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Climate Oscillations (Millennial Variability: Asia) -- Summary
The millennial-scale oscillation of climate that is responsible for the alternating several-hundred-year warm and cool climatic intervals known throughout the regions that surround the North Atlantic Ocean as the Roman Warm Period, Dark Ages Cold Period, Medieval Warm Period, Little Ice Age and Modern Warm Period is a truly global phenomenon, protestations of the world's climate alarmists notwithstanding.  To add to the wealth of evidence supportive of this assertion, we here review the results of several studies that reveal the existence of this totally natural phenomenon in Asia.

We begin in India, where on the basis of pollen analyses of a 1.25-meter sediment profile in an outwash plain located about 2.5-3 km from the snout of the Gangotri Glacier Kar et al. (2002) explored the nature of climate change over the past two millennia.  Between about 2000 and 1700 years ago, their data reveal the existence of a cooler climate than "the one prevailing at present."  Comparing this finding with the results of the study of McDermott et al. (2001) in Ireland, we see that this period of time was part of the Dark Ages Cold Period.  Then, between 1700 and 850 years ago, Kar et al.'s analysis indicates what they call an "amelioration of climate," and from McDermott et al., we see that this period of time represents the transition from the depth of the Dark Ages Cold Period to the midst of the Medieval Warm Period.  Subsequently, Kar et al.'s data show that the climate "became much cooler," indicative of its transition to Little Ice Age conditions.  Between 300 and 200 years ago, in fact, they note that the long-term retreat of the Gangotri Glacier ceased, possibly with some minor advancement.  During the last 200 years, however, when the study of Esper et al. (2002) indicates there was a rather steady warming of the planet, the glacier's snout retreated about 2 km.  The results of this study thus clearly demonstrate the exquisite harmony of climate change in the disparate regions of the North Atlantic Ocean and the distant Himalayas.

Much further north and eastward, Laing and Smol (2003) studied changes in diatom assemblages preserved in a sediment core extracted from a small lake on the western Taimyr Peninsula of northern Russia.  The last 2500 years of the sediment record was strongly indicative of fluctuating limnological conditions, characterized, in their words, by "striking successional shifts between Fragilaria pinnata and Aulacoseira distans."  They further report that this variability was "strongly correlated with other paleoclimatic data from northern Eurasia and Greenland."  Prior to 2000 years ago, for example, the rate of change of the diatom assemblage was at a several-century minimum, but it rose rapidly as the Roman Warm Period established itself.  This parameter then dropped to lower values during the Dark Ages Cold Period, but rose to new heights (the greatest of the entire 4700-year record) during the Medieval Warm Period, only to experience the greatest decline of the entire record with the appearance of the Little Ice Age, after which the development of the Modern Warm Period once again saw a rapid rise in the rate of change of the diatom assemblage.  These results are a ringing testament to the reality of the non-CO2-induced millennial-scale oscillation of climate that pervades earth's history and periodically ushers in global warming such as that of the past century and a half.  Furthermore, as the air's CO2 content was essentially constant over the bulk of the 4700-year sediment record, its rising in tandem with the planet's temperature over the past century and a half is readily recognized as being but a coincidental side effect of the concomitant progression of the Industrial Revolution, which social development is unique to the most recent cycle of the climatic oscillation.

