From Climate Change Reconsidered, a work of the Nongovernmental International Panel on Climate Change
The IPCC claims “average arctic temperatures increased at almost twice the global average rate in the past 100 years,” though it then acknowledges that “arctic temperatures have high decadal variability, and a warm period was also observed from 1925 to 1945” (IPCC 2007-I, p. 7). Later in the report, the IPCC says “the warming over land in the Arctic north of 65° is more than double the warming in the global mean from the 19th century to the 21st century and also from about the late 1960s to the present. In the arctic series, 2005 is the warmest year” (p. 248). But the IPCC then admits that “a few areas have cooled since 1901, most notably the northern North Atlantic near southern Greenland” (p. 252). So has the Artic really experienced the so-called unprecedented warming of the twentieth century?
Dahl-Jensen et al. (1998) used data from two ice sheet boreholes to reconstruct the temperature history of Greenland over the past 50,000 years. Their analysis indicated that temperatures on the Greenland Ice Sheet during the Last Glacial Maximum (about 25,000 years ago) were 23 ± 2 °C colder than at present. After the termination of the glacial period, however, temperatures increased steadily to a value that was 2.5°C warmer than at present, during the Climatic Optimum of 4,000 to 7,000 years ago. The Medieval Warm Period and Little Ice Age were also evident in the borehole data, with temperatures 1°C warmer and 0.5-0.7°C cooler than at present, respectively. Then, after the Little Ice Age, the scientists report “temperatures reached a maximum around 1930 AD” and that “temperatures have decreased during the last decades.”
The results of this study stand in stark contrast to the predictions of general circulation models of the atmosphere, which consistently suggest there should have been a significant CO2-induced warming in high northern latitudes over the past several decades. They also depict large temperature excursions over the past 10,000 years, when the air’s CO2 content was relatively stable. Each of these observations raises serious doubts about the models’ ability to correctly forecast earth’s climatic response to the ongoing rise in the air’s CO2 content.
In another study of Greenland climate that included both glacial and interglacial periods, Bard (2002) reviews the concept of rapid climate change. Of this phenomenon, he writes that “it is now recognized that the ocean-atmosphere system exhibits several stable regimes under equivalent external forcings,” and that “the transition from one state to another occurs very rapidly when certain climatic parameters attain threshold values.” Specifically, he notes that in the models “a slight increase in the freshwater flux above the modern level F produces a decrease in the NADW [North Atlantic Deep Water] convection and a moderate cooling in the North Atlantic,” but that “the system flips to another state once the flux reaches a threshold value F + deltaF,” which state has no deep convection and “is characterized by surface temperatures up to 6°C lower in and around the North Atlantic.”
With respect to what has been learned from observations, Bard concentrates on the region of the North Atlantic, describing glacial-period millennial-scale episodes of dramatic warming called Dansgaard-Oeschger events (with temperature increases “of more than 10°C”), which are evident in Greenland ice core records, as well as episodes of “drastic cooling” called Heinrich events (with temperature drops “of up to about 5°C”), which are evident in sea surface temperature records derived from the study of North Atlantic deep-sea sediment cores.
In the Greenland record, according to Bard, the progression of these events is such that “the temperature warms abruptly to reach a maximum and then slowly decreases for a few centuries before reaching a threshold, after which it drops back to the cold values that prevailed before the warm event.” He also reports that “models coupling the atmosphere, ocean, and ice sheets are still unable to correctly simulate that variability on all scales in both time and space,” which suggests we do not fully understand the dynamics of these rapid climate changes. Bard states, “all the studies so far carried out fail to answer the crucial question: How close are we to the next bifurcation [which could cause a rapid change-of-state in earth’s climate system]?” In this regard, he notes that “an intense debate continues in the modeling community about the reality of such instabilities under warm conditions,” which is a particularly important point, since all dramatic warming and cooling events that have been detected to date have occurred in either full glacials or transitional periods between glacials and interglacials.
This latter real-world fact clearly suggests we are unlikely to experience any dramatic warming or cooling surprises in the near future, as long as the earth does not begin drifting towards glacial conditions, which is another reason to not be concerned about the ongoing rise in the air’s CO2 content. In fact, it suggests that allowing more CO2 to accumulate in the atmosphere provides an “insurance policy” against abrupt climate change; interglacial warmth seems to inoculate the planet against climatic instabilities, allowing only the mild millennial-scale climatic oscillation that alternately brings the earth slightly warmer and cooler conditions typical of the Medieval Warm Period and Little Ice Age.
Focusing on the more pertinent period of the current interglacial or Holocene, we next consider a number of papers that bear upon the reality of the Medieval Warm Period and Little Ice Age: two well-known multi-century periods of significant climatic aberration. These periods of modest climatic aberration, plus the analogous warm and cool periods that preceded them (the Roman Warm Period and Dark Ages Cold Period), provide strong evidence for the existence of a millennial-scale oscillation of climate that is unforced by changes in the air’s CO2 content, which in turn suggests that the global warming of the Little Ice Age-to-Current Warm Period transition was likely totally independent of the coincidental concomitant increase in the air’s CO2 content that accompanied the Industrial Revolution.
We begin with the study of Keigwin and Boyle (2000), who briefly reviewed what is known about the millennial-scale oscillation of earth’s climate that is evident in a wealth of proxy climate data from around the world. Stating that “mounting evidence indicates that the Little Ice Age was a global event, and that its onset was synchronous within a few years in both Greenland and Antarctica,” they remark that in Greenland it was characterized by a cooling of approximately 1.7°C. Likewise, in an article titled “Was the Medieval Warm Period Global?” Broecker (2001) answers yes, citing borehole temperature data that reveal the magnitude of the temperature drop over Greenland from the peak warmth of the Medieval Warm Period (800 to 1200 A.D.) to the coldest part of the Little Ice Age (1350 to 1860 A.D.) to have been approximately 2°C, and noting that as many as six thousand borehole records from all continents of the world confirm that the earth was a significantly warmer place a thousand years ago than it is today.
McDermott et al. (2001) derived a δ18O record from a stalagmite discovered in Crag Cave in southwestern Ireland, after which they compared this record with the δ18O records from the GRIP and GISP2 ice cores from Greenland. In doing so, they found evidence for “centennial-scale δ18O variations that correlate with subtle δ18O changes in the Greenland ice cores, indicating regionally coherent variability in the early Holocene.” They additionally report that the Crag Cave data “exhibit variations that are broadly consistent with a Medieval Warm Period at ~1000 ± 200 years ago and a two-stage Little Ice Age, as reconstructed by inverse modeling of temperature profiles in the Greenland Ice Sheet.” Also evident in the Crag Cave data were the δ18O signatures of the earlier Roman Warm Period and Dark Ages Cold Period that comprised the prior such cycle of climate in that region. In concluding they reiterate the important fact that the coherent δ18O variations in the records from both sides of the North Atlantic “indicate that many of the subtle multicentury δ18O variations in the Greenland ice cores reflect regional North Atlantic margin climate signals rather than local effects.”
