, Kobashi et al. (2010) had a paper published in which they had written that “in Greenland, oxygen isotopes of ice (Stuiver et al., 1995) have been extensively used as a temperature proxy, but the data are noisy and do not clearly show multi-centennial trends for the last 1,000 years in contrast to borehole temperature records that show a clear ‘Little Ice Age’ and ‘Medieval Warm Period’ (Dahl-Jensen et al., 1998).” However, they went on to note that nitrogen (N) and argon (Ar) isotopic ratios – 15N/14N and 40Ar/36Ar, respectively – can be used to construct a temperature record that “is not seasonally biased, and does not require any calibration to instrumental records, and resolves decadal to centennial temperature fluctuations.”

After describing the development of the new approach, they used it to construct a history of the last thousand years of central Greenland surface air temperature, based on values of the isotopic ratios of nitrogen and argon previously derived by Kobashi et al. (2008) from air bubbles trapped in the GISP2 ice core that had been extracted from central Greenland, obtaining the result depicted in the figure below.

Central Greenland surface temperature reconstruction for the last millennium. Adapted from Kobashi et al. (2010).

This figure depicts the central Greenland surface temperature reconstruction produced by the six scientists; and as best as can be determined from this representation, the peak temperature of the latter part of the Medieval Warm Period – which actually began some time prior to the start of their record, as demonstrated by the work of Dansgaard et al. (1975), Jennings and Weiner (1996), Johnsen et al. (2001) and Vinther et al. (2010) – was approximately 0.33°C greater than the peak temperature of the Current Warm Period, and about 1.67°C greater than the temperature of the last decades of the 20th century.

One year closer to the present, and noting that the varve thicknesses of annually-laminated sediments laid down by Hvitarvatn, a proglacial lake in the central highlands of Iceland, is controlled by the rate of glacial erosion and efficiency of subglacial discharge from the adjacent Langjokull ice cap, Larsen et al. (2011) employed a suite of environmental proxies contained within those sediments to reconstruct the region’s climate variability and glacial activity over the past 3000 years, which proxies included varve thickness, varve thickness variance, ice-rafted debris, total organic carbon (mass flux and bulk concentration), and the C:N ratio of sedimentary organic matter. And when all was said and done, this effort indicated that “all proxy data reflect a shift toward increased glacial erosion and landscape destabilization from ca 550 AD to ca 900 AD and from ca 1250 AD to ca 1950 AD, separated by an interval of relatively mild conditions,” and they state that “the timing of these intervals coincides with the well-documented periods of climate change commonly known as the Dark Ages Cold Period, the Medieval Warm Period, and the Little Ice Age.”

In the case of the Medieval Warm Period, they additionally note that “varve thickness decreases after 950 AD and remains consistently low through Medieval time with slightly thinner annual laminations than for any other multi-centennial period in the past 3000 years,” which suggests that the MWP was the warmest period of the past three millennia, while they say that “the LIA was the most severe multi-centennial cold interval of the late Holocene” and “likely since regional deglaciation 10,000 years ago.”

Finally, for those desiring additional brief reports on the Medieval Warm Period in the Arctic, go to and search for Hill et al. (2001), Joynt and Wolfe (2001), Hantemirov and Shiyatov (2002), Andersson et al. (2003), Helama et al. (2005), Mazepa (2005), Weckstrom et al. (2006), Jiang et al. (2007), Zabenskie and Gajewski (2007), Grudd (2008), Justwan et al. (2008), Scire et al. (2008), Axford et al. (2009), Bjune et al. (2009), Cook et al. (2009), Fortin and Gajewski (2010), Büntgen et al. (2011), Divine et al. (2011), Ran et al. (2011), Velle et al. (2011), D’Andrea et al. (2012) and Esper et al. (2012), full references for which articles are included in the Reference section below.

In concluding this summary, it is clear that the suite of measurements described in the studies reviewed above continues to indicate that the Arctic – which climate models suggest should be super-sensitive to greenhouse-gas-induced warming – is still not even as warm as it was several centuries ago during portions of the Medieval Warm Period, when there was much less CO2 and methane in the air than there is today, which facts further suggest that the planet’s more modest current warmth need not be the result of historical increases in these two trace greenhouse gases.