Moving from one of the northernmost parts of Asia to one of its southernmost parts, de Garidel-Thoron and Beaufort (2001) constructed a 200,000-year history of primary productivity (PP) in the Sulu Sea north of Borneo, based on measurements of abundances of the coccolithophore Florisphaera profunda in a 36-meter giant piston core retrieved from a depth of 3600 meters.  Three time-slices were explored in detail to detect high-frequency cycles in the PP record: one from 160 to 130 thousand years ago (ka), one from 60 to 30 ka, and one from 22 to 4.1 ka.  The finest-scale repeatable feature observed in all three time-slices was a climate-driven PP oscillation that had a mean period of approximately 1500 years.  The two scientists say the occurrence of this PP cycle in the three different time-slices is suggestive of "a common origin and an almost stationary signal across different climatic conditions."  They also point out the PP cycle's similarity to the 1470-year temperature cycle observed by Dansgaard et al. (1984) in the Camp Century δ18O ice core record, the ~1500-year δ18O and chemical marker cycles observed by Mayewski et al. (1997) in the Summit ice core, the 1470-year climate cycle found by Bond et al. (1997) in North Atlantic deep-sea cores, and the 1500-year climate cycle found by Campbell et al. (1998) in an Alaskan lake.  These observations lead them to suggest there is a common origin for the cyclicity in the climate of both high and low latitudes, which view is shared by Bond et al. (2001), who attribute the origin of this cyclicity to solar forcing.

Also studying the last two glacial-interglacial cycles were Ding et al. (1999), who used a technique based on the grain sizes of particles in soil cores removed from sections of the northwestern part of the Chinese Loess Plateau to reconstruct a high-resolution record of climate changes over this period.  They report that "frequent, large-amplitude climatic oscillations on millennial timescales occurred during the penultimate glaciation in a manner similar to that during the last glaciation, suggesting that suborbital-scale climatic variations may be a common feature of the climate system during glacial periods."  During interglacial periods, on the other hand, there were no indications of amplitudes associated with these cycles that were any greater than that observed over the Medieval Warm Period to Little Ice Age transition, which suggests we should not experience the type of catastrophic global warming typically predicted to occur by climate alarmists in response to the ongoing rise in the air's CO2 content.  That degree of climate variability is just not manifest during interglacial periods.

Others working on the Chinese Loess Plateau were Ji et al. (2004), who analyzed high-resolution hematite (Hm) and goethite (Gt) data they obtained by diffuse reflectance spectroscopy, together with grain size and magnetic susceptibility data derived from two sections of the Loess Plateau (Huanxian and Yanchang), with the goal of learning something about the behavior of the East Asian Monsoon (EAM).  Their work revealed that the Hm/Gt history displays "a series of abrupt and pronounced humid and dry events which compare to the Dansgaard-Oeschger cycles and Heinrich events described in the North Atlantic Ocean and Greenland (Heinrich, 1988; Bond et al., 1993; Broecker, 1994)," with the highest ratios reflecting driest conditions, corresponding to stadials or Heinrich events at high latitudes, and the lowest ratios reflecting humid times, coinciding with interstadials or Dansgaard-Oeschger cycles.  They further note that "these pronounced humid and dry events reveal a pattern of significantly enhanced and reduced summer EAM moisture or precipitation on a millennial scale," which is "closely correlated to tropical hydrological cycles and supports a potent role of tropical Pacific changes in the millennial-scale oscillations of EAM."  Their results also demonstrate the importance of including precipitation as an integral part of this pervasive climate cycle, as done by Soon and Baliunas (2003) and Soon et al. (2003), but as criticized by Mann et al. (2003).

In a study conducted on the Tibetan Plateau, Hong et al. (2003) developed "a high-resolution composite proxy record for the Indian Ocean summer monsoon spanning around 12,000 years based on the δ13C time series of both a single plant species (Carex mulieensis) remains cellulose and the total plant assemblage cellulose in the Hongyuan peat bog from the Tibet Plateau."  They found that "on centennial to millennial time scales there is a close teleconnection between the Indian Ocean summer monsoon variations and the abrupt climate change events characterized by the IRD [ice-rafted debris] events in the North Atlantic over the last 12,000 years."  In fact, they report that "corresponding to each of the eight IRD events in the North Atlantic the monsoon strength decreased clearly, which shows that the close correlation between the Indian Ocean summer monsoon and the North Atlantic climate is present not only in the last glacial, but also in the Holocene."

