Climate alarmists are loath to acknowledge the existence of the naturally-occurring, non-CO2-induced, millennial-scale oscillation of climate that periodically brings the planet multi-century intervals of relative warmth that equal or surpass that of the Modern Warm Period. And why are they unwilling to acknowledge this fact? Because it erodes their basis for claiming that earth's modern warmth is caused by anthropogenic CO2 emissions. Hence, they also have a need to disavow the existence of the cold nodes of the oscillation. Most prominent in this regard is their unwillingness to acknowledge that the Little Ice Age, which preceded the Modern Warm Period, was anything more than a minor regional phenomenon that only affected countries bordering the North Atlantic Ocean. In this Summary, therefore, we review what is known about the severity and global extent of the earlier Dark Ages Cold Period that preceded the Medieval Warm Period, focusing on studies conducted in Asia.
Kar et al. (2002) explored the nature of climate change in the Western Himalaya region of India over the past 2000 years via pollen analyses of a sediment profile they obtained from an outwash plain located approximately 3 km from the snout of the Gangotri Glacier, which serves as the source of the Holy Ganga River. Between 2000 and 1700 years ago, their data reveal that the climate there was cooler "than the one prevailing at present," as they describe it, which corresponds well with what we know about the Dark Ages Cold Period from data collected in the only part of the world where climate alarmists admit it may have occurred: Europe.
Using nine separate climate records derived from peat, lake sediment, ice core, tree ring and other proxy sources in other parts of Asia, Yang et al. (2002) compiled a single weighted temperature history for all of China that spanned the past two thousand years. This record revealed the existence of a Dark Ages Cold Period between AD 240 and 800, just after the end of the Roman Warm Period. Likewise, Xu et al. (2002) studied plant cellulose δ18O variations in cores retrieved from peat deposits at the northeastern edge of the Qinghai-Tibetan Plateau of China. Following the demise of the Roman Warm Period, they too found evidence for the Dark Ages Cold Period, noting the existence of three major cold events centered at approximately 500, 700 and 900 AD.
Working in the central Himalayas of Tibet, Yao et al. (2002) derived a 2000-year proxy temperature (δ18O) history from an ice core retrieved from Dasuopu glacier. This record revealed, in their words, that temperature in the first century AD "was low and followed by a significant increase until 730 AD," whereupon it "reached its maximum during 730-950 AD, then it lowered again, which persisted until 1850 AD," after which temperature "increased gradually to its present levels."
The first of these intervals again corresponds to the Dark Ages Cold Period, while the others are the Medieval Warm Period, Little Ice Age and Modern Warm Period. Their occurrence in China demonstrates the importance of looking at more than just the past thousand years when attempting to gain the understanding of natural climate variability that is needed to determine what may or may not have been a contributing factor to the temperature increase of the 20th century. As Yao et al. describe the situation, "if we just analyze temperature changes in [the most] recent 1 ka, we may draw a wrong conclusion that [the] temperature recorded in [the] Dasuopu ice core goes beyond the natural variability range [near its end]," which, we might add, it clearly does not.
Paulsen et al. (2003) analyzed high-resolution records of δ13C and δ18O in a stalagmite from Buddha Cave to infer changes in climate in central China over the last 1270 years in terms of warmer or colder and wetter or drier conditions. Their record begins in the depths of the Dark Ages Cold Period, which ends about AD 965 with the commencement of the Medieval Warm Period, which continues to about AD 1475, whereupon the Little Ice Age sets in and holds sway until about AD 1825, after which the warming responsible for the Modern Warm Period begins. Their data also reveal a number of other cycles superimposed on the major millennial-scale cycle of temperature and an imbedded centennial-scale cycle of moisture, which they attribute to cyclical solar and lunar phenomena.
Working with a stalagmite from Jingdong Cave about 90 km northeast of Beijing, Ma et al. (2003) assessed the climatic history of 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 (aBP), 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 aBP, there was an equally aberrant but warm period that peaked at about 1100 aBP, which they say "corresponded to the Medieval Warm Period (AD 900-1300) in Europe." This period of peak warmth, in turn, had been preceded by the Dark Ages Cold period and the still earlier Roman Warm Period, which latter optimal climate was best defined by the colder period that had preceded it.
