The revisionist history of Mann et al. depicts a long nearly-linear temperature decline that ends with a dramatic post-1910 warming that, in its final two decades, takes the mean surface air temperature of the Northern Hemisphere to a level that appears unprecedented over the past millennium, while the similarly-developed temperature history of Mann and Jones (2003) extends this "unprecedentedness" back a full two millennia and claims to represent the entire earth.  This latter climatic history of the planet was challenged by Soon and Baliunas (2003) and Soon et al. (2003a), who in turn were challenged by Mann et al. (2003a), who in turn were challenged by Soon et al. (2003b), who in turn were challenged by Mann et al. (2003b), who in turn were, well, you get the idea: the debate continues.  In addition, the revisionist temperature history of Mann et al. was challenged on totally different grounds by McIntyre and McKittrick (2003), who in turn were challenged by Mann and others (this time on the Internet), who in turn were challenged in the same medium by McIntyre and McKitrick, and on and on it goes, again with no end in sight, but see our journal review of McIntyre and McKitrick (2005).

Nevertheless, what had a beginning must eventually have an end; and so will this debate someday come to a screeching halt, most likely as a result of ever-accumulating masses of data that allow ever more temperature histories of ever more parts of the world to be produced with ever more fidelity.  Hence, we here summarize some of the recent findings from China that are germane to this issue and may help to hasten its resolution.

Yang et al. (2002) used nine proxy climate records derived from peat, lake sediment, ice core, tree-ring and other proxy sources to compile a single weighted temperature history for the whole of China that spanned the past two thousand years.  This record revealed five distinct climate epochs: a warm stage from AD 0 to 240 (the last part 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. The record also revealed that the warmest temperatures of the past two millennia were observed during the second and third centuries AD, not the latter part of the 20th century.

Three years later, working with two hundred sets of phenological and meteorological data, Ge et al. (2003b) produced a 2000-year history of winter half-year temperature (October to April, when CO2-induced global warming is projected to be most evident) for the region of China bounded by latitudes 27 and 40°N and longitudes 107 and 120°E.  In describing their results, they note 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, "and around the AD 490s temperature reached about 1°C lower than that of the present (the 1951-80 mean)."

Then, "abruptly," as they describe it, "temperature entered a warm epoch from the AD 570s to 1310s with a warming trend of 0.04°C per century; the peak warming was about 0.3-0.6°C higher than present for 30-year periods, but over 0.9°C warmer on a 10-year basis."  This finding pretty much speaks for itself: for a considerable amount of time during the Medieval Warm Period, this large chunk of China was warmer than has yet to be experienced in modern times during the winter season.

"After the AD 1310s," as Ge et al. continue, "temperature decreased rapidly at a rate of 0.10°C per century; the mean temperatures of the four cold troughs were 0.6-0.9°C lower than the present, with the coldest value 1.1°C lower."  This period, of course, was the Little Ice Age, from which the world appears to still be in processes of recovering.  Last of all, they report that "temperature has been rising rapidly during the twentieth century, especially for the period 1981-99, and the mean temperature is now 0.5°C higher than for 1951-80."  Be that as it may, Ge et al.'s results nevertheless clearly demonstrate that, during the Medieval Warm Period, winter temperatures rose higher still, and for several 10- and 30-year periods.

Working with warm-season (May-August) data, Tan et al. (2004) established an annual layer thickness chronology (LTC) for a stalagmite from Beijing's Shihua Cave and developed a 2650-year (BC 665-1985 AD) warm-season temperature record (WTR) for Beijing by calibrating the LTC with the observed WTR of Tan et al. (2003).  They report that their warm season temperature reconstruction "is consistent with oscillations in total solar irradiance inferred from cosmogenic ¹⁰Be and ¹⁴C," and that it also "is remarkably consistent with Northern Atlantic drift ice cycles that were identified to be controlled by the sun through the entire Holocene [Bond et al., 2001]."

