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Climate Oscillations (Millennial Variability - North America) -- Summary
Bordering the North Atlantic Ocean, North America would logically be expected to provide considerable proxy evidence for the existence of the millennial-scale oscillation of climate that is so clearly revealed in the meticulous work of Bond et al. (1997, 2001). And it does!

Levac (2001) examined the Holocene history of Canada's Atlantic region using a high-resolution palynological record from the Scotian Shelf (La Have Basin). This record revealed that sea surface temperatures in February and August were up to 5C warmer than those of today from approximately 10,500 to 8,500 years ago. They then declined for the next 2,000 years, after which August temperatures generally remained similar to the August temperatures of today, while February temperatures remained about 2C warmer than what is currently the norm. Modest exceptions to these general conditions occurred at approximately 1000-year intervals, when regularly-recurring periods of significantly colder temperatures prevailed.

In another study from Canada, but on the opposite side of the continent, Cumming et al. (2002) studied a sediment core retrieved from Big Lake on the Cariboo Plateau of British Columbia, carefully dating it and deriving estimates of changes in climatically sensitive limnological variables (salinity and lake depth) from transfer functions based on modern distributions of diatom assemblages in 219 lakes of western Canada. On the basis of observed changes in diatom composition patterns over the past 5,500 years, they report that "alternating millennial-scale periods of high and low moisture availability were inferred, with abrupt transitions in diatom communities occurring 4960, 3770, 2300 and 1140 cal. yrs. BP." They also indicate that "periods of inferred lower lake depth correspond closely to the timing of worldwide Holocene glacier expansions," and that the mean length of "the relatively stable intervals between the abrupt transitions ... is similar to the mean Holocene pacing of IRD [ice rafted debris] events .. in the North Atlantic," which have been described by Bond et al. (1997) and attributed to "solar variability amplified through oceanic and atmospheric dynamics," as detailed by Bond et al. (2001).

Also working in British Columbia at high elevations in the upper Bowser River Basin in the northern Coast Mountains, Clague et al. (2004) documented glacier and vegetation changes via studies of the distributions of glacial moraines and treelines, tree-ring data, cores from two small lakes that were sampled for a variety of analyses (magnetic susceptibility, pollen, diatoms, chironomids, carbon and nitrogen content, 210Pb, 137Cs, 14C), similar analyses of materials obtained from pits and cores from a nearby fen, and by accelerator mass spectrometry radiocarbon dating of plant fossils, including wood fragments, tree bark, twigs and conifer needles and cones. Their diverse measurements yielded evidence of a glacial advance that began about 3000 years ago and "may have lasted for hundreds of years," which would have placed it within the unnamed cold period that preceded the Roman Warm Period. They then describe evidence for a second "minor phase of activity [that] began about 1300 years ago but was of short duration," which would have placed it within the Dark Ages Cold Period. Then they describe the "third and most extensive Neoglacial interval [that] began shortly after AD 1200 [following the Medieval Warm Period] and ended in the late 1800s," which was, of course, the Little Ice Age, during which period they say "glaciers achieved their greatest extent of the past 3000 years and probably the last 10,000 years." Thereafter, they report that the "climate warmed about 1-2C during the 20th century, accompanied by a rise in treeline, an increase in coniferous tree cover in the subalpine zone, and an increase in the temperature and biological productivity of ponds."

Further north, and noting that "knowledge of natural climatic variability is essential for evaluating possible human impacts on recent and future climate changes," Hu et al. (2001) "conducted multiproxy geochemical analyses of a sediment core from Farewell Lake in the northwestern foothills of the Alaska Range," obtaining what they describe as "the first high-resolution quantitative record of Alaskan climate variations that spans the last two millennia." This climate history suggested, in their words, that "at Farewell Lake SWT [surface water temperature] was as warm as the present at AD 0-300 [during the Roman Warm Period], after which it decreased steadily by ~3.5C to reach a minimum at AD 600 [during the depths of the Dark Ages Cold Period]." From that point in time, they say that "SWT increased by ~3.0C during the period AD 600-850 and then [during the Medieval Warm Period] exhibited fluctuations of 0.5-1.0C until AD 1200." Completing their narrative, they say that "between AD 1200-1700, SWT decreased gradually by 1.25C [as the world descended into the depths of the Little Ice Age], and from AD 1700 to the present, SWT increased by 1.75C," the latter portion of which warming led to the development of the Current Warm Period.