Source: (with references)

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Brian H
August 23, 2013 12:22 am

Anthony, did you prepare this marvelous summary yourself? Overwhelming “consensus” of empirical science, IMO. Kudos.
REPLY: No, see top and bottom – Anthony

August 23, 2013 12:29 am

All the longer term stuff might be OK to at least some extent, but I have serious doubts about the ability of ice cores to tell us anything at all at a decadal level. As I understand it the firn, in which there is free air movement, lasts for several decades.

Lance Wallace
August 23, 2013 12:43 am

A nice review, but would be greatly improved by adding a single graph containing the temperature estimates of all the authors over the period covered.

Village Idiot
August 23, 2013 12:52 am

Village articles of faith state that the MWP was warmer than present and global. It’s written in stone on the church wall.
As the MWP was caused by natural variation (pre-human influence), it only demonstrates how much natural variation potential there is in the system. While the Earth should have been cooling recently we have seen (unknown climate sensitivity anthropogenic) warming.
Just to be ‘alarmist’ – what if natural variation takes a MWP swing in the next 10-20-30-50 years?

Mike Haseler
August 23, 2013 1:08 am

As this study shows, the problem is not the facts as they fairly conclusively show that climate change is a real phenomena that has nothing to do with mankind, it is like the cannabis studies that only looked for harm to “prove” it was dangerous. Likewise, in the face of overwhelming evidence that climate has constantly changed, the academic fraternity have refused to consider the overwhelming evidence that large-scale climate change is constantly occurring and have falsely and fraudulently tried to pin a short-term trend that almost certainly mostly natural on a single small element of the climate matrix.
And when they start considering the effects, they look nothing short of UFO spotting lunatics seeing the absurd influence of their paranoia in every natural event.
However, what is far more worrying is that unlike cannabis where the censorship was imposed by legal constraint, the censorship on climate research is entirely self-imposed by academia itself.
So, the question I think we need to ask is: “what is it about academia & the culture of academia that has so distorted science to fabricate this scare? And … if in this very high profile subject where there has been some opposition, they have so firmly and confidently gone off-the-track/up-the-garden-path/down-the-blind-alleyway in how many other areas is this culture similarly distorting science and academic research?”
Indeed, what worries me most is that these “scientists” who have been so overwhelmingly deluded on climate are now advising government on commercial engineering (the deluded blind leading the blind).

Alan the Brit
August 23, 2013 1:10 am

Great post! So basically what they all appear to be saying, is that the Dark Ages, the Medieval Warm Period, (which the IPCC say doesn’t exist), & the Little Ice Age, did in fact exist, & that the MWP was warmer than today, which is impossible according to the “World’s leading authority on Climate Change”, because as we all know, they never make mistakes, never exaggerate, & certainly NEVER make it up as they go along! 😉

August 23, 2013 1:20 am

I like looking at studies on Greenland, it seems to be a proxy for much that happens in the rest of the world regarding large scale climate changes, and also seems to pick up such changes earlier than many other places.
Even the name ‘Greenland’ has connotations. Western Europeans (Vikings) settled there before they settled the Americas. (Another example of picking up a climate-human related trend earlier than other places). And it also seems to be cooling quicker since the 20th century than other places. This might be telling us something of what is to come.
Nice place to pick up some real science.

Peter Miller
August 23, 2013 1:23 am

In some river beds in southern Iceland, you can find the remains of large true trunks, indicating recent much warmer conditions than those prevailing today.
But Mann’s model says there is no such thing as the MWP and he should know – sarc off/

August 23, 2013 1:26 am

Mike Jonas~ I agree that ice cores may not be good at the decadal level. But we are speaking of a period – the MWP- covering several hundreds of years. And all indications are that it (the Arctic) was a good degree C warmer than it is now. And nothing bad happened.
Further- if ice cores are Not good on a decadal scale, how do we know there were not spikes of warmer temperatures?

