Filippi et al. (1999) obtained stable isotope data (δ¹⁸O and δ¹³C) from bulk carbonate and ostracode calcite in a radiocarbon-dated sediment core removed from Lake Neuchatel in the western Swiss Lowlands at the foot of the Jura Mountains, from which they reconstructed the climatic history of the region over the prior 1500 years. Their data indicated that mean annual air temperature dropped by about 1.5°C during the transition from the Medieval Warm Period (MWP) to the Little Ice Age (LIA); and they state that "the warming during the 20th century does not seem to have fully compensated the cooling at the MWP-LIA transition," noting also that during the Medieval Warm Period, mean annual air temperatures were "on average higher than at present."

Bodri and Cermak (1999) derived individual ground surface temperature histories from the temperature-depth logs of 98 separate boreholes drilled in the Czech Republic. These histories revealed the existence of a medieval warm epoch lasting from approximately AD 1100 to 1300, which they describe as "one of the warmest postglacial times." They also note that during the main phase of the Little Ice Age, from 1600-1700, all investigated territory was subjected to "massive cooling," and that "the observed recent warming may thus be easily a natural return of climate from the previous colder conditions back to a 'normal'."

Niggemann et al. (2003) utilized petrographical and geochemical properties of three stalagmites found in a cave in Sauerland, Northwest Germany, to develop a climatic history of the surrounding region covering the last 17,600 years. As they describe it, the three stalagmite records "resemble records from an Irish stalagmite (McDermott et al., 1999)," which has also been described by McDermott et al. (2001). With respect to their own records, they say they provide evidence for the existence of the Little Ice Age, Medieval Warm Period and Roman Warm Period, which also implies the existence of the unnamed cold period that preceded the Roman Warm Period and what McDermott et al. (2001) call the Dark Ages Cold Period that separated the Medieval and Roman Warm Periods. From this information it can be appreciated that the Little Ice Age was but one node of a millennial-scale climatic oscillation that has periodically bought multi-centennial intervals of both relative cold and warmth to Central Europe.

In a study of the serin, a bird that was of great interest to ornithologists of the 19th and 20th centuries due to the rapid expansion of its range in historical times, Kinzelbach (2004) examined "all the sources of records of the serin in 16th century Europe," including "both those already known and some that have been newly discovered." This work, in Kinzelbach's words, confirmed the findings of Mayr (1926) that "north of 48°N there were no free-living populations of Serinus serinus in the 16th century." During that period, the serin may have attempted to expand its range, but Kinzelbach says it "was halted by colder periods of the Little Ice Age after 1585, only resuming a rapid expansion at the beginning of the 19th century," after which it was "able to expand its range from the Mediterranean region throughout large areas of Central Europe within a mere 200 years." Interestingly, the temperature history of Esper et al. (2002) depicts post-Little Ice Age Northern Hemispheric warming beginning at about the same time the serin began its northward migration, whereas the highly-debated hockeystick temperature history of Mann et al. (1999) does not depict post-Little Ice Age warming until about a century later.

The next study we highlight is based on the work of Antal Rethly (1879-1975), a former director of the National Meteorological and Earth Magnetism Institute of Hungary, who spent the greater portion of his long professional life collecting over 14,000 historical records related to the climate of the Carpathian Basin, and who published a four-volume set of books about them in the Hungarian language (Rethly, 1962, 1970; Rethly and Simon, 1999). These works were meticulously codified and analyzed by Bartholy et al. (2004), who emphasize the importance of gaining a proper understanding of "past climate tendencies and climatological extremes," and who upon gaining that understanding report that "the warm peaks of the Medieval Warm Epoch and colder climate of the Little Ice Age followed by the recovery warming period can be detected in the reconstructed temperature index time series," either overtly or unconsciously noting that 20th-century warming is best characterized as a naturally expected event - a "recovery" from the colder era that preceded it.

