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Observations of anthropogenic global warming

Papers on the MWP as Global Event

Posted by Ari Jokimäki on September 8, 2009

This list contains papers on the medieval warm period (MWP) with emphasis on global analysis. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

UPDATE (April 22, 2013): Ahmed et al. (2013) added.
UPDATE (April 5, 2012): Diaz et al. (2011) added. Thanks to Barry for pointing it out in papers on reconstructions of modern temperatures.
UPDATE (February 9, 2012): Goosse et al. (2012) added.
UPDATE (January 6, 2012): Zhou et al. (2011) added.
UPDATE (September 20, 2011): Koch & Clague (2011) added. Thanks to Barry for pointing it out, see the comment section below.
UPDATE (June 17, 2011): Graham et al. (2010) added.
UPDATE (August 19, 2010): Ljungqvist (2009) added, thanks to Darius for pointing it out (see the comment section below).
UPDATE (May 17, 2010): Trouet et al. (2009) added.
UPDATE (January 20, 2010): Osborn & Briffa (2006) added.

Continental-scale temperature variability during the past two millennia – Ahmed et al. (2013) “Past global climate changes had strong regional expression. To elucidate their spatio-temporal pattern, we reconstructed past temperatures for seven continental-scale regions during the past one to two millennia. The most coherent feature in nearly all of the regional temperature reconstructions is a long-term cooling trend, which ended late in the nineteenth century. At multi-decadal to centennial scales, temperature variability shows distinctly different regional patterns, with more similarity within each hemisphere than between them. There were no globally synchronous multi-decadal warm or cold intervals that define a worldwide Medieval Warm Period or Little Ice Age, but all reconstructions show generally cold conditions between ad 1580 and 1880, punctuated in some regions by warm decades during the eighteenth century. The transition to these colder conditions occurred earlier in the Arctic, Europe and Asia than in North America or the Southern Hemisphere regions. Recent warming reversed the long-term cooling; during the period ad 1971–2000, the area-weighted average reconstructed temperature was higher than any other time in nearly 1,400 years.” Moinuddin Ahmed, Kevin J. Anchukaitis, Asfawossen Asrat, Hemant P. Borgaonkar, Martina Braida, Brendan M. Buckley, Ulf Büntgen, Brian M. Chase, Duncan A. Christie, Edward R. Cook, Mark A. J. Curran, Henry F. Diaz, Jan Esper, Ze-Xin Fan, Narayan P. Gaire, Quansheng Ge, Joëlle Gergis, J Fidel González-Rouco, Hugues Goosse, Stefan W. Grab, Nicholas Graham, Rochelle Graham, Martin Grosjean, Sami T. Hanhijärvi, Darrell S. Kaufman + et al. Nature Geoscience(2013), doi:10.1038/ngeo1797.

The role of forcing and internal dynamics in explaining the “Medieval Climate Anomaly” – Goosse et al. (2012) “Proxy reconstructions suggest that peak global temperature during the past warm interval known as the Medieval Climate Anomaly (MCA, roughly 950–1250 AD) has been exceeded only during the most recent decades. To better understand the origin of this warm period, we use model simulations constrained by data assimilation establishing the spatial pattern of temperature changes that is most consistent with forcing estimates, model physics and the empirical information contained in paleoclimate proxy records. These numerical experiments demonstrate that the reconstructed spatial temperature pattern of the MCA can be explained by a simple thermodynamical response of the climate system to relatively weak changes in radiative forcing combined with a modification of the atmospheric circulation, displaying some similarities with the positive phase of the so-called Arctic Oscillation, and with northward shifts in the position of the Gulf Stream and Kuroshio currents. The mechanisms underlying the MCA are thus quite different from anthropogenic mechanisms responsible for modern global warming.” Hugues Goosse, Elisabeth Crespin, Svetlana Dubinkina, Marie-France Loutre, Michael E. Mann, Hans Renssen, Yoann Sallaz-Damaz and Drew Shindell, Climate Dynamics, DOI: 10.1007/s00382-012-1297-0.

Spatial and Temporal Characteristics of Climate in Medieval Times Revisited – Diaz et al. (2011) “Developing accurate reconstructions of past climate regimes and enhancing our understanding of the causal factors that may have contributed to their occurrence is important for a number of reasons; these include improvements in the attribution of climate change to natural and anthropogenic forcing, gaining a better appreciation for the range and magnitude of low-frequency variability and previous climatic regimes in comparison with the modern instrumental period, and developing greater insights into the relationship between human society and climatic changes. This paper examine upto- date evidence regarding the characteristics of the climate in medieval times (A.D. ~950–1400). Long and high-resolution climate proxy records reported in the scientific literature, which form the basis for the climate reconstructions, have greatly expanded in the last few decades, with greater numbers of sites that now cover more areas of the globe. Some comparisons with the modern climate record and discussion of potential mechanisms associated with the patterns of medieval climate are presented here, but our main goal is to provide the reader with some appreciation of the richness of past natural climate variability in terms of its spatial and temporal characteristics.” Diaz, Henry F., Ricardo Trigo, Malcolm K. Hughes, Michael E. Mann, Elena Xoplaki, David Barriopedro, 2011: Spatial and Temporal Characteristics of Climate in Medieval Times Revisited. Bull. Amer. Meteor. Soc., 92, 1487–1500. doi: http://dx.doi.org/10.1175/BAMS-D-10-05003.1. [Full text]

