Geology's long-term perspective

This response to the contents of the Arctic Climate Impact Assessment (ACIA) concerns alarmist and highly questionable conclusions about Arctic climate and its variability. There are serious problems with this statement. from ACIAs Overview:

[The Arctic Climate Impact Assessment] is the largest, most comprehensive assessment of climate change in Arctic. The Arctic is experiencing some of the most rapid and severe climate change on earth. At least half the summer sea ice in the Arctic is projected to melt by the end of this century [as a result of increasing atmospheric CO2], along with a significant portion of the Greenland Ice Sheet, as the region is projected to warm an additional 4-7C (7 to 13F) by 2100.

     We begin with ACIAs claim that the Arctic is experiencing some of the most rapid and severe climate change on earth. This statement focuses entirely on what is happening today. A more broad perspective is called for in order to accurately assess how current change stacks up against climate change in the past. Hu et al. (2000), provide the first quantitative temperature record that continuously spans the last 2000 years from Alaska. They write:

Our [surface water temperature] reconstruction at Farewell Lake indicated that although the 20th century, represented by the uppermost three samples, was among the warmest periods of the past two millennia, two earlier periods may have been comparably warm (A.D. 0-300 and A.D. 850-1200). [B]oth the pronounced temperature minimum centered at A.D. 600 and the culmination of the Little Ice Age cooling at A.D. 1700 in the Farewell Lake region coincide with extensive glacial advances in the southern coasts and the Brooks Range of Alaska. The cooling events around A.D. 600 might have also caused the demise of the Kachemak culture in the northwestern Gulf of Alaska at this time.

     In a second example, Shiyatov (2003) finds that although large displacement of the upper treeline limit (mainly populated by the Siberian larch Larix sibirica) has been detected in the region of the Polar Ural Mountains in the past 1150 years, change during the 20th century has not been particularly exceptional or alarming (see Figure 1).

 

Figure 1: Large displacement of the upper treeline limit in the Polar Ural Mountains region (66N-67N, 65E-66E) likely as a result of climatic and environmental conditionings. Note how although instrumental thermometers record about a 1C warming of the June-July temperature in the 20th century, the treeline limit does not suggest anything exceptional or unusual in relation to the change over the past 1150 years. [Adapted from Shiyatov, 2003]

     More broad coverage of Arctic conditions posted on the National Oceanic and Atmospheric Administrations (NOAA) Paleoclimatology website (www.ngdc.noaa.gov/paleo/globalwarming/images/polarbigb.gif) as a coarse temperature map suggest that summer temperatures in the Arctics eastern hemisphere 6000 years ago may have been 2C to 4C warmer than at present. Furthermore, Kaufman and twenty-nine co-authors (2004) find clear evidence of warmer-than-present conditions during the Holocene at 120 of 140 sites they identified across the Arctics western hemisphere (see Figure 2). They estimate that at the sixteen terrestrial sites where quantitative data are available the local Holocene Thermal Maximum summer temperatures were about 1.6 0.8C higher than the average of the 20th century.
     Kaufman et al. estimate the history of sea-ice cover in the Canadian Arctic Archipelago by examining the distribution of more than 1,000 bowhead whalebone remains and walrus bones, and conclude:
     Atlantic bowheads reached their maximum abundance in the channels of the eastern and central Arctic Archipelago from 11.5 to 8.5 ka [Before Present, BP], but were excluded from areas along northeastern Baffin Island. Pacific bowhead reached their maximum abundance in the western Arctic channels connecting to the Beaufort Sea at the same time. During that interval, whales extended into areas well beyond their present ranges, and then retreated abruptly at about 8.5 ka [BP]. The bowhead range may have expanded as sea-ice export from the Archipelago was enhanced by abundant of meltwater during the interval of rapid glacial recession. Alternatively, greater summer warmth may alone account for reduced summer sea-ice cover. Sea-salt sodium concentrations in Penny Ice Cap and the Greenland Ice Sheet are at highest levels in early Holocene ice (11.5 to 9.0 ka [BP]), consistent with minimal sea-ice cover. Bowhead whale ranges re-expanded in the middle Holocene (6-3 ka) [BP] [but] the range did not attain early Holocene extent.