In a review and analysis of other pertinent scientific literature, Kvavadze and Connor (2005) "present some observations on the ecology, pollen productivity and Holocene history of Zelkova carpinifolia," a Tertiary-relict tree whose pollen "is almost always accompanied by elevated proportions of thermophilous taxa." This species, in their words, "is a mesophilous tree, requiring warm conditions," and because it requires heat and moisture during the growing period, they say that "the discovery of fossil remains in Holocene sediments can be a good indicator of optimal climatic conditions." In their analysis, for example, they find a millennial-scale oscillation of climate that places the Medieval Warm Period "from 1350 to 800 years ago," and during portions of this time interval, they report that tree lines "migrated upwards and the distribution of Zelkova broadened." What is more, they present a history of Holocene oscillations of the upper tree-line in Abkhasia -- derived by Kvavadze et al. (1992) -- that depicts slightly greater-than-present elevations during a portion of the Medieval Warm Period and much greater extensions above the current tree-line during parts of the Roman Warm Period. Last of all, and following the Medieval Warm Period, Kvavadze and Connor note that "subsequent phases of climatic deterioration (including the Little Ice Age) ... saw an almost complete disappearance of Zelkova from Georgian forests," indicative of the fact that the expected recovery warming in this region of Central Europe has not yet been completed.

Mangini et al. (2005) used precisely dated δ¹⁸O data, which they derived from a stalagmite recovered from Spannagel Cave in the Central Alps of Austria, to develop a highly-resolved record of temperature over the past 2000 years based on a transfer function they derived from a comparison of their δ¹⁸O data with the reconstructed temperature history of post-1500 Europe developed by Luterbacher et al. (2004). The lowest temperatures of the past two millennia, according to the new record, occurred during the Little Ice Age (1400-1850), while the highest temperatures were found in the Medieval Warm Period (MWP: 800-1300). Furthermore, Mangini et al. say that the highest temperatures of the MWP were "slightly higher than those of the top section of the stalagmite (1950) and higher than the present-day temperature." In fact, at three different points during the MWP, their data indicate temperature spikes in excess of 1°C above present (1995-1998) temperatures.

Mangini et al. additionally report that their temperature reconstruction compares well with reconstructions developed from Greenland ice cores (Muller and Gordon, 2000), Bermuda Rise ocean-bottom sediments (Keigwin, 1996), and glacier tongue advances and retreats in the Alps (Holzhauser, 1997; Wanner et al., 2000), as well as with the Northern Hemispheric temperature reconstruction of Moberg et al. (2005). Considered together, they say these several data sets "indicate that the MWP was a climatically distinct period in the Northern Hemisphere," emphasizing that "this conclusion is in strong contradiction to the temperature reconstruction by the IPCC, which only sees the last 100 years as a period of increased temperature during the last 2000 years."

In a second severe blow to IPCC dogma, Mangini et al. found "a high correlation between δ¹⁸O and δ¹⁴C, that reflects the amount of radiocarbon in the upper atmosphere," and they note that this correlation "suggests that solar variability was a major driver of climate in Central Europe during the past 2 millennia." In this regard, they report that "the maxima of δ¹⁸O coincide with solar minima (Dalton, Maunder, Sporer, Wolf, as well as with minima at around AD 700, 500 and 300)," and that "the coldest period between 1688 and 1698 coincided with the Maunder Minimum." Also, in a linear-model analysis of the percent of variance of their full temperature reconstruction that is individually explained by solar and CO2 forcing, they found that the impact of the sun was fully 279 times greater than that of the air's CO2 concentration, noting that "the flat evolution of CO2 during the first 19 centuries yields almost vanishing correlation coefficients with the temperature reconstructions."

Similar results were obtained by Buntgen et al. (2005), who used the regional curve standardization technique applied to ring-width measurements from both living trees and relict wood to develop a 1052-year summer (June-August) temperature proxy from high-elevation Alpine environments in Switzerland and the western Austrian Alps. This reconstruction revealed the presence of warm conditions from the beginning of the record in AD 951 to about AD 1350, which they associated with the Medieval Warm Period, after which the Little Ice Age ensued, lasting until approximately 1850.

Analyzing a much longer period of time were Holzhauser et al. (2005), who utilized high-resolution records of variations in glacier size in the Swiss Alps -- together with lake-level fluctuations in the Jura mountains, the northern French Pre-Alps and the Swiss Plateau -- in developing a 3500-year climate history of west-central Europe.