August 23, 2013 1:38 am

Notice how, in the second study, the birds don’t go extinct when the weather gets colder or warmer? When it gets colder they simply move somewhere else. Then, when it warms up in the MWP, “They’re back.”
How different this is from the Alarmist view that nature is a delicate thing that will be completely shattered to bits if we so much as look at it sideways.
Not that we shouldn’t walk softly in a beautiful forest, but some want to ban walking altogether.
In the end, nature is a heck of a lot tougher than we are.

August 23, 2013 1:42 am

And not just the Arctic.
In 2003, Lonnie Thompson admitted
For the Quelccaya Ice Cap [in Peru] this work revealed that peak temperatures of the MWP were warmer than those of the last few decades of the 20th century.

August 23, 2013 1:49 am

A wonderful and concise summary. I would love to see someone do the same kind of piece on the sea level rise, laid out in this type of chronological listing of papers with their findings.

stan stendera
August 23, 2013 1:58 am

Awesome post.

Bloke down the pub
August 23, 2013 2:41 am

So Mikey Mann got it wrong. Who’da thunk it.

August 23, 2013 2:47 am

Let’s not forget Lamb back in 1965.

H.H. Lamb1965
The early medieval warm epoch and its sequel
The Arctic pack ice was so much less extensive than in recent times that appearances of drift ice near Iceland and Greenland south of 70[deg] N, were apparently rare in the 10th century and unknown between 1020 and 1194, when a rapid increase of frequency caused a permanent change of shipping routes. Brooks suggested that the Arctic Ocean became ice-free in the summers of this epoch, as in the Climatic Optimum; but it seems more probable that there was some ‘permanent’ ice, limited to areas north of 80[deg] N….”
Elsevier Publishing Company
Palaeogeography, Palaeoclimatology, Palaeoecology, 1:1965, p. 15-16

Though not the Arctic here is a study which mentions olives and figs in Germany!!!

Medieval Climatic Optimum
Michael E Mann – University of Virginia, Charlottesville, VA, USA
It is evident that Europe experienced, on the whole, relatively mild climate conditions during the earliest centuries of the second millennium (i.e., the early Medieval period). Agriculture was possible at higher latitudes (and higher elevations in the mountains) than is currently possible in many regions, and there are numerous anecdotal reports of especially bountiful harvests (e.g., documented yields of grain) throughout Europe during this interval of time. Grapes were grown in England several hundred kilometers north of their current limits of growth, and subtropical flora such as fig trees and olive trees grew in regions of Europe (northern Italy and parts of Germany) well north of their current range. Geological evidence indicates that mountain glaciers throughout Europe retreated substantially at this time, relative to the glacial advances of later centuries……………………

August 23, 2013 3:10 am

Dr Idso has been busy. Thank you sir for your hard work. Good to see reported science not model runs proving nothing.

August 23, 2013 3:20 am

Caleb says ‘nature is a heck lot tougher than we think’
So right! – Especially the birds.
I’m approaching eighty and although I don’t deny that increasing CO2 has some potential to infuence global heat balance, I can’t get alarmed by it, because I have lived through many periods when humanity has done appalling things to itself and the end of civilisation as we know it has been predicted, along with many evironmental incidents that were predicted to be catastrophic. In both cases things have always been different afterwards, but in the first case the toughness and adaptability of Homo Sapiens has resulted in civilization surviving and in the second, the ability of eco systems to adapt has seen potential catastrophies avoided.
I know that these are broad generalisations, and I do not seek to diminish the horror that humans have had to suffer at the hands of other humans, nor to claim that there have been no casualtie in the eco system, but though changed, survival seems to be the default outcome when Alarmism indicates otherwise.
Now back to the birds. They are very bright creatures and have the unique ability to relocate rapidly if their habitat changes in a manner that they don’t like. In the UK the Royal Society for the Protection of Birds has recently got hot under the collar over the possibility of fracking in Lancashire, close to areas where birds Winter. We desparatelyn need to release the national wealth locked up in our shale gas reserves, as apart from anything else we need use gas to keep our lights on after fifteen years of ill considered Green energy policy. However, the RSPB has joined the anti fracking lobby on behalf of the birds. What nonsense, if they are disturbed they will simply shift themselves and once the production phase is reached they will come back (if they haven’t found somewhere cosier to stay) until they fly to their breading grounds in the Spring.

