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Climate Hustle

Icing the Medieval Warm Period

Posted on 4 March 2011 by Daniel Bailey

"It's cold out!"

Not strange to hear that during the winter, here in the Northern Hemisphere.  But strange to hear that raised as an objection in the warming world in which we live today.  How much warmer it's going to get and what are the related impacts is what science is currently debating.

One of the commonly raised objections from those who would have us debate even the existence of gravity is that "It was warmer in the Medieval Warm Period."  This is an innocent, but untrue, claim clearly unsupported by the available literature.  Indeed, Martín-Chivelet et al  reveals the 20th Century as the time with highest surface temperatures in Northern Spain in the last 4,000 years.

The Medieval Warm Period (MWP) was a period of supposedly warm climate during the early part of the past thousand years. How long it lasted, what areas were affected and even if it existed have been questioned.  Some areas seem to have been affected more by changes in precipitation than in temperature.

A study has been recently published which sheds new light on this debate.  Koch & Clague, in their paper Extensive glaciers in northwest North America during Medieval time, provide new evidence showing that several glaciers in western North America and elsewhere in the world advanced during Medieval time and that some of these glaciers achieved extents similar to those at the peak of the Little Ice Age, a very cold period many hundreds of years later.

What the authors' research finds is that these glacial responses could not have happened in a world with a climate similar to ours today. Indeed, recent studies (here and here) by Mauri Pelto show that glaciers without a consistent accumulation zone (where the glacier "packs on weight") will not survive.  This helps explain why today's glaciers (responding to today's warming world) are retreating to their smallest areas in many thousands of years, exposing their longer histories in the form of buried datable material for scientists like Koch & Clague to decode.

What this means for the MWP is that if summers were as warm then as today, glaciers globally should have retreated significantly.  Changes affecting glaciers around the world require global effects.  Since that did not happen, global temperatures then could only have been warm for a part of the MWP.

So what else could explain these glacier advances in a supposedly warm world?  The most likely answer is that changes in factors besides temperatures played a significant role.  Koch & Clague find a linked response between:

  • increased winter precipitation
  • changes in solar activity
  • changes in the El Niño/La Niña (a Pacific Ocean weather pattern affecting the entire globe) in response to variations in solar activity

As a result of these linked responses, Koch & Clague suggest that glaciers were able to advance during the MWP because warm regional areas were interrupted by periods of cooling, interspersed with variable patterns of precipitation.  Given the length and breadth of the information we now know, Koch & Clague make a substantial case that the MWP should be more aptly named the Medieval Climate Anomaly.



To glaciologist Mauri Pelto, for being kind enough to lend his perspectives and expertise.  To the many other contributing authors at Skeptical Science for their valued efforts as well.  Many thanks, all.

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Comments 1 to 50 out of 83:

  1. This is actually very interesting when you consider the fact that a civilization in South-Central America died out during the Medieval Period due to warming-as did the Khmer Empire-though several hundred years apart. I say that its interesting because the there was a similar dichotomy between Northern & Central temperatures as there was during the collapse of the Egyptian Old Kingdom. i.e. the equatorial regions of the world were gripped by an extended warm period, & attendant drought, whilst many of the northern latitudes were gripped by a relatively cold period. Of course this is yet another reason why we know that what caused these past two warming events is *not* what's causing warming now-because this time we're seeing a mostly globally homogeneous warming event.
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  2. Oh, correction, 2 Civilizations (The Anasazi & The Mayans) both died out during the Middle Ages-both due to extended drought which was believed to be caused by a regionally warming climate.
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  3. Was there a MWP in northwest North America ?

