Miller et al.’s “Unprecedented Recent Summer Warmth in Arctic Canada”: Bad assumptions, poor logic, and contrary to other evidence of Arctic temperatures.

Dr. Don J. Easterbrook, Western Washington University, Bellingham, WA

Miller et al. radiocarbon dated 145 rooted tundra plants revealed by receding ice in the eastern Canadian Arctic and contend that it constitutes the first direct evidence that recent temperatures now exceed those of any century in the Holocene, including the Holocene Thermal Maximum. They further contend that (1) average summer temperatures of the last ~100 years were higher than any century in the past 44,000 years and suggest that present temperatures have not been exceeded in the past ~120,000 years, at or near the end of the last interglaciation, and (2) they conclude that this ‘unprecedented’ warming was caused by anthropogenic increases in greenhouse gases. So let’s look at some of the assumptions that form the basis for their conclusions and compare their conclusions to other Arctic data.

Figure 1 A. Baffin Island showing sample sites. Circles (color-coded by their ¹⁴C age) show the 135, <5 ka, sites where rooted plants were collected at receding ice cap margins; diamonds show sites dated >47 ka. Solid lines mark the margins of the LIS at the last glacial maximum and 9 ka [A. S. Dyke, 2004]. B. Detailed map of sites older than ~45 ka.

Assertions and assumptions by Miller et al.

[1] Mille el al. contend that “although glaciers are frequently associated with deep and widespread erosion, small, cold-based ice caps that mantle relatively flat terrain typically advance by lateral accretion rather than by basal flow, and are thus capable of preserving even the most delicate features of the landscape. As these ice caps recede, they often reveal rooted tundra plants that were living at the time snow and ice last covered the site.” They further contend that “Surface-elevation contours of the continental Laurentide Ice Sheet (LIS) show that all four ice caps with pre-Holocene dated plants were above the surface of the LIS at its last glacial maximum. These sites thus supported only local ice caps then as now. And, because the ice caps occupy flat summits of less than 0.2 km2 surrounded by steep slopes, ice thicknesses of more than 70 meters could not have been sustained.”

The assumptions in these statements are:

a. Miller et al. assume that the ice caps are cold-based (i.e., basal ice is frozen to the ground below) and that there is no basal sliding of the ice and no basal erosion. However, deep fiords and ice-scoured scoured bedrock in the area attest to active subglacial erosion (i.e., basal sliding rather than frozen to the ground), although most of the obvious erosion is probably related to Pleistocene glaciation. The Greenland ice sheet just across the Davis Strait at the same latitude is not frozen to its base, and the average summer temperature at Clyde (north of the sample sites) is 3°C above freezing during June, July, August, and September (Fig. 5). Summer temperatures of all of the more than half dozen weather stations along the east coast of Baffin, where the sample sites are located, are above freezing during June, July, August, and September. Thus, the Miller et al. conclusion that the small ice caps in this study are frozen to their base is highly questionable and most like not true.

b. Miller et al. contend that the Laurentide Ice Sheet did not cover the area of the ice caps and that there has been no erosion since the Eemian Interglacial 120,000 years ago. However, the Laurentide Ice Sheet (LIS) extended eastward beyond this area to the coast (Fig. 1) and reconstructed ice surface elevations show the area to be close to the 1000 m and 2000 m contours, i.e., close to or above the present ice caps. The scale of the ice surface reconstructions is not detailed enough to show exactly how high the LIS surface was at the sites, but at least suggest a good possibility that the area was overridden by the LIS. The importance of this is their conclusion that the older sites have not been disturbed for 120,000 years, but to make this assertion they need to provide adequate evidence.

Figure 2. Reconstruction of the Laurentide Ice Sheet (Dyke, 2002)

c. The Miller et al. assertion that the ice caps were not more than 70m thick is highly questionable. The ice caps expanded noticeably during the Little Ice Age and even if the LIS didn’t overrun the ice cap sites, the ice caps must surely have thickened, especially since the surrounding lower areas were filled with LIS ice. Thus, their contention that the ice caps could not have been more than 70 m thick is most likely not valid.

[2] Miller et al. claim that recent exposure of moss by melting ice proves that modern temperatures at the site were as high or higher than at any time since the moss was covered by ice and that therefore present temperatures have not been exceeded in 120,000 years. But is this necessarily true? If a block of ice is placed on the floor of a room and the thermostat is turned to 90°F, the ice will begin to melt. If the thermostat is then turned down to 40°F before all of the ice has melted, ice will continue to melt until the floor is uncovered, but to conclude that the temperature had never risen above 40°F since the floor was first covered with ice would be totally false. The same is true of the Baffin ice caps—if moss is uncovered at today’s temperatures, that doesn’t mean that higher temperatures haven’t occurred previously. Thus, the Miller et al. conclusions that “temperatures of the past century must have exceeded those of any century in more than 44 ka” and “there has been no intervening century during which warmth exceeded that of the last 100 years” are illogical and badly flawed. One wonders how this bad logic got past peer review. In addition, we know from data in the Greenland GISP2 ice core that temperatures in Greenland rose more than 20°F per century at least three times in the past 15,000 years, well within the 120,000 years claimed by Miller et al. to have never been warmer than recently.