August 23, 2013 3:49 am

Solar activity causes the arctic climate swings. Don’t ignore the impressive 2005 Danish Meteorological Institute Report by Lassen and Thejll (
Using Iceland’s sea ice visibility and sea ice exports as proxies for temperature and using the length of the solar cycle as a proxy for solar activity, they found a huge positive correlation over the last 500 years between level of solar activity and amount of arctic ice.
Solar activity can also explain why the arctic warms while the antarctic stays cold. It protects the earth from cloud-causing cosmic rays. But Antarctica is so white, it reflects sunlight back into outer space regardless of whether or not there are clouds.

August 23, 2013 4:12 am

So it was more than just Europe? No way!

Steve Keohane
August 23, 2013 4:33 am

here’s Mikey’s pathetic squiggle in the above Kobashi et al chart from above.

August 23, 2013 5:01 am

Otter said
‘Further- if ice cores are Not good on a decadal scale, how do we know there were not spikes of warmer temperatures?’
That spike in warmer temperatures not picked up by Paleo reconstructions was precisely my point in this article
I also made the point that if paleos are coarse sieves of temperatures on a decadal basis might the equally coarse graded ice cores might not also be missing similar variations?

August 23, 2013 5:04 am

I really struggle to believe that wth the use of proxies over thousands of years, you can be accurate enough to measure temperature change to a degree of accuracy being proposed, ie. less than 1 degree C.
We seem to struggle to agree on temperature change today with thermometers, given siting issues, UHI etc.
What am I missing, very large error bands which makes all this work nice but useless?

August 23, 2013 6:13 am

My comment @3.20am
Whoops: Apologies for typos in last para due to eyesight/small IPad keyboard.
Especially the one in the last line suggesting that birds fly home to eat bread rather than breed!

August 23, 2013 6:19 am

Rule #1: The Arctic and northern latitudes are like a canary in a coal mine. They warm faster than the rest of the planet. They are a harbinger of GLOBAL warming and these northern latitudes are important. We need to pay attention to them.
Rule #2: The MWP, RWP, and others were not GLOBAL, they were only in the Arctic and northern latitudes. Therefore, they are not important and we should ignore them.
Typical alarmist reasoning. Contradict themselves constantly and never seem to realize it.
Rule #3: Global warming will warm the planet, cause ice melt and sea level to rise and more water in the atmosphere and flooding and more hurricanes/tornadoes.
Rule #4: Proof of global warming is that things change. It does not have to warm or get wetter. Some signs of CAGW are: cold, drought, less wind, etc.
Corollary: more or less sun, more or less wind, more or less clouds may also be signs.
Hmmm, more contradictions.
Rule #5: Since we are talking about climate, not weather, we should only look at longer term changes and you can never use a cold winter, or a slow hurricane season, or a cool day as an example of anything.
Rule #6: Ignore the 12 – 17 year stretch with nearly flat temperatures. Point to every single fire, dry part of a country for part of a year, hot day, flood, tropical storm, hot summer AND cold winter as due to changes caused by increasing global changiness.
Oh, for Christ’s sake!!

August 23, 2013 6:48 am

One good thing about Michael Mann’s hockey stick nonsense, it has inspired scientists from all over the world to gain a keen interest in the validity of the MWP. From what I have read, their research has confirmed the existence of the MWP as a legitimate world-wide event, time and time again. The CAGW propaganda that the MWP was just a regional, or NH event, has been proven invalid too many times to mention.

Louis Hooffstetter
August 23, 2013 7:01 am

Would someone here please clearly and succinctly explain how paleo-temperatures are reconstructed from boreholes? Even with a background in geology, I have no clue. Without knowing how this works, it seems even more far fetched than tree rings.

August 23, 2013 7:25 am

@Louis Hooffstetter
This link may help:

August 23, 2013 8:58 am

But this is merely evidence, not modeling or Consensus. What has evidence got to do with climate science?
We can simply assume that we are currently experiencing frequent Category 6 hurricanes, thousands of extinctions and the imminent demise of all coastal communities so what is the point of data collection?

