Turney, C.S.M., Kershaw, A.P., Clemens, S.C., Branch, N., Moss, P.T. and Fifield, L.K. 2004. Millennial and orbital variations of El Niņo/Southern Oscillation and high-latitude climate in the last glacial period. Nature 428: 306-310.
What was done
The authors "present a high-resolution record of surface moisture, based on the degree of peat humification and the ratio of sedges [Cyperaceae] to grass [Poaceae], from northern Queensland, Australia, covering the past 45,000 years."
What was learned
Turney et al. discovered a millennial-scale precipitation cycle with a period of 1470 years that is associated with long-term changes in ENSO in the tropical Pacific Ocean. They also found that the dry periods of this cycle, which occur during periods of frequent El Niņo events (when summer precipitation declines in northeastern Australia) correspond to Dansgaard-Oeschger events in the North Atlantic Ocean that have been shown to be part of a climatic cycle with a period of 1490 years (Bond et al. 1993; Schulz, 2002). Furthermore, they conducted a cross-spectrum analysis that "indicates that variance in the two records at the ~1500-year period is linearly correlated above the 80% confidence interval, and that, within the limitations of the two age models, the two records are in phase." In addition, they note that a similar observation can be made of the coherence between the Cyperaceae/Poaceae ratio and the GISP2 ð18O record (Stuiver and Grootes (2000).
What it means
These observations demonstrate the existence of the globally-coherent millennial-scale oscillation of climate that, during the latter part of the Holocene, has been responsible for producing the Roman Warm Period, Dark Ages Cold Period, Medieval Warm Period, Little Ice Age and, most recently, the beginnings of the Modern Warm Period, which latter climate change is thereby seen to be totally unrelated to the concomitant increase in the air's CO2 content that was spawned by the Industrial Revolution. We clearly do not owe the bulk of our current relative warmth to an augmentation of earth's atmospheric greenhouse gas concentration; it is the result of the pervasive millennial-scale oscillation of climate that prevails throughout ice age and interglacial alike.
Bond, G., Broecker, W., Johnsen, S., McManus, J., Labeyrie, L., Jouzel, J. and Bonani, G. 1993. Correlations between climate records from north Atlantic sediments and Greenland ice. Nature 365: 143-147.
Schulz, M. 2002. The tempo of climate change during Dansgaard-Oeschger interstadials and its potential to affect the manifestation of the 1470-year climate cycle. Geophysical Research Letters 29: 10.1029/2001GL013277.
Stuiver, M. and Grootes, P.M. 2000. GISP2 oxygen isotope ratios. Quaternary Research 53: 277-284.
Reviewed 19 May 2004