Volume 6, Number 47: 19 November 2003
Controversy abounds over the temperature history of the earth, particularly that of the past one to two millennia. The origins of the debate date back only a few years to the papers of Mann et al. (1998, 1999), which describe an analysis that challenged the long-accepted view of most climatologists and prompted the Intergovernmental Panel on Climate Change to disavow their original presentation of the temperature history of the Holocene (Houghton et al., 1990, reproduced in Earth's Climatic History: The Last 10,000 Years). This earlier presentation had clearly indicated there was nothing unusual or unnatural about earth's current temperature, with many prior periods of time having experienced temperatures significantly higher than those of the past few decades.
The revisionist history of Mann et al. depicts a slightly undulating 1700-year temperature decline that ends with a dramatic 20th century warming that raises the mean surface air temperature of the Northern Hemisphere to a level that is unprecedented over the past 1800 years, although the same cannot be credibly claimed for the entire planet, unless the proxy-based record of the globe is extended at its end with modern instrumental data in an "apples and oranges" type of assumed equivalency [see our Journal Review of Mann and Jones (2003)].
This revisionist history of earth's climate was recently 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 end of the debate is nowhere in sight. In addition, the revisionist climate history of Mann et al. was even more recently challenged on totally different grounds by McIntyre and McKittrick (2003), who in turn have been challenged by Mann and others (this time on the Internet), who in turn have been challenged in the same medium by McIntyre and McKitrick, and on and on it goes, again with no end in sight, even on the distant horizon.
Nevertheless, what had a beginning must eventually have an end; and so will this debate someday be decided, most likely by the ever-accumulating masses of data that allow ever more temperature histories of ever more parts of the world to be produced with ever more reliability. Hence, we continue to report on the many new developments in this field that will someday settle the issue once and for all, highlighting the two-millennia temperature history of central east China just published by Ge et al. (2003).
Working with 200 different sets of phenological and meteorological records extracted from a number of historical sources, many of which are described by Gong and Chen (1980), Man (1990, 2004), Sheng (1990) and Wen and Wen (1996), Ge et al. 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. They describe their findings thusly.
"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, 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 over a similarly-extended time span.
"After the AD 1310s, 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, of course, was the Little Ice Age, from which the world appears to still be in processes of recovering.
"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." Although such might well be true, Ge et al. report temperatures during the Medieval Warm Period that rose higher still, and for several 10- and 30-year time periods.
As new data such as these from central east China continue to come to the fore, it is our belief that scientific support for the revisionist climate history of Mann et al. will gradually erode and that this entire sorry episode will be looked back upon with both dismay and disbelief by those who follow us.
|Sherwood, Keith and Craig Idso|
Ge, Q., Zheng, J., Fang, X., Man, Z., Zhang, X., Zhang, P. and Wang, W.-C. 2003. Winter half-year temperature reconstruction for the middle and lower reaches of the Yellow River and Yangtze River, China, during the past 2000 years. The Holocene 13: 933-940.
Gong, G. and Chen, E. 1980. On the variation of the growing season and agriculture. Scientia Atmospherica Sinica 4: 24-29.
Houghton, J.T., Jenkins, G.J. and Ephraums, J.J. (Eds.). 1990. Climate Change: The IPCC Scientific Assessment. Cambridge University Press, Cambridge, UK.
Man, Z. 1990. Study on the cold/warm stages of Tang Dynasty and the characteristics of each cold/warm stage. Historical Geography 8: 1-15.
Man, Z. 2004. Climate Change in Historical Period of China. Shandong Education Press, Ji'nan, China, in press.
Mann, M., Amman, C., Bradley, R., Briffa, K., Jones, P., Osborn, T., Crowley, T., Hughes, M., Oppenheimer, M., Overpeck, J., Rutherford, S., Trenberth, K. and Wigley, T. 2003a. On past temperatures and anomalous late-20th century warmth. EOS, Transactions, American Geophysical Union 84: 256-257.
Mann, M., Amman, C., Bradley, R., Briffa, K., Jones, P., Osborn, T., Crowley, T., Hughes, M., Oppenheimer, M., Overpeck, J., Rutherford, S., Trenberth, K. and Wigley, T. 2003b. Response [to Soon et al. (2003b)]. EOS, Transactions, American Geophysical Union 84: 273, 276.
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Mann, M.E., Bradley, R.S. and Hughes, M.K. 1999. Northern Hemisphere temperatures during the past millennium: Inferences, uncertainties, and limitations. Geophysical Research Letters 26: 759-762.
Mann, M.E. and Jones, P.D. 2003. Global surface temperatures over the past two millennia. Geophysical Research Letters 30: 10.1029/2003GL017814.
McIntyre, S. and McKitrick, R. 2003. Corrections to the Mann et al. (1998) proxy data base and Northern Hemispheric average temperature series. Energy and Environment 14: 751-771.
Sheng, F. 1990. A preliminary exploration of the warmth and coldness in Henan Province in the historical period. Historical Geography 7: 160-170.
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