Old Hoya
August 23, 2013 9:04 am

This stuff is merely evidence, not a consensus or modeling. Does collecting data or measurements help us understand that we are now experiencing frequent Cat 6 hurricanes, unprecedented mass extinctions or the loss of most of the world’s coastal cities? There were no SUVs in the Middle Ages, therefore none of those measurements matter, do they? These guys should stop all this data collection stuff and get behind The Science that everybody already knows is true.

August 23, 2013 9:55 am

Citing a Michael Mann statement from above:

Agriculture was possible at higher latitudes (and higher elevations in the mountains) than is currently possible in many regions, …

So here is direct testimony from an unimpeachable climate messiah that warming expands the range of plants and being the opportunists they are, they set roots where opportunity allows. They are clearly not the climate refugees suggested in the hypotheses the consensus-constrained numpties plant in our classrooms and which are widely espoused by the muddled stream media.
The ambulatory aster myth is busted.

August 23, 2013 10:32 am

For anyone interested in looking deeper into the MWP in other regions see link. It includes peer reviewed papers covering the southern hemisphere regions of Antarctica, Australia/New Zealand, South America, Africa among others.

Dmitri Mauquoy et. al. – 2004
Late Holocene climatic changes in Tierra del Fuego based on multiproxy analyses of peat deposits
“…..Our reconstruction for warm/dry conditions between ca. A.D. 960–1020 closely agrees with Northern Hemisphere tree-ring evidence for the MWP and shows that the MWP was possibly synchronous in both hemispheres, as suggested by Villalba (1994)……”
September 7, 2011
New paper shows Earth was significantly hotter during past several thousand years
…..robust findings from the large number of proxies studied and refutes claims of the IPCC and Mann et al that the Medieval Warming Period was limited to Europe, finding that both were present in the Northern and Southern Hemispheres and were relatively synchronous…..

August 23, 2013 10:34 am

What happened to my comment?

August 23, 2013 10:36 am

Sorry, now I see it, in moderation.

August 23, 2013 11:41 am

This ought to kill the “Arctic Methane Time Bomb” myth once and for all. If the Arctic of the Medieval Warm Period, the Holocene Climatic Optimum, and Sangamonian (Eemian, MIS 5e) were respectively 1°C, 2.5°C and 5°C warmer than the “Anthropocene CAGW,” that time bomb is a dud.
Vaks et al., 2013 is the final nail in the coffin…

In this study, we use cave carbonates (speleothems) as a tool to date past permafrost and its relationship to global climate. Vadose speleothems (stalactites, stalagmites and flowstones) form when meteor-ic waters (i.e., water originating from atmospheric precipitation) seep through the vadose zone into caves. Cave temperatures usually approxi-mate the local mean annual air temperatures (MAAT), because of buffer-ing by the surrounding rock (6). When cave temperatures drop below 0°C, waters freeze and speleothem growth ceases. Speleothems found in modern permafrost regions are therefore relicts from warmer periods before permafrost formed (7–9).
We reconstruct the history of Siberian permafrost (and the aridity of the Gobi Desert) during the last ~500 kyr using U-Th dating of speleothems in six caves along a north-south transect in northern Asia from Eastern Siberia at 60.2°N to the Gobi Desert at 42.5°N (Fig. 1). The north-ernmost cave – Lenskaya Ledyanaya sits today on the boundary of continu-ous permafrost with MAAT substantial-ly below 0°C (11). The permafrost type changes to the south-west to discontin-uous, sporadic, and then to permafrost-free conditions (12) (Fig. 1).
The youngest speleothem growth in the region of modern continuous permafrost (i.e., at 60°N) occurred during interglacial MIS-11.

The authors somehow conclude that “global climates only slightly warmer than today are sufficient to thaw significant regions of permafrost;” despite the fact that they did not find evidence of such during periods in which the Arctic was significantly warmer than modern times.

August 23, 2013 11:52 am

About ice core research.
Jørgen Peder Steffensen is associate professor and curator at the centre for Ice and Climate at Niels Bohr Institute at the University of Copenhagen, Denmark.
‘Sitemap, the research pages’ at Centre for Ice and Climate University of Copenhagen.