 

 

Figure 2: Map of the Western Arctic. Numbered points represent the 140 sites examined by Kaufman et al. (2004). Kaufman finds evidence suggesting warmer-than-present conditions at 120 of these sites during the Holocene. [Adapted from Kaufman et al., 2004]

     These three examples clearly point toward harsher and more extreme Arctic conditions in the past and highlight how various Arctic habitats respond to rapid changes in climate and more gradual environmental changes.
     What about ACIAs second claim concerning a projected melting of half of the summer sea ice? Again a broader perspective using paleoclimatic data helps.

 

Figure 3: 10-year mean anomalies, relative to the 1750-2000 means, of the April (left panel) and August (right panel) sea-ice extents for the Nordic Seas. [Adapted from a conference presentation paper by Torgny Vinje of the Norwegian Polar Institute]

     Figure 3 shows the 10-year mean anomalies of the extent of sea ice around the Nordic Sea in April (spring) and August (summer) from 1750 to 2000. The time series author is Dr. Torgny Vinje of the Norwegian Polar Institute. Vinje recently remarked:

The current ice extent reduction in the European Sector of the Artic is in continuation from processes that commenced in the 18th century, prior to the main industrial epoch. It is noted that the minimum August ice extent in the 1930s [the righthand panel of Figure 3] compares with the previous minimum observed in the 1780s. The maximum temperature during the 1930s corresponds to the minimum ice extent observed in the Nordic Sea at that time. However, while extreme maximum temperature is observed during the 1990s the ice extent has not regained its 1930 extreme minimum [extension] yet.

     The portion of the April record that spans 1864 to 1998 was first published by Vinje in 2001 (with data extended back now to 1750 and shown in the lefthand panel of Figure 3). The April record shows that sea ice around this region of the North Atlantic has decreased by thirty-three percent over the latest 135 years. Vinje explains how the most likely explanation for the April sea-ice retreat is the earth recovering from the cold period of Little Ice Age (1300 to approximately 1900 AD) because there are no conceivable ties to anthropogenic greenhouse gases initiating and maintaining those sea ice extent recessions as early as 1800-1850. Vinje (2001) writes:

Nearly half of this [thirty-three percent] reduction took place before 1900, that is, before the warming of the Arctic, which took place during the first three decades of the twentieth century The time series indicates that we are in a state of continued recovery from the cooling effects of the Little Ice Age during which a maximum [April] sea-ice expansion was observed around 1800, both in the Iceland Sea and in the Barents Sea. [T]he mean annual reduction of the April ice extent is decelerating by a factor of 3 between 1880 and 1980.

     A 700- to 1000-year collection of high-resolution geochemical data collected from the Penny Ice Cap (PIC) on Baffin Island by Grumet et al. (2001) fails to reveal any exceptional sea-ice extent around this critical part of the western Arctic during the last fifty years:

The PIC record of springtime sea-ice coverage illustrates that despite warmer temperatures during the turn of the century, sea ice conditions in the Baffin Bay/Labrador Sea region, as least during the last 50 years, are within Little Ice Age variability. Our observations from the PIC record are consistent with an increase in sea-ice extent in the Baffin Bay/Labrador Sea region of the past 30 years (Chapman and Walsh 1993) and cooler surface air temperatures in this region (Hansen et al. 1996).

     Clearly, it is impossible to make credible, objective scientific claims for ACIAs alarming scenario concerning extensive melting of the Greenland Ice Sheet.
     Figure 4 shows one of the main reasons why ACIAs projected Arctic warming of 4C to 7C by 2100 is questionable and should be seriously challenged.

