Volume 6, Number 48: 26 November 2003
In our Editorial of 19 Nov 2003, we describe the work of Ge et al. (2003), who utilized 200 different sets of phenological and meteorological records to produce 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. This study provided evidence for the existence of what in other parts of the world have come to be called the Roman Warm Period, the Dark Ages Cold Period, the Medieval Warm Period, the Little Ice Age, and the Modern Warm Period. In addition, it indicated that although the temperature of the region rose rapidly during the twentieth century, especially over the period 1981-1999, temperatures during the Medieval Warm Period rose higher still, and remained higher for several 10- and 30-year time periods.
In this Editorial, we describe the somewhat similar work of Bao et al. (2003), who utilized proxy climate records (ice-core ð18O, peat-cellulose ð18O, tree-ring widths, tree-ring stable carbon isotopes, total organic carbon, lake water temperatures, glacier fluctuations, ice-core CH4, magnetic parameters, pollen assemblages and sedimentary pigments) obtained from twenty previously-published studies to derive a 2000-year temperature history of the Tibetan Plateau, after first developing similar temperature histories for its northeastern, southern and western sections. So what did they find?
The temperature histories of the three parts of the Tibetan Plateau were all significantly different from each other. In each case, however, they had one important similarity: there was more than one prior 50-year period of time when the mean temperature of each of them was warmer than it was over the most recent 50-year period. In the case of the northeastern sector of the Tibetan Plateau, these maximum-warmth intervals occurred during the Medieval Warm Period; while in the case of the western sector, they occurred near the end of the Roman Warm Period. In the case of the southern sector, however, they occurred during both warm periods, as well as during the Dark Ages Cold Period! Hence, for all three portions of the Tibetan Plateau, there has been nothing unusual or unnatural about their most recent warm temperatures.
With respect to the entire Tibetan Plateau, the story is pretty much the same: there has been nothing extraordinary about the recent past. For the whole region, however, there was only one prior 50-year period when temperatures were warmer than they were over the most recent 50-year period; and that interval occurred near the end of the Roman Warm Period, some 1850 years ago.
After presenting their findings for the Tibetan Plateau, Bao et al. compare them with those of Wang and Gong (2000) for central east China, which are significantly different. In the latter history, for example, the most recent temperatures are the warmest of the record; but the central east China record of Wang and Gong only goes back about 1200 years and thus does not include the period of most extraordinary warmth found in the record of Boa et al. Hence, the data of Wang and Gong cannot provide a definitive answer to the question of whether the warmth they document in the latter part of the central east China record is unprecedented over the past two millennia.
Nevertheless, it is possible to make this determination with the much longer central east China record of Ge et al. (2003), which is also more up-to-date and more comprehensive in terms of the number of data sets upon which it is based and is thus likely to be more accurate over the entire 2000-year period of concern. When this is done, as noted in our Editorial of 19 Nov 2003, it is found that the most recent warmth of central east China, like that of the Tibetan Plateau, is not unprecedented over the past two millennia. Hence, over two "big chunks of China," we can confidently say that modern temperatures have yet to rise to levels previously experienced over the past two thousand years.
In closing, we additionally note that the Mann and Jones (2003) study of "global surface temperatures over the past two millennia," which claims uniqueness for the warmth of the latter part of the 20th century, actually extends back in time to only AD 200 and, hence, does not include what could well be the warmest portion of the 2000-year period in question, as demonstrated by Boa et al.'s study of the Tibetan Plateau. In fact, even warmer temperatures may have occurred sometime prior to the BC-to-AD transition, as suggested by the study of McDermott et al. (2001).
When all is said and done, therefore, the analyses climate alarmists ask us to accept as definitive with respect to earth's near-surface air temperature history are by no means sufficient to prove the point they and the studies' authors are attempting to make. And, hence, there is no reason to believe that earth's current temperatures could not have risen to their present level without the help of the historical rise in the air's CO2 content.
| Sherwood, Keith and Craig Idso |
References
Bao, Y., Brauning, A. and Yafeng, S. 2003. Late Holocene temperature fluctuations on the Tibetan Plateau. Quaternary Science Reviews 22: 2335-2344.
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.
Mann, M.E. and Jones, P.D. 2003. Global surface temperatures over the past two millennia. Geophysical Research Letters 30: 10.1029/2003GL017814.
McDermott, F., Mattey, D.P. and Hawkesworth, C. 2001. Centennial-scale Holocene climate variability revealed by a high-resolution speleothem ð18O record from SW Ireland. Science 294: 1328-1331.
Wang, S.W. and Gong, D.Y. 2000. Temperature changes in China during several special periods of the Holocene. Progress in Natural Science 10: 325-332.