Also working on the Tibetan Plateau were Wang et al. (2002), who studied changes in δ18O and NO3- in an ice core retrieved from the Guliya Ice Cap.  They identified two cold events, a weak one around 9.6-9.2 ka and a strong one universally referred to as the "8.2 ka cold event."  They report that these events occurred "nearly simultaneously with two ice-rafted episodes in the North Atlantic Ocean."  Noting that evidence for the 8.2 ka cold event "occurs in glacial and lacustrine deposits from different areas," Wang et al. say this evidence "suggests that the influence of this cold event may have been global."  They also say that "comprehensive analyses indicate that the weakening of solar insolation might have been the external cause of the '8.2 ka cold event'," and that "the cause of the cold event around 9.6-9.2 ka was also possibly related to the weaker solar activity."  The authors thus conclude that "millennial-scale climatic cyclicity might exist in the Tibetan Plateau as well as in the North Atlantic."

Yet another study conducted on the Tibetan Plateau was that of Feng and Hu (2005), who derived surface air temperature histories for the last two millennia from ice core and tree-ring data acquired at five different locations.  This work revealed that the late 20th century was the warmest period of the past two millennia at two of the sites (Dasuopu, ice core; Dunde, ice core).  However, such was not the case at the other three sites (Dulan, tree ring; South Tibetan Plateau, tree ring; Guilya, ice core).  At Guilya, it was significantly warmer than it was in the final two decades of the 20th century for most of the first two centuries of the record that comprise the latter part of the Roman Warm Period.  On the South Tibetan Plateau it was also significantly warmer over another full century near the start of the record; while at Dulan it was significantly warmer for the same portion of the Roman Warm Period plus two near-century-long portions of the Medieval Warm Period.  Consequently, for the majority of the data sets investigated, there were several times over the past two millennia when it was significantly warmer, and for longer periods of time, than it was during the late 20th century.  These observations do not bode well for the climate-alarmist claim that the late 20th century experienced temperatures that were unprecedented over the past two millennia, just as it also does not bode well for their refusal to recognize the existence of the millennial-scale climatic oscillation that sequentially brought the earth the Roman Warm Period, the Dark Ages Cold Period, the Medieval Warm Period, the Little Ice Age and the Modern Warm Period.

Working in Inner Mongolia, Jin et al. (2004b) analyzed percent organic carbon and Rb/Sr ratios in a sediment core extracted from the deepest part of Daihai Lake, which is located "in the transitional zone between semi-arid and semi-humid conditions that is sensitive to East Asian monsoon variability."  They report that the two types of data they obtained both "support two distinct Little Ice Age cooling events centered at ~850 yr BP and ~150 yr BP," as well as "the Medieval Warm Period between 1200 and 900 yr BP," which they say "was warmer than the present, with higher chemical weathering than at present," citing the study of Jin et al. (2002) to this effect.  Once again, therefore, we have a study that testifies to the occurrence of the Little Ice Age and Medieval Warm Period in a location far removed from the North Atlantic Ocean, which latter region is the only place on earth where climate alarmists are willing to admit the existence of these multi-century warm and cool periods that result from the millennial-scale oscillation of climate that is a pervasive feature of both glacial and interglacial epochs alike.  In addition, we have yet another part of the world where the Medieval Warm Period has been identified by researchers as having been warmer than it is there currently.

Inner Mongolia was also the site of the study of Jin et al. (2004a), who analyzed magnetic susceptibility (related to summer monsoon intensity), organic matter (related to vegetation coverage and biomass), and granularity (related to wind speed) associated with samples of six aeolian sand layers overlapping six sandy paleosol layers that comprised an uninterrupted stratigraphic profile of the Hunshandake Desert.  Their magnetic susceptibility power spectrum analysis revealed two periodicities, one of which had a value of 1465 years that "approximates," in the words of the six scientists, "the 1450-year period of the North Atlantic Ice floating event and to the arid-humid cycle of 1450-1470 years in Arabia (Pinegina et al., 2003; Sirocko et al., 1996)."  With respect to the most recent 1800-year segment of this pervasive oscillation, they say that "cold events occurred in many regions of China during 240-800 AD (Yang et al., 2002), and even a cold climate event during 1.8-1.4 kaBP had been recorded in the south deep sea of Iceland (Bianchi and McCave, 1999), besides another ice-floating event appeared in [the] North Atlantic at 1.4 kaBP (Bond et al., 1997)."  These several events, of course, were all part of the globe-girdling Dark Ages Cold Period.