    Or was the MWP a local, European event ?
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    Moderator Response: [Daniel Bailey] The preponderance of evidence we have strongly suggests regional warming at various periods of time over several centuries that also coincided with regional cooling. Some areas warmed and others cooled. The area with best data for a localized, regional, warm period is in Europe. This period was also punctuated with brief colder periods where glaciers in the Alps underwent significant advancement. It was a complex climatic period. For more info, go here (both the Basic and Intermediate Versions). North America had warmer periods as well, but those were punctuated with extreme droughts.
  4. Daniel Bailey: I think the article should mention that the Martín-Chivelet et al study is for Iberian Peninsula only. If you want to go beyond the usual 2000-year reconstructions globally you should reference the borehole studies, for example.
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    Moderator Response: [DB] Thanks for the heads-up. I realized that after the fact, but forgot to update the text in the rush to publish. I'll fix it now.
  5. I'm guessing, Daniel, that those warmer periods you mentioned were the same as those I mentioned-the ones which wiped out the 2 big Meso-American civilizations of the day? The warming/drought that caused the end of the Egyptian Old Kingdom has been linked to a slowing of the Atlantic Conveyor (the one which causes the Gulf Stream)-which also caused Northern Europe to get cold. I wonder if something similar can explain the MWP?
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    Moderator Response: [DB] Possibly/probably. With the teleconnections being uncovered, ENSO changes in the Pacific Ocean seem to be driving subsequent "downstream" reactions and changes throughout the world. Obviously an area being looked at further; given what we now see happening in our warming world & the potential impacts discussed in Dai et al 2010 (discussed here), it's an area of critical importance.
  6. To get a better sense of the field sites and work by Koch and Clague take a look at Koch's research pages . Nice maps and photographs.
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  7. Tikal, Copan and other great Mayan city-states in the south did succumb to a combination of internecine warfare, over-population and drought induced crop failures in the 8-9th centuries, bringing the Classic Period to an end.

    That is a long way from destruction of Mayan civilization which survived in northern areas, notably Yucatan, where city-states such as Uxmal, Mayapan and Chechen Itza flourished into the 17th century. Their demise was at the hands of the Spanish, not climate change.

    Can prolonged droughts in Guatemala, Belize and Honduras in the 8-9th centuries be regarded as synonymous with the European MWP?
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  8. OK, so maybe I overstated the whole "destruction" thing in regards to the Maya, but it was used as an example of societal collapse in Jared Diamond's book of the same name-specifically where societies failed to adapt to changing environmental conditions & so hastened their own demise. Sorry if that's off-topic.
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  9. invicta

    It occurs to me that an area of the world that has a well documented dynastic cycle for at least two thousand years is China. I have never seen any references to any records from this area being used to support or deny claims for the MWP or similar globa v regional discussions.

    Are there people with knowledge of the cycles of dynastic rise and decline which do seem to have at least some links to natural disasters (famine Drought etc)?

    I have no specialist knowledge myself but would be fascinated to see some discussion of the subject in the appropriate place
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  10. Here are some paleoclimate studies from China.

    None of these are records from Chinese history, but nodern (non tree-ring) reconstructions.
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  11. "It's cold out!"... and I am suppose to believe it should be colder on average, and that the world would be better off if this were the case. As long as the price of fossil fuels is rising faster than the temperature, it's hard to imagine how winters of the future are going to be more confortable.
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  12. @Marcus
    Not so long ago in my TV - Professor L. Thompson - explaining the length of the Maya (more than 5 thousand. years) - his last end, he showed how in the Andean glaciers have advanced so quickly - it now - going back - glaciers reveal - frozen, “of unimpaired quality” plants ...

    Droughts - in this period of strong cooling (Neo-glacial) - covered most of the two continents of America. The same drought (cooling effect) destroyed the civilizations of the Sahara and Middle East.
    Stable isotopes of a subfossil Tamarix tree from the Dead Sea region, Israel, and their implications for the Intermediate Bronze Age, Frumkin, 2009.:
    “The Sedom Tamarix demonstrates a few hundred years of 13 C and 15 N isotopic enrichment, culminating in extremely high δ 13 C and δ 15 N values. Calibration using modern Tamarix stable isotopes in various climatic settings in Israel shows direct relationship between isotopic enrichment and climate deterioration, particularly rainfall decrease.” “This was apparently the most severe long-term historical drought that affected the region in the mid-late Holocene.”

    Lonie Thompson explained that the Atacama desert in the Quaternary, only once was inhabited by people - during MWA ...

    During the Roman maximum - period; around Masada was warmer and wetter - growing bushes Tamarix at the point where today it is a desert.
    Climatic effects on the δ 18 O and δ 13 C of cellulose in the desert tree Tamarix jordanis, Lipp et al., 1996.:
    “Since the Roman period, RH at Masada decreased by about 17% [!], while the δ 18 O value of local groundwater remained similar to present-day values, suggesting that changing atmospheric circulation has played a role in climate change in the Middle East over the past two millennia.”