Another study that looked at temperature variations on both sides of the North Atlantic was that of Seppa and Birks (2002), who used a recently developed pollen-climate reconstruction model and a new pollen stratigraphy from Toskaljavri, a tree-line lake in the continental sector of northern Fenoscandia (located just above 69°N latitude), to derive quantitative estimates of annual precipitation and July mean temperature. The two scientists say their reconstructions “agree with the traditional concept of a ‘Medieval Warm Period’ (MWP) and ‘Little Ice Age’ in the North Atlantic region (Dansgaard et al., 1975).” Specifically, they report there is “a clear correlation between our MWP reconstruction and several records from Greenland ice cores,” and that “comparisons of a smoothed July temperature record from Toskaljavri with measured borehole temperatures of the GRIP and Dye 3 ice cores (Dahl-Jensen et al., 1998) and the δ18O record from the Crete ice core (Dansgaard et al., 1975) show the strong similarity in timing of the MWP between the records.” Last of all, they note that “July temperature values during the Medieval Warm Period (ca. 1400-1000 cal yr B.P.) were ca. 0.8°C higher than at present,” where present means the last six decades of the twentieth century.
Concentrating solely on Greenland and its immediate environs are several other papers, among which is the study of Wagner and Melles (2001), who retrieved a sediment core from a lake on an island situated just off Liverpool Land on the east coast of Greenland. Analyzing it for a number of properties related to the past presence of seabirds there, they obtained a 10,000-year record that tells us much about the region’s climatic history.
Key to the study were certain biogeochemical data that reflected variations in seabird breeding colonies in the catchment area of the lake. These data revealed high levels of the various parameters measured by Wagner and Melles between about 1,100 and 700 years before present (BP) that were indicative of the summer presence of significant numbers of seabirds during that “medieval warm period,” as they describe it, which had been preceded by a several-hundred-year period of little to no inferred bird presence. Then, after the Medieval Warm Period, the data suggested another absence of birds during what they refer to as “a subsequent Little Ice Age,” which they note was “the coldest period since the early Holocene in East Greenland.” Their data also showed signs of a “resettlement of seabirds during the last 100 years, indicated by an increase of organic matter in the lake sediment and confirmed by bird observations.” However, values of the most recent data were not as great as those obtained from the earlier Medieval Warm Period; and temperatures derived from two Greenland ice cores led to the same conclusion: it was warmer at various times between 1,100 to 700 years BP than it was over the twentieth century.
Kaplan et al. (2002) also worked with data obtained from a small lake, this one in southern Greenland, analyzing sediment physical-chemical properties, including magnetic susceptibility, density, water content, and biogenic silica and organic matter concentrations. They discovered that “the interval from 6000 to 3000 cal yr BP was marked by warmth and stability.” Thereafter, however, the climate cooled “until its culmination during the Little Ice Age,” but from 1,300-900 years BP, there was a partial amelioration of climate (the Medieval Warm Period) that was associated with an approximate 1.5°C rise in temperature.
Following another brief warming between AD 1500 and 1750, the second and more severe portion of the Little Ice Age occurred, which was in turn followed by “naturally initiated post-Little Ice Age warming since AD 1850, which is recorded throughout the Arctic.” They report that Viking “colonization around the northwestern North Atlantic occurred during peak Medieval Warm Period conditions that ended in southern Greenland by AD 1100,” noting that Norse movements around the region thereafter “occurred at perhaps the worst time in the last 10,000 years, in terms of the overall stability of the environment for sustained plant and animal husbandry.”
We can further explore these aspects of Greenland’s climatic history from three important papers that reconstructed environmental conditions in the vicinity of Igaliku Fjord, South Greenland, before, during, and after the period of Norse habitation of this and other parts of the ice-covered island’s coast, beginning with the study of Lassen et al. (2004), who provide some historical background to their palaeoclimatic work by reporting that “the Norse, under Eric the Red, were able to colonize South Greenland at AD 985, according to the Icelandic Sagas, owing to the mild Medieval Warm Period climate with favorable open-ocean conditions.” They also mention, in this regard, that the arrival of the gritty Norsemen was “close to the peak of Medieval warming recorded in the GISP2 ice core which was dated at AD 975 (Stuiver et al., 1995),” while we additionally note that Esper et al. (2002) independently identified the peak warmth of this period throughout North American extratropical latitudes as “occurring around 990.” Hence, it would appear that the window of climatic opportunity provided by the peak warmth of the Medieval Warm Period was indeed a major factor enabling seafaring Scandinavians to establish long-enduring settlements on the coast of Greenland.
As time progressed, however, the glowing promise of the apex of Medieval warmth gave way to the debilitating reality of the depth of Little Ice Age cold. Jensen et al. (2004), for example, report that the diatom record of Igaliku Fjord “yields evidence of a relatively moist and warm climate at the beginning of settlement, which was crucial for Norse land use,” but that “a regime of more extreme climatic fluctuations began soon after AD 1000, and after AD c. 1350 cooling became more severe.” Lassen et al. additionally note that “historical documents on Iceland report the presence of the Norse in South Greenland for the last time in AD 1408,” during what they describe as a period of “unprecedented influx of (ice-loaded) East Greenland Current water masses into the innermost parts of Igaliku Fjord.” They also report that “studies of a Canadian high-Arctic ice core and nearby geothermal data (Koerner and Fisher, 1990) correspondingly show a significant temperature lowering at AD 1350-1400,” when, in their words, “the Norse society in Greenland was declining and reaching its final stage probably before the end of the fifteenth century.” Consequently, what the relative warmth of the Medieval Warm Period provided the Norse settlers, the relative cold of the Little Ice Age took from them: the ability to survive on Greenland.
More details of the saga of five centuries of Nordic survival at the foot of the Greenland Ice Cap are provided by the trio of papers addressing the palaeohistory of Igaliku Fjord. Based on a high-resolution record of the fjord’s subsurface water-mass properties derived from analyses of benthic foraminifera, Lassen et al. conclude that stratification of the water column, with Atlantic water masses in its lower reaches, appears to have prevailed throughout the last 3,200 years, except for the Medieval Warm Period. During this period, which they describe as occurring between AD 885 and 1235, the outer part of Igaliku Fjord experienced enhanced vertical mixing (which they attribute to increased wind stress) that would have been expected to increase nutrient availability there. A similar conclusion was reached by Roncaglia and Kuijpers (2004), who found evidence of increased bottom-water ventilation between AD 960 and 1285. Hence, based on these findings, plus evidence of the presence of Melonis barleeanus during the Medieval Warm Period (the distribution of which is mainly controlled by the presence of partly decomposed organic matter), Lassen et al. conclude that surface productivity in the fjord during this interval of unusual relative warmth was “high and thus could have provided a good supply of marine food for the Norse people.”
Shortly thereafter, the cooling that led to the Little Ice Age was accompanied by a gradual re-stratification of the water column, which curtailed nutrient upwelling and reduced the high level of marine productivity that had prevailed throughout the Medieval Warm Period. These linked events, according to Lassen et al., “contributed to the loss of the Norse settlement in Greenland.” Indeed, with deteriorating growing conditions on land and simultaneous reductions in oceanic productivity, the odds were truly stacked against the Nordic colonies, and it was only a matter of time before their fate was sealed. As Lassen et al. describe it, “around AD 1450, the climate further deteriorated with further increasing stratification of the water-column associated with stronger advection of (ice-loaded) East Greenland Current water masses.” This development, in their words, led to an even greater “increase of the ice season and a decrease of primary production and marine food supply,” which “could also have had a dramatic influence on the local seal population and thus the feeding basis for the Norse population.”
