Evidence for a Global Medieval Warm Period

Note the IPCC disappeared the MWP in AR3

From CO2Science:

Medieval Warm Period (Antarctica) — Summary


Was there a Medieval Warm Period somewhere in the world in addition to the area surrounding the North Atlantic Ocean, where its occurrence is uncontested? This question is of utmost importance to the ongoing global warming debate, for if the Medieval Warm Period is found to have been a global climatic phenomenon, and if the locations where it occurred were as warm in medieval times as they are currently, there is no need to consider the temperature increase of the past century as anything other than the natural progression of the persistent millennial-scale oscillation of climate that regularly brings the earth several-hundred-year periods of modestly higher and lower temperatures that are totally independent of variations in atmospheric CO2 concentration. Consequently, we here review the findings of several studies that have found evidence for the Medieval Warm Period in a region that is as far away from lands bordering on the North Atlantic Ocean as one could possibly get, i.e., Antarctica.

Hemer and Harris (2003) extracted a sediment core from beneath the Amery Ice Shelf, East Antarctica, at a point that is currently about 80 km landward of the location of its present edge. In analyzing the core’s characteristics over the past 5,700 14C years, the two scientists observed a peak in absolute diatom abundance in general, and the abundance of Fragilariopsis curta in particular-which parameters, in their words, “are associated with increased proximity to an area of primary production, such as the sea-ice zone”-at about 750 14C yr B.P., which puts the time of maximum Ice Shelf retreat in close proximity to the historical time frame of the Medieval Warm Period.

Khim et al. (2002) likewise analyzed a sediment core removed from the eastern Bransfield Basin just off the northern tip of the Antarctic Peninsula, including grain size, total organic carbon content, magnetic susceptibility, biogenic silica content, 210Pb geochronology, and radiocarbon (14C) age, all of which data clearly depicted, in their words, the presence of the “Little Ice Age and Medieval Warm period, together with preceding climatic events of similar intensity and duration.”

Working in the same general region of the continent, Hall et al. (2010) write that “over the past 50 years, the Antarctic Peninsula warmed ~2°C,” and that resultant rapid ice breakups “have destroyed several small, thin ice shelves fringing the Antarctic Peninsula (i.e., Cook and Vaughan, 2009, and references therein),” leading them to ask, “is the recent warming of the Antarctic Peninsula unique in the Holocene?”

In an effort to place the current ice recession in a broader context, the three researchers “examined organic-rich sediments exposed by the recent retreat of the Marr Ice Piedmont on western Anvers Island near Norsel Point,” where glaciers “have been undergoing considerable retreat in response to the well-documented warming.” There, they “obtained moss and reworked marine shells from natural sections within 26 meters of the present ice front,” as well as “both peat and reworked shells from sediments exposed in a tunnel beneath the residual ice mass,” samples of which were radiocarbon-dated and the results converted to calendar years.

The results they obtained by these means indicated peat from the overrun sediments dated to between 707 ± 36 and 967 ± 47 cal. yr B.P.,” which led them to conclude, “ice was at or behind its present position at ca. 700-970 cal. yr B.P. and during at least two earlier times, represented by the dates of shells, in the mid-to-late Holocene.” Then, in language pure and simple, the three researchers say their findings imply that “the present state of reduced ice on the western Antarctic Peninsula is not unprecedented.” This leads them to pose another important question: “How widespread is the event at 700-970 cal. yr B.P.?”

In answering their own query, the researchers respond that (1) “Khim et al. (2002) noted a pronounced high-productivity (warm) event between 500 and 1000 cal. yr B.P. in magnetic susceptibility records from Bransfield Basin,” (2) “dates of moss adjacent to the present ice front in the South Shetland Islands (Hall, 2007) indicate that ice there was no more extensive between ca. 650 and 825 cal. yr B.P. than it is now,” (3) “evidence for reduced ice extent at 700-970 cal. yr B.P. is consistent with tree-ring data from New Zealand that show a pronounced peak in summer temperatures (Cook et al., 2002),” (4) “New Zealand glaciers were retracted at the same time (Schaefer et al., 2009),” and (5) their most recent findings “are compatible with a record of glacier fluctuations from southern South America, the continental landmass closest to Antarctica (Strelin et al., 2008).” In light of these several observations, therefore, it would appear that much of the southernmost portion of the Earth likely experienced a period of significantly enhanced warmth within the broad timeframe of the planet’s global MWP. And this interval of warmth occurred when there was far less CO2 and methane in the atmosphere than there is today.

In one additional study from the Antarctic Peninsula, Lu et al. (2012) constructed “the first downcore δ18O record of natural ikaite hydration waters and crystals collected from the Antarctic Peninsula (AP)” that they say were “suitable for reconstructing a low resolution ikaite record of the last 2000 years.” According to the group of nine UK and US researchers, ikaite “is a low temperature polymorph of calcium carbonate that is hydrated with water molecules contained in its crystal lattice,” and they write that “ikaite crystals from marine sediments, if collected and maintained at low temperatures, preserve hydration waters and their intact crystal structures, both of which have the potential to provide isotopic constraints on past climate change.” So what did they find?

The authors report that “the ikaite record qualitatively supports that both the Medieval Warm Period and Little Ice Age extended to the Antarctic Peninsula.” They also state that the “most recent crystals suggest a warming relative to the LIA in the last century, possibly as part of the regional recent rapid warming,” but they add that “this climatic signature is not yet as extreme in nature as the MWP,” suggesting that even the dramatic recent warming of the AP may not yet have returned that region to the degree of warmth that was experienced there during the MWP, when the atmosphere’s CO2 concentration was more than 100 ppm less than it is today.

Examining a different region of the continent, Hall and Denton (2002) mapped the distribution and elevation of surficial deposits along the southern Scott Coast of Antarctica in the vicinity of the Wilson Piedmont Glacier, which runs parallel to the coast of the western Ross Sea from McMurdo Sound north to Granite Harbor. The chronology of the raised beaches they studied was determined from more than 60 14C dates of incorporated organic materials they had previously collected from hand-dug excavations (Hall and Denton, 1999); the record the dates helped define demonstrated that near the end of the Medieval Warm Period, “as late as 890 14C yr BP,” as Hall and Denton describe it, “the Wilson Piedmont Glacier was still less extensive than it is now,” demonstrating that the climate of that period was in all likelihood considerably warmer than it is currently.