    Polish scientist J. Zasadni, from the Institute of Geological Sciences, Jagiellonian University, who is preparing a doctoral thesis about shifting of glaciers in the Alps - Zillertal, after many years (and very precise) research - argues strongly that: in the days of ancient Rome and later - warming in the Middle Ages - expiring on the late fourteenth century, frequented alpine glaciers coverage certainly considerably smaller than today.
    LIA in the Alps ended only in 1950 ...
    Anasazi - “During the Pueblo II period, from 900-1100 CE, these designs were made even more bold, and the Anasazi (Hisatsinom) began to build kivas, or communal rooms for ceremonial purposes in their villages. Their population increased, and during this period small Anasazi villages began to spread throughout the southwest.”
    “During the Pueblo III period from 1100-1300 CE, the Anasazi (Hisatsinom) began to build the cliff dwellings for which they are most well-known. Many buildings in these villages under the cliffs were several stories tall.” „For unknown reasons, near the end of this period the western Anasazi (Hisatsinom) sites were completely abandoned, while the eastern sites continued to flourish and expand.”
    ... circa 1270-1300 - the beginning of the LIA in America ...
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  13. #The Inconvenient Skeptic

    ... a propos China I would add:
    Characteristics of cold–warm variation in the Hetao region and its surrounding areas in China during the past 5000 years, Li et al., 2010.: “1450 - 1000 cal yr BP: The climate was relatively warm compare with the temperature of its adjacent periods but less so than the degree of warmth at 5000 cal yr BP. This period corresponded to the Medieval Warm Period.”
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  14. The LIA in the alps did not end in 1950. That's a complete fallacy and is not supported by the literature at all. You might find one paper where a small portion advanced during that period but the fast majority of glaciers in the alps had their LIA between 1750 and 1850.
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  15. Hi,

    I don't think this is a argument against the MWP. Don't we actually have increasing glaciers in Norway, New Zealand and the Karakorum? Don't we have regions in the world, not getting warmer?

    I am writing about this on my post "Nicht alle Gletscher schrumpf(t)en" (Not all glaciers we/a-re melting)

    If you want to read more, take a look on my German blog:

    Feel free to post comments!!

    Willam of Baskerville

    Ps. I've made interviews on this topic - MWP - with scientists like Dr. Heinz Wanner, Dr. Ulf Büntgen, Frederic Ljungqvist and others.
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    Moderator Response: [DB] No one is suggesting that the warming of the globe will be a uniform or linear process. But it is indeed a global process, as you can see here:
  16. There are a few advancing glaciers, but most of the advances are quite limited and hence not overrunning developed forest vegetation. The evidence uncovered here is pretty systematic for the time periods noted in Table 1. The difference between a glacier advancing and disappearing like Helm Glacier, one of the sample sites is vast.
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    Moderator Response: [DB] Thanks, Mauri!
  17. I think that this publication speaks in a way that best condensed - all:
    Climatic fluctuations in the Central Region of Argentina in the last 1000 years, Cioccale, 1999.:

    “The Medieval Warm Period was characterized by a humid and warm climate in the plains and recession of the Andean glaciers. In contrast, during the Little Ice Age the plains had temperate, semi-arid to arid climates, and Andean glaciers advanced.

    The “fall” of civilization that (so far) is always cool - never warming.
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  18. @Robert Way

    I do not know all the work of J. Zasadni, perhaps this applies only to the Zillertal
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  19. [ -Edit: Complaints about moderation removed- ] However this post speaks directly to the relation between historic events and climate, a special interest for me.

    I applaud the author for providing several interesting links. After reading everything that was not behind a pay wall, I was encouraged to find that the Martín-Chivelet et al abstract claims clear correlations with ice core data and historical events such as the Roman and Medieval Warm Periods.

    Thank you for an excellent post Daniel Bailey although it does pretty much the opposite of what the title suggests. As Willam of Baskerville says this is not an argument against the MWP. For example, here is the concluding paragraph from Matin-Chivelet et. al:

    "Spectral analysis of the time series shows consistent climatic cycles of ~ 400, ~ 900 and ~ 1300 yr, comparable with those recognized in the North Atlantic marine record, the Greenland ice cores, and other terrestrial records for the middle – late Holocene, suggesting common climate forcing mechanisms related to changes in solar irradiance and North Atlantic circulation patterns."
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    Moderator Response: [DB] Actually, all the data we have shows that the MWP to not be an analog for modern warming in both scope and degree. In addition, the available data shows the MWP to be a heterogeneous mix of cooling, warming and drought over similarly varied geographic and temporal areas. And what warming data there is for the MWP shows it to fall short of the warming of the last 30 years, which is now comparable to levels last achieved in the Holocene Altithermal.
  20. ... a propos Anasasi - generally: the drought in MWP. From the papers cited here:

    Land surface temperature changes in Northern Iberia since 4000 yr BP, based on δ13C of speleothems, Martín-Chivelet et al., 2011.:
    - “... 1350–750 yr BP warm period (Medieval Warm Period) punctuated by two cooler events at ~ 1250 [!] and ~ 850 yr BP ...”