The end result of these several conjoined phenomena, in the words of Lassen et al., was that “climatic and hydrographic changes in the area of the Eastern Settlement were significant in the crucial period when the Norse disappeared.” Also, Jensen et al. report that “geomorphological studies in Northeast Greenland have shown evidence of increased winter wind speed, particularly in the period between AD 1420 and 1580 (Christiansen, 1998),” noting that “this climatic deterioration coincides with reports of increased sea-ice conditions that caused difficulties in using the old sailing routes from Iceland westbound and further southward along the east coast of Greenland, forcing sailing on more southerly routes when going to Greenland (Seaver, 1996).”
In light of these observations, Jensen et al. state that “life conditions certainly became harsher during the 500 years of Norse colonization,” and that this severe cooling-induced environmental deterioration “may very likely have hastened the disappearance of the culture.” At the same time, it is also clear that the more favorable living conditions associated with the peak warmth of the Medieval Warm Period—which occurred between approximately AD 975 (Stuiver et al., 1995) and AD 990 (Esper et al., 2002)—were what originally enabled the Norse to successfully colonize the region. In the thousand-plus subsequent years, there has never been a sustained period of comparable warmth, nor of comparable terrestrial or marine productivity, either locally or hemispherically (and likely globally, as well), the strident protestations of Mann et al. (2003) notwithstanding.
Concentrating on the twentieth century, Hanna and Cappelen (2003) determined the air temperature history of coastal southern Greenland from 1958-2001, based on data from eight Danish Meteorological Institute stations in coastal and near-coastal southern Greenland, as well as the concomitant sea surface temperature (SST) history of the Labrador Sea off southwest Greenland, based on three previously published and subsequently extended SST datasets (Parker et al., 1995; Rayner et al., 1996; Kalnay et al., 1996). The coastal temperature data showed a cooling of 1.29°C over the period of study, while two of the three SST databases also depicted cooling: by 0.44°C in one case and by 0.80°C in the other. Both the land-based air temperature and SST series followed similar patterns and were strongly correlated, but with no obvious lead/lag either way. In addition, it was determined that the cooling was “significantly inversely correlated with an increased phase of the North Atlantic Oscillation (NAO) over the past few decades.” The two researchers say this “NAO-temperature link doesn’t explain what caused the observed cooling in coastal southern Greenland but it does lend it credibility.”
In referring to what they call “this important regional exception to recent ‘global warming’,” Hanna and Cappelen note that the “recent cooling may have significantly added to the mass balance of at least the southern half of the [Greenland] Ice Sheet.” Consequently, since this part of the ice sheet is the portion that would likely be the first to experience melting in a warming world, it would appear that whatever caused the cooling has not only protected the Greenland Ice Sheet against warming-induced disintegration but actually fortified it against that possibility.
Several other studies have also reported late-twentieth century cooling on Greenland. Based on mean monthly temperatures of 37 Arctic and seven sub-Arctic stations, as well as temperature anomalies of 30 grid-boxes from the updated dataset of Jones, for example, Przybylak (2000) found that “the level of temperature in Greenland in the last 10-20 years is similar to that observed in the 19th century.” Likewise, in a study that utilized satellite imagery of the Odden ice tongue (a winter ice cover that occurs in the Greenland Sea with a length of about 1,300 km and an aerial coverage of as much as 330,000 square kilometers) plus surface air temperature data from adjacent Jan Mayen Island, Comiso et al. (2001) determined that the ice phenomenon was “a relatively smaller feature several decades ago,” due to the warmer temperatures that were prevalent at that time. In addition, they report that observational evidence from Jan Mayen Island indicates temperatures there cooled at a rate of 0.15 ± 0.03°C per decade during the past 75 years.
Taurisano et al. (2004) examined the temperature history of the Nuuk fjord during the last century, where their analyses of all pertinent regional data led them to conclude that “at all stations in the Nuuk fjord, both the annual mean and the average temperature of the three summer months (June, July and August) exhibit a pattern in agreement with the trends observed at other stations in south and west Greenland (Humlum 1999; Hanna and Cappelen, 2003).” As they describe it, the temperature data “show that a warming trend occurred in the Nuuk fjord during the first 50 years of the 1900s, followed by a cooling over the second part of the century, when the average annual temperatures decreased by approximately 1.5°C.” Coincident with this cooling trend there was also what they describe as “a remarkable increase in the number of snowfall days (+59 days).” What is more, they report that “not only did the cooling affect the winter months, as suggested by Hannna and Cappelen (2002), but also the summer mean,” noting that “the summer cooling is rather important information for glaciological studies, due to the ablation-temperature relations.”
In a study of three coastal stations in southern and central Greenland that possess almost uninterrupted temperature records between 1950 and 2000, Chylek et al. (2004) discovered that “summer temperatures, which are most relevant to Greenland ice sheet melting rates, do not show any persistent increase during the last fifty years.” In fact, working with the two stations with the longest records (both over a century in length), they determined that coastal Greenland’s peak temperatures occurred between 1930 and 1940, and that the subsequent decrease in temperature was so substantial and sustained that current coastal temperatures “are about 1°C below their 1940 values.” Furthermore, they note that “at the summit of the Greenland ice sheet the summer average temperature has decreased at the rate of 2.2°C per decade since the beginning of the measurements in 1987.” Hence, as with the Arctic as a whole, it would appear that Greenland has not experienced any net warming over the most dramatic period of atmospheric CO2 increase on record. In fact, it has cooled during this period.
At the start of the twentieth century, however, Greenland was warming, as it emerged, along with the rest of the world, from the depths of the Little Ice Age. Between 1920 and 1930, when the atmosphere’s CO2 concentration rose by a mere 3 to 4 ppm, there was a phenomenal warming at all five coastal locations for which contemporary temperature records are available. In the words of Chylek et al., “average annual temperature rose between 2 and 4°C [and by as much as 6°C in the winter] in less than ten years.” And this warming, as they note, “is also seen in the 18O/16O record of the Summit ice core (Steig et al., 1994; Stuiver et al., 1995; White et al., 1997).”
In commenting on this dramatic temperature rise, which they call the “great Greenland warming of the 1920s,” Chylek et al. conclude that “since there was no significant increase in the atmospheric greenhouse gas concentration during that time, the Greenland warming of the 1920s demonstrates that a large and rapid temperature increase can occur over Greenland, and perhaps in other regions of the Arctic, due to internal climate variability such as the NAM/NAO [Northern Annular Mode/North Atlantic Oscillation], without a significant anthropogenic influence.” These facts led them to speculate that “the NAO may play a crucial role in determining local Greenland climate during the 21st century, resulting in a local climate that may defy the global climate change.”
A recent study by Humlum et al. (2011) reaffirms the suggestion that Greenland will not melt away if atmospheric CO2 emissions are not severely reduced. Using an analytical model to show the temperature variations during the late Holocene period, the authors used both the Fourier and wavelet transform methods to extract natural climatic signals from temperature records at Svalbard from 1912-2010 and at Central Greenland GISP2 site for the past 4000 years.
