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Little Ice Age (Regional - Antarctica) -- Summary
In an attempt to rewrite climatic history, certain scientists involved in the ClimateGate fiasco claimed that the Little Ice Age and Medieval Warm Period were neither global phenomena nor strong enough where they did occur to have a discernable influence on mean global air temperature, in order to make the warming of the latter part of the 20th century appear highly unusual, which they equated with anthropogenic-induced, which they associated with the historical rise in the air's CO2 content, which gave them a reason to call for dramatic reductions in the use of fossil fuels, such as coal, gas and oil, which we believe to be unwarranted. Consequently, we weekly peruse the emerging scientific literature for newly-discovered real-world paleoclimatic evidence related to the question of whether or not the Little Ice Age and Medieval Warm Period were truly global phenomena; and this brief review summarizes what we have learned about the Little Ice Age in Antarctica in this regard over the past few years.

Domack et al. (2001) analyzed ocean sediment cores obtained from a prominent depression -- the Palmer Deep -- located on the inner continental shelf of the western Antarctic Peninsula (64 51.71' S, 64 12.47' W), obtaining thereby a high-resolution proxy temperature history spanning the past 13,000 years. This history displayed five prominent palaeoenvironmental intervals: (1) a Neoglacial cool period beginning 3360 years ago and continuing to the present, (2) a warm mid-Holocene "climatic optimum" from 9070 to 3360 years ago, (3) a cool period beginning 11,460 years ago and ending at 9070 years ago, (4) a warm period from 13,180 to 11,460 years ago, and (5) cold glacial conditions prior to 13,180 years ago.

Subsequent spectral analyses of the data revealed that superimposed upon these broad climatic intervals were decadal and centennial-scale temperature cycles; and throughout the Neoglacial period and continuing to the present, the researchers reported finding "very significant" (above the 99% confidence level) peaks, or oscillations, that occurred at intervals of 400, 190, 122, 85 and 70 years, which they say may have been driven by solar variability. In addition, they noted the presence of a "Little Ice Age" that started about 700 years before present and ended approximately 100 years ago.

Not far away, Khim et al. (2002) analyzed a number of sediment properties and different types of geochemical data obtained from a core removed from the eastern Bransfield Basin just off the northern tip of the Antarctic Peninsula (6158.9'S, 5557.4'W). These data clearly depicted, as they clearly stated, the presence of the "Little Ice Age and Medieval Warm period, together with preceding climatic events of similar intensity and duration." They also wrote 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)," noting further 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)." Indeed, analysis of a sediment core from beneath the Amery Ice Shelf, East Antarctica, suggests that since the cessation of the ice shelf's retreat some 750 14C yr B.P., there has been a major seaward extension of the ice shelf's edge, possibly driven by the cooling that was associated with the development and progression of the Little Ice Age (Hemer and Harris, 2003).

More evidence that the chilling grip of the Little Ice Age enveloped Antarctica came from the study of Stenni et al. (2002), who examined a number of paleoclimatic indicators in two firn cores that were retrieved from the Talos Dome area of East Antarctica, and who compared them with those of other East Antarctica ice core records obtained from Dome C EPICA, Taylor Dome and the South Pole. In the words of these researchers, the several records "suggest cooler climate conditions between the middle of [the] 16th and the beginning of [the] 19th centuries, which might be related to the Little Ice Age (LIA) cold period." In addition, they documented a decrease in snow accumulation rate "during part of the LIA followed by an increment of about 11% in accumulation during the 20th century." And after discussing still other findings, they concluded that "more and more evidence coming from ice core records, glacier extension and other proxy records are leading to the idea that the Antarctic continent or at least East Antarctica also experienced the LIA cool episode."