Several years later, but also working in the Ross Sea region of Antarctica, Bertler et al. (2011) obtained new deuterium (δD) data acquired via analysis of the top fifty meters of a 180-meter-long ice core that had been extracted from the ice divide of Victoria Lower Glacier in the northernmost McMurdo Dry Valleys, which they converted to temperature data by means of a temperature-isotope relationship developed by Steig et al. (1998) from data obtained from the Taylor Dome ice core record. In doing so, Bertler et al. report that they identified three distinct time periods in their record: the last 150 years of the Medieval Warm Period (AD 1140 to 1287), the Little Ice Age (AD 1288 to 1807), and the Modern Era (AD 1808 to 2000). And with respect to the Medieval Warm Period, they write that “the McMurdo Dry Valleys were 0.35°C warmer during the MWP than during ME, accompanied by warmer conditions in the Ross Sea.” The three researchers also note that “a magnetic susceptibility record from Palmer Deep marine core (PD92 30MS) also supports warmer MWP conditions, this time in Drake Passage (Domack and Mayewski, 1999).”

Noon et al. (2003) used oxygen isotopes preserved in authigenic carbonate retrieved from freshwater sediments of Sombre Lake on Signy Island (60°43’S, 45°38’W) in the Southern Ocean to construct a 7,000-year history of that region’s climate. This work revealed that the general trend of temperature at the study site has been downward. Of most interest to the present discussion, however, is the millennial-scale oscillation of climate that is apparent in much of the record. This climate cycle is such that approximately 2,000 years ago, after a thousand-year gap in the data, Signy Island experienced the relative warmth of the last vestiges of the Roman Warm Period, as delineated by McDermott et al. (2001) on the basis of a high-resolution speleothem δ18O record from southwest Ireland. Then comes the Dark Ages Cold period, which is also contemporaneous with what McDermott et al. observe in the Northern Hemisphere, after which the Medieval Warm Period appears at the same point in time and persists for the same length of time that it does in the vicinity of Ireland, whereupon the Little Ice Age sets in just as it does in the Northern Hemisphere. Finally, there is an indication of late twentieth century warming, but with still a long way to go before conditions comparable to those of the Medieval Warm Period are achieved.

Two years later, Castellano et al. (2005) derived a detailed history of Holocene volcanism from the sulfate record of the first 360 meters of the Dome Concordia ice core that covered the period 0-11.5 kyr BP, after which they compared their results for the past millennium with similar results obtained from eight other Antarctic ice cores. Before doing so, however, they normalized the results at each site by dividing their several volcanic-induced sulfate deposition values by the value produced at that site by the AD 1816 Tambora eruption, in order to reduce deposition differences among sites that might have been induced by differences in local site characteristics. This work revealed that most volcanic events in the early last millennium (AD 1000-1500) exhibited greater among-site variability in normalized sulphate deposition than was observed thereafter.

Citing Budner and Cole-Dai (2003) in noting that “the Antarctic polar vortex is involved in the distribution of stratospheric volcanic aerosols over the continent,” Castellano et al. say that assuming the intensity and persistence of the polar vortex in both the troposphere and stratosphere “affect the penetration of air masses to inland Antarctica, isolating the continental area during cold periods and facilitating the advection of peripheral air masses during warm periods (Krinner and Genthon, 1998), we support the hypothesis that the pattern of volcanic deposition intensity and geographical variability [higher values at coastal sites] could reflect a warmer climate of Antarctica in the early last millennium,” and that “the re-establishment of colder conditions, starting in about AD 1500, reduced the variability of volcanic depositions.”

Describing this phenomenon in terms of what it implies, Castellano et al. say “this warm/cold step could be like a Medieval Climate Optimum-like to Little Ice Age-like transition.” They additionally cite Goosse et al. (2004) as reporting evidence from Antarctic ice-core δD and δ18O data “in support of a Medieval Warming-like period in the Southern Hemisphere, delayed by about 150 years with respect to Northern Hemisphere Medieval Warming.” And the researchers conclude by postulating that “changes in the extent and intra-Antarctic variability of volcanic depositional fluxes may have been consequences of the establishment of a Medieval Warming-like period that lasted until about AD 1500.”

A year later, Hall et al. (2006) collected skin and hair (and even some whole-body mummified remains) from Holocene raised-beach excavations at various locations along Antarctica’s Victoria Land Coast, which they identified by both visual inspection and DNA analysis as coming from southern elephant seals, and which they analyzed for age by radiocarbon dating. By these means they obtained data from 14 different locations within their study region-which they describe as being “well south” of the seals’ current “core sub-Antarctic breeding and molting grounds”-that indicate that the period of time they denominate the Seal Optimum began about 600 BC and ended about AD1400, the latter of which dates they describe as being “broadly contemporaneous with the onset of Little Ice Age climatic conditions in the Northern Hemisphere and with glacier advance near [Victoria Land’s] Terra Nova Bay.”

In describing the significance of their findings, the US, British, and Italian researchers say they are indicative of “warmer-than-present climate conditions” at the times and locations of the identified presence of the southern elephant seal, and that “if, as proposed in the literature, the [Ross] ice shelf survived this period, it would have been exposed to environments substantially warmer than present,” which would have included both the Roman Warm Period and Medieval Warm Period.

Advancing one year closer to the present, Williams et al. (2007) presented methyl chloride (CH3Cl) measurements of air extracted from a 300-m ice core that was obtained at the South Pole, Antarctica, covering the time period 160 BC to AD 1860. In describing what they found, the researchers say “CH3Cl levels were elevated from 900-1300 AD by about 50 ppt relative to the previous 1000 years, coincident with the warm Medieval Climate Anomaly (MCA),” and that they “decreased to a minimum during the Little Ice Age cooling (1650-1800 AD), before rising again to the modern atmospheric level of 550 ppt.” Noting that “today, more than 90% of the CH3Cl sources and the majority of CH3Cl sinks lie between 30°N and 30°S (Khalil and Rasmussen, 1999; Yoshida et al., 2004),” they say “it is likely that climate-controlled variability in CH3Cl reflects changes in tropical and subtropical conditions.” They go on to say that “ice core CH3Cl variability over the last two millennia suggests a positive relationship between atmospheric CH3Cl and global [italics added] mean temperature.”

