Taking the long view of things to get a broad perspective of the subject, we note that central Alaska and the Yukon were much warmer during the previous interglacial than they are today.  Based upon evidence of expanded boreal forest ranges in these areas during that earlier time, Muhs et al. (2001) estimate that the mean summer temperatures of that period were at least 1-2°C warmer than they are currently, and that in some locations they may have been as much as 3-5°C higher, which suggests that the warmth of today is far from "unprecedented" in this expanded time frame.

As for the past 10,000 years of the current interglacial - the Holocene - Darby et al. (2001) developed a multi-parameter environmental record from a thick sequence of post-glacial sediments obtained from cores retrieved from the upper continental slope off the shelf of the Chukchi Sea.  As they describe it, these data reveal the existence of "previously unrecognized millennial-scale variability in Arctic Ocean circulation and climate," along with evidence which suggests that "in the recent past, the western Arctic Ocean was much warmer than it is today."  In fact, they say their data indicate that "during the middle Holocene the August sea surface temperature fluctuated by 5°C and was 3-7°C warmer than it is today," which also makes both the mean state and variability of the region's current climate look pretty mundane by comparison.

Highlighting these facts, Darby et al. state that past Holocene variability in the western Arctic was "larger than any change observed in this area over the last century" and that the region's temperatures "may have been 5°C warmer only a few thousand years ago."  Consequently, since there is no evidence that the air's CO2 concentration was either higher or fluctuating wildly during that period -- it was, in fact, lower and very stable [see Carbon Dioxide (History - The Last 250,000 Years) in our Subject Index] -- something else had to have been responsible for the significantly warmer and more variable climate of that period, which means that an even lesser manifestation of that "something else" could well be responsible for the more ordinary climate changes of the past century.

Another long-term (but slightly shorter) perspective of Arctic climate was provided by Kasper and Allard (2001), who used soil deformations caused by ice-wedge activity to reconstruct a 4000-year climatic history of the area near Salluit in northern Quebec, Canada.  Their data revealed that generally cold conditions prevailed until approximately AD 140, after which it warmed to about AD 1030.  Thereafter, however, cooling occurred; and from AD 1500 to 1900 ice-wedge activity was at its peak, suggesting that this latter period was the coldest interval of the past 4000 years.  It then warmed from about 1900 to 1945, as the earth recovered from the global chill of the Little Ice Age.  However, cold conditions returned for the last half of the 20th century, in direct contradiction of the climate-alarmist claim that this period was one of unprecedented warming.

Decreasing the length of time investigated still more, Naurzbaev and Vaganov (2000) developed a 2200-year temperature history from tree-ring data obtained from trees growing near the upper timberline in Siberia.  They too observed relative coolness in the first couple of centuries AD, followed by warming that culminated in the Medieval Warm Period, which lasted from about AD 850 to 1150.  Then came the Little Ice Age, which was followed by the recovery warming of the 20th century.  In regard to this modern warming, however, Naurzbaev and Vaganov once again report -- in unmistakable contradiction of the claims of the world's climate alarmists -- that it was "not extraordinary."

Further reducing the interval of the time studied, Moore et al. (2001) derived a 1240-year record of average summer temperatures from sediment cores extracted from Donard Lake, Baffin Island, Canada.  Again, anomalously warm temperatures occurred around AD 1000 to 1100; and at the start of the 13th century, Donard Lake witnessed what Moore et al. describe as "one of the largest climatic transitions in over a millennium," as "average summer temperatures rose rapidly by nearly 2°C from 1195-1220."  Then came the Little Ice Age, which was followed by gradual warming from 1800 to 1900.  Between 1900 and 1950, however, there was significant cooling.  Warming then occurred in the 1950s and 60s, after which cooling was observed to persist to the end of the record (about 1990) when climate alarmists claim we should have seen dramatic warming, especially in the Arctic, which they describe as "the place to watch for global warming."

