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North America (Alaska) Temperature Trends -- Summary
In order to assess the significance of recent temperature changes anywhere on earth, it is necessary to have a knowledge of how temperatures have varied at that location in the past.  In this summary we briefly recount the findings of a number of papers that provide this context for Alaska.

Calkin et al. (2001) reviewed what they call "the most current and comprehensive research of Holocene glaciation" along the northernmost Gulf of Alaska between the Kenai Peninsula and Yakutat Bay.  In doing so, they noted several periods of glacial advance and retreat during the past 7000 years.  Most recently, there was a general retreat during the Medieval Warm Period that lasted for "at least a few centuries prior to AD 1200," after which there were three major intervals of Little Ice Age glacial advance: the early 15th century, the middle 17th century, and the last half of the 19th century.  During these latter periods, glacier equilibrium line altitudes were depressed from 150 to 200 m below present values as Alaskan glaciers "reached their Holocene maximum extensions."  Consequently, it is likely that Alaskan temperatures reached their Holocene minimums during these periods; and it thus should come as no surprise that there should be a significant warming associated with the region's recovery from the coldest period of the current interglacial, as it returns to a less extreme climatic state.

In another glacier study, Wiles et al. (2004) derived a composite Glacier Expansion Index (GEI) for Alaska based on "dendrochronologically-derived calendar dates from forests overrun by advancing ice and age estimates of moraines using tree-rings and lichens" for three climatically-distinct regions (the Arctic Brooks Range, the southern transitional interior straddled by the Wrangell and St. Elias mountain ranges, and the Kenai, Chugach and St. Elias coastal ranges) after which they compared this history of glacial activity with "the 14C record preserved in tree rings corrected for marine and terrestrial reservoir effects as a proxy for solar variability" and with the history of the Pacific Decadal Oscillation (PDO) derived by Cook (2002).  This work revealed, in their words, that "Alaska shows ice expansions approximately every 200 years, compatible with a solar mode of variability," specifically, the de Vries 208-year solar cycle; and by merging this cycle with the cyclical behavior of the PDO, they obtained a dual-parameter forcing function that is even better correlated with the Alaskan composite GEI, with major glacial advances clearly associated with the Sporer, Maunder and Dalton solar minima.

In discussing the significance of these findings, Wiles et al. say that "increased understanding of solar variability and its climatic impacts is critical for separating anthropogenic from natural forcing and for predicting anticipated temperature change for future centuries."  In this regard, it is most interesting that they make no mention of possible CO2-induced global warming, presumably because there is no need to do so.  Alaskan glacial activity, which, in their words, "has been shown to be primarily a record of summer temperature change (Barclay et al., 1999)," appears to be sufficiently well described within the context of solar and PDO variability alone.

In a related report, i.e., the Barclay et al. (1999) study cited by Wiles et al. in the preceding paragraph, tree-ring width data were used to construct an 1119-year proxy temperature record for southern Alaska covering the period AD 873 to 1991.  This history indicates there were a number of intervals with both cooler and warmer air temperatures than those of the present.  The cooler intervals were centered on AD 1400, 1660 and 1870, while the warmer intervals were centered on AD 1300, 1440 and 1820.  This study reveals the naturally-fluctuating nature of southern Alaskan climate and how it was both warmer and colder than it is presently over various portions of the first thousand years of the record when the air's CO2 concentration fluctuated hardly at all, which indicates that climate change in southern Alaska marches to the tune of a vastly different drummer than the air's CO2 concentration.

In another tree-ring width study, D'Arrigo et al. (2005) combined a data series they derived from 14 white spruce chronologies from the Seward Peninsula that covered the period 1358-2001 with similar chronologies from northwest Alaska to produce two versions of a much longer data series that extended all the way back to AD 978.  The first chronology was created using traditional methods of standardization (STD), which do not perform well in capturing multi-decadal or longer climate cycles, while the second chronology utilized the regional curve standardization (RCS) method, which better preserves low-frequency variations at multi-decadal time scales and longer.

Each of these chronologies revealed, in the words of D'Arrigo et al., "several intervals of persistent above-average growth that broadly coincide with the timing of the late Medieval Warm Period."  However, the warming is much more pronounced in the RCS chronology, where the greatest warmth occurred in the early to middle 1200s, with lesser peaks in the early to middle 1100s and early 1400s.  In addition, the severe cold of the Little Ice Age is more pronounced and of longer duration in the RCS chronology, where it occurred between about 1500 and 1700.  What the records fail to do, however, is to provide any evidence for what climate alarmists call "unprecedented warmth" in the last decades of the 20th century.  Quite to the contrary, the northwest Alaska temperatures of the last four decades have actually hovered around the long-term average.