A comparison of the Medieval Warm Period, Little Ice Age and 20th century warming simulated by the FGOALS climate system model – Zhou et al. (2011) “To compare differences among the Medieval Warm Period (MWP), Little Ice Age (LIA), and 20th century global warming (20CW), six sets of transient and equilibrium simulations were generated using the climate system model FGOALS_gl. This model was developed by the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences. The results indicate that MWP warming is evident on a global scale, except for at mid-latitudes of the North Pacific. However, the magnitude of the warming is weaker than that in the 20th century. The warming in the high latitudes of the Northern Hemisphere is stronger than that in the Southern Hemisphere. The LIA cooling is also evident on a global scale, with a strong cooling over the high Eurasian continent, while the cooling center is over the Arctic domain. Both the MWP and the 20CW experiments exhibit the strongest warming anomalies in the middle troposphere around 200–300 hPa, but the cooling center of the LIA experiment is seen in the polar surface of the Northern Hemisphere. A comparison of model simulation against the reconstruction indicates that model’s performance in simulating the surface air temperature changes during the warm periods is better than that during the cold periods. The consistencies between model and reconstruction in lower latitudes are better than those in high latitudes. Comparison of the inter-annual variability mode of East Asian summer monsoon (EASM) rainfall during the MWP, LIA and 20CW reveals a similar rainfall anomalies pattern. However, the time spectra of the principal component during the three typical periods of the last millennium are different, and the quasi-biannual oscillation is more evident during the two warm periods. At a centennial time scale, the external mode of the EASM variability driven by the changes of effective solar radiation is determined by the changes of large scale land-sea thermal contrast. The rainfall anomalies over the east of 110°E exhibit a meridional homogeneous change pattern, which is different from the meridional out-of-phase change of rainfall anomalies associated with the internal mode.” TianJun Zhou, Bo Li, WenMin Man, LiXia Zhang and Jie Zhang, Chinese Science Bulletin, Volume 56, Numbers 28-29, 3028-3041, DOI: 10.1007/s11434-011-4641-6. [Full text]

Extensive glaciers in northwest North America during Medieval time – Koch & Clague (2011) “The Medieval Warm Period is an interval of purportedly warm climate during the early part of the past millennium. The duration, areal extent, and even existence of the Medieval Warm Period have been debated; in some areas the climate of this interval appears to have been affected more by changes in precipitation than in temperature. Here, we provide new evidence showing that several glaciers in western North America advanced during Medieval time and that some glaciers achieved extents similar to those at the peak of the Little Ice Age, many hundred years later. The advances cannot be reconciled with a climate similar to that of the twentieth century, which has been argued to be an analog, and likely were the result of increased winter precipitation due to prolonged La Niña-like conditions that, in turn, may be linked to elevated solar activity. Changes in solar output may initiate a response in the tropical Pacific that directly impacts the El Niño/Southern Oscillation and associated North Pacific teleconnections.” Johannes Koch and John J. Clague, Climatic Change, Volume 107, Numbers 3-4, 593-613, DOI: 10.1007/s10584-010-0016-2.

Support for global climate reorganization during the “Medieval Climate Anomaly” – Graham et al. (2010) “Widely distributed proxy records indicate that the Medieval Climate Anomaly (MCA; ~900–1350 AD) was characterized by coherent shifts in large-scale Northern Hemisphere atmospheric circulation patterns. Although cooler sea surface temperatures in the central and eastern equatorial Pacific can explain some aspects of medieval circulation changes, they are not sufficient to account for other notable features, including widespread aridity through the Eurasian sub-tropics, stronger winter westerlies across the North Atlantic and Western Europe, and shifts in monsoon rainfall patterns across Africa and South Asia. We present results from a full-physics coupled climate model showing that a slight warming of the tropical Indian and western Pacific Oceans relative to the other tropical ocean basins can induce a broad range of the medieval circulation and climate changes indicated by proxy data, including many of those not explained by a cooler tropical Pacific alone. Important aspects of the results resemble those from previous simulations examining the climatic response to the rapid Indian Ocean warming during the late twentieth century, and to results from climate warming simulations—especially in indicating an expansion of the Northern Hemisphere Hadley circulation. Notably, the pattern of tropical Indo-Pacific sea surface temperature (SST) change responsible for producing the proxy-model similarity in our results agrees well with MCA-LIA SST differences obtained in a recent proxy-based climate field reconstruction. Though much remains unclear, our results indicate that the MCA was characterized by an enhanced zonal Indo-Pacific SST gradient with resulting changes in Northern Hemisphere tropical and extra-tropical circulation patterns and hydroclimate regimes, linkages that may explain the coherent regional climate shifts indicated by proxy records from across the planet. The findings provide new perspectives on the nature and possible causes of the MCA—a remarkable, yet incompletely understood episode of Late Holocene climatic change.” N. E. Graham, C. M. Ammann, D. Fleitmann, K. M. Cobb and J. Luterbacher, Climate Dynamics, DOI: 10.1007/s00382-010-0914-z. [Full text]

Global Signatures and Dynamical Origins of the Little Ice Age and Medieval Climate Anomaly – Mann et al. (2009) “Global temperatures are known to have varied over the past 1500 years, but the spatial patterns have remained poorly defined. We used a global climate proxy network to reconstruct surface temperature patterns over this interval. The Medieval period is found to display warmth that matches or exceeds that of the past decade in some regions, but which falls well below recent levels globally.” [Link to PDF]

Centennial Variations of the Global Monsoon Precipitation in the Last Millennium: Results from ECHO-G Model – Liu et al. (2009) “The authors investigate how the global monsoon (GM) precipitation responds to the external and anthropogenic forcing in the last millennium by analyzing a pair of control and forced millennium simulations with the ECHAM and the global Hamburg Ocean Primitive Equation (ECHO-G) coupled ocean–atmosphere model. … Conversely, strong GM was simulated during the model Medieval Warm Period (ca. 1030–1240). … The simulated change of GM in the last 30 yr has a spatial pattern that differs from that during the Medieval Warm Period, suggesting that global warming that arises from the increases of greenhouse gases and the input solar forcing may have different effects on the characteristics of GM precipitation.”