The results mirror those of a similar study by Kobashi et al. (2011) that provides evidence of the presence of large natural temperature variations in Greenland surface temperatures on multicentennial and multidecadal timescales. The large cooling tendency of about 1.5°C predicted by Humlum et al. for the next 800 years poses a serious challenge to IPCC climate projection scenarios that only consider rising atmospheric CO2 as the significant modulator of surface temperature changes in Greenland.
Clearly, there is no substance to the claim that Greenland provides evidence for an impending CO2-induced warming. These many studies of the temperature history of Greenland depict long-term oscillatory cooling ever since the Climatic Optimum of the mid-Holocene, when it was perhaps 2.5°C warmer than it is now, within which cooling trend is included the Medieval Warm Period, when it was about 1°C warmer than it is currently, and the Little Ice Age, when it was 0.5 to 0.7°C cooler than now, after which temperatures rebounded to a new maximum in the 1930s, only to fall steadily thereafter.
Rest of Arctic
Overpeck et al. (1997) combined paleoclimatic records obtained from lake and marine sediments, trees, and glaciers to develop a 400-year history of circum-Arctic surface air temperature. From this record they determined that the most dramatic warming of the last four centuries of the past millennium (1.5°C) occurred between 1840 and 1955, over which period the air’s CO2 concentration rose from approximately 285 ppm to 313 ppm, or by 28 ppm. Then, from 1955 to the end of the record (about 1990), the mean circum-Arctic air temperature declined by 0.4°C, while the air’s CO2 concentration rose from 313 ppm to 354 ppm, or by 41 ppm. On the basis of these observations, which apply to the entire Arctic, it is not possible to assess the influence of atmospheric CO2 on surface air temperature or even to conclude it has any effect at all. Why? Because over the first 115 years of warming, as the air’s CO2 concentration rose by an average of 0.24 ppm/year, air temperature rose by an average of 0.013°C/year; over the final 35 years of the record, when the air’s CO2 content rose at a mean rate of 1.17 ppm/year (nearly five times the rate at which it had risen in the prior period), the rate-of-rise of surface air temperature decelerated, to a mean value (0.011°C/year) that was nearly the same as the rate at which it had previously risen.
Naurzbaev and Vaganov (2000) developed a 2,200-year temperature history using tree-ring data obtained from 118 trees near the upper-timberline in Siberia for the period 212 BC to AD 1996, as well as a similar history covering the period of the Holocene Climatic Optimum (3300 to 2600 BC). They compared their results with those obtained from an analysis of isotopic oxygen data extracted from a Greenland ice core. This work revealed that fluctuations in average annual temperature derived from the Siberian record agreed well with air temperature variations reconstructed from the Greenland data, suggesting to the two researchers that “the tree ring chronology of [the Siberian] region can be used to analyze both regional peculiarities and global temperature variations in the Northern Hemisphere.”
Naurzbaev and Vaganov reported that several warm and cool periods prevailed for several multi-century periods throughout the last two millennia: a cool period in the first two centuries AD, a warm period from AD 200 to 600, cooling again from 600 to 800 AD, followed by the Medieval Warm Period from about AD 850 to 1150, the cooling of the Little Ice Age from AD 1200 though 1800, followed by the recovery warming of the twentieth century. In regard to this latter temperature rise, however, the two scientists say it was “not extraordinary,” and that “the warming at the border of the first and second millennia [AD 1000] was longer in time and similar in amplitude.” In addition, their reconstructed temperatures for the Holocene Climatic Optimum revealed there was an even warmer period about 5,000 years ago, when temperatures averaged 3.3°C more than they did over the past two millennia.
Contemporaneously, Vaganov et al. (2000) also used tree-ring width as a temperature proxy, reporting temperature variations for the Asian subarctic region over the past 600 years. Their graph of these data reveals that temperatures in this region exhibited a small positive trend from the beginning of the record until about AD 1750. Thereafter, a severe cooling trend ensued, followed by a 130-year warming trend from about 1820 through 1950, after which temperatures fell once again.
In analyzing the entire record, the researchers determined that the amplitude of twentieth century warming “does not go beyond the limits of reconstructed natural temperature fluctuations in the Holocene subarctic zone.” And in attempting to determine the cause or causes of the temperature fluctuations, they report finding a significant correlation with solar radiation and volcanic activity over the entire 600-year period (r = 0.32 for solar radiation, r = -0.41 for volcanic activity), which correlation improved over the shorter interval (1800-1990) of the industrial period (r = 0.68 for solar radiation, r = -0.59 for volcanic activity). It is also enlightening to note, in this regard, that in this region of the world, where climate models predict large increases in temperature as a result of the historical rise in the air’s CO2 concentration, real-world data show an actual cooling trend since around 1940. Where warming does exist in the record—between about 1820 and 1940—much of it correlates with changes in solar irradiance and volcanic activity, two factors that are free of anthropogenic influence.
One year later, Moore et al. (2001) analyzed sediment cores extracted from Donard Lake, Baffin Island, Canada (~66.25°N, 62°W), to produce a 1,240-year record of mean summer temperature for this region that averaged 2.9°C over the period AD 750-1990. Within this period there were several anomalously warm decades with temperatures that were as high as 4°C around AD 1000 and 1100, while at the beginning of the thirteenth century Donard Lake witnessed what they called “one of the largest climatic transitions in over a millennium,” as “average summer temperatures rose rapidly by nearly 2°C from AD 1195-1220, ending in the warmest decade in the record,” with temperatures near 4.5°C. This latter temperature rise was then followed by a period of extended warmth that lasted until an abrupt cooling event occurred around AD 1375, resulting in the following decade being one of the coldest in the record and signaling the onset of the Little Ice Age on Baffin Island, which lasted 400 years. At the modern end of the record, a gradual warming trend occurred over the period 1800-1900, followed by a dramatic cooling event that brought temperatures back to levels characteristic of the Little Ice Age, which chilliness lasted until about 1950. Thereafter, temperatures rose once more throughout the 1950s and 1960s, whereupon they trended downwards toward cooler conditions to the end of the record in 1990.
Gedalof and Smith (2001) compiled a transect of six tree ring-width chronologies from stands of mountain hemlock growing near the treeline that extends from southern Oregon to the Kenai Peninsula, Alaska. Over the period of their study (AD 1599-1983), they determined that “much of the pre-instrumental record in the Pacific Northwest region of North America [was] characterized by alternating regimes of relatively warmer and cooler SST [sea surface temperature] in the North Pacific, punctuated by abrupt shifts in the mean background state,” which were found to be “relatively common occurrences.” They concluded that “regime shifts in the North Pacific have occurred 11 times since 1650.” A significant aspect of these findings is the fact that the abrupt 1976-77 shift in this Pacific Decadal Oscillation, as it is generally called, is what was responsible for the vast majority of the past half-century’s warming in Alaska, which some commentators wrongly point to as evidence of CO2-induced global warming.
About the same time, Kasper and Allard (2001) examined soil deformations caused by ice wedges (a widespread and abundant form of ground ice in permafrost regions that can grow during colder periods and deform and crack the soil). Working near Salluit, northern Quebéc (approx. 62°N, 75.75°W), they found evidence of ice wedge activity prior to AD 140, reflecting cold climatic conditions. Between AD 140 and 1030, however, this activity decreased, reflective of warmer conditions. Then, from AD 1030 to 1500, conditions cooled; and from 1500 to 1900 ice wedge activity was at its peak, when the Little Ice Age ruled, suggesting this climatic interval exhibited the coldest conditions of the past 4,000 years. Thereafter, a warmer period prevailed, from about 1900 to 1946, which was followed by a return to cold conditions during the last five decades of the twentieth century, during which time more than 90 percent of the ice wedges studied reactivated and grew by 20-30 cm, in harmony with a reported temperature decline of 1.1°C observed at the meteorological station in Salluit.