[3] Among the 145 ¹⁴C dates on exposed moss in this study are10 dates ranging in age from 23,900 to 50,700 years, leading to their conclusion that temperatures today are the hottest in >50 ka and most likely in the past 120 ka. They explain the disparity between these old dates and the multitude of young Holocene dates as due to higher elevations of the older samples so the younger sites could be exposed by melting of ice while the higher, older sites remained ice covered. But as shown by their data, this really isn’t true. Figures 1 and 3 show site M10-231v as an ‘Eemian’ site with dates ranging from 23,900 to 44,300 years. But ages at two nearby sites, M10-B226v and M10-223v, whose ages are shown as 2-3,000 and 4-5,000 years old, are higher than the site with old dates (Figure 4).

Figure 3. Site M10-231v, dated at 23.9 ka to 44.3 ka at an altitude of 1395m (4577 ft) and sites M10-226v at 1438m (4718 ft.) and M10-223v at 1405mm (4609 ft). (Google Earth image)

Figure 4. Elevations of sites M10-223v (2-3,000 yrs) and M10-226v (4-5,000 yrs) are higher than the ‘Eemian’ site >47,000 years.

This totally destroys their argument for no temperature as warm as the present since the Eemian Interglacial. All they have shown is that melting of the ice caps on Baffin Island wasn’t complete during the Holocene and recent warming has continued the melting.

Comparison of Miller et al. conclusons with other Arctic data.

The conclusions of the Miller et al. paper are that “there has been no intervening century during which summer warmth exceeded that of the last ~100 years” and “average summer temperatures of the last ~100 years are now higher than any century in more than 44,000 years.” How do these conclusions stack up against other data concerning past Arctic temperatures? Let’s compare them with recent recorded temperatures in Greenland and with past temperatures derived from Greenland ice core data.

Comparison with recent Arctic temperatures

Summer temperature records at Clyde, north of the sample sites, show no warming from 1940 to 2009 (Fig. 5). How is it that “temperatures of the past century must have exceeded those of any century in more than 44 ka” when temperature records clearly show no warming over the past 70 years? This makes no sense at all!

Figure 5. Summer temperatures at Clyde, north of sample sites.

Temperature records from Greenland and other Arctic areas also show no unusual warming. Yes, temperatures have warmed and cooled, but the 1930s were consistently warmer than the more recent warming from 1978 to 1998 (Figs. 6, 7, 8, 9).

Figure 6. Temperatures in Angmagssalk, Figure 7. Arctic temperatures (70-90 N latitude, -180

Greenland were warmer in the 1930s (before to 180 longitude) between 1880 and 2000 show that

CO2 began to rise sharply) than during recent the 1930s and early 1940s were warmer than recent

warming from 1978-1998. warming (1978-1998). (Modified from Chylek et al.

2004, 2006)

Figure 8. Arctic temperatures in Iceland, Norway, Figure 9. Average Arctic annual temperatures were

and Russia from 1890 to 2010 show that the 1930s warmer in the 1930s (before CO2 began to rise

and early 1940s were warmer than recent warming sharply) than during recent warming from 1978-

from 1978-1998. 1998.

Comparison with temperatures recorded in Greenland GISP2 ice cores

Figure 10 shows that virtually all of the period from 1500 years ago to 5000 years ago was warmer than modern temperatures. This data is directly contrary to the Miller et al. conclusion that “average summer temperatures of the last ~100 years are now higher than any century in more than 44,000 years.”

Figure 10. Temperatures during the Medieval Warm Period, the Roman Warm Period, and the rest of the time back to 5000 years ago were all warmer than the past century, directly contradicting the conclusion of Miller et al.

Looking still farther back in time, about 90% of the past 10,000 years were warmer than temperatures of the past century (Fig. 11). Thus, the Miller et al. conclusion that “temperatures of the past century must have exceeded those of any century in more than 44 ka” cannot be true.

Figure 10. Temperatures during ~90% of the past 10,000 years were warmer than the past century. (Modified from Cuffy and Clow, 1997; Alley,2000).

Temperatures during the late Pleistocene fluctuated dramatically, rising 20°F in a single century at least three times. These rates of warming were far greater (~20 times greater) than warming during the past century. Thus, the Miller et al. conclusions cannot be valid.

Conclusions

From the foregoing data and analyses, what is abundantly clear is that the Miller et al. paper is so badly flawed with unwarranted assumptions, poorly thought out assertions, and astonishingly bad logic that their conclusion “temperatures of the past century must have exceeded those of any century in more than 44 ka” cannot be considered valid. How could reputable scientists come to such incorrect conclusions? Perhaps the last sentence in their conclusions section gives us a clue: “anthropogenic emissions of greenhouse gases have now resulted in unprecedented recent summer warmth that is well outside the range of that attributable to natural climate variability.” Even if the conclusions in the paper were correct, they wouldn’t prove anything about CO₂ as the cause of climatic warming, so this statement suggests that the real purpose of the paper was to push CO₂ at the expense of objective science.