Persistent Positive North Atlantic Oscillation Mode Dominated the Medieval Climate Anomaly – Trouet et al. (2009) “The Medieval Climate Anomaly (MCA) was the most recent pre-industrial era warm interval of European climate, yet its driving mechanisms remain uncertain. We present here a 947-year-long multidecadal North Atlantic Oscillation (NAO) reconstruction and find a persistent positive NAO during the MCA. Supplementary reconstructions based on climate model results and proxy data indicate a clear shift to weaker NAO conditions into the Little Ice Age (LIA). Globally distributed proxy data suggest that this NAO shift is one aspect of a global MCA-LIA climate transition that probably was coupled to prevailing La Niña–like conditions amplified by an intensified Atlantic meridional overturning circulation during the MCA.” [Full text]

Temperature proxy records covering the last two millenia: a tabular and visual overview – Ljungqvist (2009) “Here, the first systematic survey is presented, with graphic representations, of most quantitative temperature proxy data records covering the last two millennia that have been published in the peer-reviewed literature. In total, 71 series are presented together with basic essential information on each record. This overview will hopefully assist future palaeoclimatic research by facilitating an orientation among available palaeotemperature records and thus reduce the risk of missing less well-known proxy series. The records show an amplitude between maximum and minimum temperatures during the past two millennia on centennial timescales ranging from c. 0.5 to 4°C and averaging c. 1.5–2°C for both high and low latitudes, although these variations are not always occurring synchronous. Both the Medieval Warm Period, the Little Ice Age and the 20th century warming are clearly visible in most records, whereas the Roman Warm Period and the Dark Age Cold Period are less clearly discernible.”

How the Rate of Volcanism Initiated the Medieval Warm Period and Controlled Its Periods of Drought – Ward (2008) “During the Medieval Warm Period, most large volcanic eruptions are contemporaneous with short-term decreases in Northern Hemisphere temperature determined using high-resolution proxy data (Mann and Jones, 2003). When such large eruptions occur more frequently than every few years, however, the oxidizing capacity of the atmosphere is exceeded, greenhouse gases accumulate, and the earth warms. … Only 27% of these ice layers contained “volcanic” sulfate and there were only 3 instances where more than 6 contiguous layers contained “volcanic” sulfate: 179-140 BC (16 layers), the onset of the Roman Climate Optimum, 818-840 AD (11 layers), the onset of the Medieval Warm Period, and 1929-1984 AD (34 layers), the onset of the modern warming period caused by anthropogenic SO2.” [Presentation material 1, Presentation material 2]

Blueprints for Medieval hydroclimate – Seager et al. (2007) “A review of proxy evidence from around the world indicates that North American megadroughts were part of a global pattern of Medieval hydroclimate that was distinct from that of today. … A positive North Atlantic Oscillation (NAO) also helps to explain the Medieval hydroclimate pattern. … Tentative modeling results indicate that a multi-century La Niña-like state could have arisen as a coupled atmosphere–ocean response to high irradiance and weak volcanism during the Medieval period and that this could in turn have induced a persistently positive NAO state.” [Link to PDF]

The Spatial Extent of 20th-Century Warmth in the Context of the Past 1200 Years – Osborn & Briffa (2006) “Positive anomalies during 890 to 1170 and negative anomalies during 1580 to 1850 are consistent with the concepts of a Medieval Warm Period and a Little Ice Age, but comparison with instrumental temperatures shows the spatial extent of recent warmth to be of greater significance than that during the medieval period.” [Link to PDF]

A late medieval warm period in the Southern Ocean as a delayed response to external forcing? – Goosse et al. (2004) “On the basis of long simulations performed with a three-dimensional climate model, we propose an interhemispheric climate lag mechanism, involving the long-term memory of deepwater masses. Warm anomalies, formed in the North Atlantic when warm conditions prevail at surface, are transported by the deep ocean circulation towards the Southern Ocean. There, the heat is released because of large scale upwelling, maintaining warm conditions and inducing a lagged response of about 150 years compared to the Northern Hemisphere. Model results and observations covering the first half of the second millenium suggest a delay between the temperature evolution in the Northern Hemisphere and in the Southern Ocean. The mechanism described here provides a reasonable hypothesis to explain such an interhemipsheric lag.” [Link to PDF]

Climate in Medieval Time – Bradley et al. (2003) “although the High Medieval (1100 to 1200 A.D.) was warmer than subsequent centuries, it was not warmer than the late 20th century. Moreover, the warmest Medieval temperatures were not synchronous around the globe. Large changes in precipitation patterns are a particular characteristic of “High Medieval” time.”

Medieval Climatic Optimum – Mann (2002) “Thus, current evidence does not support the notion of a Medieval Climatic Optimum as an interval of hemispheric or global warmth comparable to the latter 20th century.” [Link to PDF]

Was the Medieval Warm Period Global? – Broecker (2001) “During the Medieval Warm Period (800 to 1200 A.D.), the Vikings colonized Greenland. In his Perspective, Broecker discusses whether this warm period was global or regional in extent. He argues that it is the last in a long series of climate fluctuations in the North Atlantic, that it was likely global, and that the present warming should be attributed in part to such an oscillation, upon which the warming due to greenhouse gases is superimposed.” [Link to PDF]

How Warm Was the Medieval Warm Period? – Crowley & Lowery (2000) “Despite clear evidence for Medieval warmth greater than present in some individual records, the new hemispheric composite supports the principal conclusion of earlier hemispheric reconstructions and, furthermore, indicates that maximum Medieval warmth was restricted to two-three 20–30 year intervals, with composite values during these times being only comparable to the mid-20 th century warm time interval. Failure to substantiate hemispheric warmth greater than the present consistently occurs in composites because there are significant offsets in timing of warmth in different regions; ignoring these offsets can lead to serious errors concerning inferences about the magnitude of Medieval warmth and its relevance to interpretation of late 20 th century warming.” [Link to PDF]