Similar findings were reported by Arseneault and Payette (1997), who analyzed tree-ring and growth-form sequences obtained from more than 300 spruce remains buried in a presently-treeless peatland in northern Québec in their quest to produce a proxy record of climate for this region between AD 690 and 1591.  Over the course of this 900-year period, the trees of the region experienced several alternating episodes of suppressed and rapid growth, indicative of colder and warmer conditions, respectively, than those of the present.  Colder conditions prevailed during the periods AD 760-860 and 1025-1400, while warmer conditions were prevalent during the periods AD 700-750, 860-1000, 1400-1450 and 1500-1570.

Analysis of the warm interval between AD 860 and 1000 led Arseneault and Payette to conclude that the warmth experienced in northern Quebec at that time was part of the Medieval Warm Period that occurred throughout the North Atlantic and Northern Europe.  At their study site this period's warmth, as they describe it, "exceeded in duration and magnitude both the 16th and 20th century warm periods identified previously using the same methods."  Also, on the basis of current annual temperatures at their study site and the northernmost 20th century location of the forest that is presently 130 km south of their site, the two scientists concluded that the "Medieval Warm Period was approximately 1°C warmer than the 20th century."  Hence, given the natural oscillatory behavior of climate in the subarctic region of North America, as demonstrated in this study, if the region were to warm by another degree or so in the current century, such warming would still not qualify as proof of CO2-induced global warming.

Large climatic transitions of the type detected by Arseneault and Payette in northern Québec have also been documented in the North Pacific Ocean, where Gedalof and Smith (2001) identified eleven decadal-scale sea surface temperature regimes shifts that have occurred since 1650, the characteristics of which led them to conclude that "another regime-scale shift in the North Pacific is almost certainly imminent."  The significance of this finding resides in the fact that the abrupt 1976-77 shift in this Pacific Decadal Oscillation, as it is generally called, is what is responsible for the vast majority of the past half-century's temperature increase in Alaska, which climate alarmists wrongly cite as evidence of CO2-induced global warming.  Take away what occurred in that single year, which clearly cannot be due to CO2, and Alaska is no different from the rest of the world, with most of its temperature stations showing either no subsequent warming or even an actual cooling.

Moving to the Asian Subarctic, a 600-year tree-ring-derived temperature history was produced for this region by Vaganov et al. (2000).  It starts with a modest warming that continues to about 1750, whereupon the region experiences severe cooling, which is followed by a 130-year warming trend from about 1820 to 1950.  Vaganov et al. state, however, that this temperature rise "does not go beyond the limits of reconstructed natural temperature fluctuations," once again in contradiction of the climate-alarmist claim that the warming of the 20th century is unprecedented over the past two millennia.  Also, adding insult to injury, as it were, the last 50 years of the Vaganov et al. temperature history -- like many of the other records we have reviewed -- depicts cooling.

In another tree-ring study covering the same time period, Briffa et al. (2004) reviewed the results of several analyses of maximum latewood density data obtained from a widespread set of tree-ring chronologies spanning three to six centuries that were derived from trees at nearly 400 locations.  For all land area of the globe lying poleward of 20°N latitude, they found that the warmest period of the past six centuries occurred in the 1930s and early 1940s, well before the majority of the anthropogenic CO2 emitted to the atmosphere during the industrial era had ever entered the atmosphere.  What is more, after anthropogenic CO2 emissions really began to rise, the temperature of this huge region dropped, and dropped rather dramatically, although it recovered somewhat over the last two decades of the 20th century.  Even then, however, its final value was still below the mean value of the 1400s and portions of the 1500s.  Consequently, Briffa et al. say that these and other unsettling questions prevent them "from claiming unprecedented hemispheric warming during recent decades on the basis of these tree-ring density data alone."