In another study from the same year, Zeeberg and Forman (2001) analyzed twentieth century changes in glacier terminus positions on north Novaya Zemlya, a Russian island located between the Barents and Kara Seas in the Arctic Ocean, providing in the process a quantitative assessment of the effects of temperature and precipitation on glacial mass balance. This work revealed a significant and accelerated post-Little Ice Age glacial retreat in the first and second decades of the twentieth century; but by 1952, the region’s glaciers had experienced between 75 to 100 percent of their net twentieth century retreat. During the next 50 years, the recession of more than half of the glaciers stopped, and many tidewater glaciers actually began to advance. These glacial stabilizations and advances were attributed by the two scientists to observed increases in precipitation and/or decreases in temperature. In the four decades since 1961, for example, weather stations at Novaya Zemlya show summer temperatures to have been 0.3° to 0.5°C colder than they were over the prior 40 years, while winter temperatures were 2.3° to 2.8°C colder than they were over the prior 40-year period. Such observations, in Zeeberg and Forman’s words, are “counter to warming of the Eurasian Arctic predicted for the twenty-first century by climate models, particularly for the winter season.”
Comiso et al. (2000) utilized satellite imagery to analyze and quantify a number of attributes of the Odden ice, including its average concentration, maximum area, and maximum extent over the period 1979-1998. They used surface air temperature data from Jan Mayen Island, located within the region of study, to infer the behavior of the phenomenon over the past 75 years.
The Odden ice tongue was found to vary in size, shape, and length of occurrence during the 20-year period, displaying a fair amount of interannual variability. Quantitatively, trend analyses revealed that the ice tongue had exhibited no statistically significant change in any of the parameters studied over the short 20-year period. However, a proxy reconstruction of the Odden ice tongue for the past 75 years revealed the ice phenomenon to have been “a relatively smaller feature several decades ago,” due to the significantly warmer temperatures that prevailed at that time.
The fact that the Odden ice tongue has persisted, virtually unchanged in the mean during the past 20 years, is in direct contrast with predictions of rapid and increasing warmth in earth’s polar regions as a result of CO2-induced global warming. This observation, along with the observational evidence from Jan Mayen Island that temperatures there actually cooled at a rate of 0.15 ± 0.03°C per decade during the past 75 years, bolsters the view that there has been little to no warming in this part of the Arctic, as well as most of its other parts, over the past seven decades.
Polyakov et al. (2002b) used newly available long-term Russian observations of surface air temperature from coastal stations to gain new insights into trends and variability in the Arctic environment poleward of 62°N. Throughout the 125-year history they developed, they identified “strong intrinsic variability, dominated by multi-decadal fluctuations with a timescale of 60-80 years”; they found temperature trends in the Arctic to be highly dependent on the particular time period selected for analysis. They found they could “identify periods when Arctic trends were actually smaller or of different sign [our italics] than Northern Hemisphere trends.” Over the bulk of the twentieth century, when they say “multi-decadal variability had little net effect on computed trends,” the temperature histories of the two regions were “similar,” but they did “not support amplified warming in polar regions predicted by GCMs.”
In a concomitant study, Naurzbaev et al. (2002) developed a 2,427-year proxy temperature history for the part of the Taimyr Peninsula, northern Russia, lying between 70°30’ and 72°28’ North latitude, based on a study of ring-widths of living and preserved larch trees, noting that it has been shown that “the main driver of tree-ring variability at the polar timber-line [where they worked] is temperature (Vaganov et al., 1996; Briffa et al., 1998; Schweingruber and Briffa, 1996).” This work revealed that “the warmest periods over the last two millennia in this region were clearly in the third [Roman Warm Period], tenth to twelfth [Medieval Warm Period] and during the twentieth [Current Warm Period] centuries.” With respect to the second of these three periods, they emphasize that “the warmth of the two centuries AD 1058-1157 and 950-1049 attests to the reality of relative mediaeval warmth in this region.” Their data also reveal three other important pieces of information: (1) the Roman and Medieval Warm Periods were both warmer than the Current Warm Period has been to date, (2) the beginning of the end of the Little Ice Age was somewhere in the vicinity of 1830, and (3) the Current Warm Period peaked somewhere in the vicinity of 1940.
All of these observations are at odds with what is portrayed in the Northern Hemispheric “hockey stick” temperature history of Mann et al. (1998, 1999) and its thousand-year global extension developed by Mann and Jones (2003), wherein (1) the Current Warm Period is depicted as the warmest such era of the past two millennia, (2) recovery from the Little Ice Age does not begin until after 1910, and (3) the Current Warm Period experiences it highest temperatures in the latter part of the twentieth century’s final decade.
Przybylak (2002) conducted a detailed analysis of intraseasonal and interannual variability in maximum, minimum, and average air temperature and diurnal air temperature range for the entire Arctic—as delineated by Treshnikov (1985)—for the period 1951-1990, based on data from 10 stations “representing the majority of the climatic regions in the Arctic.” This work indicated that trends in both the intraseasonal and interannual variability of the temperatures studied did not show any significant changes, leading Przybylak to conclude that “this aspect of climate change, as well as trends in average seasonal and annual values of temperature investigated earlier (Przybylak, 1997, 2000), proves that, in the Arctic in the period 1951-90, no tangible manifestations of the greenhouse effect can be identified.”
Isaksson et al. (2003) retrieved two ice cores (one from Lomonosovfonna and one from Austfonna) far above the Arctic Circle in Svalbard, Norway, after which the 12 cooperating scientists from Norway, Finland, Sweden, Canada, Japan, Estonia, and the Netherlands used δ18O data to reconstruct a 600-year temperature history of the region. As would be expected—in light of the earth’s transition from the Little Ice Age to the Current Warm Period—the international group of scientists reported that “the δ18O data from both Lomonosovfonna and Austfonna ice cores suggest that the twentieth century was the warmest during at least the past 600 years.” However, the warmest decade of the twentieth century was centered on approximately 1930, while the instrumental temperature record at Longyearbyen also shows the decade of the 1930s to have been the warmest. In addition, the authors remark that, “as on Svalbard, the 1930s were the warmest decade in the Trondheim record.” Consequently, there was no net warming over the last seven decades of the twentieth century in the parts of Norway cited in this study.
In the same year, Polyakov et al. (2003) derived a surface air temperature history that stretched from 1875 to 2000, based on measurements carried out at 75 land stations and a number of drifting buoys located poleward of 62°N latitude. From 1875 to about 1917, the team of eight U.S. and Russian scientists found the surface air temperature of the huge northern region rose hardly at all; but then it climbed 1.7°C in just 20 years to reach a peak in 1937 that was not eclipsed over the remainder of the record. During this 20-year period of rapidly rising air temperature, the atmosphere’s CO2 concentration rose by a mere 8 ppm. But then, over the next six decades, when the air’s CO2 concentration rose by approximately 55 ppm, or nearly seven times more than it did throughout the 20-year period of dramatic warming that preceded it, the surface air temperature of the region poleward of 62°N experienced no net warming and, in fact, may have cooled.