Was there a ‘medieval warm period’, and if so, where and when? – Hughes & Diaz (1994) “Our review indicates that for some areas of the globe (for example, Scandinavia, China, the Sierra Nevada in California, the Canadian Rockies and Tasmania), temperatures, particularly in summer, appear to have been higher during some parts of this period than those that were to prevail until the most recent decades of the twentieth century. These warmer regional episodes were not strongly synchronous. Evidence from other regions (for example, the Southeast United States, southern Europe along the Mediterranean, and parts of South America) indicates that the climate during that time was little different to that of later times, or that warming, if it occurred, was recorded at a later time than has been assumed. Taken together, the available evidence does not support a global Medieval Warm Period, although more support for such a phenomenon could be drawn from high-elevation records than from low-elevation records.” [Link to PDF]

39 Responses to “Papers on the MWP as Global Event”

  1. Ari Jokimäki said

    I added Mann et al. (2009).

  2. Ari Jokimäki said

    I added Osborn & Briffa (2006).

  3. Brendon said

    Hi, I noticed this one and wondered if it’s appropriate.

    http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0009972

  4. Ari Jokimäki said

    Thank you for the suggestion. The paper you suggested is for Europe, but I’d like to keep this list for global analysis only (there are lot of papers doing a regional analysis). I will keep this in mind, though, because I’ll probably make another list at some point for these regional reconstructions. We’ll see. :)

  5. Ari Jokimäki said

    I added Trouet et al. (2009).

  6. Max Mustermann said

    Hi,
    you added 12 papers – 4 from persons involved in CG. Good job! I have more than 200 papers pro MWP.

  7. Darius said

    Why didn’t you add Ljungqvist, is it because he finds evidence in his records for a globally MWP?

  8. Ari Jokimäki said

    Thank you for pointing out that paper (even if you only gave very vague reference). I added it (the Ljungqvist, 2009). You know, most of the others suggesting new papers here haven’t had any trouble to just point out the paper without assuming any dishonest motives for me to not include those papers. I even include a note to all my lists saying that the lists are not complete. Perhaps you just missed it. It is in the first paragraph above.

    The conclusions of Ljunqvist paper also seem to be quite in line with many other studies, namely that even if there are signs of global warm events during MWP, the events have not occurred at the same time. Ljungqvist says: “…although these variations are not always occurring synchronous.”

  9. Ari Jokimäki said

    I added Graham et al. (2010).

  10. barry said

    This might fit here:

    Koch & Klague 2011 – Extensive glaciers in northwest North America during Medieval time

    The Medieval Warm Period is an interval of purportedly warm climate during the early part of the past millennium. The duration, areal extent, and even existence of the Medieval Warm Period have been debated; in some areas the climate of this interval appears to have been affected more by changes in precipitation than in temperature. Here, we provide new evidence showing that several glaciers in western North America advanced during Medieval time and that some glaciers achieved extents similar to those at the peak of the Little Ice Age, many hundred years later. The advances cannot be reconciled with a climate similar to that of the twentieth century, which has been argued to be an analog, and likely were the result of increased winter precipitation due to prolonged La Niña-like conditions that, in turn, may be linked to elevated solar activity. Changes in solar output may initiate a response in the tropical Pacific that directly impacts the El Niño/Southern Oscillation and associated North Pacific teleconnections.

    http://www.springerlink.com/content/a42l382370422365/

  11. Ari Jokimäki said

    Added, thanks. It’s sort of borderline case – a regional paper but seems also to discuss global situation. By the way, I wrote a brief news article on this paper in Finnish back in March.

  12. Oksanna said

    I wonder why Oppo, D.W., Rosenthal, Y. and Linsley, B.K. 2009. 2,000-year-long temperature and hydrology reconstructions from the Indo-Pacific warm pool. Nature 460: 1113-1116 was not included?
    Oppo and others found that climate reconstructions based on proxies from Indonesia paralleled proxies from Europe over 2,000 years, including MWP.
    http://www.nature.com/nature/journal/v460/n7259/abs/nature08233.html

  13. Ari Jokimäki said

    There are generally two reasons why some paper is not included to the list. First, the paper might not have been surfaced in my paper search – hence the mention above that the list is not complete (this was also already told to another person in above discussion). Second, paper might not be relevant for the list.

    The paper you highlighted is not included at least because of the second reason. It only studies one site (so not even a regional study) and this list contains papers that do global analysis (or at least a regional analysis with discussion on the global situation). By the way, the paper by Graham et al. (2010) included in my list discusses also about this Indo-Pacific situation.

  14. Ari Jokimäki said

    I added Zhou et al. (2011).

  15. S Churchill PhD said

    Peter Ward’s 2008 paper (talk/pdf and also full poster) are available on-line if you do a search of the title. Peter has his own website and has published one or two papers on his theory of opposed effects (short-term vs longer duration volcanic SO2 releases) that explain the proposed mechanism a bit better.

    I wouldn’t discount his theory, as it’s validated if you consider aerosol effects at regional/global scale. Thanks for putting together and maintaining this website.

  16. Ari Jokimäki said

    I added the presentation materials to Ward (2008).

    I also added a new paper by Goosse et al. (2012) which was published just few days ago.

  17. Ari Jokimäki said

    I added Diaz et al. (2011).

