Noon, P.E., Leng, M.J. and Jones, V.J. 2003. Oxygen-isotope (ð18O) evidence of Holocene hydrological changes at Signy Island, maritime Antarctica. The Holocene 13: 251-263.
What was done
Oxygen isotopes preserved in authigenic carbonate retrieved from freshwater sediments of Sombre Lake on Signy Island (60°43'S, 45°38'W) in the Southern Ocean were used to construct a 7000-year history of that region's climate.
What was learned
Over the past seven millennia, the general trend of temperature at the study site has been downward. Of most interest to us, however, is the millennial-scale oscillation of climate that is apparent in much of the record.
Approximately 2000 years ago, after a thousand-year gap in the data, Signy Island is seen to have experienced the relative warmth of the last vestiges of the Roman Warm Period, as delineated by McDermott et al. (2001) on the basis of a high-resolution speleothem ð18O record from southwest Ireland. Then comes the Dark Ages Cold period, which is also contemporaneous with what McDermott et al. observe in the Northern Hemisphere, after which the Medieval Warm Period appears at the same point in time and persists for the same length of time that it does in the vicinity of Ireland, whereupon the Little Ice Age sets in just as it does in the Northern Hemisphere. Finally, there is an indication of late 20th century warming, but with still a long way to go before conditions comparable to those of the Medieval Warm Period are achieved.
What it means
Many climate alarmists refuse to acknowledge that recurring alternating intervals of relative warmth and cold, such as the Medieval Warm Period and Little Ice Age, were ever global in extent, while others refuse to even acknowledge their existence. Now, however, the striking correspondence of this Southern Hemispheric millennial-scale climatic oscillation with the similar climatic oscillation revealed by MeDermott et al.'s Northern Hemispheric study provides convincing evidence for both the reality and global extent of the many several-century-long warm and cold periods that reverberate throughout the Holocene.
This observation is of great significance, because it demonstrates that the global warming of the past century, which led to the demise of the Little Ice Age, is but the most recent phase of a natural climatic oscillation that is totally unrelated to the increase in the air's CO2 content that just happened to coincide with its occurrence.
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.
Reviewed 23 July 2003