Also employing this approach to palaeoclimate reconstruction, 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 of Alaska, analyzing the data in such a way as to "directly relate changes in radial growth to annual variations in the North Pacific ocean-atmosphere system" for the period 1599-1983.  In doing so, they determined that "much of the pre-instrumental record in the Pacific Northwest region of North America is characterized by alternating regimes of relatively warmer and cooler 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 discovered, for example, that "regime shifts in the North Pacific have occurred 11 times since 1650" and that "another regime-scale shift in the North Pacific is almost certainly imminent."  What is more, the last of these abrupt regime shifts, that of 1976-77, was responsible for the vast majority of the past half-century's warming in Alaska, which climate alarmists wrongly hype as evidence of gradual CO2-induced global warming.  Take away what occurred in that single year, and Alaska is no different from the rest of the United States, with most of its temperature stations showing either no subsequent warming or an actual cooling trend.

In a slight variation of the technique employed in the prior three studies, D'Arrigo et al. (2004) sampled white spruce trees from 14 sites near the elevational treeline on the eastern Seward Peninsula of Alaska, obtaining 46 cores from 38 trees, which they used to develop a maximum latewood density (MXD) chronology for the period AD 1389 to 2001.  Calibrating a portion of the latter part of this record (1909-1950) against May-August monthly temperatures obtained from the Nome meteorological station, they then converted the entire MXD chronology to warm-season temperatures.  This exercise revealed that the mid-20th century exhibited the warmest 20-year interval since 1640.  In viewing their plot of reconstructed temperatures, however, it can readily be seen there was a nearly equivalent warm period near the end of the 1600s, as well as a two-decade period of close-to-similar warmth in the mid-1500s.  What is more, in the latter part of the 1400s, there is a decade that is actually warmer than that of the mid-20th century.  Consequently, it is clear that on the eastern Seward Peninsula of Alaska no part of the 20th-century exhibited warmth that could be described as "unprecedented" over the past six centuries, much less over the past one to two millennia, as claimed for the Northern Hemisphere by Mann et al. (1998, 1999) and Mann and Jones (2003).  Quite to the contrary, the work of D'Arrigo et al. supports the findings of Esper et al. (2002, 2003), McIntyre and McKitrick (2003), and Loehle (2004), which indicate there were several periods over the past millennium or more when it was equally as warm as, or even warmer than, it was during any part of the 20th century.

In another study of maximum latewood density, Barber et al. (2004) note that "a robust result of General Circulation Model simulations is that high-latitude land masses in the Northern Hemisphere will experience the greatest magnitude of warming under scenarios of increased anthropogenically produced greenhouse gases (Houghton et al., 1996)," and because of this theoretical model-based result, they say "it is tempting to interpret recent warming and ecological changes in Alaska as evidence for the greenhouse gas-climate warming theory."  And indeed it is.  In fact, the temptation has proven to be truly irresistible for the world's climate alarmists, who repeatedly claim just that.  Before such an attribution can validly be made, however, Barber et al. correctly state that "it is crucial to know whether other similar rapid climate changes and conditions occurred in the past," when anthropogenic-produced greenhouse gases were not a part of the picture.

To acquire this essential knowledge, the four Alaskan researchers used maximum latewood density and δ13C discrimination measurements made on Interior Alaska white spruce to reconstruct summer (May-August) temperature for the period 1800-1996.  The resulting temperature history was characterized by seven decadal-scale regimes, with abrupt shifts occurring at 1816, 1834, 1879, 1916, 1937 and 1974.  Barber et al. additionally found that the latter part of the 20th century was "characterized by some of the warmest summers in the 200-year interval."  However, they note that mid-19th century summer temperatures also "reconstruct as some of the warmest over the 200-year period."  In fact, they say that summer temperatures during two periods in the mid-1800s "are about as warm as present."  Furthermore, they "show additional tree ring data that support [their] reconstruction of these warm periods."  As a result, it is clear that the recent warmth in Alaska is in no way unprecedented in either its degree or rate of development, having been replicated at least twice in the 19th century alone.  Thus, it is truly disingenuous to claim, as climate alarmists do, that current Alaskan warmth is a product of anthropogenically-produced greenhouse gases; it just ain't so.  Hence, current Alaskan warmth is also not the elusive canary-in-the-coal-mine that everyone is seeking but no one can seem to find, most likely because there is no such bird.