In commenting on these findings, Hu et al. remark that "the warmth before AD 300 at Farewell Lake coincides with a warm episode extensively documented in northern Europe ... whereas the AD 600 cooling is coeval with the European 'Dark Ages'." They also say that "the relatively warm climate AD 850-1200 at Farewell Lake corresponds to the Medieval Climatic Anomaly, a time of marked climatic departure over much of the planet." And they say that "these concurrent changes suggest large-scale teleconnections in natural climatic variability during the last two millennia, likely driven by atmospheric controls."

Noting further that "20th-century climate is a major societal concern in the context of greenhouse warming," Hu et al. concluded by reiterating that their record "reveals three time intervals of comparable warmth: AD 0-300, 850-1200, and post-1800," and they say that "these data agree with tree-ring evidence from Fennoscandia, indicating that the recent warmth is not atypical of the past 1000 years," in unmistakable contradiction of those who claim that it is.

Dropping all the way down to California, and noting there is a "problem of detecting effects of anthropogenic forcing on natural climate change," Field and Baumgartner (2000) developed "a robust time series of stable isotope [δ18O from Neogloboquadrina dutertrei] variability over the past millennium from the varved sediments of the Santa Barbara Basin," which they related to observed environmental variability within this part of the California Current over the past half-century, wherein they demonstrate that "thermal variability dominates the δ18O signal." Armed with this knowledge they inferred that "an anomalously warm coastal ocean persisted at the multicentennial-scale from roughly AD 1200 to 1450," which time interval, as they describe it, "coincides with the age generally assigned to the 'Medieval Warm Period'." They also report that "the period of positive anomalies in the low-frequency series of δ18O from N. dutertrei that continues from ~AD 1450 to ~1800 is consistent with the dates associated with the cooling and neoglaciation of the 'Little Ice Age' in both the Southern and Northern Hemispheres." In addition, they note that "the long-term ocean warming and cooling of the California Current region appears to be in phase with the warming and cooling of the midlatitude North Atlantic described by Keigwin (1996)."

Crossing back to the east coast of the United States, Willard et al. (2005) utilized pollen assemblages identified in four sediment cores extracted from the mainstem of Chesapeake Bay as a proxy for the winter temperature of this region over the past 10,000 years. Multi-taper harmonic and power spectral analyses of these data revealed five highly significant centennial- to millennial-scale oscillations with periods of 148, 177, 282, 521 and 1429 years, the troughs of the latter of which oscillations are temporally correlated with relatively prolonged minima in Pinus abundance and represent winter temperature declines of up to 2C. The most recent such minimum was associated with the Little Ice Age and represented a two-stage event. The first and more severe low-temperature stage occurred between 650 and 550 years BP, while the second occurred between 450 and 350 years BP. With respect to the cause of the 1429-year oscillation, Willard et al. note that the climate cycle correlates well with a similar-scale cycle of solar activity evident in cosmogenic isotope records. In addition, they say it is well correlated with proxy climate cycles found in records from Greenland, the North Atlantic and Alaska, which have also been shown to be correlated with cyclical changes in solar activity.

In New Jersey, Li et al. (2006) recovered a 14,000-year mineral-magnetic record from a hardwater lake (White Lake) containing organic-rich sediments. They report that "comparison of the White Lake data with climate records from the North Atlantic sediments shows that low lake levels at ~1.3, 3.0, 4.4, and 6.1 ka [1000 years before present] in White Lake occurred almost concurrently with the cold events at ~1.5, 3.0, 4.5, and 6.0 ka in the North Atlantic Ocean (Bond et al., 2001)," and that "these cold events are associated with the 1500-year warm/cold cycles in the North Atlantic during the Holocene" that have "been interpreted to result from solar forcing (Bond et al., 2001)." The four researchers go on to conclude that "the close correlation between White Lake and the North Atlantic suggests that, in response to the decreased temperatures, the White Lake area climate [is] expressed as periods of reduced moisture abundance," and, therefore, that "the Holocene 1500-year lake level fluctuations of White Lake probably represent responses to the broad-scale climate variability in the continental North Atlantic region."

Another eastern seaboard study of note was conducted by Noren et al. (2002), who employed a variety of techniques to identify and date terrigenous in-wash layers that depict the frequency of storm-related floods in sediment cores that were extracted from thirteen small lakes distributed across a 20,000-km2 region of Vermont and eastern New York, USA. The results of their analysis indicated that "the frequency of storm-related floods in the northeastern United States has varied in regular cycles during the past 13,000 years (13 kyr), with a characteristic period of about 3 kyr."

