Greenland ice cap
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From Climate Change Reconsidered, a work of the Nongovernmental International Panel on Climate Change
Studies of the growth and decay of polar ice sheets are of great importance because of the relationships of these phenomena to global warming and the impacts they can have on sea level.
In the March 24, 2006 issue of Science, several commentaries heralded accelerating discharges of glacial ice from Greenland and Antarctica, while dispensing dire warnings of an imminent large, rapid, and accelerating sea-level rise (Bindschadler, 2006; Joughin, 2006; Kerr, 2006; Kennedy and Hanson, 2006). This distressing news was based largely on three reports published in the same issue (Ekstrom et al., 2006; Otto-Bliesner et al., 2006; Overpeck et al., 2006), wherein the unnerving phenomena were attributed to anthropogenic-induced global warming.
Consider the report of Ekstrom et al., who studied “glacial earthquakes” caused by sudden sliding motions of glaciers on Greenland. Over the period from January 1993 to October 2005, they determined that (1) all of the best-recorded quakes were associated with major outlet glaciers on the east and west coasts of Greenland between approximately 65 and 76°N latitude, (2) “a clear increase in the number of events is seen starting in 2002,” and (3) “to date in 2005, twice as many events have been detected as in any year before 2002.”
With respect to the reason for the recent increase in glacial activity on Greenland, Clayton Sandell of ABC News on March 23, 2006 quoted Ekstrom as saying “I think it is very hard not to associate this with global warming,” which sentiment appears to be shared by almost all of the authors of the seven Science articles. Unwilling to join that conclusion, however, was Joughin, who in the very same issue presented histories of summer temperature at four coastal Greenland stations located within the same latitude range as the sites of the glacial earthquakes, which histories suggest that it was warmer in this region back in the 1930s than it was over the period of Ekstrom et al.’s analysis.
Based on these data, Joughin concluded that the recent warming in Greenland “is too short to determine whether it is an anthropogenic effect or natural variability,” a position that is supported by many scientists.
A study based on mean monthly temperatures of 37 Arctic and seven sub-Arctic stations and temperature anomalies of 30 grid-boxes from the updated dataset of Jones by Przybylak (2000) found (1) “in the Arctic, the highest temperatures since the beginning of instrumental observation occurred clearly in the 1930s,” (2) “even in the 1950s the temperature was higher than in the last 10 years,” (3) “since the mid-1970s, the annual temperature shows no clear trend,” and (4) “the level of temperature in Greenland in the last 10-20 years is similar to that observed in the 19th century.” These findings led him to conclude that 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,” because, in his words, “the temperature predictions produced by numerical climate models significantly differ from those actually observed.”
In light of these several other studies of real-world observations, it is clear that the recent upswing in glacial activity on Greenland likely has had nothing to do with anthropogenic-induced global warming, as temperatures there have yet to rise either as fast or as high as they did during the great warming of the 1920s, which was clearly a natural phenomenon. It is also important to recognize the fact that coastal glacial discharge represents only half of the equation relating to sea-level change, the other half being inland ice accumulation derived from precipitation; and when the mass balance of the entire Greenland ice sheet was recently assessed via satellite radar altimetry, quite a different result was obtained than that suggested by the seven Science papers.
Zwally et al. (2005) found that although “the Greenland ice sheet is thinning at the margins,” it is “growing inland with a small overall mass gain.” In fact, for the 11-year period 1992-2003, Johannessen et al. (2005) found that “below 1500 meters, the elevation-change rate is [a negative] 2.0 ± 0.9 cm/year, in qualitative agreement with reported thinning in the ice-sheet margins,” but that “an increase of 6.4 ± 0.2 cm/year is found in the vast interior areas above 1500 meters.” Spatially averaged over the bulk of the ice sheet, the net result, according to the latter researchers, was a mean increase of 5.4 ± 0.2 cm/year, “or ~60 cm over 11 years, or ~54 cm when corrected for isostatic uplift.” Consequently, the Greenland Ice Sheet would appear to have experienced no net loss of mass over the last decade for which data are available. To the contrary, it was likely host to a net accumulation of ice, which Zwally et al. found to be producing a 0.03 ± 0.01 mm/year decline in sea-level.
In an attempt to downplay the significance of these inconvenient findings, Kerr quoted Zwally as saying he believes that “right now” the Greenland Ice Sheet is experiencing a net loss of mass. Why? Kerr says Zwally’s belief is “based on his gut feeling about the most recent radar and laser observations.” Gut feelings are a poor substitute for comprehensive real-world measurements, and even if Zwally’s intestines are ultimately found to be correct, their confirmation would only demonstrate just how rapidly the Greenland environment can change. We would have to wait and see how long the mass losses prevailed in order to assess their significance within the context of the CO2-induced global warming debate. For the present and immediate future, therefore, we have no choice but to stick with what existent data and analyses suggest; i.e., that cumulatively since the early 1990s and conservatively (since the balance is likely still positive), there has been no net loss of mass from the Greenland Ice Sheet.