At about the same time, Hall and Denton (2002) mapped the distribution and elevation of surficial deposits along the southern Scott Coast of Antarctica in the vicinity of the Wilson Piedmont Glacier, which runs parallel to the coast of the western Ross Sea from McMurdo Sound north to Granite Harbor. The chronology of these raised beaches was determined from more than 60 14C dates of incorporated organic materials they had previously collected from hand-dug excavations (Hall and Denton, 1999). They also evaluated more recent changes in snow and ice cover based on aerial photography and observations carried out since the late 1950s. Near the end of the Medieval Warm Period -- "as late as 890 14C yr BP," as they put it -- "the Wilson Piedmont Glacier was still less extensive than it is now." Hence, they concluded that the glacier had to have advanced within the last several hundred years, although its eastern margin had retreated "within the last 50 years."

The two scientists also reported a number of similar observations that had been made by other investigators. Citing evidence collected by Baroni and Orombelli (1994a), they noted there was "an advance of at least one kilometer of the Hell's Gate Ice Shelf ... within the past few hundred years." And they report that Baroni and Orombelli (1994b) "documented post-fourteenth century advance of a glacier near Edmonson's Point." Summarizing these and other findings, they concluded that evidence from the Ross Sea area suggests "late-Holocene climatic deterioration and glacial advance (within the past few hundred years) and twentieth century retreat."

In speaking of the significance of the "recent advance of the Wilson Piedmont Glacier," Hall and Denton stated that it "overlaps in time with the readvance phase known in the Alps [of Europe] as the 'Little Ice Age'," which they note "has been documented in glacial records as far afield as the Southern Alps of New Zealand (Wardle, 1973; Black, 2001), the temperate land mass closest to the Ross Sea region." And they further note that "Kreutz et al. (1997) interpreted the Siple Dome [Antarctica] glaciochemical record as indicating enhanced atmospheric circulation intensity at AD ~1400, similar to that in Greenland during the 'Little Ice Age' (O'Brien et al., 1995)." In addition, they note that "farther north, glaciers in the South Shetland Islands adjacent to the Antarctic Peninsula underwent a late-Holocene advance, which has been correlated with the 'Little Ice Age' (Birkenmajer, 1981; Clapperton and Sugden, 1988; Martinex de Pison et al., 1996; Bjoreck et al., 1996)."

Hall and Denton thus concluded that "the Wilson Piedmont Glacier appears to have undergone advance at approximately the same time as the main phase of the 'Little Ice Age', followed by twentieth-century retreat at some localities along the Scott Coast," although noting that "the magnitude of the late-Holocene advance of the Wilson Piedmont Glacier does not approach that of similar-sized glaciers in the Swiss Alps." Nevertheless, they concluded that "the Wilson Piedmont Glacier record is tantalizing in that it shows glacier advance about the same time as seen in the 'Little Ice Age' elsewhere," which testifies to the global scope and significant cooling of that cold climatic period.

Shortly thereafter, Noon et al. (2003) analyzed oxygen isotopes preserved in authigenic carbonate retrieved from freshwater sediments of Sombre Lake on Signy Island (6043'S, 4538'W) in the Southern Ocean, which they used to construct a 7000-year history of that region's climate. This work revealed that over the past seven millennia, the general trend of temperature at the study site was downward. Of even more interest, 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 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 18O record obtained from southwest Ireland. Then came the Dark Ages Cold period, which was also 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 the Northern Hemisphere. Finally, there was 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. Hence, the entire record provided a striking correspondence with the similar climatic oscillation revealed by MeDermott et al.'s Northern Hemispheric study.

Two years later, Castellano et al. (2005) derived a detailed history of Holocene volcanism from the sulfate record of the first 360 meters of the Dome Concordia ice core that covered the period 0-11.5 kyr BP, after which they compared their results for the past millennium with similar results obtained from eight other Antarctic ice cores. Before doing so, however, they normalized the data at each site by dividing each site's several volcanic-induced sulfate deposition values by the value produced at each site by the AD 1816 Tambora eruption, in order to reduce deposition differences among sites that might have been induced by differences in local site characteristics. This protocol then revealed that most volcanic events in the early last millennium (AD 1000-1500) exhibited greater among-site variability in normalized sulphate deposition than was observed thereafter.