As best as can be determined from the graphical representation of their data, the peak CH3Cl concentration measured by Williams et al. during the MCA is approximately 533 ppt, which is within 3 percent of its current mean value of 550 ppt and well within the range of 520 to 580 ppt that characterizes methyl chloride’s current variability. It may therefore be validly concluded that the mean peak temperature of the MCA (which is herein referred to as the Medieval Warm Period) over the latitude range 30°N to 30°S-and possibly over the entire globe-may not have been materially different from the mean peak temperature so far attained during the Current Warm Period.

In one final study, Hall (2007) presented “radiocarbon and geomorphologic data that constrain [the] late-Holocene extent of the Collins Ice Cap on Fildes Peninsula (King George Island, South Shetland Islands: 62°10’51″S, 58°54’13″W),” which, in her words, “yield information on times in the past when climate in the South Shetland Islands must have been as warm as or warmer than today,” based on field mapping of moraines and glacial deposits adjacent to the ice cap, as well as radiocarbon dates of associated organic materials. Such data, according to Hall, “indicate ice advance after ~650 cal. yr BP (AD ~1300),” which she notes is “broadly contemporaneous with the ‘Little Ice Age’, as defined in Europe.” She also says that this was “the only advance that extended beyond the present ice margin in the last 3500 years, making the Little Ice Age in that part of the world likely the coldest period of the current interglacial. And the fact that “the present ice cap margin … is still more extensive than it was prior to ~650 cal. yr BP” led her to conclude that the climate prior to that time — which would have comprised the Medieval Warm Period — may have been “as warm as or warmer than present.” And this conclusion, along with the findings of the other studies reviewed herein, suggests there is nothing that is unusual, unnatural or unprecedented about the current level of Earth’s warmth, which further suggests that the historical increase in the atmosphere’s CO2 concentration may not have had anything to do with concomitant 20th-century global warming.

References

Bertler, N.A.N., Mayewski, P.A. and Carter, L. 2011. Cold conditions in Antarctica during the Little Ice Age — Implications for abrupt climate change mechanisms. Earth and Planetary Science Letters 308: 41-51.

Budner, D. and Cole-Dai, J. 2003. The number and magnitude of large explosive volcanic eruptions between 904 and 1865 A.D.: Quantitative evidence from a new South Pole ice core. In: Robock, A. and Oppenheimer, C. (Eds.), Volcanism and the Earth’s Atmosphere, Geophysics Monograph Series 139: 165-176.

Castellano, E., Becagli, S., Hansson, M., Hutterli, M., Petit, J.R., Rampino, M.R., Severi, M., Steffensen, J.P., Traversi, R. and Udisti, R. 2005. Holocene volcanic history as recorded in the sulfate stratigraphy of the European Project for Ice Coring in Antarctica Dome C (EDC96) ice core. Journal of Geophysical Research 110: 10.1029/JD005259.

Cook, A.J. and Vaughan, D. 2009. Overview of areal changes of the ice shelves on the Antarctic Peninsula over the past 50 years. The Cryosphere Discussions 3: 579-630.

Cook, E., Palmer, J., and D’Arrigo, R. 2002. Evidence for a “Medieval Warm Period” in a 1100-year tree-ring reconstruction of past austral summer temperatures in New Zealand. Geophysical Research Letters 29: 10.1029/2001GL014580.

Domack, E.W. and Mayewski, P.A. 1999. Bi-polar ocean linkages: evidence from late-Holocene Antarctic marine and Greenland ice-core records. The Holocene 9: 247-251.

Goosse, H., Masson-Delmotte, V., Renssen, H., Delmotte, M., Fichefet, T., Morgan, V., van Ommen, T., Khim, B.K. and Stenni, B. 2004. A late medieval warm period in the Southern Ocean as a delayed response to external forcing. Geophysical Research Letters 31: 10.1029/2003GL019140.

Hall, B.L. 2007. Late-Holocene advance of the Collins Ice Cap, King George Island, South Shetland Islands. The Holocene 17: 1253-1258.

Hall, B.L. and Denton, G.H. 1999. New relative sea-level curves for the southern Scott Coast, Antarctica: evidence for Holocene deglaciation of the western Ross Sea. Journal of Quaternary Science 14: 641-650.

Hall, B.L. and Denton, G.H. 2002. Holocene history of the Wilson Piedmont Glacier along the southern Scott Coast, Antarctica. The Holocene 12: 619-627.

Hall, B.L., Hoelzel, A.R., Baroni, C., Denton, G.H., Le Boeuf, B.J., Overturf, B. and Topf, A.L. 2006. Holocene elephant seal distribution implies warmer-than-present climate in the Ross Sea. Proceedings of the National Academy of Sciences USA 103: 10,213-10,217.

Hall, B.L., Koffman, T., and Denton, G.H. 2010. Reduced ice extent on the western Antarctic Peninsula at 700-907 cal. yr B.P. Geology 38: 635-638.

Hemer, M.A. and Harris, P.T. 2003. Sediment core from beneath the Amery Ice Shelf, East Antarctica, suggests mid-Holocene ice-shelf retreat. Geology 31: 127-130.

Khalil, M.A.K. and Rasmussen, R.A. 1999. Atmospheric methyl chloride. Atmospheric Environment 33: 1305-1321.

Khim, B-K., Yoon, H.I., Kang, C.Y. and Bahk, J.J. 2002. Unstable climate oscillations during the Late Holocene in the Eastern Bransfield Basin, Antarctic Peninsula. Quaternary Research 58: 234-245.

Krinner, G. and Genthon, C. 1998. GCM simulations of the Last Glacial Maximum surface climate of Greenland and Antarctica. Climate Dynamics 14: 741-758.

Lu, Z., Rickaby, R.E.M., Kennedy, H., Kennedy, P., Pancost, R.D., Shaw, S., Lennie, A., Wellner, J. and Anderson, J.B. 2012. An ikaite record of late Holocene climate at the Antarctic Peninsula. Earth and Planetary Science Letters 325-326: 108-115.