August 23, 2013 12:52 pm

“in how many other areas is this culture similarly distorting science and academic research?”
Mike Haseler’s above comment says it all. If it happens in climate research, it is probably happening elsewhere, and that is worrying.

Gail Combs
August 23, 2013 1:11 pm

Birdieshooter says:
August 23, 2013 at 1:49 am
A wonderful and concise summary. I would love to see someone do the same kind of piece on the sea level rise….
Check out Pop Tech’s site with the sea level papers listed HERE and write Anthony a similar story. Nothing is stopping you.

August 23, 2013 2:13 pm

Oh boy, this report is not going to go over well with Michael Manngelo who spent all that time chiseling away those natural variations to craft his infamous hockey stick.
Come to think of it, this won’t go over well with Steve Mosher either. I wonder why that is?

Ulric Lyons
August 23, 2013 4:48 pm

” Donard Lake witnessed “one of the largest climatic transitions in over a millennium,” as “average summer temperatures rose rapidly by nearly 2°C from 1195-1220 AD, ending in the warmest decade in the record” with temperatures near 4.5°C.
This rapid warming of the 13th century was followed by a period of extended warmth that lasted until an abrupt cooling event occurred around 1375,”
Looking elsewhere to see what the AO was doing, there’s much cold in the UK early 1200’s:
and reports of low solar activity:
“In fact, the aurora of 1192 marked the end of any major solar
disturbances for a long while. It was not until 1375 that the
Chinese observers registered a few years of relatively high sun
spot counts, and European chronicles recorded a flurry of auroras
during that same period. The years from 1192 to 1375 marked one
of those lulls in solar activity that have been called a “quiet
With 1375 noted as exceptionally warm:

Jeff Alberts
August 23, 2013 5:57 pm

The following year, Grudd et al. (2002) assembled tree-ring widths from 880 living, dead, and subfossil northern Swedish pines into a continuous and precisely dated chronology covering the period 5407 BC to AD 1997.

I thought we determined tree rings totally suck for temperature time series.

Janice Moore
August 23, 2013 10:01 pm

@ Louis Hooffstetter (re: Q at 7:01AM today: How do they determine historic temperatures… )
This page, via the excellent link, Pip Me provided (thanks, Pip! — is your name a Dickens Great Expectations allusion meaning, “Make me successful?”), may help you (it helped me!):
“Water Isotope Measurements”

Janice Moore
August 23, 2013 10:17 pm

Mr. Alberts,
That was a good question (at 5:57pm). I hope one of the wonderful WUWT scientists or researchers comes along and answers you. Maybe, if this layperson makes a lame attempt, it will annoy them to the point that they come stomping back and give you a good answer.
I believe the main beef anti-CAGW scientists (could have just said “real scientists,” lol) have with tree ring proxies is that while tree growth is primarily determined by CO2, not temperature, The Backward Boys Science Club claims it’s the other way around. CO2 lags temperature (See, e.g., Dr. Murry Salby’s recent work — his 2012 book and his great April 18, 2013, Hamburg lecture on You Tube are two good sources). Thus, the trees are a useful temperature proxy: if CO2 went up, temperatures already had.
I hope that my attempt gets you some higher quality responses. Or, at least, aids you in doing your own research on the question.

Ulric Lyons
August 24, 2013 3:58 am

” The most dramatic departure from this long-term decline was centered on about 850 years BP, during the Medieval Warm Period, when the temperature rose by more than 1°C above the line describing the long-term downward trend to effect an almost complete recovery from the colder temperatures of the Dark Ages Cold Period, after which temperatures continued their descent into the Little Ice Age, ending with a final most recent value of approximately 6.3°C. Hence, their data clearly showed that the Medieval Warm Period in this part of the Arctic was significantly warmer than it is there now.”
Nice, it should be centered around 840BP, and it was another cold period for elsewhere:

Ulric Lyons
August 24, 2013 4:55 am

” They also note that “minimum sea-surface temperatures were reached at around 350 cal. BP, when very cold conditions were indicated by several proxies.”
At 350yrs before 2004, that would be 1651-4 then:
Obviously it was coldest from ~1670 to ~1700