Citing Budner and Cole-Dai (2003) in noting that "the Antarctic polar vortex is involved in the distribution of stratospheric volcanic aerosols over the continent," Castellano et al. went on to say that assuming the intensity and persistence of the polar vortex in both the troposphere and stratosphere "affect the penetration of air masses to inland Antarctica, isolating the continental area during cold periods and facilitating the advection of peripheral air masses during warm periods (Krinner and Genthon, 1998), we support the hypothesis that the pattern of volcanic deposition intensity and geographical variability [higher values at coastal sites] could reflect a warmer climate of Antarctica in the early last millennium," and that "the re-establishment of colder conditions, starting in about AD 1500, reduced the variability of volcanic depositions."

Describing the phenomenon in terms of what it implies, Castellano et al. stated that "this warm/cold step could be like a Medieval Climate Optimum-like to Little Ice Age-like transition." And they additionally cited Goosse et al. (2004) as reporting evidence from Antarctic ice-core dD and 18O data "in support of a Medieval Warming-like period in the Southern Hemisphere, delayed by about 150 years with respect to Northern Hemisphere Medieval Warming." Hence, the ten researchers concluded by postulating that "changes in the extent and intra-Antarctic variability of volcanic depositional fluxes may have been consequences of the establishment of a Medieval Warming-like period that lasted until about AD 1500."

Shortly thereafter, Hall et al. (2006) collected skin and hair -- and even some whole-body mummified remains -- from Holocene raised-beach excavations at various locations along Antarctica's Victoria Land Coast, which they identified by both visual inspection and DNA analysis as coming from southern elephant seals (Mirounga leonina), and which they analyzed for age by means of radiocarbon dating. Results from fourteen different locations within their study region -- which they describe as being "well south" of the seals' current "core sub-Antarctic breeding and molting grounds" -- indicated that the period of time they denominated the Seal Optimum began about 600 BC and ended about AD1400, which latter date they described as being "broadly contemporaneous with the onset of Little Ice Age climatic conditions in the Northern Hemisphere and with glacier advance near [Victoria Land's] Terra Nova Bay."

The US, British and Italian researchers say their findings indicate "warmer-than-present climate conditions" at the times and locations of the identified presence of the southern elephant seal, and that "if, as proposed in the literature, the [Ross] ice shelf survived this period, it would have been exposed to environments substantially warmer than present." Their data also indicate that the level of this warmth (which began with the inception of the Roman Warm Period and ended with the demise of the Medieval Warm Period) was so significant that the intervening Dark Ages Cold Period -- which is readily evident in various types of paleoclimate data obtained from many places around the world -- was not intense enough to drive the seals from Antarctica.

In a very different type of study, and noting that Montzka et al. (2003) indicate that "methyl chloride (CH3Cl) is the largest natural source of chlorine to the stratosphere and the most abundant halocarbon in the troposphere, with a global average mixing ratio of 550 30 parts per trillion (ppt)," Williams et al. (2007) analyzed CH3Cl concentrations in air extracted from a 300-m ice core that was obtained at the South Pole, covering the time period 160 BC to AD 1860. From this material they determined that "CH3Cl levels were elevated from 900-1300 AD by about 50 ppt relative to the previous 1000 years, coincident with the warm Medieval Climate Anomaly (MCA)," and that these levels "decreased to a minimum during the Little Ice Age cooling (1650-1800 AD), before rising again to the modern atmospheric level of 550 ppt."

Noting that "today, more than 90% of the CH3Cl sources and the majority of CH3Cl sinks lie between 30N and 30S (Khalil and Rasmussen, 1999; Yoshida et al., 2004)," the four researchers say "it is likely that climate-controlled variability in CH3Cl reflects changes in tropical and subtropical conditions." In fact, they go on to state that "ice core CH3Cl variability over the last two millennia suggests a positive relationship between atmospheric CH3Cl and global mean temperature."

In perusing their data, it can be seen that the peak CH3Cl concentration measured by Williams et al. during the MCA is -- as best we can determine from the graphical representation of their data -- approximately 533 ppt, which is within 3% of its current mean value of 550 ppt and well within the range of 520 to 580 ppt that characterizes methyl chloride's current variability. Hence, we may validly conclude that the mean peak temperature of the MCA (which we refer to as the Medieval Warm Period) over the latitude range 30N to 30S -- and possibly over the entire globe -- may not have been materially different from the mean peak temperature so far attained during the Current Warm Period, i.e., that of the last few years. And this conclusion suggests that there is nothing unusual, unnatural or unprecedented about the current level of earth's warmth, which further suggests that 20th-century global warming may not have had anything to do with the concomitant historical increase in the atmosphere's CO2 concentration.