The recent study by Eldrett et al. (2007) provides further evidence that the IPCC’s view of melting sea ice is wrong. The five researchers from the School of Ocean and Earth Science of the National Oceanography Centre of the University of Southampton in the UK report they “have generated a new stratigraphy for three key Deep Sea Drilling Project/Ocean Drilling Program sites by calibrating dinocyst events to the geomagnetic polarity timescale.” In doing so, they say their detailed core observations revealed evidence for “extensive ice-rafted debris, including macroscopic dropstones, in late Eocene to early Oligocene sediments from the Norwegian-Greenland Sea that were deposited between about 38 and 30 million years ago.” They further report that their data “indicate sediment rafting by glacial ice, rather than sea ice, and point to East Greenland as the likely source,” and they conclude that their data thus suggest “the existence of (at least) isolated glaciers on Greenland about 20 million years earlier than previously documented.”
What is particularly interesting about this finding, as Eldrett et al. describe it, is that it indicates the presence of glacial ice on Greenland “at a time when temperatures and atmospheric carbon dioxide concentrations were substantially higher.” How much higher? According to graphs the researchers present, ocean bottom-water temperatures were 5-8°C warmer, while atmospheric CO2 concentrations were as much as four times greater than they are today.
The problem these observations provide for those who hold to the view that global warming will melt the Greenland Ice Sheet, to quote Eldrett et al., is that “palaeoclimate model experiments generate substantial ice sheets in the Northern Hemisphere for the Eocene only in runs where carbon dioxide levels are lower (approaching the pre-anthropogenic level) than suggested by proxy records,” which records indicate atmospheric CO2 concentrations fully two to seven times greater than the pre-anthropogenic level during the time of the newly detected ice sheets.
“Regardless,” as the researchers say, their data “provide the first stratigraphically extensive evidence for the existence of continental ice in the Northern Hemisphere during the Palaeogene,” which “is about 20 million years earlier than previously documented, at a time when global deep water temperatures and, by extension, surface water temperatures at high latitude, were much warmer.” Therefore—and also “by extension”—we now have evidence of a much warmer period of time that failed to melt the Greenland Ice Sheet.
Continuing, Krabill et al. (2000) used data obtained from aircraft laser-altimeter surveys over northern Greenland in 1994 and 1999, together with previously reported data from southern Greenland, to evaluate the mass balance of the Greenland Ice Sheet. Above an elevation of 2,000 meters they found areas of both thinning and thickening; and these phenomena nearly balanced each other, so that in the south there was a net thinning of 11 ± 7 mm/year, while in the north there was a net thickening of 14 ± 7 mm/year. Altogether, the entire region exhibited a net thickening of 5 ± 5 mm/year; but in correcting for bedrock uplift, which averaged 4 mm/year in the south and 5 mm/year in the north, the average thickening rate decreased to practically nothing. The word used by Krabill et al. to describe the net balance was “zero.”
At lower elevations, thinning was found to predominate along approximately 70 percent of the coast. Here, however, flight lines were few and far between; so few and far between, in fact, that the researchers said that “in order to extend our estimates to the edge of the ice sheet in areas not bounded by our surveys, we calculated a hypothetical thinning rate on the basis of the coastal positive degree day anomalies.” Then, they interpolated between this calculated coastal thinning rate and the nearest observed elevation changes to obtain their final answer: a total net reduction in ice volume of 51 km3/year.
Unfortunately, it is difficult to know what estimates derived from interpolations based on calculations of a hypothetical thinning rate mean. We question their significance; and the researchers themselves do the same. They note that they do not have a “satisfactory explanation” for the “widespread thinning at elevations below 2000 m,” which suggests that the reason this phenomenon is unexplainable is that it may not be real. The authors further note that even if the thinning was real, it could not be due to global or regional warming, since Greenland temperature records indicate “the 1980s and early 1990s were about half a degree cooler than the 96-year mean.”
After discussing some other factors that could be involved, Krabill et al. state they are left with changes in ice dynamics as the most likely cause of the hypothetical ice sheet thinning. But they admit in their final sentence that “we have no evidence for such changes, and we cannot explain why they should apply to many glaciers in different parts of Greenland.” It would seem logical to admit this study resolves almost nothing about the mass balance of the coastal regions of the Greenland Ice Sheet and nothing about the subject of global warming and its effect or non-effect upon this hypothetical phenomenon.
In a preliminary step required to better understand the relationship of glacier dynamics to climate change in West Greenland, Taurisano et al. (2004) described the temperature trends of the Nuuk fjord area during the past century. This analysis 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.” Finally, they report there was no significant trend in annual precipitation. In their concluding discussion, Taurisano et al. remark that the temperature data they studied “reveal a pattern which is common to most other stations in Greenland.”
Rignot and Kanagaratnam (2005) used satellite radar interferometry observations of Greenland to detect what they described as “widespread glacier acceleration.” Calculating that this phenomenon had led to a doubling of the ice sheet mass deficit in the past decade and, therefore, a comparable increase in Greenland’s contribution to rising sea levels, they went on to claim that “as more glaciers accelerate … the contribution of Greenland to sea-level rise will continue to increase.”