McDermott, F., Mattey, D.P. and Hawkesworth, C. 2001. Centennial-scale Holocene climate variability revealed by a high-resolution speleothem δ18O record from SW Ireland. Science 294: 1328-1331.

Noon, P.E., Leng, M.J. and Jones, V.J. 2003. Oxygen-isotope (δ18O) evidence of Holocene hydrological changes at Signy Island, maritime Antarctica. The Holocene 13: 251-263.

Schaefer, J., Denton, G., Kaplan, M., Putnam, A., Finkel, R., Barrell, D.J.A., Andersen, B.G., Schwartz, R., Mackintosh, A., Chinn, T., and Schluchter, C. 2009. High-frequency Holocene glacier fluctuations in New Zealand differ from the northern signature. Science 324: 622-625.

Steig, E.J., Brook, E.J., White, J.W.C., Sucher, C.M., Bender, M.L., Lehman, S.J., Morse, D.L., Waddington, E.D. and Clow, G.D. 1998. Synchronous climate changes in Antarctica and the North Atlantic. Science 282: 92-95.

Strelin, J., Casassa, G., Rosqvist, G., and Holmlund, P. 2008. Holocene glaciations in the Ema Glacier valley, Monte Sarmiento Massif, Tierra del Fuego. Palaeogeography, Palaeoclimatology, Palaeoecology 260: 299-314.

Williams, M.B., Aydin, M., Tatum, C. and Saltzman, E.S. 2007. A 2000 year atmospheric history of methyl chloride from a South Pole ice core: Evidence for climate-controlled variability. Geophysical Research Letters 34: 10.1029/2006GL029142.

Yoshida, Y., Wang, Y.H., Zeng, T. and Yantosea, R. 2004. A three-dimensional global model study of atmospheric methyl chloride budget and distributions. Journal of Geophysical Research 109: 10.1029/2004JD004951.

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Edohiguma

We’ve had this evidence for a long time now. This just adds more to it. Primarily the evidence was found in historic records. Wine was planted as high as Denmark and in Japan the first novel of mankind was written. All this shows the same pattern as in the Roman warming period. In both cases culture exploded.

Brian D Finch

Excellent article, but I thought the late John L Daly had this well covered years ago when he wrote:
‘From all corners of the world, the Medieval Warm Period and Little Ice Age clearly shows up in a variety of proxy indicators, proxies more representative of temperature than the inadequate tree rings used by Michael Mann.’
The `Hockey Stick’: A New Low in Climate Science
http://www.john-daly.com/hockey/hockey.htm

Hemer and Harris (2003) – do you really trust the chronology of this core that much? Besides, radiocarbon dates need calibrating before they can be compared with dates on a calendar time scale.
This list shows that there are warm events in the low southern latitudes. It does not show that they are synchronous, and it does not show that they are synchronous with the North Atlantic MWP.
But if you could demonstrate that there was a large globally synchronous MWP, it would mean that climate sensitivity must be high and the change in climate forcings between the MWP and the pre-industrial are low.
REPLY: Wait until our next post at 10:30AM PDT and tell us again why you think you could demonstrate climate sensitivity is high during the MWP. – Anthony

I wonder if this excellent study was peer reviewed.
What this is an example of is that the emperical scientists are catching up to the desk bound computer scientists [?]. What else it’s an example of is that more and more and more studies have come out that reveal that AGW is bunk and more bunk and still more bunk.
It is also revelent that more and more MSM outlets are just beginning to catch on. When they fully catch on their wrath at the so called climate scientists will be a sight to behold. Couldn’t happen to a more deserving group of so called people. It will be ironic if the final death knell of the warmists is delivered by the MSM who did so much to promote them.

My God I must be”‘white listed”, my comment got posted immediatly. I warn you, Anthony, I’ve been snipped a number of times.

GlynnMhor

I fear it will be another lustrum or maybe even two before persistent lack of warming makes a serious dent in the public perception of the supposed ‘climate crisis’.

Any bets this work will be rubbished by the AGW crowd as soon as they can find a shill willing to produce a contrarian ‘proof’ that the MWP and Roman Warm Period never happened? If they can’t we can be sure they’ll go for ad hominem attacks on the authors and attempt to block further publication or referencing.

richard verney

Edohiguma says:
April 11, 2013 at 7:20 am
“… All this shows the same pattern as in the Roman warming period. In both cases culture exploded”
////////////////////////////////////////////////////////
There can be little doubt that as far as mankind is concerned, the world is too cold. Mankind developed in warm Africa and it is only because of our ability to adapt ourselves (cover ourselves in animal skins and furs) and/or to adapt our environment (build shelters and fires) that we have been able to colonize the globe. If you look at where mankind can survive without such modifications, it will be noted that it is within a very narrow tropical band, particularly tropical rain forests.
You can trace the advancement of mankind and its link to temperature from the onset of the bronze and iron ages, to civilisation in general. Advancement comes first to warm climates. A stark example is that whilst those living in cold Britain were building Stonehenge, the Egyptioan were building mighty Pyramids, obalisks and temples. The engineering feat of the great pyramid is immense. The base was carved from the rocks of the Giza Plateau using cooper chisels to an accuracy that we would have trouble achieving today. The base extends over some 230 metres and is level to within 2.1cm. That is much the same tolerance as is found in the tallest buildings in the world built these past 20 years. This skill set was developed because the Egyptians were not struggling for survival holed up in some cave or taking shelter around a campfire in some wooden shack.
Those in fuel poverty can easily see how cold stunts achievement. When very cold, people take more to their beds, sleeping for longer periods or take root on the sofa with a quilt and a warm drink, instead of being active and doing something.
There has never been a notable northern climb civilisation. The nearest candidate would be the Vikings, and guess what, they were active in the Viking warm period and fell away when it bagan to cool.
The same is so for animal life. Far more bio diversity in warm and wet environs, and least bio diversity in cold and arid environs. Cold stunts whereas warmth stimulates.
One of the areas where I consider the greatest failings have occurred is in the proper evaluation of the effects of climate change. I am of the firm view that a warmer planet would generally be of great benefit to both mankind and the animal world.