Briffa et al. (2004) reviewed several prior analyses of maximum latewood density data obtained from a widespread network of tree-ring chronologies that spanned three to six centuries and were derived from nearly 400 locations. For the land area of the globe poleward of 20°N latitude, they too found that the warmest period of the past six centuries occurred in the 1930s and early 1940s. Thereafter, the region’s temperature dropped dramatically, although it did recover somewhat over the last two decades of the twentieth century. Nevertheless, its final value was still less than the mean value of the entire 1400s and portions of the 1500s.
Averaged across all land area poleward of 50°N latitude, there was a large divergence of reconstructed and instrumental temperatures subsequent to 1960, with measured temperatures rising and reconstructed temperatures falling, such that by the end of the record there was an approximate 1.5°C difference between them. Briffa et al. attempted to relate this large temperature differential to a hypothesized decrease in tree growth that was caused by a hypothesized increase in ultraviolet radiation that they hypothesized to have been caused by declining stratospheric ozone concentrations over this period. The results of their effort, however, proved “equivocal,” as they themselves described it, leaving room for a growing urban heat island effect in the instrumental temperature record to be the principal cause of the disconcerting data divergence. The three researchers wrote that these unsettled questions prevented them “from claiming unprecedented hemispheric warming during recent decades on the basis of these tree-ring density data.”
About the same time that Briffa et al. were struggling with this perplexing problem, Polyakov et al. (2004) were developing a long-term history of Atlantic Core Water Temperature (ACWT) in the Arctic Ocean using high-latitude hydrographic measurements that were initiated in the late nineteenth century, after which they compared the results of this exercise with the long-term history of Arctic Surface Air Temperature (SAT) developed by Polyakov et al. (2003). Their ACWT record, to quote them, revealed the existence of “two distinct warm periods from the late 1920s to 1950s and in the late 1980s-90s and two cold periods, one at the beginning of the record (until the 1920s) and another in the 1960s-70s.” The SAT record depicted essentially the same thing, with the peak temperature of the latter warm period being not quite as high as the peak temperature of the former warm period. In the case of the ACWT record, however, this relationship was reversed, with the peak temperature of the latter warm period slightly exceeding the peak temperature of the former warm period. But the most recent temperature peak was very short-lived; and it rapidly declined to hover around a value that was approximately 1°C cooler over the last few years of the record.
In discussing their findings, Polyakov et al. say that, like Arctic SATs, Arctic ACWTs are dominated, in their words, “by multidecadal fluctuations with a time scale of 50-80 years.” In addition, both records indicate that late twentieth century warmth was basically no different from that experienced in the late 1930s and early 1940s, a time when the air’s CO2 concentration was fully 65 ppm less than it is today.
Knudsen et al. (2004) documented climatic changes over the past 1,200 years via high-resolution multi-proxy studies of benthic and planktonic foraminiferal assemblages, stable isotopes, and ice-rafted debris found in three sediment cores retrieved from the North Icelandic shelf. These efforts resulted in their learning that “the time period between 1200 and around 7-800 cal. (years) BP, including the Medieval Warm Period, was characterized by relatively high bottom and surface water temperatures,” after which “a general temperature decrease in the area marks the transition to … the Little Ice Age.” They also found that “minimum sea-surface temperatures were reached at around 350 cal. BP, when very cold conditions were indicated by several proxies.” Thereafter, they report that “a modern warming of surface waters … is not registered in the proxy data,” and that “there is no clear indication of warming of water masses in the area during the last decades,” even in sea surface temperatures measured over the period 1948-2002.
Raspopov et al. (2004) presented and analyzed two temperature-related datasets. The first was “a direct and systematic air temperature record for the Kola Peninsula, in the vicinity of Murmansk,” which covered the period 1880-2000, while the second was an “annual tree-ring series generalized for 10 regions (Lovelius, 1997) along the northern timberline, from the Kola Peninsula to Chukotka, for the period 1458-1975 in the longitude range from 30°E to 170°E,” which included nearly all of northern Eurasia that borders the Arctic Ocean.
The researchers’ primary objectives in this work were to identify any temporal cycles that might be present in the two datasets and to determine what caused them. With respect to this dual goal, they report discovering “climatic cycles with periods of around 90, 22-23 and 11-12 years,” which were found to “correlate well with the corresponding solar activity cycles.” Of even more interest, however, was what they learned about the temporal development of the Current Warm Period (CWP).
Raspopov et al.’s presentation of the mean annual tree-ring series for the northern Eurasia timberline clearly shows that the region’s thermal recovery from the coldest temperatures of the Little Ice Age (LIA) may be considered to have commenced as early as 1820 and was in full swing by at least 1840. In addition, it shows that the rising temperature peaked just prior to 1950 and then declined to the end of the record in 1975. Thereafter, however, the Kola-Murmansk instrumental record indicates a significant temperature rise that peaked in the early 1990s at about the same level as the pre-1950 peak; but after that time, the temperature once again declined to the end of the record in 2000.
The latter of these findings (that there has been no net warming of this expansive high-latitude region over the last half of the twentieth century) is in harmony with the findings of the many studies reviewed above, while the former finding (that the thermal recovery of this climatically sensitive region of the planet began in the first half of the nineteenth century) is also supported by a number of other studies (Esper et al., 2002; Moore et al., 2002; Yoo and D’Odorico, 2002; Gonzalez-Rouco et al., 2003; Jomelli and Pech, 2004), all of which demonstrate that the Little Ice Age-to-Current Warm Period transition began somewhere in the neighborhood of 1820 to 1850, well before the date (~1910) that is indicated in the Mann et al. (1998, 1999) “hockey stick” temperature history.
One further study from 2004 yields much the same conclusion, but arrives at it by very different means. Benner et al. (2004) set the stage for what they did by stating that “thawing of the permafrost which underlies a substantial fraction of the Arctic could accelerate carbon losses from soils (Goulden et al., 1998).” In addition, they report that “freshwater discharge to the Arctic Ocean is expected to increase with increasing temperatures (Peterson et al., 2002), potentially resulting in greater riverine export of terrigenous organic carbon to the ocean.” And since the organic carbon in Arctic soils, in their words, “is typically old, with average radiocarbon ages ranging from centuries to millennia (Schell, 1983; Schirrmeister et al., 2002),” they set about to measure the age of dissolved organic carbon (DOC) in Arctic rivers to see if there were any indications of increasing amounts of older carbon being transported to the ocean, which (if there were) would be indicative of enhanced regional warming.
Specifically, they sampled two of the largest Eurasian rivers, the Yenisey and Ob’ (which drain vast areas of boreal forest and extensive peat bogs, accounting for about a third of all riverine DOC discharge to the Arctic Ocean), as well as two much smaller rivers on the north slope of Alaska, the Ikpikpuk and Kokolik, whose watersheds are dominated by Arctic tundra. In doing so, they found modern radiocarbon ages for all samples taken from all rivers, which indicates, in their words, that Arctic riverine DOC “is derived primarily from recently fixed plant litter and near-surface soil horizons.” Thus, because warming should have caused the average radiocarbon age of the DOC of Arctic rivers to increase, the absence of aging implied by their findings provides strong evidence for the absence of recent large-scale warming there.