Jeff Alberts
August 24, 2013 9:23 am

Janice Moore says:
August 23, 2013 at 10:17 pm
I believe the main beef anti-CAGW scientists (could have just said “real scientists,” lol) have with tree ring proxies is that while tree growth is primarily determined by CO2, not temperature, The Backward Boys Science Club claims it’s the other way around. CO2 lags temperature (See, e.g., Dr. Murry Salby’s recent work — his 2012 book and his great April 18, 2013, Hamburg lecture on You Tube are two good sources). Thus, the trees are a useful temperature proxy: if CO2 went up, temperatures already had.

It’s my understanding that tree growth (plant growth in general) is determined by the most limiting factor; e.g. moisture, temperature, nutrients (including CO2, Nitrogen, Potassium, etc). Without a complete record of the climate in the immediate area, using tree rings (width, density, etc) won’t tell you which of those factors was in control at any given time. Briffa’s Yamal chronology is a good example of that, only one tree shows a hockey stick, the rest are all over the place. And, of course, there’s the infamous Divergence Problem of “Hide the Decline” fame.
There’s no consensus amongst the trees.

August 24, 2013 11:13 am

Also one must remember the large temperature swings that took place between the end of the last glacial maximum to the ending of the Younga Dryas period.
The overall temperature trend was up from the end of the last glacial maximum to the Holocene maximum but it was not steady(as shown above) in the least rather there were many sharp downward temperature reversals during this time ,with the most notable one being called the Younga Dryas but this was not the only such notable period.
These reversals in temperature from the end of the last glacial maximum to the end of the Younga Dryas were much greater in contrast to the temperaure reversals between the MEDIEVAL WARM PERIOD and the LITTLE ICE AGE, although that reversal is very significant and real.
The upshot being the article(first paragraph) does not bring out the fact that the temperature trend from the last glacial maximum to the Holocenc Climatic Optimum,had many sudden sharp reversals along the way.

August 24, 2013 3:45 pm

Any reliance on proxy data is absurd. Generalities may be assumed for ka, but in determining any value/condition for any decade or century seems like pure wishful thinking.
Why must we bother with paleoclimatology at all?(rhetorical)
To do so would only encourage a polarization among those that support AGW, rather than create evidence to negate it.
While some wish to discuss contentious data of the supposed MWP and LIA periods, there are no empirical standards upon which to defend those periods.
Even among the current ice core proxies at our disposal, there is no concrete evidence to establish any credibility with paleoclimatology.
But that doesn’t stop the AGW police.
An example that is used to justify similar occurrences at a later time can be found in this article:
The 8.2 ka event from Greenland ice cores
Within the abstract, we find this comment:
Greenland ice cores give only weak evidence for effects outside the North Atlantic region.
Let me take this a step further.
Ice cores give no evidence for any climatic effects within or beyond the North Atlantic regions at rates below 60 years. While certain cycles may be determined to rise or fall with any one core reading, there is no supporting data from other ice cores to establish a congruence.
If the CAGW teams wish to continue their drum beats of catastrophy with such weak evidence, a skeptic cannot provide a better alternative using those same methods.
The skeptic must point out the failings of that/any respective/particular science in order to achieve any credibility, rather than use the same type of science to refute it.
Our best attack is to use what we know which can be empirically proven.
Our best defense comes in what we can disprove.
Why not start with the failings of ice core data.
Given what I’ve stated above, it is easier for me to discredit the reliability of any one ice core, than prove any one particular ice core can defend a position I wish to take.
What ways can we disprove the authenticity of any one ice core?
Its been suggested recently that within the Arctic,Greenland, and Antarctic ice sheets, that massive ice melt is occuring.
It has also been suggested that there are some mass gains within certain regions of each or these ice sheets, but how much or how little is yet to be determined.
Two recent studies,, and, tells us that.
I mention these studies, not so much to establish any position on either side of the climate change debate(though i do think it clearly shows a cooling trend in spite of any so-called warming), but to bring a certain attention to:
a. the concept of melting ice,
b. the reliability of isotopes within ice cores,
c. the ability to ascertain cycles within glaciers.
If we were to arbitrarily pick any one point within an ice core, what can we know with any certainty about that time/climate/condition of that particular piece of ice?
Ice withing those cores isn’t static.There is no fixed or stationary condition with any part of that particular ice or any other point along an ice core.
Ice melts and moves across the surface.
Ice melts and moves within the surface of the ice.
Winds sweep across the surface of the ice, bringing with it dust, vapor, etc, that may or may not be of any one time, but possibly from different regions/time.
Ice bubbles.
Ice bubbles along lines of least resistance.
Air molecules decay.
Water molecules evaporate.
Dust disintegrates, breaks down and decomposes into more basic elements.
These processes I mention don’t just happen rarely, but more often than not, happen with too much regularity.
When we look at any one point along an ice core, it can not be conclusive to say that it represents any one time, condition, or state.
We might as well be looking at the event horizon of a black hole, and ask ourselves what time it is there.
If we want to spend any time defending a skeptical position, I think it’s time we spent it exposing the reliablity of paleoclimatology.
There is enough empirical data to suggest a cooling event is taking place. How long and to what degree it will cool should be a skeptics focus.
Using vague experiments in paleoclimatology shouldn’t be.
Attack it instead.