There you go again, trying to use actual data and proper science to counter the psychotic beliefs of the deranged alarmists. It won’t work. Only their paranoia counts for them. Reality is irrelevant to their demands to stop the future and for mankind to commit suicide. I won’t even grace their madness with the label “religion”. It is too insane for even that label to be applicable.
Is there an answer? Yes! Stop feeding them.

Let’s see them put that into their rear view legacy climate models. Err, perhaps not. There’s a “C” and a “2” missing.

richard verney

When discussing the MWP and debating whether it was or was not a global event, one often overlooks what is happening today.
Modern global warming is predominantlya Northern Hemisphere phenomen and much of it is found in warmer winter conditions. There is some evidence that the warming disproportionally consists of warmer winter night time temperatures.
This is quite important whan considering proxies. Since today’s warmth is predominantly occuring in the NH, it comes as no surprise that proxies of past warming periods may also show more warming in the NH compared to that in the SH. There is little doubt that the distribution of oceans (and their thermal damping) and land masses predominantly in the NH plays a part. Since the warming of today consists more of a change in winter temperatures 9ratherthan summer temperatures), again it would come as no surprise if proxies may dampen response to this warming since the growing period of the proxy may not be in the winter months, particularly if this was winter night time temperatures.
Certainly the IPCC 1990 -2001 appears to be the better fit with what e know from historical written record and archaelogical digs. In fact, i think that we have probably under-estimated the warth of the MWP. For Viking settlement to have flourished in Greenland for several hundred years, the weather must have been benign and these farmsteads could not be hanging on the edge of subsitence levels, Obviously even in warm periods there will always be the odd one or two harsh winters. The settlement in Greenland would not have survived unless generally times were bountiful so that they had surplus to enable to get through the odd bad winter or two.
Here in the UK where we have had a coldish winter, livestock farmers in Wales and Scotland are really struggling with much live stock casualties. This is notwithstanding our modern machinery, vast reserves of feedstock, heated barns etc. Just imaginge how the Viking farmers would have coped with similar conditions. It makes me consider that Greenland must have been a lot warmer (5 to 8 degC) warmer than today if they were to survive for hundreds of years.

jc

Maybe its time to start compiling what might be called a Dossier on all actual evidence that has been overlooked, obscured, or just “disappeared” over the course of this perversion.
And structure it in a time line from when it was available back to 1988 or earlier. Including all accounts and historical references, undeniable agricultural practices, and the like, along with specific scientific studies. In other words the sum total of human knowledge that relates to climate that was built over centuries and has been either obliterated or ignored.
Show these things, and hold these people to account for much more than just touting a particular ideologically based speculation: the trashing of human history and culture itself.

MikeN

>Wait until our next post at 10:30AM PDT and tell us again why you think you could demonstrate climate sensitivity is high during the MWP.
I won’t wait. I’ll answer right now.
Michael Mann has argued that the Medieval Warm Period is not global because there was a negative feedback that caused LaNina like conditions in the tropics, and posited Cain’s Pacific Thermostat hypothesis as a possible culprit. When asked if this meant that in response to global warming, there would be a long term negative feedback and therefore climate models vastly overstate warming, Mann responded “I agree with that. I have a reputation as some sort of climate alarmist, but I think there is a missing negative feedback.” This was preceded by Mann joking to the questioner, “You don’t look like Dick.”
So if you say that MWP was global, then you have taken away a natural negative feedback.

commieBob

Let’s not forget the “Medieval Warm Period Project” over at CO2 Science:

Was there a Medieval Warm Period? YES, according to data published by 1156 individual scientists from 663 research institutions in 46 different countries … and counting! Our latest Medieval Warm Period Record comes from Taibai Lake, China. http://www.co2science.org/

One of my hobbies is history and when ‘they’ tried to erase the Medieval Warm period, I started paying a lot more attention to the global warming issue. Until that very moment I was willing to believe that the planet was warming because of our CO2 emissions. History tells us that there was a warm period in Europe and China and that it was followed by a cold period. It was a “big deal”. It looked to me like they were stooping to fraud to get rid of the MWP. Hmmm. What else might be wrong with CAGW?

“But if you could demonstrate that there was a large globally synchronous MWP, it would mean that climate sensitivity must be high and the change in climate forcings between the MWP and the pre-industrial are low.
REPLY: Wait until our next post at 10:30AM PDT and tell us again why you think you could demonstrate climate sensitivity is high during the MWP. – Anthony
##############################
Anthony he is not saying sensitivity is high DURING the MWP. he is noting this:
Have a look at the swing between the high of the MWP and the low of the LIA.
That is delta T.
Sensitivity is Delta T/ Delta F where F is change in forcing. Steve Mcintyre has also pointed this out. If you argue for a higher MWP you are basically arguing for a higher climate sensitivity.
If Delta T ( as shown above ) is ca. 1.25C and the change in forcing is .5 watts
then you’ve got a sensitivity of 2.5… and a sensitivity to doubling c02 of 2.5 * 3.7
big number. If delta T is .5C and the change in forcing is .5 W, then you have
a sensitivity of 1, and a sensitivity to doubling c02 of 3.7.
Bottomline: the bigger the swing between the MWP and the LIA, the HIGHER the sensitivity.
The bigger the swing in natural oscillations the higher our risk from anthro forcing.

Steve Keohane

Seems like the normal purveyance of climate that I read about from 1960-1990, prior to the anthro-CO2 fantasy.

