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Abrupt Changes in the Asian Monsoon
Reference
Dykoski, C.A., Edwards, R.L., Cheng, H., Yuan, D., Cai, Y., Zhang, M., Lin, Y., Qing, J., An, Z. and Revenaugh, J.  2005.  A high-resolution, absolute-dated Holocene and deglacial Asian monsoon record from Dongge Cave, China.  Earth and Planetary Science Letters 233: 71-86.

What was done
High-resolution records of stable oxygen and carbon isotope ratios were obtained from a speleothem recovered from Dongge Cave in south China ((25°17'N, 108°05'E) and utilized in developing a proxy history of Asian monsoon variability over the last 16,000 years.

What was learned
Numerous centennial- and multi-decadal-scale oscillations were present in the record that were up to half the amplitude of interstadial events of the last glacial period, indicating that "significant climate variability characterizes the Holocene."  As to what causes this variability, spectral analysis of δ14C data revealed significant peaks at solar periodicities of 208 yr, 86 yr, and 11 yr, which the authors say is "clear evidence that some of the variability in the monsoon can be explained by solar variability."  However, there are other natural influences related to ocean and atmospheric circulation that also likely contribute to the monsoon's variability, given the fact there was significant spectral power from centennial to sub-decadal scales of non-solar frequencies in Dykoski et al.'s data.  One such other phenomenon is the El Niņo-Southern Oscillation (ENSO), which is likely responsible for significant periodicities in the speleothem record in the 3-6 year band.

What it means
If the Asian monsoon experienced a major fluctuation in our day, climate alarmists would be quick to name global warming as the culprit that caused it.  But where would the proof be?  As the results of this study show, large fluctuations in the Asian monsoon are natural and not uncommon; and there is no reason not to believe that the natural fluctuations reported by Dykoski et al. will continue into the future, independent of any change in the air's CO2 content.

Reviewed 7 September 2005