  18. cjshaker said

    Evidence that the MWP affected other regions of the planet: “Evidence for a ‘Medieval Warm Period’ in a 1,100 year tree-ring reconstruction of past austral summer temperatures in New Zealand”, by Edward R. Cook Lamont-Doherty Earth Observatory, Palisades, NY, USA, Jonathan G. Palmer Palaeocology Centre, Queens University, Belfast, Northern Ireland, UK, Rosanne D. D’Arrigo Lamont-Doherty Earth Observatory, Palisades, NY, USA, GEOPHYSICAL RESEARCH LETTERS, VOL. 29, NO. 14, 1667, 10.1029/2001GL014580, 2002
    http://ruby.fgcu.edu/courses/twimberley/EnviroPhilo/CookPalmer.pdf

  19. cjshaker said

    Regarding claims that the MWP did not apply to North America, A 3,000-year record from 52 of the world’s oldest trees shows that California’s western Sierra Nevada was “droughty and often fiery” from 800 to 1300, the University of Arizona said today. Scientists reconstructed the 3,000-year history of fire by dating fire scars on ancient giant sequoia trees, Sequoiadendron giganteum, in the Giant Forest of Sequoia National Park.”…”During the Medieval Warm Period extensive fires burned through parts of the Giant Forest at intervals of about 3 to 10 years, he said. Any individual tree was probably in a fire about every 10 to 15 years.”…”Increasingly, researchers all over the world are using charcoal to reconstruct fire histories, Swetnam said. Many scientists are analyzing the global record of charcoal to study relationships between climate, fire and the resulting addition of carbon dioxide to the atmosphere.”…“The scientists found the years from 800 to 1300, known as the Medieval Warm Period, had the most frequent fires in the 3,000 years studied. Other research has found that the period from 800 to 1300 was warm and dry,” the university said.
    “What’s not so well known about the Medieval Warm Period is how warm it was in the western U.S.,” Swetnam said. “This is one line of evidence that it was very fiery on the western slopes of the Sierra Nevada–and there’s a very strong relationship between drought and fire.”
    Droughts are typically both warm and dry, he added.”
    http://newswatch.nationalgeographic.com/2010/03/18/sequoias_endured_500_years_fire_and_drought/

    This is the paper that they are talking about in National Geographic
    http://nps01.origin.cdn.level3.net/seki/naturescience/upload/swetnam%20etal%202010_Multi-Millennial%20Fire%20History%20of%20the%20Giant%20Forest,%20Sequoia%20National%20Park,%20California,%20USA-final.pdf

  20. cjshaker said

    Lots of data on reconstructed temperatures around the world from the Medieval Warm Period at the Woods Hole web page. Go there and search for ‘Medieval Warm Period’

    http://www.whoi.edu/search.do?q=Medieval+Warm+Period&g=ext&search=Search&type=search

    Woods Hole Oceanographic Institution Examines 2,000 years of sediment records for temperature reconstruction

    “A new 2,000-year-long reconstruction of sea surface temperatures (SST) from the Indo-Pacific warm pool (IPWP) suggests that temperatures in the region may have been as warm during the Medieval Warm Period as they are today.”

    “Water temperature during the late Medieval Warm Period, between about A.D. 1000 to 1250, was within error of modern annual sea surface temperatures. (Oppo, Rosenthal, Linsley; 2009)”

    http://www.whoi.edu/page.do?pid=7545&tid=282&cid=59106&ct=162

    Found another interesting page about sediment record analysis at Woods Hole, covering the Medieval Warm Period and the Little Ice Age

    http://www.whoi.edu/oceanus/viewArticle.do?id=3842

    “Events warmer than today occurred about 500 and 1,000 years ago, during the Medieval Warm Period, and it was even warmer than that prior to about 2,500 years ago.”

    “Because the Sargasso Sea has a rather uniform temperature and salinity distribution near the surface, it seems that these events must have had widespread climatic significance. The Sargasso Sea data indicate that the Medieval Warm Period may have actually been two events separated by 500 years, perhaps explaining why its timing and extent have been so controversial. Second, it is evident that the climate system has been warming for a few hundred years, and that it warmed even more from 1,700 years ago to 1,000 years ago.”

    This graph of the Sargasso Sea Surface Temperature, reconstructed from sediment cores, shows what they are talking about

    http://www.whoi.edu/oceanus/viewImage.do?id=8722&aid=3842

  21. cjshaker said

    Got started searching for these papers by Googling for evidence of the Medieval Warm Period at Google Scholar. Lots of data showing that the MWP affected diverse areas around the globe.

    Paper offering high resolution temperature proxy data from an Alaskan lake over the past 6,000 yrs, derived from midge analysis on the sediments. Shows temperatures there were higher in the past 3,000 yrs than today

    “Although the Moose Lake TJuly record displays an increasing trend over the past 150 years, the TJuly values in several warm intervals of the past 6000 years were comparable to or exceeded early 20th-century values. For example, the TJuly values during the MCA were generally higher than the early 20th-century values (Fig. 4C). ”

    http://www.life.illinois.edu/hu/publications/Clegg_et_al_2010.pdf

  22. cjshaker said

    Evidence for the existence of the medieval warm period in China
    “Abstract
    The collected documentary records of the cultivation of citrus trees andBoehmeria nivea (a perennial herb) have been used to produce distribution maps of these plants for the eighth, twelfth and thirteenth centuries A.D. The northern boundary of citrus andBoehmeria nivea cultivation in the thirteenth century lay to the north of the modern distribution. During the last 1000 years, the thirteenth-century boundary was the northernmost. This indicates that this was the warmest time in that period. On the basis of knowledge of the climatic conditions required for planting these species, it can be estimated that the annual mean temperature in south Henan Province in the thirteenth century was 0.9–1.0°C higher than at present. A new set of data for the latest snowfall date in Hangzhou from A.D. 1131 to 1264 indicates that this cannot be considered a cold period, as previously believed.”

    http://www.springerlink.com/content/gh98230822m7g01l/

  23. cjshaker said

    “The warming of the middle of the twentieth century is not extraordinary. The warming at the end of the first and beginning of the second millennia (“Medieval Warm Period”) was longer in time and closer in amplitude.””