Going backwards in time, both of the above records clearly depict the start of the Modern Warm Period, the Little Ice Age, the Medieval Warm Period, the Dark Ages Cold Period, the Roman Warm Period, and the cold climate at the start of both records.  In light of these findings, Tan et al. conclude that "the synchronism between the two independent sun-linked climate records therefore suggests that the sun may directly couple hemispherical climate changes on centennial to millennial scales."  In addition, the cyclical nature of the millennial-scale oscillation of climate that is evident in both climate records further suggests there is no need to invoke rising atmospheric CO2 concentrations as a cause of the development of the Modern Warm Period.

Utilizing the same warm-season temperature data as Ge et al. (2003b), Ge et al. (2003a) identified a millennial-scale oscillation with a periodicity of approximately 1350 years.  Hence, to see if there was anything unusual or unnatural about the warming of the recent past, and especially the past three decades, they compared similar portions of the two most recent cycles of this natural oscillation by plotting 30-year anomalies of reconstructed temperatures from the AD 1500s-1990s against similar anomalies from the AD 150s-650s and fitting a linear regression to the resulting data.

The scientists report that "the temperature anomaly in the 1980s-1990s is much higher than the regression value," stating that "if the regression value is regarded as the basic value of temperature changes in nature, the unusual high temperature in the 1980s-1990s could likely be regarded as the forcing of the greenhouse effect induced by human activities on climatic changes," which they say "coincides with the conclusion that the greenhouse effect induced by human activities has been increasing remarkably since the 1950s [as] concluded by the IPCC based on results of modeling."

This conclusion, however, is erroneous; for there are other data points that are even further removed from the regression line than is the 1980s-1990s data point; and these more aberrant data points all occurred during the 1600s, well before any major changes in the air's CO2 concentration.  The data point labeled 1635, for example, extends further above the regression line than does the most recent data point, while the very next data point labeled 1665 deviates the most of all, but below the regression line.  What is more, the next data point labeled 1695 reverses course to once again extend further above the line than does the most recent data point.  Hence, the relative warmth of the 1980s-1990s is not at all anomalous; and, therefore, it is not a manifestation of CO2-induced global warming.  It is merely a consequence of natural climatic variability about a well-defined climatic oscillation.

The results of these several studies demonstrate that the so-called unprecedented warmth of the late 20th century is simply a myth, as far as China is concerned.  The apparent great warmth of this period in this particular part of the world was but a manifestation of naturally-induced, regularly-recurring conditions similar to those experienced in prior millennia.  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, as well as an extensive Roman Warm Period and Dark Ages Cold Period, as well as cyclical climate changes in general.  It's time for such folks (IPCC functionaries, climate alarmists and certain politicians) to wake up and recognize the dynamic nature of real-world climate!

In closing, we comment briefly on one final study, that of Zhai and Pan (2003), who derived trends in the frequencies of warm days and nights, cool days and nights, and hot days and frost days for the whole of China for the period 1951-1999, based on daily surface air temperature data obtained from approximately 200 weather observation stations scattered across the country.  The two scientists report that over this period, and especially throughout the 1980s and 90s, there were increases in the numbers of warm days and nights, while there were decreases in the numbers of cool days and nights, consistent with an overall increase in mean daily temperature.  At the extreme hot end of the temperature spectrum, however, the authors report that "the number of days with daily maximum temperature above 35°C showed a slightly decreasing trend for China as a whole," while at the extreme cold end of the spectrum, the number of frost days with daily minimum temperature below 0°C declined at the remarkable rate of 2.4 days per decade.

In terms of human health, these changes in extreme temperature are very beneficial, for as is made abundantly clear in the many scientific journal articles whose reviews we have filed in the Health Effects (Temperature) section of our Subject Index, extreme cold is by far a greater cause of death in humans than is extreme heat; and since extreme cold weather has become less frequent in China without any increase in the frequency of extreme hot weather, it is clear that the global warming (which is defined as an increase in average air temperature) of the last half of the 20th century was a positive thing for the people of the China in terms of their health and longevity.

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