With respect to these contentions, we have no problem with what the two researchers have observed with respect to Greenland’s glaciers; but we feel compelled to note that what they have calculated with respect to the mass balance of Greenland’s Ice Sheet and what they say it implies about sea level are contradicted by more inclusive real-world data. One reason for this discrepancy is that instead of relying on measurements for this evaluation, Rignot and Kanagaratnam relied on the calculations of Hanna et al. (2005), who used meteorological models “to retrieve annual accumulation, runoff, and surface mass balance.” When actual measurements of the ice sheet via satellite radar altimetry are employed, a decidedly different perspective is obtained, as indicated by the work of Zwally et al. (2005) and Johannessen et al. (2005), which we cited earlier. Consequently, and contrary to the claim of Rignot and Kanagaratnam, Greenland would appear to have experienced no ice sheet mass deficit in the past decade.
Shepherd and Wingham (2007) reviewed what is known about sea-level contributions arising from wastage of the Antarctic and Greenland Ice Sheets, concentrating on the results of 14 satellite-based estimates of the imbalances of the polar ice sheets that have been derived since 1998. These studies have been of three major types—standard mass budget analyses, altimetry measurements of ice-sheet volume changes, and measurements of the ice sheets’ changing gravitational attraction—and they have yielded a diversity of values, ranging from a sea-level-rise-equivalent of 1.0 mm/year to a sea-level-fall-equivalent of 0.15 mm/year. The two researchers conclude that the current “best estimate” of the contribution of polar ice wastage (from both Greenland and Antarctica) to global sea-level change is a rise of 0.35 millimeters per year, which over a century amounts to only 35 millimeters.
Even this unimpressive sea-level increase may be too large an estimate, for although two of Greenland’s largest outlet glaciers doubled their rates of mass loss in less than a year in 2004—causing the IPCC to claim the Greenland Ice Sheet was responding much more rapidly to global warming than anyone had ever expected—Howat et al. (2007) report that the two glaciers’ rates of mass loss “decreased in 2006 to near the previous rates.” And these observations, in their words, “suggest that special care must be taken in how mass-balance estimates are evaluated, particularly when extrapolating into the future, because short-term spikes could yield erroneous long-term trends.”
Ettema et al. (2009) contend that "to better quantify and predict the mass balance and freshwater discharge of the Greenland Ice Sheet requires improved knowledge of its surface mass balance (SMB)," the annual sum of mass accumulation (snowfall, rain) and ablation (sublimation, runoff). To do so, the researchers applied a regional atmospheric climate model at "unprecedented high horizontal resolution (11 km).” This was coupled to a physical snow model that treats surface albedo as a function of snow/firn/ice properties, meltwater percolation, retention, and refreezing. The atmospheric part of the model was forced at the lateral boundaries and the sea surface by the global model of the European Centre for Medium-Range Weather Forecasts for the period September 1957 to September 2008.
The modeling showed "total annual precipitation in the Greenland ice sheet for 1958-2007 to be up to 24% and surface mass balance up to 63% higher than previously thought." The total ice sheet's SMB averaged over the entire study period was 469 ± 41 Gt per year. Since 1990, there has been a slight downward trend in Greenland's SMB of 12 ± 4 Gt per year, which should be noted with caution, considering that from 1995 to 1996 SMB rose by a whopping 250%.
In conclusion, the part of the Northern Hemisphere that holds the lion’s share of the hemisphere’s ice has been cooling for the past half-century, and at a very significant rate, making it unlikely that its frozen water will be released to the world’s oceans. In addition, because the annual number of snowfall days over much of Greenland has increased so dramatically over the same time period, it is possible that enhanced accumulation of snow on its huge ice sheet may be compensating for the melting of many of the world’s mountain glaciers and keeping global sea level in check for this reason too. Lastly, Greenland’s temperature trend of the past half-century has been just the opposite—and strikingly so—of that which is claimed for the Northern Hemisphere and the world by the IPCC.
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Mmm, I can definitely hear a rohcus of editors lamenting the slow but inevitable decline of their profession; what was once so complex a manipulation of celluloid is now no more than trivial clicks-n'-drags on a computer screen. But it does go to show that the editor is probably best thought of in the same sense as the camera operator or the sound technician they are craftsmen, highly skilled at what they do but always in the service of the ultimate creative vision, be that the director, producer, whatever. In that sense, I believe the editor is probably just as necessary as ever, as there will always be people better at editing than others, even if the process is so much easier nowadays (and FCP X has replaced our complicated but powerful shears with plastic scissors).And on the subject of command+z I believe whole books could be written on the ridiculously sweeping change the possibility of undo-ing an action has made on the creative world at large. I dabble in music, filmmaking, writing and blogging, and I think I would have given up on all of them long ago were it not for the beautiful invention of undo'!