Working with 200 different sets of phenological and meteorological records extracted from a number of historical sources, Ge et al. (2003,2004) produced a 2000-year history of winter half-year temperature for the region of China bounded by latitudes 27 and 40°N and longitudes 107 and 120°E. They found that "from the beginning of the Christian era, climate became cooler at a rate of 0.17°C per century," which correlates well with the fact that this is the period of time when the planet slipped out of the Roman Warm Period and entered into the Dark Ages Cold Period. Continuing, they note that "around the AD 490s temperature reached about 1°C lower than that of the present (the 1951-80 mean)," after which temperature warmed from the AD 570s to 1310s at the slow rate of 0.04°C per century as the Dark Ages Cold Period gradually came to an end. In addition, the work of Feng and Hu (2005) reveals the existence of the Dark Ages Cold Period in four other 2000-year temperature records from the Tibetan Plateau (Dunde, ice core; Dulan, tree ring; South Tibetan Plateau, tree ring; Guilya, ice core).
Far to the south, and at a much lower elevation, Wei et al. (2004) obtained high-resolution Sr/Ca ratios of two Porites corals from the coast of the Leizhou Peninsula in the northern South China Sea using inductively coupled plasma atomic spectrometry, while the ages of the corals were determined via U-Th dating, after which a transfer function relating the Sr/Ca ratio to temperature was derived for a modern Porites lutea coral by calibrating against sea surface temperatures (SSTs) measured from 1989 to 2000 at a nearby meteorological station. One of the two coral sections was dated to AD 489-500 in the middle of the Dark Ages Cold Period, while the other was dated to 539-530 BC in the middle of the Roman Warm Period. For the Dark Ages Cold Period portion of the coral record, Wei et al. determined that the average annual SST was approximately 2.0°C colder than it was during the last decade of the 20th century, while for the Roman Warm Period portion of the record they obtained a mean annual temperature that was identical to that of the 20th century's last decade.
Rounding out our summary of the Dark Ages Cold Period in Asia, Hsu (2004) recounts some fascinating history of a region of China south of Inner Mongolia that lies some 380 km west of Beijing and 500 km north of Luoyang in Shanxi Province. The Taiwanese scientist begins by saying the ancient historian Sima Guang (1019~1086 AD) wrote that in AD 494, during the Dark Ages Cold Period, "the Emperor of Wei moved his capitol to Luoyang because of the severe climate that often occurred at Pingcheng, where snowfall in June and dust storms are common." In addition, he notes that Hezhenshan, a shrine mountain northeast of Datong, was covered with snow and frost in both winter and summer at the time of the capitol's relocation, and that "during summer, birds were frozen to death."
Hsu also writes that "the existence of 'ice-houses' built on Fuzhoushan in Nanjiang around AD 500 showed that the winter temperature and annual temperature during that time were approximately 2°C and 1°C lower, respectively, than that at present" (Zhu, 1979). In addition, he reports that "tree-ring analyses on the Tibet Plateau support the conclusion of a cold-spell in the period between 300 AD and 600 AD" (Zhang et al., 2000), that "analyses of organic constituents for the lake sediment of Daguihu in Taiwan Province showed that there was an obvious cold and dry trend from 420 AD to 500 AD" (Luo et al., 1997), and that "analyses of stalagmites collected near Beijing also revealed that a cold period existed around 500 AD" (Tan et al., 2003).
Finally, noting that frost events are meticulously recorded in the ancient documents of Weishu, Zizhitongjian and Shanxitongzhi, Hsu was able to compare the 30-year Beiwei Frost Season (BFS) of the period 479 AD to 509 AD with the Recent Frost Season (RFS) of the last 30 years. In doing so, he found that "the BFS, on average, started 13.55 days earlier and ended 8.97 days later than the RFS," indicative of a 22.52-day extension of the BFS compared to the RFS. And since "changes in the duration of frost period are directly related to air temperature," according to Hsu, "the additional 22.52 days of frost from 479 AD to 509 AD could correspond to a decrease of the lowest temperature by 2.48°C when compared with the RFS."
These observations suggest that the transference of governmental powers from the location of present-day Datong to Luoyang in 494 AD may indeed have been prompted by the severe cold of that time, which is part of the 210 to 560 AD cold period that Ge et al. (2004) describe as "the only one comparable with [the] Little Ice Age for the past 2000 years." It is little wonder, therefore, that this earlier period of close-to-equivalent low temperatures is known far and wide as the Dark Ages Cold Period, but truly amazing that the world's climate alarmists claim it never existed. On the other hand, it's probably not so amazing, considering that to acknowledge the existence of the Roman Warm Period, Dark Ages Cold Period, Medieval Warm Period and Little Ice Age is to acknowledge the existence of the naturally-occurring, non-CO2-induced, millennial-scale oscillation of climate that is likely responsible for the Modern Warm Period. That's something the world's climate alarmists truly can't acknowledge, for it undermines everything for which they've worked so long and hard to achieve in the political arena.
References
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Last updated 11 May 2005