Focusing on a pressing contemporary concern of which we hear much from climate alarmists, Romanovsky et al. (2002) describe "an emerging system for comprehensive monitoring of permafrost temperatures," which they say is needed for "detection and tracking of climatic changes" and "verification of GCM outputs."  In the course of this endeavor, they present a 1924-2001 history of mean annual temperatures for Barrow, Alaska at soil depths of 0.08 m (the "active layer"), 0.5 m, and 1.0 m (about 60 cm below the permafrost table), reporting that permafrost temperatures were "very similar during the 1940s and 1990s (except for unprecedented warm extremes of 1998 and 1999)."  However, even including these "unprecedented warm extremes," we calculate from data in their paper that the mean temperature about 60 cm into the permafrost from 1990 and onward (-9.15C) was no warmer than, and possibly even colder than, the mean temperature of the 16-year period 1937-1952 (-9.06C).  Consequently, and in spite of all the climate-alarmist hype about recent dramatic warming in the permafrost regions of Alaska, real-world data demonstrate - at least for Barrow - that it is no warmer there now than it was half a century ago, and that the area's permafrost is in no more danger of disappearing today than it was in the days of our grandparents.  Furthermore, Romanovsky et al. note that degradation of permafrost does not proceed as rapidly as climate alarmists would have one believe.  As they describe it, "degradation of permafrost is a slow process," and "if recent trends continue, it will take several centuries to millennia [our italics] for permafrost in the present discontinuous zone to disappear completely in the areas where it is actively warming and thawing."

In another study related to the potential thawing of permafrost, Benner et al. (2004) set the stage for their work by stating that "the fate of soil carbon in high latitude soils is uncertain, as the effects of global warming and climate change are predicted to be magnified in the Arctic (Serreze et al., 2000)."  They also note 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."  Therefore, since the organic carbon in Arctic soils, as they describe it, "is typically old, with average radiocarbon ages ranging from centuries to millennia (Schell, 1983; Schirrmeister et al., 2002)," they set about to measure the ages of dissolved organic carbon (DOC) in Arctic rivers.  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 relatively small rivers on the north slope of Alaska, the Ikpikpuk and Kokolik, whose watersheds are dominated by Arctic tundra.

As a result of this work, Benner et al. say 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."  They then note that warming should cause the average radiocarbon age of the DOC in Artic 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 Arctic warming, as is also indicated by the region-wide temperature data we discuss in our Editorials of 10 Mar 2004, 17 Mar 2004 and 24 Mar 2004.

In conclusion, the many real-world observations described in the preceding paragraphs clearly indicate there is nothing unusual or "unprecedented" about the recent temperature history of Alaska.  It is currently no warmer there now than it has been many times in the past, when the air's CO2 content was considerably lower than it is currently.  And when Alaska's climate has changed - in prior years, centuries and millennia - it has been in response to changes in forcing factors other than atmospheric CO2 concentration.

References
Barber, V.A., Juday, G.P., Finney, B.P. and Wilmking, M.  2004.  Reconstruction of summer temperatures in interior Alaska from tree-ring proxies: Evidence for changing synoptic climate regimes.  Climatic Change 63: 91-120.

Barclay, D.J., Wiles, G.C. and Calkin, P.E.  1999.  A 1119-year tree-ring-width chronology from western Prince William Sound, southern Alaska.  The Holocene 9: 79-84.

Benner, R., Benitez-Nelson, B., Kaiser, K. and Amon, R.M.W.  2004.  Export of young terrigenous dissolved organic carbon from rivers to the Arctic Ocean.  Geophysical Research Letters 31: 10.1029/2003GL019251.

Calkin, P.E., Wiles, G.C. and Barclay, D.J.  2001.  Holocene coastal glaciation of Alaska.  Quaternary Science Reviews 20: 449-461.

Cook, E.R.  2002.  Reconstructions of Pacific decadal variability from long tree-ring records.  EOS: Transactions, American Geophysical Union 83: S133.