Laidre and Heide-Jorgensen (2005) published a most unusual paper, in that it dealt with the danger of oceanic cooling. Using a combination of long-term satellite tracking data, climate data, and remotely sensed sea ice concentrations to detect localized habitat trends of narwhals—a species of whale with a long spear-like tusk—in Baffin Bay between Greenland and Canada, home to the largest narwhal population in the world. They studied the species’ vulnerability to recent and possible future climate trends. They found “since 1970, the climate in West Greenland has cooled, reflected in both oceanographic and biological conditions (Hanna and Cappelen, 2003),” with the result that “Baffin Bay and Davis Strait display strong significant increasing trends in ice concentrations and extent, as high as 7.5 percent per decade between 1979 and 1996, with comparable increases detected back to 1953 (Parkinson et al., 1999; Deser et al., 2000; Parkinson, 2000a,b; Parkinson and Cavalieri, 2002; Stern and Heide-Jorgensen, 2003).”
Humlum et al. (2005) noted that state-of-the-art climate models were predicting that “the effect of any present and future global climatic change will be amplified in the polar regions as a result of feedbacks in which variations in the extent of glaciers, snow, sea ice and permafrost, as well as atmospheric greenhouse gases, play key roles.” However, they also said Polyakov et al. (2002a,b) had “presented updated observational trends and variations in Arctic climate and sea-ice cover during the twentieth century, which do not support the modeled polar amplification of surface air-temperature changes observed by surface stations at lower latitudes,” and “there is reason, therefore, to evaluate climate dynamics and their respective impacts on high-latitude glaciers.” They proceeded to do just that for the Archipelago of Svalbard, focusing on Spitsbergen (the Archipelago’s main island) and the Longyearbreen glacier located in its relatively dry central region at 78°13’N latitude.
In reviewing what was already known about the region, Humlum et al. report that “a marked warming around 1920 changed the mean annual air temperature (MAAT) at sea level within only 5 years from about -9.5°C to -4.0°C,” which change, in their words, “represents the most pronounced increase in MAAT documented anywhere in the world during the instrumental period.” Then, they report that “from 1957 to 1968, MAAT dropped about 4°C, followed by a more gradual increase towards the end of the twentieth century.”
With respect to the Longyearbreen glacier, their own work revealed that it had “increased in length from about 3 km to its present size of about 5 km during the last c. 1100 years,” and they stated that “this example of late-Holocene glacier growth represents a widespread phenomenon in Svalbard and in adjoining Arctic regions,” which they describe as a “development towards cooler conditions in the Arctic” that “may explain why the Little Ice Age glacier advance in Svalbard usually represents the Holocene maximum glacier extension.”
As for what it all means, climate change in Svalbard over the twentieth century appears to have been a real rollercoaster ride, with temperatures rising more rapidly in the early 1920s than has been documented anywhere else before or since, only to be followed by a nearly equivalent temperature drop four decades later, both of which transitions were totally out of line with what climate models suggest should have occurred. In addition, the current location of the terminus of the Longyearbreen glacier suggests that, even now, Svalbard and “adjoining Arctic regions” are still experiencing some of the lowest temperatures of the entire Holocene, and at a time when atmospheric CO2 concentrations are higher than they have been for millions of years.
In one final paper from 2005, Soon (2005) explores the question of what was the more dominant driver of twentieth century temperature change in the Arctic: the rising atmospheric CO2 concentration or variations in solar irradiance. This he did by examining the roles the two variables may have played in forcing decadal, multi-decadal, and longer-term variations in surface air temperature (SAT). He performed a number of statistical analyses on (1) a composite Arctic-wide SAT record constructed by Polyakov et al. (2003), (2) global CO2 concentrations taken from estimates made by the NASA GISS climate modeling group, and (3) a total solar irradiance (TSI) record developed by Hoyt and Schatten (1993, updated by Hoyt in 2005) over the period 1875-2000.
The results of Soon’s analyses indicated a much stronger statistical relationship exists between SAT and TSI than between SAT and atmospheric CO2 concentration. Solar forcing generally explained well over 75 percent of the variance in decadal-smoothed seasonal and annual Arctic temperatures, while CO2 forcing explained only between 8 and 22 percent. Wavelet analysis further supported the case for solar forcing of SAT, revealing similar time-frequency characteristics for annual and seasonally averaged temperatures at decadal and multi-decadal time scales. By contrast, wavelet analysis gave little to no indication of a CO2 forcing of Arctic SSTs. Based on these findings, it would appear that it is the sun, and not atmospheric CO2, that has been driving temperature change in the Arctic over the twentieth century.
A recent study by Soon et al. (2011) shows an empirical relationship between Chinese surface temperatures and the best reconstructed total solar irradiance (TSI) records over the period 1880-2002. It offers additional prospects and plausible physical pathways for how the Arctic-Atlantic initiated changes may be connected to solar modulated changes within the East and South Asian monsoonal climate regimes. The results show a correlation between Chinese surface temperature and the two different measures of solar radiation, potentially providing a very strong physical constraint on how the Sun's irradiation can systematically modulate surface air temperature in China, essentially resolving the difficult hurdle of having to find out how the transparency of an atmospheric column actually changes over time, either through changing cloud fields and/or through merely changing transparency by having more or less loading of particulate matters.
Hanna et al. (2006) developed a 119-year history of Icelandic Sea Surface Temperature (SST) based on measurements made at 10 coastal stations located between latitudes 63°24’N and 66°32’N. This work revealed the existence of past “long-term variations and trends that are broadly similar to Icelandic air temperature records: that is, generally cold conditions during the late nineteenth and early twentieth centuries; strong warming in the 1920s, with peak SSTs typically being attained around 1940; and cooling thereafter until the 1970s, followed once again by warming—but not generally back up to the level of the 1930s/1940s warm period.”
Hansen et al. (2006) analyzed meteorological data from Arctic Station (69°15’N, 53°31’W) on Disko Island (West Greenland) for the period 1991-2004, after which their results were correlated, in the words of the researchers, “to the longest record available from Greenland at Ilulissat/Jakobshavn (since 1873).” Once this was done, marked changes were noted over the course of the study period, including “increasing mean annual air temperatures on the order of 0.4°C per year and 50% decrease in sea ice cover.” In addition, due to “a high correlation between mean monthly air temperatures at the two stations (1991-2004),” Hansen et al. were able to place the air temperature trend observed at Disko “in a 130 years perspective.” This exercise led them to conclude that the climate changes of the past decade were “dramatic,” but that “similar changes in air temperatures [had] occurred previous[ly] within the last 130 years.” More specifically, they report that the changes they observed over the last decade “are on the same order as changes [that] occurred between 1920 and 1930.”