Subsequently, Jin et al. report that a "warming event happened in Daihai Lake in the southern part of the study region during 1.2-0.9 kaBP (Jin et al., 2002), and most of the China region had warming event records during 800-1400 AD (Yang et al., 2002), even the track records had been discovered all over the world (Bianchi and McCave, 1999; Stuiver et al., 1997; Cronin et al., 2003), which indicated that this was the Medieval Warm Period."  During the period AD 1300-1800, Jin et al. say their data recorded the last cold event of their study, and that "more records of this cold event had been discovered in China and even in other parts of the world (Bond et al., 1997; Yang et al., 2002; Bianchi and McCave, 1999; Cronin et al., 2003; Wang et al., 1998)."  In addition, they state that "the extreme of this cold event took place at about 400 aBP, corresponding to the Little Ice Age cold event."  Last of all, Jin et al. note that "the arid events of the study area coincided with the cold events in North Atlantic and arid events in middle to low latitudinal zones, which indicated that the periodical change of Holocene climate in Hunshandake Desert has global significance," as evidence continues to pile upon evidence for the reality of a global millennial-scale oscillation of climate that is totally independent of, and totally unforced by, changes in atmospheric CO2 concentration.

In a different approach to the subject, Ma et al. (2003) worked with a stalagmite from Jingdong Cave, which is located about 90 km northeast of Beijing, to reconstruct the climatic history of that part of China for the past 3000 years at 100-year intervals on the basis of δ18O data, the Mg/Sr ratio, and the solid-liquid distribution coefficient of Mg.  Between 200 and 500 years ago (BP, before present), they report that "air temperature was about 1.2°C lower than that of the present, corresponding to the Little Ice Age in Europe."  Earlier, between 1000 and 1300 BP, there was an equally aberrant but warm period that peaked at about 1100 BP, which they say "corresponded to the Medieval Warm Period (AD 900-1300) in Europe."  This time of peak warmth in the Chinese record had been preceded by the Dark Ages Cold Period, which in turn had been preceded by the Roman Warm Period, which in the stalagmite record is best defined by the much colder period that preceded it.  Hence, this study, like that of Kar et al. (2002), demonstrates the exquisite harmony of what occurred in this part of Asia and the regions surrounding the North Atlantic Ocean over the past three millennia.

Turning to review and analysis type studies, Yang et al. (2002) used nine separate proxy climate records derived from peat, lake sediment, ice core, tree ring and other sources to compile a single weighted temperature history for China spanning the past two thousand years.  This composite temperature record revealed five distinct climate epochs: a warm stage from AD 0 to 240 (the tail-end of the Roman Warm Period), a cold interval between AD 240 and 800 (the Dark Ages Cold Period), a return to warm conditions from AD 800-1400 (which included the Medieval Warm Period between AD 800 and 1100), a cool interval between 1400 and 1820 (the Little Ice Age), and the current warm regime (the Modern Warm Period) that followed the increase in temperature that began in the early 1800s.  Another important finding of their study was the fact that the warmest temperatures of the past two millennia were observed during the second and third centuries AD.

Rounding out our summary of papers dealing with the late-Holocene climatic history of Asia is the review and analysis study of Ge et al. (2004), who introduce their assessment of 2000 years of reconstructed winter half-year temperatures of eastern China by saying "it is important to study the temperature change during the past 2000 years for understanding the issues such as the greenhouse effect and global warming induced by human activities," and by additionally stating that "China has advantages in reconstructing historical climate change for its abundant documented historical records and other natural evidence obtained from tree rings, lake sediments, ice cores, and stalagmites."