There were four major storminess peaks during this period, occurring at approximately 2.6, 5.8, 9.1 and 11.9 kyr ago, with the most recent upswing in storminess beginning "at about 600 years BP, coincident with the beginning of the Little Ice Age." Noren et al. say that this pattern "is consistent with long-term changes in the average sign of the Arctic Oscillation [AO], suggesting that modulation of this dominant atmospheric mode may account for a significant fraction of Holocene climate variability in North America and Europe." They also note that several "independent records of storminess and flooding from around the North Atlantic show maxima that correspond to those that characterize [their] lake records [Brown et al., 1999; Knox, 1999; Lamb, 1979; Liu and Fearn, 2000; Zong and Tooley, 1999]."

Noren et al. additionally determined that "during the past ~600 years, New England storminess appears to have been increasing naturally," and they suggest that "changes in the AO, perhaps modulated by solar forcing, may explain a significant portion of Holocene climate variability in the North Atlantic region." They further state that their explanation is appealing "because it makes a specific prediction that New England storminess should be at its greatest when Europe is cold (characteristic of the low-phase AO)," such as during Little Ice Age conditions; and they report that "comparison of our results with the other climate records [cited below], including European glacier fluctuations, suggest that, as predicted, intense storms in New England tend to occur more frequently during periods that are cooler than average in Europe [Mayewski et al., 1994; O'Brien et al., 1995; Holmes et al., 2001; Karlen and Kuylenstierna, 1996; Matthews et al., 2000]."

Moving to the center of the country, Sharma et al. (2005) used δ13C values of Sphagnum remains from peat deposits located along a sequence of beach ridges of Lake Superior to reconstruct changes in regional water balance from about 1000 to 3500 years BP (where elevated δ13C values correspond to wetter conditions), after which they compared their findings with reconstructed water levels of Lake Michigan derived by Baedke and Thompson (2000) from sedimentological studies covering the past 4000 years. In doing so, the researchers report they "found two maxima of Sphagnum δ13C values in peat deposits developed from 3400 to 2400 years BP and from 1900 to 1400 years BP," which closely match two periods of Lake Michigan high-water stands evident in the lake level record of Baedke and Thompson. These two periods coincide with the cooler climatic conditions that prevailed on either side of the Roman Warm Period, the earlier of which is unnamed but the most recent of which is the well known Dark Ages Cold Period. This latter cold high-water period was then followed by a period of low water and declining δ13C values, which coincide with the well known Medieval Warm Period that ultimately gave way to the Little Ice Age. Thereafter, there are no more δ13C data; but the lake level data reveal a third low-level stand of Lake Michigan from about 600 to 500 years BP that coincides with the Little Medieval Warm Period we have identified in many paleoclimate records.

Dropping all the way down to the Gulf of Mexico (GOM), Poore et al. (2003) developed a 14,000-year record of Holocene climate based primarily on the relative abundance of the planktic foraminifer Globigerinoides sacculifer found in two sediment cores. In reference to North Atlantic millennial-scale cool events 1-7 identified by Bond et al. (2001) as belonging to a pervasive climatic oscillation with a period of approximately 1500 years, Poore et al. say of their own study that distinct excursions to lower abundances of G. sacculifer "match within 200 years the ages of Bond events 1-6," noting that "major cooling events detected in the subpolar North Atlantic can be recognized in the GOM record." They additionally note that "the GOM record includes more cycles than can be explained by a quasiperiodic 1500-year cycle," but that such centennial-scale cycles with periods ranging from 200 to 500 years are also observed in the study of Bond et al., noting further that their results "are in agreement with a number of studies indicating the presence of substantial century-scale variability in Holocene climate records from different areas," specifically citing the reports of Campbell et al. (1998), Peterson et al. (1991) and Hodell et al. (2001). Last of all, they discuss evidence that leads them to conclude that "some of the high-frequency variation (century scale) in G. sacculifer abundance in our GOM records is forced by solar variability."

In introducing their paper, Poore et al. had reported that "North Atlantic marine and mountain glacier data suggest that climate throughout the Holocene has oscillated between warm and cold end-members with the Medieval Warm Period and Little Ice Age representing the most recent examples of the cycle extremes." Their study suggests that this same millennial-scale oscillation of climate is also evident in the Gulf of Mexico, adding to the burgeoning wealth of evidence that this phenomenon is of global extent.

