Earth's climate oscillates on a number of different timescales, one of the longer of which is the millennial-scale oscillation that produced the several-hundred-year relative warm and cool intervals known in the regions surrounding the North Atlantic Ocean as the Roman Warm Period, Dark Ages Cold Period, Medieval Warm Period, Little Ice Age and, most recently, the Modern Warm Period. Climate revisionists such as Mann et al. (1998, 1999) and Mann and Jones (2003), however, are loath to admit the existence and global expression of this cyclical fluctuation of climate, for these properties of the naturally-occurring (and likely solar-induced) phenomenon suggest there is nothing unusual about the development of the Modern Warm Period over the past century or so, which development climate revisionists strive to attribute to the concomitant increase in the air's CO2 content. To challenge them on this issue, we continually scan the emerging scientific literature for studies that demonstrate the existence and characteristics of these several warm and cold periods in different parts of the world; and in this Summary we report on what we have learned about their occurrence in Antarctica, which is about as far removed from the North Atlantic Ocean as one can get and still remain on the planet.
Khim et al. (2002) analyzed sediment properties and geochemical data, including grain size, total organic carbon content, magnetic susceptibility, biogenic silica content, 210Pb geochronology and radiocarbon (14C) age, which were derived from a sediment core that was removed from the eastern Bransfield Basin just off the northern tip of the Antarctic Peninsula. Their efforts revealed, in their words, the presence of the "Little Ice Age and Medieval Warm period, together with preceding climatic events of similar intensity and duration."
Expanding on this statement, the authors say that "two of the most significant climatic events during the late Holocene are the Little Ice Age (LIA) and Medieval Warm Period (MWP), both of which occurred globally (Lamb, 1965; Grove, 1988)." They also note that "evidence of the LIA has been found in several studies of Antarctic marine sediments (Leventer and Dunbar, 1988; Leventer et al., 1996; Domack et al., 2000)." To this list of scientific journal articles documenting the existence of the Little Ice Age in Antarctica can now be added the authors' own paper, which also demonstrates the occurrence of the Medieval Warm Period there, as well as earlier warm and cold periods analogous to the Roman Warm Period and Dark Ages Cold Period of the Northern Hemisphere.
Noon et al. (2003) used measurements of oxygen isotopes preserved in authigenic carbonate retrieved from freshwater sediments of Sombre Lake on the Southern Ocean's Signy Island (60°43'S, 45°38'W) to construct a 7000-year history of that region's climate. Over the past seven millennia, they determined that the general trend of temperature at their study site was downward. Of most interest to us, however, is the millennial-scale oscillation of climate that was apparent in much of the record. About 2000 years ago, after a thousand-year gap in the data, Signy Island 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 came the Dark Ages Cold period, which was contemporaneous with what McDermott et al. observed in the Northern Hemisphere, after which the Medieval Warm Period appeared at the same point in time and persisted for the same length of time that it did in the vicinity of Ireland, whereupon the Little Ice Age set in just as it did in that region of the North Atlantic. Finally, there is an indication of late 20th century warming, but with a long way to go before conditions comparable to those of the Medieval Warm Period are achieved.
Watanabe et al. (2003) describe the large-scale features of the ð18O record obtained from an ice core extracted from Dome Fuji, which is situated about 1,500 km from Vostok in a different sector of East Antarctica, after which they compare this record with the Vostok ðD (deuterium) record, which is also a measure of temperature, over the last three glacial-interglacial cycles that span a period of 330,000 years. Among the many things they learned, three findings stand out. First, they say "the similarities between the inferred Dome Fuji and Vostok climate records, which hold for the whole period and even for very detailed features, are remarkable given the distance between the two sites and a plausible different precipitation origin." Second, they note that the Dome Fuji record adds considerably to the geographical significance of millennial-scale events which, "for the last glacial period (Bender et al., 1999; Blunier and Brook, 2001), are counterparts of the Dansgaard-Oeschger events recorded in the Greenland records (Dansgaard et al., 1993)." Third, the temperature peaks of the last three interglacials (marine stages 5.5, 7.5 and 9.3) "were much warmer than the most recent 1,000 years (~4.5°C for stage 5.5 and up to 6°C for stage 9.3)."
The first of these observations, in the words of Watanabe et al., "clearly supports the conclusion that the broad features of the Vostok record are of geographical significance for a large area (Antarctica and part of the Southern Hemisphere)," which is to say they are of more than just local significance. The second observation demonstrates that the same type of millennial-scale cycling of climate that occurs in the Northern Hemisphere also occurs in the Southern Hemisphere, essentially confirming the global nature of this pervasive phenomenon. The third observation, as we have noted in other of our writings, confirms that earth's current warmth is indeed unprecedented -- and over at least the last third of a million years -- but that its uniqueness lies not in the fact that it is warmer than normal, but that it is very much colder than normal, i.e., than what has been typical of the peak warmth of the several prior interglacials (see our Journal Reviews of Petit et al. (1999) and Herbert et al. (2001), as well as our Editorials of 9 August 2000, 8 May 2002, 26 June 2002 and 2 April 2003).
Taken together, these findings strengthen the emerging realization of most thinking people, i.e., that the Modern Warm Period is simply the most recent incarnation of the warm node of the millennial-scale oscillation of global climate that was manifest in the Medieval Warm Period and the earlier Roman Warm Period, and that if there is anything unusual about these climatic intervals it is that they have all been far cooler than the peak warmth of the most recent prior interglacials, when the air's CO2 content was much lower than it is today, all of which observations suggest that the increase in atmospheric CO2 concentration that began with the Industrial Revolution has had nothing whatsoever to do with the current warmth that was naturally programmed to follow the cold of the Little Ice Age.
No wonder Mann and company (Mann et al., 2003a, 2003b) complain so bitterly about the publication of papers (Soon and Baliunas, 2003; Soon et al., 2003a, 2003b) that reveal the true nature of this phenomenon!
References
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