In another revealing study, Overpeck et al. (1997) combined paleoclimatic records from lake and marine sediments with data from 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 (1.5°C) occurred between 1840 and 1955, over which period the atmosphere'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 actually declined by 0.4°C, while the atmosphere'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 within this region, or even conclude that it has had any effect at all.  Why?  Because over the first 115 years of warming (when 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, while over the final 35 years of the record (when the increase in the air's CO2 content really began to accelerate, rising at a mean rate of 1.17 ppm/year or nearly five times the rate at which it had risen in the prior period), the rate of rise of surface air temperature did not accelerate anywhere near that fast.  In fact, it did not accelerate at all.  In fact, it decelerated, to a mean rate of change (0.011°C/year) that was nearly the same as the rate at which it had previously risen but in the opposite direction, i.e., downward.  Clearly, therefore, there was something that totally overpowered whatever effect the rise in the air's CO2 content over the first period may, or may not, have had on the temperature of the Arctic, as well as the effect of the nearly five times greater rate of rise in the air's CO2 content over the second period.

Evidence of dramatic 20th-century warming is also nowhere to be found in a 300-year record of permafrost degradation in the Tanana River Valley lowlands of central Alaska.  According to Jorgenson et al. (2001), who utilized a combination of methods to determine the extent, history and rate of progression of this phenomenon, 83% of the degradation that was evident at the time of their study had occurred between 1750 and 1949, well before the lion's share of the historical increase in the air's CO2 content had occurred.  These results thus highlight another instance where climate model projections do not mesh with reality; for the models suggest that permafrost degradation should be accelerating as a result of ever-increasing CO2-induced global warming, and that it should be amplified in high northern latitudes.  Yet, as these data show, most of the melting that has occurred to date took place before most of the historical increase in the air's CO2 content.

Shifting focus to the more recent past, Zeeberg and Forman (2001) analyzed changes in glacier terminus positions on the northern portion of Novaya Zemlya, a Russian island located between the Barents and Kara Seas in the Arctic Ocean.  In harmony with the many studies that have revealed significant Arctic warming over the first part of the 20th century, they observed a significant glacial retreat in the first and second decades of this period.  By 1952, however, the island's glaciers had experienced between 75 to 100% of their net 20th century retreat; and during the next 50 years, the recession of over half of the glaciers stopped, while many actually began to advance, probably due to the fact that summer temperatures on Novaya Zemlya in the four decades since 1961 have been 0.3 to 0.5°C colder than those of the prior 40 years, while winter temperatures have been between 2.3 to 2.8°C colder.  These observations, the two scientists note, are "counter to warming of the Eurasian Arctic predicted for the twenty-first century by climate models, particularly for the winter season," which is starting to sound like a recurring theme, i.e., the real world seems to be telling us a very different story than the climate models do.

In another research report dealing with the past century, Comiso et al. (2001) describe their satellite study of the Odden ice tongue, which is a winter ice cover of the Greenland Sea that has a length of about 1300 km and an aerial coverage of as much as 330,000 km².  Coincident with the purported unprecedented warming of 1979-1998, they observed a fair amount of interannual variability in the size of the ice tongue, but they could detect no statistically significant overall change in any of its properties.  Of even more interest is the fact that a 75-year reconstruction of Odden ice tongue behavior suggests it was a much smaller feature several decades ago, based on correlations of its size and duration with temperatures recorded on nearby Jan Mayen Island, which depict a cooling of 0.15°C per decade over the past three-quarters of a century.

With respect to Greenland itself, Chylek et al. (2004) studied three coastal stations in southern and central Greenland that possess almost uninterrupted temperature records between 1950 and 2000.  They 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."

At the start of the 20th century, however, Greenland was warming, as it emerged, along with the rest of the world, from the depths of the Little Ice Age.  What is more, 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 fact, 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," which 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."

With still other near-surface air temperatures of the instrumental era, Polyakov et al. (2002) developed a 125-year (1875-2000) Arctic air temperature history from measurements made at 75 land stations and a number of drifting buoys located poleward of 62°N latitude.  Their analysis of these data revealed "strong intrinsic variability, dominated by multi-decadal fluctuations with a timescale of 60-80 years."  Because of this fact, they found temperature trends in the Arctic to be highly dependent on the time period selected for analysis.  In fact, they identified periods when Arctic trends were actually smaller or even of different sign than Northern Hemispheric trends.