    The same can be seen and here: Ababneh, 2006.

    Hence the declaration: “This drought marks the middle of the Medieval Warm Period - an interval of warmer temperatures between approximately AD 800-1300 characterized by greater drought duration and frequency in the Northern Great Plains compared to more modern times.” by Stambaugh et al., 2011.; does not give decisive argument to statements: drought = MWA - even regionally.
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  21. There have been a lot of discussions about the spatio-temporal pattern of the Medieval Warm Period in the last two decades. But the statements, often made, that the evidence for a Medieval Warm Period is most clear in Europe simply does not hold true. The evidences are in fact even better, and more numerous, from China. Also, the data from Greenland are quite good. I do not know why the Chinese scholarship, mostly published in English, so often are overlooked in the context of the Medieval Warm Period. This is a pity! The second half of the 10th century was pretty warm, well above the 1961–1990 mean, in most regions in the extra-tropical Northern Hemisphere where we have data (China, Europe, Greenland, Alaska, and Siberia). The data from the tropics and Southern Hemisphere still too spare to say anything certain still about the amplitude and extent of the Medieval Warm Period compare to the recent warming. What we do know is that it was synchronically warm in Greenland, Europe and China, and Siberia as well as, probably, over large parts of North America, c. AD 950–1050. Only this time interval shows evidence of coherent warm conditions in multiple regions. Later in medieval times (and earlier) the conditions were more geographically heterogeneous although quite similar still in Europe and China.
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    Moderator Response: [Daniel Bailey] Thank you for taking the time to share your perspectives and expertise, Dr. Ljungqvist. An expert's presence is always welcome here.
  22. @ DB
    "No one is suggesting that the warming of the global will be a uniform or linear process. But it is indeed a global process, as you can see here"

    If it is ok for the current warming not to be a uniform or linear process, why it is/was not ok for the so called MWP?

    I am convinced that the MWP was at least a bi-hemispheric event. Unfortunately we have not enough data to give information about the existence of a "MWP" in the equatorial areas of the world. I have listed some in my post:

    For me there is no doubt at all that we have hundreds of pr-papers affirming the claim of H. Lamb for the Northern Hemisphere. Even scientists, sceptical towards the terminus "MWP" say that "mean temperatures during this interval were warmer than the subsequent Little Ice Age" (P.e. Crowley, Lowery: How Warm Was the Medieval Warm Period?, in: Ambio, Vol. 29 No 1, Feb. 2000, 54).

    We have also evidence for the existence of a MWP in Southern America, Africa, the Antarctica and New Zealand.

    On the other hand it looks like that there's a broad consent within scientific community that the LIA was a global event (p.e. Wanner 2008; the newest paper by Lane et al.: Oxygen isotope evidence of Little Ice Age aridity on the Caribbean slope of the Cordillera Central Dominican Republic. They write: "Climate change during the so-called Little Ice Age (LIA) of the 15th to 19th centuries was once thought to be limited to the high northern latitudes, but increasing evidence reflects significant climate change in the tropics").

    If we accept that the LIA was a global event and, as Wanner wrote, one of the coldest periods within the last several thousand years, we have imho to accept that the temperatures at the foregoing time period were warmer than they were in the LIA too. Why don`t call it MWP like Lamb called it?

    For me one thing is clear. If you don`t accept the MWP as a warm period you can't accept the current warm period as a warm period either. As I said before, there are glaciers increasing in the Karakorum, in Norway and New Zealand even in Argentina. Don`t you know that the highest temperatures in Scandinavia were in the 30 and 40s of the 20th century?

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    Moderator Response: [DB] Please read this post and then this post for background on the Medieval Warm Period. If you then still maintain the MWP was a global phenomenon, continue that conversation there. For posterity and context, current northern hemisphere temps greatly exceed those of the MWP:
    Northern Hemisphere Temperature Reconstruction by Moberg et al. (2005) shown in blue, Instrumental Temperatures from NASA shown in Red
  23. williambaskerville, a quick Google found this WIKIPEDIA page which states that, in Denmark, July 2006 was the warmest July ever and the second highest temperature ever recorded there - only beaten by August 1997.
    It also states that Sweden's highest daily average temperatures were in 1994 although, indeed, the highest individual temperature readings were in 1947 and 1933.
    It also states that many high temperature records were broken over many parts of Central and Southern Finland.