Near the beginning of the study period, their analysis revealed that "during the late Bronze Age Optimum from 1350 to 1250 BC, the Great Aletsch glacier was approximately 1000 m shorter than it is today," and they note that "the period from 1450 to 1250 BC has been recognized as a warm-dry phase in other Alpine and Northern Hemisphere proxies (Tinner et al., 2003)." Then, after an intervening unnamed cold-wet phase, when the glacier grew in both mass and length, they say that "during the Iron/Roman Age Optimum between c. 200 BC and AD 50," which is perhaps better known as the Roman Warm Period, the glacier again retreated and "reached today's extent or was even somewhat shorter than today." Next came the Dark Ages Cold Period, which they say was followed by "the Medieval Warm Period, from around AD 800 to the onset of the Little Ice Age around AD 1300," which latter cold-wet phase was "characterized by three successive [glacier length] peaks: a first maximum after 1369 (in the late 1370s), a second between 1670 and 1680, and a third at 1859/60," following which the glacier began its latest and still-ongoing recession in 1865.

Data pertaining to the Gorner glacier (the second largest of the Swiss Alps) and the Lower Grindelwald glacier of the Bernese Alps tell much the same story, as Holzhauser et al. report that these glaciers and the Great Aletsch glacier "experienced nearly synchronous advances" throughout the study period.

With respect to what was responsible for the millennial-scale climatic oscillation that produced the alternating periods of cold-wet and warm-dry conditions that fostered the similarly-paced cycle of glacier growth and retreat, the Swiss and French scientists report that "glacier maximums coincided with radiocarbon peaks, i.e., periods of weaker solar activity," which in their estimation "suggests a possible solar origin of the climate oscillations punctuating the last 3500 years in west-central Europe, in agreement with previous studies (Denton and Karlen, 1973; Magny, 1993; van Geel et al., 1996; Bond et al., 2001)." And to underscore that point, they conclude their paper by stating that "a comparison between the fluctuations of the Great Aletsch glacier and the variations in the atmospheric residual ¹⁴C records supports the hypothesis that variations in solar activity were a major forcing factor of climate oscillations in west-central Europe during the late Holocene."

Also producing a paper about this same time were Chapron et al. (2005), who documented the Holocene evolution of Rhone River clastic sediment supply in Lake Le Bourget via sub-bottom seismic profiling and multidisciplinary analysis of well-dated sediment cores. Their work revealed that "up to five 'Little Ice Age- like' Holocene cold periods developing enhanced Rhone River flooding activity in Lake Le Bourget [were] documented at c. 7200, 5200, 2800, 1600 and 200 cal. yr BP," and that "these abrupt climate changes were associated in the NW Alps with Mont Blanc glacier advances, enhanced glaciofluvial regimes and high lake levels." They also report that "correlations with European lake level fluctuations and winter precipitation regimes inferred from glacier fluctuations in western Norway suggest that these five Holocene cooling events at 45°N were associated with enhanced westerlies, possibly resulting from a persistent negative mode of the North Atlantic Oscillation."

Situated between these Little Ice Age-like periods, of course, would have been Current Warm Period-like conditions. The most recent of these prior warm regimes (the Medieval Warm Period) would thus have been centered somewhere in the vicinity of AD 1100, while the next one back in time (the Roman Warm Period) would have been centered somewhere in the vicinity of 200 BC, which matches well with what we know about these warm regimes from many other studies (see Medieval Warm Period and Roman Warm Period in our Subject Index). In addition, since something other than an increase in the atmosphere's CO2 concentration was obviously responsible for the establishment of these prior Current Warm Period-like regimes, it is reasonable to assume that another increase in that same "something" -- and not the coincidental rise in the air's CO2 content -- was likely responsible for terminating the Little Ice Age and ushering in the Current Warm Period.