In further analyzing these data, Polyakov et al. (2003) found that from 1875 to about 1917, the surface air temperature of the huge northern region rose hardly at all; but then it took off like a rocket, climbing 1.7°C in just 20 years to reach a peak in 1937 that has yet to be eclipsed.  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 it rose by approximately 55 ppm, or nearly seven times more than it did throughout the 20-year period of dramatic warming that had preceded it, the surface air temperature of the region poleward of 62°N experienced no net warming and, in fact, may have actually cooled a bit.

Totally independent evidence for this conclusion comes from Benner et al.'s (2004) study of riverine transport of dissolved organic carbon (DOC) to the Arctic Ocean via two of the largest Eurasian rivers, the Yenisey and Ob' (which drain vast areas of boreal forest and extensive peat bogs), as well as two relatively small rivers on the north slope of Alaska, the Ikpikpuk and Kokolik, whose watersheds are dominated by Arctic tundra.  All four of these rivers were sampled within about three months of their peak discharges, when most DOC is exported to the ocean; and Benner et al. report that 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."  In contrast, radiocarbon ages of DOC in tropical and temperate rivers range from modern to over 1300 years (Hedges et al., 1986; Raymond and Bauer, 2001), indicative of what Benner et al. call "variable retention and aging in soil."  Their high-latitude data, on the other hand, indicate almost complete retention of old soil carbon in the Arctic.  What is the significance of this finding?

Benner et al. note that warming should cause the average radiocarbon age of the DOC in Arctic rivers to increase, which - if it happened - would, in their words, "provide strong evidence of the mobilization of the vast and relatively old carbon stored in [Arctic] soils," in harmony with the climate-alarmist claim that catastrophic carbon loss from Arctic soils would be one of the major consequences of rising temperatures in that part of the world.  This being the case, the total absence of any aging of Arctic riverine DOC implied by Benner et al.'s measurements provides "strong evidence" of the exact opposite, i.e., the total absence of any recent large-scale warming there.

To underscore the fundamental message of this summary, we conclude by reporting the findings of Przybylak (2000, 2002).  In the first of these papers, Przybylak used the mean monthly temperatures of 37 Arctic and 7 sub-Arctic stations, as well as the temperature anomalies of 30 grid-boxes from the updated data set of Jones, to derive a spatial and temporal history of Arctic near-surface air temperature over the last 70 years.  The results of this analysis revealed that "in the Arctic, the highest temperatures since the beginning of instrumental observation occurred clearly in the 1930s."  Even in the 1950s, according to Przybylak, "the temperature was higher than in the last 10 years."  In fact, he reports that "the level of temperature in Greenland in the last 10-20 years is similar to that observed in the 19th century."  In his second paper, Przybylak analyzed the intraseasonal (within season) and interannual (between years) variability in maximum, minimum and average air temperature for the entire Arctic for the period 1951-1990; and once again, in his words, "no tangible manifestations of the greenhouse effect [could] be identified," as "trends in both the intraseasonal and interannual temperature variability of the temperature variables studied [did] not show any significant changes."

In concluding the first of these two papers, Przybylak says the meteorological record "shows that the observed variations in air temperature in the real Arctic are in many aspects not consistent with the projected climatic changes computed by climatic models for the enhanced greenhouse effect."  Why?  Because, says he, "temperature predictions produced by numerical climate models significantly differ from those actually observed."

This is also the message conveyed by the several long-term temperature reconstructions described in this review: at the times and in the places where climate alarmists say "unprecedented" CO2-induced global warming should be most clearly evident, real-world data demonstrate its conspicuous absence.  Accepting the climate model-inspired dictum of Meadows (2001), therefore, that "the place to watch for global warming - the sensitive point, the canary in the coal mine - is the Arctic," we can only conclude there has been no historical CO2-induced global warming … anywhere.

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