    What are you trying to prove ?
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  24. Moderators:
    1. Where did you get / how did you prepare the graphic in # 15? Could you also show the same but using, say, a 1959-1980 baseline vs 2000-2010?
    2. Given the ability of Skeptical Science to present and clarify global climate, have you thought of a time series of the MWP? In other words, in a certain period of 50 to 100 years the MWP was in South America, then in the Caribbean, at another time in Europe, and at these times other regions were perhaps cool. Some newer temperature series (single spot 'hockey sticks') that have been mentioned here would be useful for this project.
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    Moderator Response: [DB] That is a NASA graphic for which I lost the link (irritating, yes). However, I was able to quickly find that version on (they added the obvious text, but the rest of the graphic matched my aging memory). I'll try & track down the exact NASA link. If you go to here you can create this output: The rest of your suggestion, while intriguing, would amount to repudiating a Gish Gallop, in my opinion.
  25. Concerning Scandinavian temperature:

    It is only in the northern part of Scandinavia that temperatures were about as high in the 1930s and 1940s as in the post-1990 period. In southern Scandinavia the last two decades have been generally warmer than the 1930s and 1940s.
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  26. TIS & AS thanks for the links I'll get reading
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  27. @ JMurphy
    Don't be aggressive, Mr. Murphy. Infact it is maybe true that my statement is correct only for the norhern part of Scandinavia. Even if Dr. Büntgen in my interview told me:

    "Speziell sei noch darauf hingewiesen, dass gerade aus Skandinavien die vielleicht besten regional-scale summer, i.e. June-August temperature reconstructions based on annually measurements of conifer maximum latewood density kommen. Eine Divergenz zwischen ansteigenden Sommertemperaturen und geringerem Jahrringwachstum ist in Skandinavien eh kein Thema, da die höchsten Temperaturen in den 1930er Jahren lagen (der Sommer von 1937 war extrem warm)."

    Unless that, my argument is still correct. What do I want to proof? Nothing. I only add my opinion on the MWP and it's extend.

    @ Moderator
    Thank's I'll do so.
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  28. William B: "there are glaciers increasing"

    That statement holds little meaning on the global basis. Isolated increasing glacier references can indeed be found, but the entire picture is negative:

    Annual mass balance at World Glacier Monitoring Project
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  29. Pete Dunkelberg #24

    Maybe this post about a Mann 2009 paper can be a partial answer to your second question. It's not really a time series, but two snapshots: one of the MWP temp averages over the world, and one of the Little Ice Age.

    You can see there many cold spots during the MWP.
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  30. william - it is common to quote that two valley glaciers are advancing as evidence that its cold in NZ. In fact those two are in long term retreat but advance/retreat with ENSO-driven changes in snow. Virtually all the rest of NZ glaciers are in retreat, mostly very rapid retreat. Picking one or items is Cherry Picking. Look at the overall picture.

    As for opinion on MWP - opinions are worthless unless based on data. For more complete picture of MWP globally, then try here. Note the marked variations when you put it all together.
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    Moderator Response: [DB] Good points, all. Alpine glacier advance is a function of temperature and precipitation in the accumulation zone, with terrain and slope a modifying variable. Thus, it is quite conceivable for a few NZ glaciers to be advancing in a warmer world even though the vast majority are receding. Saying otherwise is to simply be in denial.
  31. @ muoncounter
    "That statement holds little meaning on the global basis. Isolated increasing glacier references can indeed be found, but the entire picture is negative"

    So what? You did obviously not get my argument. We can turn your statement on the LIA and the MWP too.

    In the LIA glaciers were increasing on a global basis but some were decreasing and in the MWP the same vice versa. This does not mean that the LIA was not a global phenomenon and one of the coldest periods within the last several thousand years.

    This does also not contradict my opinion on the MWP as a bi-hemispheric phenomenon (for some the evidence for the Southern Hemisphere ist not "good" enough for this statement but ever since I've gone through papers of Lara, Villalba (1990a, b), Villalba (1994), Stine (1994), Thompson et al. (2000, 2006), Boninsegna et al. (2009), Ljungqvist (2009), von Gunten (2009 - Inauguraldissertation), von Gunten et al. (2009), Moy et al. (2009-Springer) and Neukom et al. (2010) on the (southern) South America and Huffman, Holmgren, Holmgren 2003, Holmgren and Öberg 2006, Robertshaw and Taylor 2000, Tierney et al, Lamb et al. 2007, Verschuren et al. 2000 and Ngomanda et al. 2007, for Africa, I am quite sure for this part too).