In a paper published one year later, Joerin et al. (2006) write that "the exceptional trend of warming during the twentieth century in relation to the last 1000 years highlights the importance of assessing natural variability of climate change." Why? Because we need to determine, by comparison, if there is anything unusual, unnatural, or unprecedented about the past century's increase in temperature, since these adjectives are commonly used by the world's climate alarmists to describe 20th-century global warming.

In their quest to accomplish this objective, the three Swiss researchers examined glacier recessions in the Swiss Alps over the past ten thousand years based on radiocarbon-derived ages of materials found in proglacial fluvial sediments of subglacial origin, focusing on subfossil remains of wood and peat. Combining their results with earlier data of a similar nature, they then constructed a master chronology of Swiss glacier fluctuations over the course of the Holocene.

This work revealed, in the words of the researchers who conducted it, that "alpine glacier recessions occurred at least 12 times during the Holocene," once again demonstrating the reality of the millennial-scale oscillation of climate that has reverberated throughout glacial and interglacial periods alike (see Climate Oscillations (Millennial Variability) in our Subject Index); and as a result of this particular finding, it is clear that 20th-century global warming was not unusual. It was merely the latest example of what has been the norm throughout hundreds of thousands of years.

Second, Joerin et al. determined that glacier recessions have been decreasing in frequency since approximately 7000 years ago, and especially since 3200 years ago, "culminating in the maximum glacier extent of the 'Little Ice Age'." Consequently, the significant warming of the 20th century cannot be considered strange, since it represents a climatic rebounding from the coldest period of the current interglacial, which interglacial just happens to be the coldest of the last five interglacials (Petit et al., 1999). And when the earth has been that cold for a few centuries, it is not unnatural to expect that, once started, warming would be rather significant.

Third, the last of the major glacier recessions in the Swiss Alps occurred between about 1400 and 1200 years ago, according to Joerin et al.'s data, but between 1200 and 800 years ago, according to the data of Holzhauser et al. (2005) for the Great Aletsch Glacier. Of this discrepancy, Joerin et al. say that given the uncertainty of the radiocarbon dates, the two records need not be considered inconsistent with each other. What is more, their presentation of the Great Aletsch Glacier data indicates that the glacier's length at about AD 1000 -- when there was fully 100 ppm less CO2 in the air than there is today -- was just slightly less than its length in 2002, suggesting that the peak temperature of the Medieval Warm Period likely was slightly higher than the peak temperature of the 20th century. Consequently, 20th-century warming has likely not been unprecedented over the past millennium. And being neither unusual, unnatural nor unprecedented, there is no compelling reason to attribute 20th-century global warming to anthropogenic CO2 emissions; it has been simply a run-of-the-mill consequence of cyclically-recurring forces of nature that have manifested themselves again and again throughout earth's history at millennial-scale intervals.

About this same time, Buntgen et al. (2006) developed an annually-resolved mean summer (June-September) temperature record for the European Alps. Covering the period AD 755-2004 and based on 180 recent and historic larch (Larix decidua Mill.) maximum latewood density series, the temperature history was derived using the regional curve standardization method that preserves interannual to multi-centennial temperature-related variations.

Among a number of other things, notable features identified by the researchers in this history were high temperatures in the late tenth, early thirteenth, and twentieth centuries and a prolonged cooling from ~1350 to 1700, or as they describe it: "warmth during medieval and recent times, and cold in between." Also of great interest, they report that the coldest decade of the record was the 1810s, and that even though the record extended all the way through 2004, the warmest decade of the record was the 1940s. In addition, they observed that "warm summers seem to coincide with periods of high solar activity, and cold summers vice versa." Finally, they report that comparing their newest temperature record with other regional- and large-scale reconstructions "reveals similar decadal to longer-term variability." As a result, Buntgen et al. concluded -- in the final sentence of their paper -- that in terms of being a reason for 20th-century global warming, "the twentieth-century contribution of anthropogenic greenhouse gases and aerosol remains insecure."