 

Figure 4. Temperature changes resulting from two slightly different schemes for the parameterization of its heat transfer efficiency within the atmospheric boundary layer. Note the drastic differences between them: For Greenland, a temperature discrepancy of 2C to 10C appears depending on a weaker vs. stronger heat mixing parameterization scheme. [Adapted from Viterbo et al., 1999]

     Figure 4 shows the extreme sensitivity of surface winter temperature change on local and regional scales, and the way a model represents the physics of the boundary layer the few hundred meters-thick layer of turbulent air between the surface and free troposphere. This boundary layer is critical to how heat and moisture are exchanged between the surface and the free atmosphere, especially during winter and spring over Greenland. Figure 4 shows how with a very slight change or tuning of the manner in which heat is exchanged or mixed, a models prediction of the winter surface temperature can vary as much as 2C to 10C. Such a large uncertainty raises serious questions concerning the ability of state-of-the-art climate models to make reasonable predictions of warming, let alone forecast a warming of 3C to 7C for the Arctic that could melt the Greenland Ice Sheet!
     It long has been known that the Greenland Ice Sheet probably originated about 2.4 million years ago. Geological records indicate the Greenland Ice Sheet most likely is the only Northern Hemisphere ice sheet to have survived the last Interglacial warm period of 130,000 to 115,000 years ago (roughly the Eemian warm period as identified using terrestrial records from Europe).
     Dramatic climatic and environmental changes were observed during the last interglacial around the North Atlantic region. A closed canopy of tall, mixed-hardwood forests covered much of Europe during the peak warm period. But beginning some 115,000 years ago open vegetation replaced those mixed forests in northwestern Europe.
    Despite rather extreme climatic conditions and swings during the last interglacial, the Greenland Ice Sheet failed to melt away. During the persistent warmth of the Eemian Interglacial, climatic records for the North Atlantic-Greenland region indicate no signs of a weakening or shutting down of the North Atlantic thermohaline circulation. This is remarkable given the distinct possibility of excessive freshening of the North Atlantic Ocean due to enhanced rainfall and melting of Greenland coastal ice during the last interglacial warm period around 130,000 to 115,000 years ago.
     ACIAs gloom and doom perspective on Arctic climate and changes we might anticipate over the next century cannot be justified. The best available scientific evidence does not support such claims. Worse still, ACIAs proposed prescription fixing the ills by taking steps to reduce anthropogenic greenhouse gases emissions is revealed to be a political posture not a legitimate scientific conclusion.
     As Professor Marcel Leroux of the University of Jean Moulin at Lyon, France, comments, The global warming scenario as asserted today is not proven. But, by reason of its moral content one must be either for or against it, a choice that is indeed a nonsense from a scientific point of view. In what domain does conviction take the place of knowledge? A reformulation of the [global warming] issue is therefore urgent, and needs to be made carefully and without complacency, strictly devoted to climatology. (p. 298 of Leroux 2003)

References:
Arctic Climate Impact Assessment (ACIA) Overview Report, 2004. Impacts of a Warming Arctic: Arctic Climate Impact Assessment (Cambridge University Press). [available online at http://amap.no/acia/]

Grumet et al., 2001. Variability of sea-ice extent in Baffin Bay over the last millennium. Climatic Change, 49, 129-145.

Hu et al., 2000. Pronounced climatic variations in Alaska during the last two millennia. Proceedings of the National Academy of Sciences, 98, 10552-10556.

Kaufman et al., 2004. Holocene thermal maximum in the western Arctic (0-180W). Quaternary Science Reviews, 23, 529-560.

Leroux, 2003. Global Warming: Myth or reality? Energy and Environment, 14 (nos. 2&3), 297-322.

Shiyatov, 2003. Rates of change in the upper treeline ecotone in the Polar Ural Mountains. PAGES News, 11 (no.1), 8-10.

Vinje, 2001. Anomalies and trends of sea-ice extent and atmospheric circulation in the Nordic Seas during the period 1864-1998. Journal of Climate, 14, 255-267.

Viterbo et al., 1999. The representation of soil moisture freezing and its impact on the stable boundary layer. Quarterly Journal of the Royal Meteorological Society, 125, 2401-2426.

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