D'Arrigo, R., Mashig, E., Frank, D., Jacoby, G. and Wilson, R.  2004.  Reconstructed warm season temperatures for Nome, Seward Peninsula, Alaska.  Geophysical Research Letters 31: 10.1029/2004GL019756.

D'Arrigo, R., Mashig, E., Frank, D., Wilson, R. and Jacoby, G.  2005.  Temperature variability over the past millennium inferred from Northwestern Alaska tree rings.  Climate Dynamics 24: 227-236.

Esper, J., Cook, E.R. and Schweingruber, F.H.  2002.  Low-frequency signals in long tree-ring chronologies and the reconstruction of past temperature variability.  Science 295: 2250-2253.

Esper, J., Shiyatov, S.G., Mazepa, V.S., Wilson, R.J.S., Graybill, D.A. and Funkhouser, G.  2003.  Temperature-sensitive Tien Shan tree ring chronologies show multi-centennial growth trends.  Climate Dynamics 21: 699-706.

Gedalof, Z. and Smith, D.J.  2001.  Interdecadal climate variability and regime-scale shifts in Pacific North America.  Geophysical Research Letters 28: 1515-1518.

Goulden, M.L., Wofsy, S. C., Harden, J.W., Trumbore, S.E., Crill, P.M., Gower, S.T., Fries, T., Daube, B.C., Fan, S., Sutton, D.J., Bazzaz, A. and Munger, J.W.  1998.  Sensitivity of boreal forest carbon balance to soil thaw.  Science 279: 214-217.

Houghton, J.J., Meiro Filho, L.G., Callander, B.A., Harris, N., Kattenberg, A. and Maskell, K. (Eds.).  1996.  The Science of Climate Change. Contribution of Working Group I to the Second Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), Vol. I. Climate Change 1995.  Cambridge University Press, Cambridge, UK.

Loehle, C.  2004.  Climate change: detection and attribution of trends from long-term geologic data.  Ecological Modelling 171: 433-450.

Mann, M.E., Bradley, R.S. and Hughes, M.K.  1998.  Global-scale temperature patterns and climate forcing over the past six centuries.  Nature 392: 779-787.

Mann, M.E., Bradley, R.S. and Hughes, M.K.  1999.  Northern Hemisphere temperatures during the past millennium: Inferences, uncertainties, and limitations.  Geophysical Research Letters 26: 759-762.

Mann, M.E. and Jones, P.D.  2003.  Global surface temperatures over the past two millennia.  Geophysical Research Letters 30: 10.1029/2003GL017814.

McIntyre, S. and McKitrick, R.  2003.  Corrections to the Mann et al. (1998) proxy data base and Northern Hemispheric average temperature series.  Energy and Environment 14: 751-771.

Peterson, B.J., Holmes, R.M., McClelland, J.W., Vorosmarty, C.J., Lammers, R.B., Shiklomanov, A.I., Shiklomanov, I.A. and Rahmstorf, S.  2002.  Increasing river discharge in the Arctic Ocean.  Science 298: 2171-2173.

Romanovsky, V., Burgess, M., Smith, S., Yoshikawa, K. and Brown, J.  2002.  Permafrost temperature records: Indicators of climate change.  EOS, Transactions, American Geophysical Union 83: 589, 593-594.

Schell, D.M.  1983.  Carbon-13 and carbon-14 abundances in Alaskan aquatic organisms: Delayed production from peat in Arctic food webs.  Science 219: 1068-1071.

Schirrmeister, L., Siegert, C., Kuznetsova, T., Kuzmina, S., Andreev, A., Kienast, F., Meyer, H. and Bobrov, A.  2002.  Paleoenvironmental and paleoclimatic records from permafrost deposits in the Arctic region of northern Siberia.  Quaternary International 89: 97-118.

Serreze, M., Walsh, J.E., Chapin III, F.S., Osterkamp, T., Dyurgerov, M., Romanovsky, V., Oechel, W.C., Morison, J., Zhang, T. and Barry, R.G.  2000.  Observational evidence of recent change in the northern high-latitude environment.  Climatic Change 46: 159-207.

Wiles, G.C., D'Arrigo, R.D., Villalba, R., Calkin, P.E. and Barclay, D.J.  2004.  Century-scale solar variability and Alaskan temperature change over the past millennium.  Geophysical Research Letters 31: 10.1029/2004GL020050.

Last updated 24 August 2005