In yet another study from the same year, Eiriksson et al. (2006) reconstructed the near-shore thermal history of the North Atlantic Current along the western coast of Europe over the last two millennia, based on measurements of stable isotopes, benthic and planktonic foraminifera, diatoms and dinoflagellates, as well as geochemical and sedimentological parameters, which they acquired on the Iberian margin, the West Scotland margin, the Norwegian margin and the North Icelandic shelf. In addition to identifying the Roman Warm Period (nominally 50 BC-AD 400) -- which exhibited the warmest sea surface temperatures of the last two millennia on both the Iberian margin and the North Icelandic shelf -- and the following Dark Ages Cold Period (AD 400-800), Eiriksson et al. report detecting the Medieval Warm Period (AD 800-1300) and the Little Ice Age (AD 1300-1900), which was followed in some records by a strong warming to the present. However, they make a point of stating that this latter warming "does not appear to be unusual when the proxy records spanning the last two millennia are examined," pretty much echoing the conclusions of the authors of several of the other papers we have discussed.

Extending the work of Mangini et al. (2005), who developed a 2000-year temperature history of the central European Alps based on an analysis of δ¹⁸O data obtained from stalagmite SPA 12 of Austria's Spannagel Cave, Vollweiler et al. (2006) used similarly-measured δ¹⁸O data obtained from two adjacent stalagmites (SPA 128 and SPA 70) within the same cave to create a master δ¹⁸O history covering the last 9000 years, which Mangini et al. (2007) compared with the Hematite-Stained-Grain (HSG) history of ice-rafted debris in North Atlantic Ocean sediments developed by Bond et al. (2001), who had reported that "over the last 12,000 years virtually every centennial time-scale increase in drift ice documented in our North Atlantic records was tied to a solar minimum." This work revealed there was an almost unbelievably good correspondence between the peaks and valleys of the master δ¹⁸O curve and the HSG curve of Bond et al., leading Mangini et al. (2007) to conclude that (1) "the excellent match between the curves obtained from these two independent data sets gives evidence that the δ¹⁸O signal recorded in Spannagel cave reflects the intensity of the warm North Atlantic drift, disproving the assumption that the Spannagel isotope record is merely a local phenomenon," and, therefore, that (2) their δ¹⁸O curve "can reasonably be assumed to reflect non-local conditions," implying that it has wide regional applicability.

Having established this important point, Mangini et al. next focused on why their δ¹⁸O curve "displays larger variations for the last 2000 years than the multi-proxy record in Europe, which is mainly derived from tree-ring data" and "from low resolution archives (Mann et al., 1998, 1999; Mann and Jones, 2003)." The most probable answer, in their words, "is that tree-rings rather record the climate conditions during spring and summer," whereas both the HSG and δ¹⁸O curves "mirror winter-like conditions, which are only poorly recorded in tree-rings."

One important consequence of these differences is that whereas the Mann et al. and Mann and Jones data sets do not reflect the existence of the Medieval Warm Period and Little Ice Age, the Spannagel Cave data do. And applying the calibration curve derived for SPA 12 by Manginni et al. (2005) to the new δ¹⁸O curve, it can readily be determined that the peak temperature of the Medieval Warm Period was approximately 1.5°C higher than the peak temperature of the Current Warm Period. Consequently, not only does the new data set of Manginni et al. (2007) confirm the inference of Bond et al.'s finding that over the last 12,000 years virtually every centennial-scale cooling of the North Atlantic region "was tied to a solar minimum," it also demonstrates that the data sets of Mann et al. and Mann and Jones fail to capture the full range of temperature variability over the past two millennia. As a result, the new data set clearly depicts the existence of both the Little Ice Age and Medieval Warm Period, the latter of which is seen to have been substantially warmer over periods of centuries than the warmest parts of the 20th century, almost certainly as a result of enhanced solar activity, and in spite of the fact that the air's CO2 concentration during the Medieval Warm Period was more than 100 ppm less than it is today.

In conclusion, the findings of the several Central Europe palaeoclimate studies we have reviewed -- as well as those of the many additional studies cited in those reports -- suggest that the IPCC-endorsed hockeystick temperature history of Mann et al. (1999) does not reflect the true thermal history of the Northern Hemisphere over the past thousand or so years. In addition, they indicate that the IPCC appears to be focusing on the wrong instigator of climate change, i.e., CO2, when solar activity appears to be the primary culprit in this regard.

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