Returning to the Little Ice Age, Hall (2007) presented "radiocarbon and geomorphologic data that constrain [the] late-Holocene extent of the Collins Ice Cap on Fildes Peninsula (King George Island, South Shetland Islands: 6210'51"S, 5854'13"W)," and these data, in her words, "yield information on times in the past when climate in the South Shetland Islands must have been as warm as or warmer than today," based on field mapping of moraines and glacial deposits adjacent to the ice cap, as well as radiocarbon dates of associated organic materials. In addition, her data "indicate ice advance after ~650 cal. yr BP (AD ~1300)," which she notes is "broadly contemporaneous with the 'Little Ice Age', as defined in Europe." Hall also says that this was "the only advance that extended beyond the present ice margin in the last 3500 years, making the Little Ice Age in that part of the world likely the coldest period of the current interglacial. And the fact that "the present ice cap margin ... is still more extensive than it was prior to ~650 cal. yr BP" leads her to conclude that the climate prior to that time -- which would have comprised the Medieval Warm Period -- may have been "as warm as or warmer than present." These observations help to demonstrate the worldwide nature of the millennial-scale oscillation of climate that has alternately brought the planet century-scale warm and cold periods independent of any variations in atmospheric CO2 concentration.

Last of all, we come to the study of Li et al. (2009), who conducted chemical analyses of a shallow (82.5-m) ice core that they obtained from "a location [7632.5'S, 7701.5'E] in the essentially unexplored area of Princess Elizabeth Land, East Antarctica," which they used to construct "a continuous, high-resolution 780-year (AD 1207-1996) glaciochemical record." As they describe it, "the period of AD 1450-1850 in this record is characterized by sharply reduced snow accumulation rates and decreased concentrations of several chemical species that suffer post-depositional losses linked to very low accumulation rates." In fact, they found that "the average accumulation rate between 1450 and 1810 is nearly 80% lower than the twentieth century average," noting that "such sharply reduced accumulation suggests that the climate conditions in this region during this period of 400 years were colder than the earlier and later periods." And they correctly state that "this period of unusually cold climate conditions in the eastern Indian Ocean sector in East Antarctica coincides with the time frame of the Little Ice Age, which has been found to be a common neoglacial episode in many Northern Hemisphere locations and in a few places in the Southern Hemisphere."

So if there was a Little Ice Age in Antarctica that separated the Current Warm Period from something else, that "something else" must have been the Medieval Warm Period, which is thus demonstrated by the study of Li et al. to have occurred in Princess Elizabeth Land, where Roberts et al. (2001) also found evidence for it. In addition, Li et al. report that the Little Ice Age has been demonstrated to have made its presence felt at Antarctica's Law Dome (Morgan and Van Ommen, 1997), Dronning Maud Land (Karlof et al., 2000), Northern Victoria Land (Stenni et al., 2002), and the Antarctic Peninsula (Fabres et al., 2000; Domack et al., 2001; Shevenell and Kennett, 2002). Hence, the Medieval Warm Period must have preceded the Little Ice Age at these locations as well, reconfirming the global presence of that earlier low-CO2 high-temperature period that climate alarmists are reticent to recognize, because of the implications it holds for the non-CO2-induced global warming of the 20th century.

In conclusion, it is clear that the emerging scientific literature continues to report ever more evidence for the occurrence of the Little Ice Age in Antarctica, in contradiction of the claims of climate alarmists that this climatic interval was localized to regions about the North Atlantic Ocean. This literature also highlights the inherent natural variability of climate, and suggests the high probability that 20th century warming did not have an anthropogenic origin, but was the result of natural variability, as the earth recovered from the global chill of the Little Ice Age.

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Last updated 13 January 2010