Ulric Lyons
August 24, 2013 4:31 pm

ClimateForAll says:
August 24, 2013 at 3:45 pm
“Any reliance on proxy data is absurd.”
I don’t know about that, they have been very specific with the 1375 AD date. Though I’m not so sure that they realise that this “abrupt cooling” would been a very warm episode for mid-upper latitude regions due to a positive AO/NAO, driven by a sharp rise in solar activity:

August 24, 2013 6:10 pm

Ulric Lyons says:
August 24, 2013 at 4:31 pm
“I don’t know about that, they have been very specific with the 1375 AD date. Though I’m not so sure that they realise that this “abrupt cooling” would been a very warm episode for mid-upper latitude regions due to a positive AO/NAO, driven by a sharp rise in solar activity.”
Im not sure how your previous comment on AO and Solar cycles for 1375 relates with faults in ice core proxies.
Unless climatology can create a concensus that everyone can agree upon, where the MWP and LIA lie in terms of length of time and weight of temperature, I suggest we quit playing their(alarmist) game.
The hockey stick is one glaring example that proxies are relied upon too heavily with the Algorites of the world.
I am just inserting an idea that it would be better to attack those methodologies held, rather than try to use the same methods to defend.
I also think there is enough empirical evidence to suggest that Co2 is not the dominant driver behind global temperatures.
Lets quit playing this game of ‘who has the better proxy’ and renounce everything we think we know and focus more on what we do know.

Ulric Lyons
August 25, 2013 1:37 am

ClimateForAll says:
“Im not sure how your previous comment on AO and Solar cycles for 1375 relates with faults in ice core proxies.”
It doesn’t, it was from sediment cores from Donard Lake, Baffin Island.

Ulric Lyons
August 25, 2013 10:12 am

”The most dramatic departure from this long-term decline was centered on about 850 years BP,”
In fact looking at the graph, it starts ~1115, which is at the start of a pair of weak solar cycles which makes more sense.

Brian H
August 25, 2013 12:54 pm

Salvatore Del Prete says:
August 24, 2013 at 11:13 am


Uh, that would be “YOUNGER DRYAS”.
Younger, Older — Get it?

August 26, 2013 8:11 am

I think I could use you as my editor.

August 27, 2013 4:50 am

I think there is enough empirical evidence to suggest that Co2 is not the dominant driver behind global temperatures.

Ulric Lyons
August 27, 2013 6:15 am

The same with Alaska, the retreats increase in years that are colder for the upper temperate zone, hence during negative AO/NAO conditions:
Which is why the Alaska retreat ceased since 1973.

Ulric Lyons
August 27, 2013 6:41 am

So warming in the Frigid Zone is accompanied by cooling in the Temperate Zone. We have been told all along that they move in unison, and that Arctic warming is the best sign of global warming, how wrong they are.

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