    Within the MWP - for South America more specific "the late Medieval Warmperiod" mean temperatures were warmer than in the LIA. Of course this does not mean that the mean temperatures in Europe in contrast to the temperatures of the subsequent LIA in Europe have to be the same in Africa. It depends on the region.
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  32. No, I got your argument entirely. I agree with your "LIA glaciers were increasing on a global basis," signifying a cold period.

    I took your earlier statement to suggest that the presence of a few 'increasing' glaciers today, along with a reference to warmer temps in the '30s and '40s, to mean that we are not in a global warm period. Most glaciers today are not increasing, as shown by the WGMP mass balance.

    The question is hardly a comparison of MWP vs. LIA; it seems to be comparison of MWP vs. the current warm period.
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  33. @ scaddemp
    "As for opinion on MWP - opinions are worthless unless based on data. For more complete picture of MWP globally, then try here."

    My opinions are based on data. Quite ignorant your post. Maybe you take a look on the reconstructions listed on the NOAA or my summary on mittelalterlichewarmperiode and then you get a better understanding :)

    @ muoncounter
    ".. it seems to be comparison of MWP vs. the current warm period."

    Yes, indeed. I don't know if medieval temperatures were warmer than the temperatures are today.

    I say, you can't count some glacier advances in the MWP against a MWP but on the other hand some glacier advances today not as an argument against a current Warm Period. To say: We have global warming now contra Northern Hemispheric Warming at medieval times is no argument in this case.

    If we had a global LIA we also had a global MWP with regional differences in warming, as we see them today. If there was no global LIA there was (at least) a bi-hemispheric MWP. Btw if the sun was the main factor in past, medieval warming, this would be an argument for a global MWP, as Dr. Büntgen stated:

    Gehen Sie von den möglichen Steuergrößen aus. Was bleibt übrig? Alles läuft auf dieser Skala auf die Sonne hinaus. Wenn dem so ist, müsste man sicher von einer globalen Anomalie ausgehen dürfen; natürlich durch interne Oszillationen modifiziert

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  34. Fredrik Charpentier Ljungqvist at 02:14 AM on 5 March, 2011

    Dr. Ljungqvist,
    would you not agree however that your reconstruction of the extra-tropical northern hemisphere demonstrated that the temperatures are currently above those during the warmest decades of the MWP. I have often wondered why your 1990s decade shows lower temperatures than the 1980s and correspondingly why the instrumental record for the 2000s was not plotted. Nevertheless I would wonder if perhaps results might differ if tree rings (33% of the reconstruction) were not included because they tend to have issues with low frequencies.

    Either way I do agree that proxy data from the southern hemisphere is too sparse for global reconstructions but examples of attempts such as from Huang et al (2008)

    do demonstrate current global warmth exceeding the warmth during the MWP.
    Furthermore when we think of the most sensitive of indicators of climate change ice caps are undoubtedly amongst the most sensitive. Evidence from Anderson et al (2008) demonstrate that ice cap recession on baffin island is beyond any period over the last 1700 years. Although the results of this study are of a low temporal resolution, conclusions such that ice cap recession is unprecedented over at least the last 1700 years are assured.

    Each individual study obviously has their pitfalls but I do find it challenging that using annually to decadally resolved proxies for reconstructions are the only way of determining the magnitude of MWP to CWP comparisons. Perhaps Moberg's wavelet method is a plausible solution?
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    Moderator Response: [DB] Enabled in-line graphic.
  35. Another interesting paper using low resolution proxies is Viau et al (2006) which is based on pollen records and reconstructs temperatures similar to the MWP for up to 1950.
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    Moderator Response: [DB] Enabled in-line graphic.
  36. I recall a controversy over the McShane/Wynter (sp?) paper trying to show the confidence for the 1990s being the warmest decade.

    Does Martín-Chivelet et al effectively refute their claim that there was a relatively low confidence that the 90s were the warmest of the last 2000 years (at least for Spain)?

    Please, I am not asking for a rehash, just to understand if we are more or less past McShane.
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  37. What I argue is that you cannot take isolated pieces of data and draw conclusions. The paper I pointed to did that and all proxy data used in supplementary data. Can you explain why you think the methodology used for regional reconstruction of temperatures in that paper is flawed compared to yours?