AnonyMoose

Sarcastically: Gee, how did the IPCC miss this?
(Yes, I know they’re only required to study human-caused warming)

Loehle’s reconstruction clearly shows presence of the MWP.
Dr. Jean Dickey of NASA’s Jet Propulsion Laboratory, Pasadena suggest there is a possible link between the Earth’s magnetic field and the global temperature variability (see link below).
If Dr Dickey is correct than should be a measurable correlation between the Loehle’s reconstruction data and changes in the geomagnetic field; indeed that is the case
http://www.vukcevic.talktalk.net/LL.htm

End GRANT SCIENCE and financing for results – give us what we demand and we will give you more research money – AKA as you can keep your University.think tank job. If this project is passed to the millions now looking for a way to make government smaller. Send this to all you know on your email list so it can be VIRAL . . No IRS, no EPA, no Species act, no law suits to stop or delay projects and job creation.
http://articlevprojecttorestoreliberty.com/todays-patriots-and-article-v-will-save-this-nation.html

I like what happens when you add the gold-price [sice 1265AD] to that MWP signature:
http://i.imgur.com/NZC5Zf2.jpg

Mark Bofill

Steven Mosher says:
April 11, 2013 at 8:25 am

If Delta T ( as shown above ) is ca. 1.25C and the change in forcing is .5 watts
then you’ve got a sensitivity of 2.5… and a sensitivity to doubling c02 of 2.5 * 3.7
big number. If delta T is .5C and the change in forcing is .5 W, then you have
a sensitivity of 1, and a sensitivity to doubling c02 of 3.7.
Bottomline: the bigger the swing between the MWP and the LIA, the HIGHER the sensitivity.
The bigger the swing in natural oscillations the higher our risk from anthro forcing.
————
Meh. Maybe. Maybe I’m not understanding your argument Steven. It seems to me this argument presupposes that CO2 is an important driver in the first place.
Let’s think this through. Say there is some currently unknown solar amplification mechanism that has driven climate variability in the past. Or whatever; it doesn’t have to be solar. Start without the presupposition that the mechanism is specifically CO2 related. Supposing natural climate variability exhibited wider swings due to such a mechanism does not appear to speak to the question of the effect of CO2 and particularly positive feedbacks involved with increase atmospheric CO2 at all.
What am I missing?

“This list shows that there are warm events in the low southern latitudes. It does not show that they are synchronous, and it does not show that they are synchronous with the North Atlantic MWP.”
The dispute is over the global synchronicity. So much sceptical discussion does not recognise this. SAR and TAR rejected FAR’s findings on the evidence. The graph in FAR was not based on global evidence and should not be trotted out again and again as though it is a standard to which the IPCC should return.

It is time to take positive actions to end the usurping Federal government – end the IRS, EPA, BLM, FHA, HLS, NDAA and all the rest of the alphabet agencies that are not included in Article I section 8 of the enumerated powers. . . GRANT SCIENCE IS BRIBERY BY THE GOVERNMENT.
http://articlevprojecttorestoreliberty.com/todays-patriots-and-article-v-will-save-this-nation.html

@richard verney Sorry dude, you cannot cut granite with copper chisels… No way no how in any universe… Simple physics… You might be able to make a case that they traded for iron and hardened it… Otherwise from the tooling marks in left over granite and the perfect geometry of certain cuts you are stuck with the Egyptians having advanced tools like rock saws and such….
Back to Climate…

Reblogged this on Climate Ponderings and commented:
EXCELLENT!

Beta Blocker

Mosher: Bottomline: the bigger the swing between the MWP and the LIA, the HIGHER the sensitivity. The bigger the swing in natural oscillations the higher our risk from anthro forcing.

That is a very mechanistic perspective concerning how the earth’s climate system actually works.
Let’s start with a presumption that the Medievel Warm Period was present, was global, and that temperatures approximated today’s GMT.
What kinds of sources could be postulated as candidates for the forcings which drove the WMP?

James Evans

Steven Mosher,
“Bottomline: the bigger the swing between the MWP and the LIA, the HIGHER the sensitivity.”
Doesn’t this rather assume that the forcings are very well understood? If we don’t even know whether there was a MWP or not, then clearly we don’t have a great understanding of the forcings. So that makes the whole “sensitivity” issue rather moot, surely.

Mark Bofill

Mark Bofill says:
April 11, 2013 at 8:58 am
Steven Mosher says:
April 11, 2013 at 8:25 am
————-
I guess to frame my problem with this more in line with your original point, how do we know what sort of changes in forcings were involved in past climate variability; why are we assuming it was low?

O Olson

Steven Mosher says:
April 11, 2013 at 8:25 am
Nope. Straw man. Climate doesn’t have just one sensitivity. Sensitivity to each particular forcing will be different. We don’t know for sure what the forcing change was during the MWP but it wasn’t SUVs.

richard verney says: April 11, 2013 at 7:58 am
Since the warming of today consists more of a change in winter temperatures (rather than summer temperatures), again it would come as no surprise if proxies may dampen response to this warming since the growing period of the proxy may not be in the winter months.
The CET data agree,
http://www.vukcevic.talktalk.net/MidSummer-MidWinter.htm
England’s tree core proxies are more likely to show summer precipitation than the annual temperature.

Steven Mosher,
No, there might very well be a natural variability causing the climate to vary as it has without any variation in external ‘forcings’ causing this. The response to an assumed ‘forcing’ described by an equally assumed scalar value of ‘sensitivity’ is something distinctly different than ‘natural variability’, and of course both phenomena might have been present during the last millenium.
And as others have pointed out, the description of one climate, ruled by one (sum of all) forcing, through one sensitivity parameter is of course a very crude and only descriptice simplification. I cannot be used as an ‘explanation’ of what is going on.

William Marshall

Edohiguma says: April 11, 2013 at 7:20 am
‘Wine was planted as high as Denmark’ and you can grow grapes today in England!

Brian

Interesting points about negative feedbacks MikeN. Perhaps we are running into a similar situation now, with a warming Arctic but relatively stable temperatures elsewhere.

Jonas N

Richard Verney
What you say about predominantly NH warming, and there predominantly in winter and at night makes sense, and may indicate that it this indeed is due to an enhanced greenhouse effect. But it also means that the scare of massive, large and global feedback effects sound almost implausible, and that there really is no reason for any climate alarmism …

Chris Schoneveld

Sensitive to what? We don’t know the cause of the MWP hence we don’t know what kind of forcing we are talking about (there is no proxi that suggests higher CO2 during the MWP) or how big that unknown forcing was. Maybe the forcing was very strong and the resulting delta T relatively small (whilst in absolute terms quite considerable and impacting our climate globally) and thus one could argue a negative feedback and rather low sensitivity.