Ge et al.'s most fundamental finding was the existence of "an about 1350-year periodicity in the historical temperature change," which revealed a number of multi-century warm and cold periods.  Preceding the Modern Warm Period, for example, was the Little Ice Age (LIA), which "in China," in their words, "began in the early 14th century (the 1320s) and ended in the beginning of the 20th century (the 1910s)."  It included four cold stages and three short warming phases.  The LIA, in turn, was preceded by the Medieval Warm Period, which Ge et al. say "began in the 930s and ended in the 1310s."  It was composed of two warm stages, each of over 100 years duration, and a shorter intervening cold stage.

Continuing further back in time, the Chinese scientists found a cold period from the 780s to the 920s and a warm period from the 570s to the 770s, which was in turn preceded by a cold period from the 210s to the 560s, which they say "was the only one comparable with [the] LIA for the past 2000 years."  This ultra-cold spell, of course, was the Dark Ages Cold Period that followed on the heels of the Roman Warm Period.

Since one of the purposes of their study was "to test whether the warming in the 20th century has exceeded the maximum magnitude in the past 2000 years," Ge et al. considered this question in some detail.  At the centennial scale, they report that "the temperature anomaly of the 20th century is not only lower than that of the later warm stage of the Medieval Warm Period (the 1200s~1310s), but also slightly lower than that of the warm period in the Sui and Tang dynasties (the 570s~770s) and the early warm stage of the Medieval Warm Period (the 930s~1100s)."

On a 30-year scale, they likewise report that "the warmest 30-year temperature anomaly in the 20th century is roughly equal to the warmest 30-year one in the Sui and Tang dynasties warm period, but a little lower than that of the Medieval Warm Period."  And on the decadal scale, they say that "the warmest decadal temperature anomaly in the 20th century is approximately at the same level of the warmest decade of the early stage of the Medieval Warm Period."

Last of all, Ge et al. additionally note that "although the warming rate in the early 20th century has reached 1.1°C per century, such a rapid change is not unique during the alternation from the cold period[s] to the warm period[s]" of the prior 2000 years.  For example, they report that the per-century warming rate from the 480s~500s to the 570s~590s was 1.3°C, from the 1140s~1160s to the 1230s~1250s was 1.4°C, and from the 1650s~1670s to the 1740s~1760s was 1.2°C.

In discussing the implications of these several observations of pre-20th-century faster-than-recent warming and higher-than-recent temperatures, Ge et al. say that their analysis "gives a different viewpoint from that 'the 20th century is the warmest century in the past 1000 years', presented by IPCC, and is of great significance for better understanding the phenomena of the greenhouse effect and global warming etc. induced by human activities."  And what would that "different viewpoint" be?   In the words of Ge et al., "the temperature of the 20th century in eastern China is still within the threshold of the variability of the last 2000 years," which observation clearly indicates that the Chinese data provide no evidence for the hypothesis that the eastern part of the country's 20th-century warming - or even a small part of it - was human-induced.

The results of this study and the others reviewed in this summary and its companion summaries strongly suggest that the climate-alarmist claim of unprecedented CO2-induced global warmth in the 20th century is merely a myth.  The warmth of this period did not substantially exceed that of prior warm nodes of the millennial-scale climatic oscillation that has defined Holocene climate variability, nor did it have anything to do with the concomitant rise in the air's CO2 content.  It was simply a manifestation of a naturally-occurring phenomenon that has operated as far back in time as we have the ability to discern (Oppo et al., 1998; Raymo et al., 1998).  These results also serve as a testimony against those who would deny the existence of an extensive (hemispheric or global) Medieval Warm Period and Little Ice Age.  Clearly, it's time for such folks (Mann et al., 1998; Mann et al., 1999; Mann and Jones, 2003) to wake up and recognize the reality of the planet's non-CO2-induced millennial-scale oscillation of climate.

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Last updated 29 June 2005