    As to global - I agree that LIA appears to be global. However, it also appears to have been much stronger in NH than in SH based on the patterns of glaciations in both. (Unfortunately papers on this at work).
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  38. Mcshane and Wyner had about 8 comments on their study by climatologists, many found substantial errors. Mann et al (2010) in their response found that Mcshane and Wyner should have concluded based upon proper analysis that there was an 86% probability that the 10-year period from 1997-2006 was the warmest on record.
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  39. I would add further comment on glacier's as a climate proxy (though Mauri could say more). Glacier response varies depending on quite a number of variable. NZ West Coast valley glaciers in deep shaded valleys response to snowfall is marked. They have further complication that rock load from valley sides protect the ice from melting so may respond to earthquakes (increasing rock cover) as well.

    A better determination is done by looking at glacier system as a whole, or chosing glacier locations where response in highly dependent on terminal temperature. Either way, NZ is warming (as temperature records would also show), as is Argentina. Whether other glacier record in Asia support or defy a MWP cannot be taken in isolation without either surveys of larger system or data on response.
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  40. scaddenp -Virtually all the rest of NZ glaciers are in retreat, mostly very rapid retreat. Picking one or items is Cherry Picking. Look at the overall picture.

    You mean like this overall picture Phil?.

    See NIWA
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  41. @ Robert Painting
    Very interesting picture - especially the periods 1979-1981, 1982-1987, 1988-1989, 1990-1997, 2000-2001, 2002-2005 and 2006-2007.
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  42. Williambaskerville - that's nuthin. The Franz Joesph glacier (a tourist spot) info centre has a number of photos of the glacier dating back over a hundred years. Despite periods of advance the long-term retreat of the glacier is spectacular. When you walk to the glacier face, there are pegs marking where the face/front used to be at a particular time in the past.

    I can't find copies online but here's an indication:

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  43. scaddenp at 08:30 AM on 5 March, 2011

    Individual glaciers as a proxy can be dubious but widespread changes are a good indicator of climatic changes. Furthermore, ice caps in the high arctic such as those mentioned previously by me are extremely sensitive to climatic changes with a small climatic change soliciting a large response.
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  44. I think Williambaskerville as a point. Looking at the moderator's response @24, it is clear that the entire eastern Siberian peninsular was cooler in the 2000's than during the period from 1959 to 1980. No one here would want to argue from that that the world has not warmed during the interval.

    From the article, I gather there is firm evidence that Spain, and a significant area of the Rocky Mountains is much warmer now then during the MWP. However, this is again just regional evidence. We should not argue from just two regions that global temperatures in the MWP were significantly lower than current temperatures. In that much, WB is right.

    He does not help his case, however, by his clear propensity to cherry pick, as by using individual glaciers rather than data from glaciers for a particular region. And his comments @41 are just silly. (On a side note, posting German (?) quotes on an English speaking site without translation is both discourteous and unhelpfull.)

    Nor does he help his case be ignoring the fact that reconstructions of past hemispheric or global temperatures consistently show peak MWP temperatures equivalent in some decade in the period 1950-2000, with modern temperatures clearly exceeding that range. That is not a slam dunk for a cooler MWP once error bars are taken into account, but it does show that a cooler MWP is more likely than not on current evidence, and possibly even likely in IPCC parlance ( > 66% probability).

    What I do not understand is the rhetorical battle over the MWP. If peak global temperatures during the MWP were 0.5 degrees C greater than at present, what would it matter. The presumed forcings of the MWP are still absent today; and global temperatures are expected to rise by 6 to 8 times that on conservative estimates. The denier focus on the MWP seems to me to be futile point scoring based on an attempt to cultivate ignorance.
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  45. I will clarify the glacier issue in New Zealand, since I live there. There have been short term periods of advance of most glaciers as in 1990, which has now turned into an extended retreat.

    Over the last 100 years the trend is most glaciers are retreating, or a nett decrease in ice mass. From NIWAS website

    "Despite the sensitivity of New Zealand glaciers to changes in both precipitation and temperature, the volume of ice in the Southern Alps dropped by roughly 50% during the last century. New Zealand’s temperature increased by about 1 °C over the same period."
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  46. The time period (say, 1910 to the present) of current warming (global or hemispheric) obviously can be well defined. The same cannot be said for the skeptic's proposed warmer 'MWP'.
    How coterminous are their geographical data points?
    Which century is favored?