Geoff Withnell

Steven Mosher says:
April 11, 2013 at 8:25 am
“But if you could demonstrate that there was a large globally synchronous MWP, it would mean that climate sensitivity must be high and the change in climate forcings between the MWP and the pre-industrial are low.
REPLY: Wait until our next post at 10:30AM PDT and tell us again why you think you could demonstrate climate sensitivity is high during the MWP. – Anthony
##############################
Anthony he is not saying sensitivity is high DURING the MWP. he is noting this:
Have a look at the swing between the high of the MWP and the low of the LIA.
That is delta T.
Sensitivity is Delta T/ Delta F where F is change in forcing. Steve Mcintyre has also pointed this out. If you argue for a higher MWP you are basically arguing for a higher climate sensitivity.
If Delta T ( as shown above ) is ca. 1.25C and the change in forcing is .5 watts
then you’ve got a sensitivity of 2.5… and a sensitivity to doubling c02 of 2.5 * 3.7
big number. If delta T is .5C and the change in forcing is .5 W, then you have
a sensitivity of 1, and a sensitivity to doubling c02 of 3.7.
Bottomline: the bigger the swing between the MWP and the LIA, the HIGHER the sensitivity.
The bigger the swing in natural oscillations the higher our risk from anthro forcing.
*************
You are making the assumption that the oscillations are due to a change in input, aka forcing. Do you have any data that the system is not in a state of oscillation much like a pendulum, just swinging back and forth from some kick (the end of the last ice age?) or some small periodic input?

ITSTEAPOT

A very important question is, how does the world switch from cold to warm and back again in pre history when there was no Human activity to blame?

Robert Austin

richard telford says:
April 11, 2013 at 7:26 am
“But if you could demonstrate that there was a large globally synchronous MWP, it would mean that climate sensitivity must be high and the change in climate forcings between the MWP and the pre-industrial are low.”
I support what Jonas N says.
Mosher reiterates Richard’s point but the concept presupposes that a change in global temperature must be driven by a change in forcing external to the system. In the complex, chaotic system that is earth’s climate, one must not dismiss the idea that perturbations occur without external forcing changes. I think that Dr. Roy Spencer has made the same point on his blog.

We definitely need to get the messages of John L. Daly and the other scientists who have demonstrated the global reality of the MWP out to the general public.
But even more than that, we need to communicate to middle-class and low-income people how the green agenda, and the specific agenda of the Obama administration, will harm them. Posters here may recall the “Stop global warming hype” billboard put up by CFACT. Here are suggrestions for two more billboards, which I will also communicate to CFACT:
THE OBAMA ADMINISTRATION MEANS TO INCREASE YOUR ENERGY COSTS.
IF YOU ARE LIVING ON A LOW INCOME:
• How will gasoline at $8, maybe even $10 a gallon affect you?
• How will electricity at 30 cents per kilowatt hour affect you?
• How will natural gas at $20 a therm affect you?
THESE ARE THE PRICES FOR ENERGY PLANNED BY THE OBAMA ADMINISTRATION.
THINK ABOUT IT. DO YOU WANT THIS?
(in Spanish):
LA ADMINISTRACION DEL PRESIDENTE OBAMA INTENTA SUBIR SUS COSTOS DE ENERGIA.
SI VD. VIVE POR INGRESOS BAJOS:
• ?Cómo le importa a Vd. la gasolina al precio de $8, quizás aún $10 por galón?
• ?Cómo le importa a Vd. la electricidad al precio de 30 centavos por kilowatt-hora?
• ?Cómo le importa a Vd. el gas natural al precio de $20 por therm?
ESTOS SON LOS PRECIOS PROYECTADOS POR LA ADMINISTRACION DEL PRESIDENTE OBAMA.
PIENSE VD. SOBRE ELLO. ?ES LO QUE QUIERE VD.?
(my apologies for the upside-down question marks – not available on Microsoft’s character map).

TimC

Steven Mosher said (at 8:25 above) “If you argue for a higher MWP you are basically arguing for a higher climate sensitivity”.
But we are not involved in a debate or argument – only evidence, wherever that might lead to. If it’s to higher (dT/dF) climate sensitivity then that is the fact of it.

mikerossander

Brant Ra at 9:22 above says that “you cannot cut granite with copper chisels”. I assume he is basing that statement on the Mohs Hardness test – that in a contest between the two materials, copper, the softer material must yield. That is incorrect. Consider, for example, glass and wood. Glass is by far the harder material. Yet place a fine wineglass on the floor and drop a log on it. The glass will yield.
The issue is not hardness but the transfer of force. Soft tools may transfer large forces if used properly. By transferring the forces in just the right places, granite can be split in remarkably straight lines. Even carving and polishing can be accomplished without the hypothesized need to continually resharpen copper tools. Drilling doesn’t require metal at all. Percussive drilling techniques can make very neat holes in granite using nothing more than wood, rope and another piece of rock.
It is possible that the pyramid-makers had access to iron tools from the Hittites. It is also plausible that they accomplished their construction with only copper. Given the brittleness of iron at that time (not to mention the cost), I consider unlikely that they used pure iron tools. It possible that they may have used a third option – primarily copper tools with embedded harder materials at the edge, similar to when you edge-weld a piece of higher-carbon steel as the bit of your axe. But that’s purely speculation on my part.