    This paper was sent to Keith Briffa Wed, 9 Dec 1998
    http://foia2011.org/index.php?id=4726

    Variation of early summer and annual temperature in east Taymir and Putoran (Siberia) over the last two millennia inferred from tree rings

    “Regional tree ring chronology with extension 2209 years (from 212 B.C. till 1996 A.D.) was built for east Taymir and Putoran according to wood of living trees, well-preserved remains of dead trees, and subfossil wood from alluvial bank deposits by the cross-dating method. In addition, the “floating” tree ring width chronology for the period of Holocene optimum (3300–2600 B.C.) was built with extention 685 years and supported by several radiocarbon dates. High values of synchrony and correlation of individual tree ring series show a prevailing effect of one external factor on radial tree growth change in the studied region of the Siberian subarctic. It was established that the main factors of growth variability are the early summer and annual temperature, which explain up to 70% of tree growth rate variability. Cyclic components stable for two millennia were revealed at analysis of the tree ring chronology: double secular (∼180 years), secular (78–90 years), and intrasecular (44, 28, 11, and 6.7–6.9 years) variations. Models for reconstruction of the early summer and annual air temperature were obtained according to tree ring variability. Temperature dynamics in the eastern part of Taymir for the last two millenia agree well with temperature variations in the Northern Hemisphere obtained according to other indirect sources. The warming of the middle of the twentieth century is not extraordinary. The warming at the end of the first and beginning of the second millennia (“Medieval Warm Period”) was longer in time and closer in amplitude.”
    http://www.agu.org/pubs/crossref/2000/1999JD901059.shtml

    You can read the whole text of the paper via the Climategate emails
    http://foia2011.org/index.php?id=5379

  24. cjshaker said

    I found those papers by Googling ‘Evidence of the Medieval Warm Period’ at Google Scholar. There are a ton more papers showing proof that the MWP affected diverse parts of the globe

    http://scholar.google.com/scholar?hl=en&q=Evidence+of+the+Medieval+Warm+Period&btnG=Search&as_sdt=0%2C38&as_ylo&as_vis=0

    Evidence of the Medieval Warm Period is very easy to find. Why do CO2 alarmists have to pretend that it did not exist?

  25. Ari Jokimäki said

    Above list is for papers doing global analysis. It is well known that some warm events during this long time-frame are seen also elsewhere than in North-Atlantic area. If there is a strong regional climate change in North-Atlantic, it will have some effect also globally.

    It is also well-known that there are plenty of local papers from where one can find evidence for practically any argument. Global analysis of the situation, as presented in the paperlist above, is that MWP was strong event only in North-Atlantic region, but it did have some hot spots also elsewhere.

    Mainstream climate science is not claiming that MWP didn’t exist. You are building straw man argument here. Why do people who use words like “CO2 alarmists” always have to use logical fallacies to build an argument?

  26. cjshaker said

    It seems that CO2 alarmists call any argument they don’t like a ‘straw man’ argument.

    It is interesting to contrast these many papers showing evidence of a warmer climate during the MWP at diverse points around the globe with the view put forth by Skeptical Science and by RealClimate

    Skeptical Science says

    “Firstly, evidence suggests that the Medieval Warm Period was in fact warmer than today in many parts of the globe such as in the North Atlantic. This warming thereby allowed Vikings to travel further north than had been previously possible because of reductions in sea ice and land ice in the Arctic. However, evidence also suggests that some places were very much cooler than today including the tropical pacific. All in all, when the warm places are averaged out with the cool places, it becomes clear that the overall warmth was likely similar to early to mid 20th century warming. Since that early century warming, temperatures have risen well-beyond those achieved during the Medieval Warm Period across most of the Globe. This has been confirmed by the National Academy of Sciences Report on Climate Reconstructions. Further evidence (Figure 1) suggests that even in the Northern Hemisphere where the Medieval Warm Period was the most visible, temperatures are now beyond those experienced during Medieval times.”

    http://www.skepticalscience.com/medieval-warm-period.htm

    If you go to Dr. Mann’s RealClimate site, you’ll find the following entry on the MWP, where you’ll find they really downplay the MWP as myth and bad science!

    http://www.realclimate.org/index.php/archives/2004/11/medieval-warm-period-mwp/

    At Google Scholar you can find yourself many papers showing warmer temperatures than today during the MWP. The differences between what the CO2 Alarmists say and what Geology and Oceanography says is interesting to me

  27. Ari Jokimäki said

    It seems that CO2 alarmists call any argument they don’t like a ‘straw man’ argument.

    You said that “Why do CO2 alarmists have to pretend that it did not exist?” Go ahead and show that CO2 arlarmists do that. Above you have shown examples where instances you apparently consider “CO2 alarmists” actually discuss it as existing phenomenon. This goes against your claim. That is why I called your argument a straw man because you are trying to make it look like they are saying different things than they actually are.

    Now, back up your claim and show that “CO2 alarmists” have to pretend that MWP did not exist.

    Also, insults are not allowed here, even if they are directed to third parties, so drop your tone or you won’t post here again.

    It is interesting to contrast these many papers showing evidence of a warmer climate during the MWP at diverse points around the globe with the view put forth by Skeptical Science and by RealClimate

    I don’t understand what is interesting about it, as you didn’t bring anything new to the table, but just cherry-picked a few local papers that show the result you like. Like I said above, there are lots of papers on this issue and if you stick with selected local papers without doing proper global analysis, you can make it look like MWP was warmer than currently. For example, I can cite papers from Europe showing current age warmer and Europe was in region where MWP was supposed to be strong.