Shifting gears just slightly, we note that perhaps the most stunning results of all of the analyses that have been devoted to detecting the degree of repeatability of the millennial-scale oscillation of earth's climate were obtained by Rahmstorf (2003), who analyzed the GISP2 ice core record from Greenland with respect to the timing of Dansgaard-Oeschger (DO) warm events and found that these abrupt climate changes "appear to be paced by a 1,470-year cycle with a period that is probably stable to within a few percent." With 95% confidence, for example, his analysis indicates that this period is maintained to better than 12% over at least 23 cycles during the time interval 51 to 10 thousand years BP. In fact, Rahmstorf reports that "the five most recent events, arguably the best-dated ones, have a standard deviation of only 32 years (2%)." He thus concludes, and rightly so, that this finding "strongly supports the idea that the events are paced by a regular 1,470 year cycle" and that "the highly precise clock points to an origin outside the Earth system." He additionally notes "there is some evidence that this cycle may also be present in the Holocene but does not trigger DO events then, possibly because the Atlantic ocean circulation is not close to a threshold in a warm climate," suggesting further that "the so-called 'little ice age' of the 16th-18th century may be the most recent cold phase of this cycle."

Preceding most of the other studies reviewed here, Staufer et al. (1998) derived a common timescale for earth's last glacial period from records of atmospheric methane concentrations obtained from both Greenland and Antarctica, after which they used their findings to compare millennial-scale climate oscillations inferred from Greenland ice cores with concurrent variations in atmospheric CO2 concentration inferred from Antarctic ice cores. During large rapid warmings over Greenland, which were followed by slower cooling regimes that returned the climate to full glacial conditions, atmospheric CO2 concentrations typically varied by less than 10 ppm. Furthermore, the weak correspondence between the two parameters was considered to have been caused by the change in climate, rather than by the change in CO2.

Last of all, in a study that spanned the entire continent, Viau et al. (2002) analyzed 3,076 14C dates from the North American Pollen Database in an effort to determine whether climate-driven millennial-scale cycles are present in the continent's terrestrial pollen record. Results of their statistical analyses indicated there were nine millennial-scale oscillations during the past 14,000 years in which continent-wide synchronous vegetation changes with a periodicity of roughly 1650 years were recorded in the pollen records. The most recent of the vegetation transitions was centered at approximately 600 years BP (before present). This event, in the words of Viau et al., "culminat[ed] in the Little Ice Age, with maximum cooling 300 years ago." Prior to that event, a major transition that began approximately 1600 years BP represents the climatic amelioration that "culminat[ed] in the maximum warming of the Medieval Warm Period 1000 years ago." And so it goes, on back through the Holocene and into the preceding late glacial period, with the times of all major pollen transitions being "consistent with ice and marine records."

In discussing the implications of their findings, Viau et al. say that "the large-scale nature of these transitions and the fact that they are found in different proxies confirms the hypothesis that Holocene and late glacial climate variations of millennial-scale were abrupt transitions between climatic regimes as the atmosphere-ocean system reorganized in response to some forcing." In this regard they further state that "although several mechanisms for such natural forcing have been advanced, recent evidence points to a potential solar forcing (Bond et al., 2001) associated with ocean-atmosphere feedbacks acting as global teleconnections agents." In addition, they note that "these transitions are identifiable across North America and presumably the world."

In light of these observations, all responsible people must confront what we call the problem of the three difficulties. First, it is difficult to deny the existence of the pervasive millennial-scale oscillation of climate that alternately produces periods of relative warmth and coolness (such as the Modern Warm Period and Little Ice Age) at regular intervals throughout both glacial and interglacial periods alike. Second, it is difficult to deny that the phenomenon responsible for the extreme regularity of the climatic transitions that produce these alternating warm and cool periods has its origin somewhere beyond earth. Third, it is difficult to deny that the other-worldly place of origin of this phenomenon is the sun.

Of course, it is no problem at all if one does not deny the reality of these observations; but one must then conclude that 20th-century global warming was most probably just the most recent phase of this natural climatic oscillation that is totally independent of the historical increase in the air's CO2 content. But that, of course, would be politically incorrect. Hence, it would appear that one must make a choice in this matter between science and political agenda. We prefer the former. How about you?

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Last updated 11 July 2007