    Increasing snowfall (and its timing) explains many of the anomalously advancing glaciers. This is the explanation for the Karakoram glaciers that are growing, while the Himalayan glaciers are retreating.
    Some high latitude glaciers can benefit from the increased water vapor in the atmosphere, picked up over warmer oceans.
    And, as I remember it, Mt. Shasta glaciers in California benefit from both El Nino weather south of it, and La Nina weather north of it.
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  47. @ Tom Curtis
    "He does not help his case, however, by his clear propensity to cherry pick, as by using individual glaciers rather than data from glaciers for a particular region. And his comments @41 are just silly."

    What is my case? You've got the point in "I think ..." and "From ..." It is not a "Cherry Picking" at all. "Regional evidence" is the point. If you take it as an evidence on case A but not on case B. That is "Cherry Picking"! I only wanted to show that.

    "And his comments @41 are just silly. (On a side note, posting German (?) quotes on an English speaking site without translation is both discourteous and unhelpfull.)"

    The comments aren't silly at all. If Scaddenp argues "virtually all the rest of NZ glaciers retreat", and Rob Painting does post a picture to confirm, than I have imho the right to point out that in several years within the period 1977-2009 the glaciers advanced. The same right for all!

    Btw it is not my task to translate interviews. Google is in general a good "thing", I've learned from the post of Mr. Murphy, so why can`t you take a google-translator? Is it to silly to do so?

    My point is not that a MWP was warmer than the current WP. OK?
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  48. WB, your "point" is that there are regionally cooling areas in the modern warm period, so that identifying regionally cooling areas in the 10th and 11th centuries does not disprove the existence of a global MWP. I think that point is valid, as I have said.

    However, you identify as one of your regionally cooling regions New Zealand. As it happens, NZ has been warming over the course of the 20th century, and over that period its glaciers have been retreating, with some short duration exceptions. Therefore picking on NZ as one of your cooling regions on the basis of just one or two glacier records for only decade (instead of the whole century) is cherry picking. If you don't like the term, don't do it.

    Seeing a graph that obviously shows an overall decline in and then picking out just those sections of the graph which show an increase in mass balance is very silly. It is cherry picking when the refuting evidence is directly in front of us, and can only make the person who does it look a fool. Either you have a bizzare straw man view of global warming that says that all temperature rises, or glacial retreats will be monotonic; or you suffer under the mistaken notion that Koch and Clague only show occasional decades of glacier expansion against a backdrop of centuries long decline (rather than the reverse as they claim); or by pointing out short periods of increase against a backdrop of overall decline, you are cherry picking.

    Finally, you are apparently a German speaker. If you were not, then presenting an untranslated German text as evidence would be simple foolishness for you would not know what it means. As a German speaker, with evidently reasonable English skills translating the text should be no problem to you. If, however, you think the text is so unimportant that the Google translator can be trusted to give its sense, then I will take that assessment at its face value, and not bother. Anything whose sense is so unimportant that it can be trusted to google is not worth reading.

    (Your refusal to translate the German passages is a fair indication that you are merely making an implicit appeal to authority. It is the "Dr" in front of the name that is evidently important, not what they said, which you cannot be bothered conveying to us.)
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  49. #15 williambaskerville:

    I did read one recent paper on Himalayan glaciers in Karakoram. It was widely reported as 'Himalayan glaciers growing' (although the Telegraph have now changed their title on that article as far as I can see).

    This paper looked only at area changes, and isn't a proper mass balance. But changes in accumulation might be increasing their volume there. Maybe.

    In terms of area, more than half were expanding there, but the mean change in area was negative i.e. total area went down in Karakoram.

    The data is available if you look in the supplementary material, I decided to check for myself after all the popular media rants about how they were growing...

    williambaskerville at 22:49 PM on 4 March, 2011

    I don't think this is a argument against the MWP. Don't we actually have increasing glaciers in Norway, New Zealand and the Karakorum? Don't we have regions in the world, not getting warmer?
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  50. In the United States we have had a very severe recession over the last 30 months. The vast majority of companies had layoffs and suffered financial losses, a number went out of business. That a few companies continued to grow is not evidence there was not a recession. The same holds for glaciers. Almost all are losing considerably volume, some are disappearing, a very few are not losing volume. The glacier volume loss is global and a strong indicator of global warming. The glaciers advancing noted by Koch and Clague are sufficient in number to indicate that they are not the small anomaly of today's advancing glaciers. The advances were also large enough to advance well beyond their former margin, that is not happening anywhere today. Again look at the synchronous response of northwestern North America glaciers in terms of mass balance change, and how this curve looks like the global signal, Rainbow Glacier charts near bottom. The latter graph I just submitted this week for BAMS State of Climate Report 2010, for the glacier section.
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