markx

I have posted this before …::
It is really worth going back to assess Mann’s original contention that the MWP was ‘cooler than the present’ (of course, he has to rename it the MCA, the Medieval Climate Anomoly, as otherwise the whole thing would fail the Orwellian test).
Available here: (needs a log in – no cost)
Global Signatures and Dynamical Origins of the Little Ice Age and Medieval Climate Anomaly. Michael E. Mann, Zhihua Zhang, Scott Rutherford, Raymond S. Bradley, Malcolm K. Hughes, Drew Shindell, Caspar Ammann, Greg Faluvegi, Fenbiao Ni
http://www.sciencemag.org/content/326/5957/1256.short
http://www.sciencemag.org/content/326/5957/1256.full.pdf
Note Figure 2 – the top figures showing the temperature anomaly map of the world for the MCA (compared to the 1961 to 1990 period) ..and the weighted proxies on the right…to me it is an incredible construct:
Note all the blue (cooler than recent times) on the map.
However, there is warming indicated in the immediate area of the majority of the proxies!!
Starting in northern America we see a cluster of proxies – by the temperature anomaly map, all apparently warmer than now, except for one cooler site. Down to the Caribbean … neutral, but heavily weighted.
Peru, Ecuador, looks like it was warm there….
Back up to Greenland … a very warm spot…,
Across to Europe, only two proxies, one heavily weighted, but both warmer,
Across to northern Russia …one isolated proxy with an isolated warmer spot …
To central China, there is a cooler spot …then head a bit east in China..another very hot spot…
Then all the way down to Tasmania and New Zealand – Tasmania is cooler, NZ is warmer than now……
Back to Africa, 3 proxies, one cooler (and heavily weighted) and one very lightly weighted and warmer, and one neutral…
Then look at all the modeled cooling on the map … right across central Asia, based on only 4 proxies (!!), all of which were warmer except one…
ALL of the Southern Ocean, the southern Indian Ocean, and southern Atlantic oceans were supposedly much cooler, (based on Tasmania, and three proxies in Africa?!!)
All of the eastern Pacific is shown as cooler, … based on a string of proxies in the western Americas, which were mainly warmer, and perhaps those in eastern China ..which were warmer also?
Methinks perhaps the model was overtweaked.
Caption of Fig. 2. Reconstructed surface temperature pattern for MCA (950 to 1250 C.E.) and LIA (1400 to 1700 C.E.). Shown are the mean surface temperature anomaly (left) and associated relative weightings of various proxy records used (indicated by size of symbols) for the low-frequency component of the reconstruction (right). Anomalies are defined relative to the 1961– 1990 reference period mean.

Michael Cohen

Could someone help me to understand Steven Mosher’s sensitivity argument? If the delta T is some number that results from an unknown combination of forcings and feedbacks represented as an equivalent TOA forcing, how does that constrain sensitivity? How does he know what the net delta F was a thousand years ago?

And still they “deny” the MWP!

Mark Bofill

Michael Cohen says:
April 11, 2013 at 11:36 am
Could someone help me to understand Steven Mosher’s sensitivity argument? If the delta T is some number that results from an unknown combination of forcings and feedbacks represented as an equivalent TOA forcing, how does that constrain sensitivity? How does he know what the net delta F was a thousand years ago?
—————–
Michael,
As to the first question, I think he’s simply defining sensitivity that way. Not saying I’ve got a problem with that definition. As to the second, that’s the real question, yes. I don’t know.

@profitup10 –
The item your link refers to is aboiut the LAST thing we would want to say, if we want people of color to support the effort to discredit AGW. You want to repeal the 14th Amendment? Get real.
That item is a true display of rightwing craziness, right up there with and no different from the left’s craziness.

John Hall

Steven Mosher says:
April 11, 2013 at 8:25 am
“Bottomline: the bigger the swing between the MWP and the LIA, the HIGHER the sensitivity.
The bigger the swing in natural oscillations the higher our risk from anthro forcing”
Zero times Zero is still ZERO

Steven Mosher [April 11, 2013 at 8:25 am] says:
Bottomline: the bigger the swing between the MWP and the LIA, the HIGHER the sensitivity.
The bigger the swing in natural oscillations the higher our risk from anthro forcing.

Wait, what? That is illogical and easily disproved. Hypothetical: suppose there was a large impact event around 1400, one larger than Tunguska but obviously not a global killer (or if you prefer, a string of monster volcanic eruptions) and created a discernable 400 year LIA. In these cases, by definition your theory falls flat. Period.
The point is this, under that hypothetical impact/volcanic scenario the MWP to LIA sine wave is in fact a non-Anthro natural oscillation. So your quote, stated as fact, is patently ridiculous. It only exists in your modeling rationalizations.

Michael Cohen: Could someone help me to understand Steven Mosher’s sensitivity argument?
It is easy to explain. First, you assume the model used to transform your proxy measurements into temperature. Then you presume that the modeled delta T is due to a combination of forcings . Then you conjure a delta forcing and divide that into your modeled delta T and *poof* you have your scientifically and exactly calibrated sensitivity to be reported to n significant figures.
In other words you have a conjecture divided by a guess multiplied by a made up fudge factor that results in the value close to what you wanted to see in the first place. Said process and result being hidden in many pages of obtuse verbiage and irrelevant mathematical and statistical nonsense. In the event that doesn’t work, select and/or correct your data set until it does. Then lose both your corrections, selections, adjustments, models and the original data. Unfortunately, the same thing is generally done by both sides of the argument. It is anything but science. It only has to look sciency.
It is as always: everyone talks about the weather but no one can do anything about it but come in out of the rain, wind, and cold. The favorite cure by the alarmists, stopping the use of fossil fuels and insisting on replacing it with “alternative energy”, will have the same impact upon the weather as the human sacrifices of the Aztecs. There will be no measurable effect on the weather However, far more people will die as a result and likely already have which, I contend, was the goal of the alarmists from the get go.

Theo Goodwin

Steven Mosher says:
April 11, 2013 at 8:25 am
“Anthony he is not saying sensitivity is high DURING the MWP. he is noting this:
Have a look at the swing between the high of the MWP and the low of the LIA.
That is delta T.
Sensitivity is Delta T/ Delta F where F is change in forcing. Steve Mcintyre has also pointed this out. If you argue for a higher MWP you are basically arguing for a higher climate sensitivity.”
Your argument turns on a crucial ambiguity in the word “forcing.” You must distinguish between known and unknown forcings. Some forcings are known, such as aerosols from volcanoes. Most forcings are unknown; that is, we do not have a clue what caused the change in temperature.. There is a debate over the magnitude of the forcing from CO2.

Steve Mosher:
What are you talking about? GHGes had nothing to do with the MWP, so how can you conclude that climate sensitivity to radiatively active gases is “high” based on the MWP?
The system responds to any forcing in the manner that best achieves thermal-kinetic equilibrium. The solar wind, for example, dynamically perturbs the upper atmosphere via ozone depletion and the QBO/tropopause height, hence heavily affecting the behavior of the MJO through lower stratospheric warming/cooling, and thus provoking a direct response from the Hadley Cells, Angular Momentum, the Rossby wave train, tropical cloud cover, etc.
The manner in which the system would respond to increased GHGes is unknown.