In Iceland, Bradwell et al. (2006) examined the link between late Holocene fluctuations of Lambatungnajokull (an outlet glacier of the Vatnajokull ice cap of southeast Iceland) and variations in climate, using geomorphological evidence to reconstruct patterns of past glacier fluctuations and lichenometry and tephrostratigraphy to date glacial landforms created by the glacier over the past four centuries. This work revealed “there is a particularly close correspondence between summer air temperature and the rate of ice-front recession of Lambatungnajokull during periods of overall retreat,” and “between 1930 and 1950 this relationship is striking.” They also report that “ice-front recession was greatest during the 1930s and 1940s, when retreat averaged 20 m per year.” Thereafter, however, they say the retreat “slowed in the 1960s,” and “there has been little overall retreat since the 1980s.” The researchers also report that “the 20th-century record of reconstructed glacier-front fluctuations at Lambatungnajokull compares well with those of other similar-sized, non-surging, outlets of southern Vatnajokull,” including Skaftafellsjokull, Fjallsjokull, Skalafellsjokull, and Flaajokull. They find “the pattern of glacier fluctuations of Lambatungnajokull over the past 200 years reflects the climatic changes that have occurred in southeast Iceland and the wider region.”
Contemporaneously, Drinkwater (2006) decided “to provide a review of the changes to the marine ecosystems of the northern North Atlantic during the 1920s and 1930s and to discuss them in the light of contemporary ideas of regime shifts,” where he defined regime shift as “a persistent radical shift in typical levels of abundance or productivity of multiple important components of the marine biological community structure, occurring at multiple trophic levels and on a geographical scale that is at least regional in extent.” As a prologue to this effort, he first determined that “in the 1920s and 1930s, there was a dramatic warming of the air and ocean temperatures in the northern North Atlantic and the high Arctic, with the largest changes occurring north of 60°N,” which warming “led to reduced ice cover in the Arctic and subarctic regions and higher sea temperatures,” as well as northward shifts of multiple marine ecosystems. This change in climate occurred “during the 1920s, and especially after 1925,” according to Drinkwater, when he reports that “average air temperatures began to rise rapidly and continued to do so through the 1930s,” when “mean annual air temperatures increased by approximately 0.5-1°C and the cumulative sums of anomalies varied from 1.5 to 6°C between 1920 and 1940 with the higher values occurring in West Greenland and Iceland.” Thereafter, as he describes it, “through the 1940s and 1950s air temperatures in the northernmost regions varied but generally remained relatively high,” declining in the late 1960s in the northwest Atlantic and slightly earlier in the northeast Atlantic, which cooling has only recently begun to be reversed in certain parts of the region.
In the realm of biology, the early twentieth century warming of North Atlantic waters “contributed to higher primary and secondary production,” in the words of Drinkwater, and “with the reduced extent of ice-covered waters, more open water allow[ed] for higher production than in the colder periods.” As a result, cod “spread approximately 1200 km northward along West Greenland,” and “migration of ‘warmer water’ species also changed with earlier arrivals and later departures.” In addition, Drinkwater notes that “new spawning sites were observed farther north for several species or stocks while for others the relative contribution from northern spawning sites increased.” Also, he writes that “some southern species of fish that were unknown in northern areas prior to the warming event became occasional, and in some cases, frequent visitors.” Consequently, and considering all aspects of the event, Drinkwater states that “the warming in the 1920s and 1930s is considered to constitute the most significant regime shift experienced in the North Atlantic in the 20th century.”
Groisman et al. (2006) reported using “a new Global Synoptic Data Network consisting of 2100 stations within the boundaries of the former Soviet Union created jointly by the [U.S.] National Climatic Data Center and Russian Institute for Hydrometeorological Information … to assess the climatology of snow cover, frozen and unfrozen ground reports, and their temporal variability for the period from 1936 to 2004.” They determined that “during the past 69 years (1936-2004 period), an increase in duration of the period with snow on the ground over Russia and the Russian polar region north of the Arctic circle has been documented by 5 days or 3% and 12 days or 5%, respectively,” and they note this result “is in agreement with other findings.”
In commenting on this development, plus the similar findings of others, the five researchers say “changes in snow cover extent during the 1936-2004 period cannot be linked with ‘warming’ (particularly with the Arctic warming).” Why? Because, as they continue, “in this particular period the Arctic warming was absent.”
A recent essay that appeared in Ambio: A Journal of the Human Environment, by Karlén (2005) asks if temperatures in the Arctic are “really rising at an alarming rate,” as some have claimed. His answer is a resounding no. Focusing on Svalbard Lufthavn (located at 78°N latitude), which he later shows to be representative of much of the Arctic, Karlén reports that “the Svalbard mean annual temperature increased rapidly from the 1910s to the late 1930s,” that “the temperature thereafter became lower, and a minimum was reached around 1970,” and that “Svalbard thereafter became warmer, but the mean temperature in the late 1990s was still slightly cooler than it was in the late 1930s,” indicative of a cooling trend of 0.11°C per decade over the last seventy years of the twentieth century.
Karlén goes on to say “the observed warming during the 1930s is supported by data from several stations along the Arctic coasts and on islands in the Arctic, e.g. Nordklim data from Bjornoya and Jan Mayen in the north Atlantic, Vardo and Tromso in northern Norway, Sodankylaeand Karasjoki in northern Finland, and Stykkisholmur in Iceland,” and “there is also [similar] data from other reports; e.g. Godthaab, Jakobshavn, and Egedesmindde in Greenland, Ostrov Dikson on the north coast of Siberia, Salehard in inland Siberia, and Nome in western Alaska.” All of these stations, to quote him further, “indicate the same pattern of changes in annual mean temperature: a warm 1930s, a cooling until around 1970, and thereafter a warming, although the temperature remains slightly below the level of the late 1930s.” In addition, he says “many stations with records starting later than the 1930s also indicate cooling, e.g. Vize in the Arctic Sea north of the Siberian coast and Frobisher Bay and Clyde on Baffin Island.” Finally, Karlén reports that the 250-year temperature record of Stockholm “shows that the fluctuations of the 1900s are not unique,” and that “changes of the same magnitude as in the 1900s occurred between 1770 and 1800, and distinct but smaller fluctuations occurred around 1825.”
Karlén notes that “during the 50 years in which the atmospheric concentration of CO2 has increased considerably, the temperature has decreased,” which leads him to conclude that “the Arctic temperature data do not support the models predicting that there will be a critical future warming of the climate because of an increased concentration of CO2 in the atmosphere.” And this is especially important, in Karlén’s words, because the model-based prediction “is that changes will be strongest and first noticeable in the Arctic.”
Chylek et al. (2006) provides a more up-to-date report on average summer temperatures recorded at Ammassalik, on Greenland’s southeast coast, and Godthab Nuuk on the island’s southwestern coast, covering the period 1905 to 2005. They found “the 1955 to 2005 averages of the summer temperatures and the temperatures of the warmest month at both Godthab Nuuk and Ammassalik are significantly lower than the corresponding averages for the previous 50 years (1905-1955). The summers at both the southwestern and the southeastern coast of Greenland were significantly colder within the 1955-2005 period compared to the 1905-1955.”
Chylek et al. also compared temperatures for the 10-year periods of 1920-1930 and 1995-2005. They found the average summer temperature for 2003 in Ammassalik was a record high since 1895, but “the years 2004 and 2005 were closer to normal being well below temperatures reached in the 1930s and 1940s.” Similarly, the record from Godthab Nuuk showed that while temperatures there “were also increasing during the 1995-2005 period,they stayed generally below the values typical for the 1920-1940 period.” The authors conclude that “reports of Greenland temperature changes are …. diverse suggesting a long term cooling and shorter warming periods.”
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