    If you go to Dr. Mann’s RealClimate site, you’ll find the following entry on the MWP, where you’ll find they really downplay the MWP as myth and bad science!

    http://www.realclimate.org/index.php/archives/2004/11/medieval-warm-period-mwp/

    Bad science is not mentioned in that page and they don’t call MWP myth either (they explicitly acknowledge that MWP was real – contrary to your claim). Why are you claiming these obviously false things?

    At Google Scholar you can find yourself many papers showing warmer temperatures than today during the MWP.

    You can do that with Google Scholar if you wish to stick with cherry-picking. You can also use it for looking at all the evidence instead of just those papers that show MWP warmer. If you are interested in this issue, with Google Scholar you can do a real global analysis instead of cherry-picking few MWP was warmer papers. That would be so much more convincing.

  28. cjshaker said

    http://www.realclimate.org/index.php/archives/2004/11/medieval-warm-period-mwp/

    “Medieval Warm Period (“MWP”)
    Filed under: Glossary — group @ 28 November 2004
    Period of relative warmth in some regions of the Northern Hemisphere in comparison with the subsequent several centuries. Also referred to as the Medieval Warm Epoch (MWE). As with the ‘Little Ice Age’ (LIA), no well-defined precise date range exists. The dates A.D. 900–1300 cover most ranges generally used in the literature. Origin is difficult to track down, but it is believed to have been first used in the 1960s (probably by Lamb in 1965). As with the LIA, the attribution of the term at regional scales is complicated by significant regional variations in temperature changes, and the utility of the term in describing regional climate changes in past centuries has been questioned in the literature. As with the LIA, numerous myths can still be found in the literature with regard to the details of this climate period. These include the citation of the cultivation of vines in Medieval England, and the settlement of Iceland and southwestern Greenland about 1000 years ago, as evidence of unusual warmth at this time. As noted by Jones and Mann (2004) [Jones, P.D., Mann, M.E., Climate Over Past Millennia, Reviews of Geophysics, 42, RG2002, doi: 10.1029/2003RG000143, 2004], arguments that such evidence supports anomalous global warmth during this time period is based on faulty logic and/or misinterpretations of the available evidence.”

    I’m referring specifically to the first sentence, and to the last sentence. If you read this entry from RealClimate, you’d be left with the impression that the MWP did not affect the Southern Hemisphere at all. As we’ve seen from papers available at Google Scholar, the warming shows up in New Zealand and in Antarctica as well. Glad to see that you worked the ‘cherry picking’ accusation in there. Want to throw in ‘link bombing’ as well to make your argument complete?

  29. Ari Jokimäki said

    I repeat as you forgot to answer my question: “Bad science is not mentioned in that page and they don’t call MWP myth either (they explicitly acknowledge that MWP was real – contrary to your claim). Why are you claiming these obviously false things?”

  30. cjshaker said

    You do not think that “arguments that such evidence supports anomalous global warmth during this time period is based on faulty logic and/or misinterpretations of the available evidence.” means “bad science”?

  31. cjshaker said

    I note that you have not commented on the impression a reader of RealClimate would get that the MWP only affected the Northern Hemisphere

  32. cjshaker said

    Looking for examples showing that the MWP appears in the proxy climate record in other parts of the globe is ‘cherry picking’?

  33. cjshaker said

    Your comments inspired me to look for more examples of studies showing the MWP impacting the southern hemisphere. This Climate Wiki page has a list of climate proxy studies in South America, at least some of which show temperatures warmer than today during the MWP

    http://www.climatewiki.org/index.php/South_America's_Medieval_Warm_Period

    That article lists the following papers about climate reconstructions in South America

    Brohan, P., Kennedy, J.J., Harris, I., Tett, S.F.B., and Jones, P.D. 2006. Uncertainty estimates in regional and global observed temperature changes: A new data set from 1850. Journal of Geophysical Research 111: 10.1029/2005JD006548.
    Eichler, A., Brutsch, S., Olivier, S., Papina, T., and Schwikowski, M. 2009. A 750-year ice core record of past biogenic emissions from Siberian boreal forests. Geophysical Research Letters 36: 10.1029/2009GL038807.
    Kang, S.C., Mayewski, P.A., Qin, D., Yan, Y., Zhang, D., Hou, S., and Ren, J. 2002. Twentieth century increase of atmospheric ammonia recorded in Mount Everest ice core. Journal of Geophysical Research 107: 10.1029/2001JD001413.
    Kellerhals, T., Brutsch, S., Sigl, M., Knusel, S., Gaggeler, H.W., and Schwikowski, M. 2010. Ammonium concentration in ice cores: A new proxy for regional temperature reconstruction? Journal of Geophysical Research 115: 10.1029/2009JD012603.
    Rebolledo, L., Sepulveda, J., Lange, C.B., Pantoja, S., Bertrand, S., Hughen, K., and Figueroa, D. 2008. Late Holocene marine productivity changes in Northern Patagonia-Chile inferred from a multi-proxy analysis of Jacaf channel sediments. Estuarine, Coastal and Shelf Science 80: 314–322.
    Sepulveda, J., Pantoja, S., Hughen, K.A., Bertrand, S., Figueroa, D., Leon, T., Drenzek, N.J., and Lange, C. 2009. Late Holocene sea-surface temperature and precipitation variability in northern Patagonia, Chile (Jacaf Fjord, 44°S). Quaternary Research 72: 400–409.

  34. cjshaker said

    Africa’s Medieval Warm Period
    http://www.climatewiki.org/index.php/Africa%27s_Medieval_Warm_Period

    “With respect to the MWP, they state it was “marginally warmer than present.””

