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Decadal-Scale Climate Oscillations (Asia) -- Summary
Earth's climate is forever changing, on one time scale or another.  Over the past million years, the 100,000-year glacial-interglacial cycle has been the most pronounced of these climatic periodicities; but there is also evidence for a pattern of persistent millennial-scale, centennial-scale and decadal-scale climate oscillations.  Our understanding of these naturally-occurring cycles, including their causes and periodicities, is crucial to the global warming debate; for the reality and consistency of these phenomena could indicate that the warming of the past century or so may have been nothing more than the natural "next phase" of climatic progression following on the heels of the Little Ice Age.  In this summary, we thus examine some of these natural climate cycles at decadal time-scales as manifest in Asia.

We begin with the study of Xu et al. (2002), who analyzed plant cellulose 18O variations in cores retrieved from peat deposits at the northeastern edge of the Qinghai-Tibetan Plateau (32 46'N, 102 30'E), China.  Power spectrum analyses of their data revealed decadal- and centennial-scale periodicities of 79, 88 and 123-127 years, "suggesting," in the words of the authors, "that the main driving force of Hongyuan climate change is from solar activities."

The past climate of the Qinghai-Tibet Plateau was also studied by Yafeng et al. (1999), who analyzed high-resolution records of 18O obtained from the Guliya ice cap (35.2N, 81.5E) as a proxy for temperature over the past 2000 years.  Among other things, these authors report there have been 33 abrupt climatic shifts on the order of 3C that took place over the course of two or three decades over the past 2000 years.  Furthermore, among these 33 abrupt decadal-scale transitions, there have been "several large ones," including a 7C decrease between 250 and 280 AD and a 7C increase between 550 and 580 AD.  Another 7C increase was seen over the longer time interval between 1120 and 1260 AD, corresponding to the Medieval Warm Period.

Further south and west, Berger and von Rad (2002) analyzed two cores of varved sediments retrieved from the upper continental slope of the Arabian Sea west of Karachi, Pakistan (2450' N, 6555' E) that covered close to the past 5000 years, searching for "cyclicity in the series of varve thickness ('varve' cycles), of unusually large excursions in varve thickness ('agitation' cycles), and of abundance of turbidites ('turbidite' cycles)."  From the analysis, the authors determined there were a number of high-frequency decadal-scale cycles with periods ranging from 10 to 100 years.  Because a large proportion of the cycles were composed of multiples of basic tidal cycles, the authors ascribed a large proportion of the cyclicity they discovered to tidal action.

Lastly, much closer to the present, Kripalani and Kulkarni (2001) examined seasonal summer monsoon (June-September) rainfall data from 120 east Asia stations for the period 1881-1998.  A series of statistical tests revealed the presence of short-term variability in rainfall amounts on decadal and longer time scales, the longer "epochs" of which were found to last for about three decades over India and China and approximately five decades over Japan.  In spite of year-to-year fluctuations and the decadal variability in the rainfall records, no significant long-term trends were observed in the data.  As for the decadal variability inherent in the record, the authors state that it "appears to be just a part of natural climate variations."

In view of these several real-world observations of decadal-scale climate variability in Asia, as well as elsewhere (see our other Climate Oscillations - Decadal Variability sub-categories), it should be clear we must have a solid understanding of their past history and current status before anything can be said about the cause of what climate alarmists claim to be the unprecedented warming of the past two decades, which they are clearly much too quick to attribute to anthropogenic CO2 emissions.

Berger, W.H. and von Rad, U.  2002.  Decadal to millennial cyclicity in varves and turbidites from the Arabian Sea: hypothesis of tidal origin.  Global and Planetary Change 34: 313-325.

Kripalani, R.H. and Kulkarni, A.  2001.  Monsoon rainfall variations and teleconnections over south and east Asia.  International Journal of Climatology 21: 603-616.

Overpeck, J. and Webb, R.  2000.  Nonglacial rapid climate events: Past and future.  Proceedings of the National Academy of Sciences USA 97: 1335-1338.

Xu, H., Hong, Y., Lin, Q., Hong, B., Jiang, H. and Zhu, Y.  2002.  Temperature variations in the past 6000 years inferred from 18O of peat cellulose from Hongyuan, China.  Chinese Science Bulletin 47: 1578-1584.

Yafeng, S., Tandong, Y. and Bao, Y.  1999.  Decadal climatic variations recorded in Guliya ice core and comparison with the historical documentary data from East China during the last 2000 years.  Science in China Series D-Earth Sciences 42 Supp.: 91-100.