    References

    Alley, R.B., Meese, D.A., Shuman, C.A., Gow, A.J., Taylor, K.C., Grootes, P.M., White, J.C.W., Ram, M., Waddington, E.D., Mayewski, P.A., and Zielinski, G.A. 1993. Abrupt increase in Greenland snow accumulation at the end of the Younger Dryas event. Nature 362: 527–529.
    Bianchi, G.G. and McCave, I.N. 1999. Holocene periodicity in North Atlantic climate and deep-ocean flow south of Iceland. Nature 397: 515–517.
    Bond, G., Showers, W., Cheseby, M., Lotti, R., Almasi, P., deMenocal, P., Priore, P., Cullen, H., Hajdas, I., and Bonani, G. 1997. A pervasive millennial-scale cycle in North Atlantic Holocene and Glacial climate. Science 278: 1257–1266.
    Bond, G., Showers, W., Elliot, M., Evans, M., Lotti, R., Hajdas, I., Bonani, G., and Johnson, S. 1999. The North Atlantic’s 1–2 kyr Climate Rhythm: Relation to Heinrich Events, Dansgaard/Oeschger Cycles, and the Little Ice Age. In Mechanisms of Global Climate Change at Millennial Scales, edited by P.U. Clark, R.S. Webb, and L.D. Keigwin, 35–58. Washington, DC: American Geophysical Union.
    COHMAP Members. 1988. Climatic changes of the last 18,000 years: Observations and model simulations. Science 241: 1043–1052.
    DeMenocal, P., Ortiz, J., Guilderson, T., and Sarnthein, M. 2000. Coherent high- and low-latitude climate variability during the Holocene warm period. Science 288: 2198–2202.
    Gasse, F. and Van Campo, E. 1994. Abrupt post-glacial climate events in West Asia and North Africa monsoon domains. Earth and Planetary Science Letters 126: 435–456.
    Keigwin, L.D. 1996. The Little Ice Age and Medieval Warm Period in the Sargasso Sea. Science 274: 1504–1507.
    O’Brien, S.R., Mayewski, P.A., Meeker, L.D., Meese, D.A., Twickler, M.S., and Whitlow, S.E. 1995. Complexity of Holocene climate as reconstructed from a Greenland ice core. Science 270: 1962–1964.

  35. Ari Jokimäki said

    I note that you have ignored just about anything I said in my first reply to you (post #25).

    You first proceeded with a notion that “CO2 alarmists” claim MWP did’t exist at all. After I questioned that, you then gave couple of examples of what you mean and all of a sudden it’s only about impression of what they say or don’t say about MWP in southern hemisphere. I’m still trying to get your first claim solved as you didn’t acknowledge any of it and ignored all my arguments about it. RealClimate text seems to be quite well in line with global analyses on the issue.

    Your actions here are definitely cherry-picking. You only cite studies that show what you want. That is cherry-picking. For example, you cite a study from New Zealand but don’t seem to make any effort of finding what other studies say from that area. You are not making any effort of discussing the timing of the event in different parts of the Earth. You cite very old studies showing MWP warmer than “today” but don’t seem to be making any effort of determining what that “today” mean in those studies. Last but not least, you seem to be ignoring already made global analyses on the issue and try to override them with few selected local studies. Textbook example of cherry-picking.

    You do not think that “arguments that such evidence supports anomalous global warmth during this time period is based on faulty logic and/or misinterpretations of the available evidence.” means “bad science”?

    You left some relevant parts out of your quote. Whole thing reads: “These include the citation of the cultivation of vines in Medieval England, and the settlement of Iceland and southwestern Greenland about 1000 years ago, as evidence of unusual warmth at this time. As noted by Jones and Mann (2004) [Jones, P.D., Mann, M.E., Climate Over Past Millennia, Reviews of Geophysics, 42, RG2002, doi: 10.1029/2003RG000143, 2004], arguments that such evidence supports anomalous global warmth during this time period is based on faulty logic and/or misinterpretations of the available evidence”

    You claimed this: “If you go to Dr. Mann’s RealClimate site, you’ll find the following entry on the MWP, where you’ll find they really downplay the MWP as myth and bad science!”

    “They downplay MWP as bad science” is your claim here. For this claim you cited a statement where couple of arguments about MWP are said to be “based on faulty logic and/or misinterpretations of the available evidence”. That statement is not about MWP itself, it is about those arguments which indeed are based on faulty logic and/or misinterpretations of the available evidence. Why would you try to present this statement as a proof of your claim which was about MWP itself? This also was just one part of the answer. Where they downplay MWP as myth? Where they say that MWP didn’t exist at all?

  36. cjshaker said

    You can’t seem to understand the idea of paraphrasing. You can read about what that means here:

    http://en.wikipedia.org/wiki/Paraphrase

    You don’t seem willing to admit that there is anything wrong with the the RealClimate entry on the MWP? You don’t seem willing to admit that it implies that the MWP was merely a regional phenomenon?

    Chris Shaker

  37. Ari Jokimäki said

    Paraphrasing? Complete nonsense. Try dramatic exaggaration and false interpretation.

    You haven’t been able to show anything wrong in that entry. I already said that it is in line with existing global analyses, but you just ignored it like just about everything else I said.

    You don’t seem willing to admit that your few local studies don’t make a global analysis.

  38. Ari Jokimäki said

    Davis et al. (2003) is an example that shows how local studies can be misleading when trying to estimate global situation. They have reconstructed european temperatures during Holocene. See their figure 3 which shows summer and winter temperature reconstructions of six different regions in Europe. Notice how different even the large scale temperature evolution is in each of these sites. And Europe is actually quite small place in global context.

    For example, I could pick up some European local reconstructions and use them to “prove” that holocene climate optimum didn’t exist. You can also see that I can do the same with MWP in Europe; there’s no sign of it in NW summer & winter, NE summer, CW winter, CE winter, and SE winter. Local studies are worthless when trying to determine if MWP was global or not.

  39. Ari Jokimäki said

    I added Ahmed et al. (2013).

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