Greenland's Oscillating Glaciers
Melting glaciers are once again in the news, along with the associated threat of rising sea levels. NASA satellites have reported wide spread melting across Greenland which has the climate change alarmists all atwitter. But the NASA satellites are providing data never before available, so it is hard to say if the summer melting pattern is unusual. Meanwhile, some 80 year old scientific data has revealed that this is not the first time that there has been a period of glacial retreat in Greenland. This formerly lost data shows that many land-terminating glaciers underwent a more rapid retreat in the 1930s than in the 2000s. Even more interesting is that the two periods of retreat were interrupted by a period of widespread advance from 1943 to 1972. Greenland's glaciers seem to be oscillating with a period of around a century.
Sometimes reality is stranger than fiction. A series of photos detailing the extent of Greenland's glaciers were collected during 1932 and 1933 by an expedition led by the Danish explorer Knud Rasmussen. Due to political conflict between Norway and Denmark at the time, most of those photos were classified as secret and effectively lost for 80 years. Recently rediscovered, the photos document glacier conditions at the start of a previous warming event that was comparable in magnitude to the present one for southeast Greenland. This warm period persisted from the early 1930s to the early 1950s, and featured anomalously warm temperatures of both air and ocean.
A team of researchers led by Anders A. Bjørk, from the Centre for GeoGenetics, Natural History Museum of Denmark, University of Copenhagen, have used the rediscovered photos to gauge the responses of individual outlet glaciers, both those that terminate on land and those terminating in the ocean. There results, described in “An aerial view of 80 years of climate-related glacier fluctuations in southeast Greenland,” published in the journal Nature Geoscience, are enlightening:
The 1930s and 2000s retreat events were associated with both rising air- and SSTs well above the mean. These two retreat periods are also seen as the peak calving periods in a study of fjord sediments from Sermilik Fjord where the Helheim Glacier terminates and here it was documented that decadal scale variability in frontal positions is related to decadal scale changes in both air and sea temperatures. Notably, our findings show that decadal scale climate-forced glacier changes are not restricted to the large Helheim Glacier, but that most of the glaciers along the southeast coast followed a similar retreat pattern. Of all glaciers, 35% show higher retreat rates during the 1930s and 20% show similar retreat rates. For land-terminating glaciers 42% were faster during the 1930s and 33% similar.
What this says is that the glaciers of Greenland were shrinking about as fast as today's “unprecedented” rate during the 1930s. Though today the marine-terminating glaciers are retreating faster than land-terminating glaciers the overall message is the same: the current rate of glacial melting was matched almost 80 years ago. That was before most of the global warming attributed to human CO2 occurred. The report's findings are not restricted to a few, selected glaciers either.
“We analyse the frontal behaviour of 132 glaciers along more than 600 km of the southeast Greenland coastline, between 61.5° N and 66.5° N latitude,” the authors state. “Combining aerial photographs (1931–1933, 1943, 1981–1985), terrestrial photographs (1933) and satellite images (1965, 1972, 2000, 2010) we determine frontal changes over a period of 80 years.” The results are shown in the figure below.
Average frontal changes of glaciers and temperature records.
The authors note that more glaciers retreated during the 2000s. Of the seven glaciers undergoing high retreat rates during the 2000s (>200 m yr−1 over a ten-year period), all are relatively large marine-terminating outlet glaciers that have proved especially sensitive to changes in ocean temperature. It seems that the air may have been warmer in the 1930s but the ocean waters stayed relatively cool. Today, the situation is reversed, with warmer ocean water causing more calving from marine-terminating glaciers but the land-terminating glaciers remaining mostly intact. Perhaps even more interesting is what happened after the early twentieth-century warming (ECW).
As the ECW faded, a period of cooling began in the mid 1950s that lasted until the early 1970s. The glacier response to the cooling was an advance, primarily among marine-terminating glaciers. Surprisingly, a large portion (60%) of our glaciers advanced, many already at the beginning of the period, whereas another 12% were stationary during the period. This shows that the glaciers in this region are more sensitive to climate change and react more rapidly to cooling than indicated both by earlier studies and by more recent studies investigating marine-terminating outlets from 1972 onwards. Exploring SST data we find that a period of colder-than-usual temperatures reached the coast of southeast Greenland in the late 1960s. However, the influence of cold water on the terminus of marine-terminating outlets does not explain the entire advance as numerous land-terminating glaciers advance in the period 1943–1981.
In all, the authors found that the glaciers of southeast Greenland have responded “vigorously” on a decadal scale to both warming and cooling. Furthermore, the recent warming period is not the only documented episode of noticeable glacial retreat; such a retreat followed the warming early in the 20th century, when air and ocean temperatures were similar to the present. In other words, this has all happened before, and not that long ago.
This has not diminished the temptation for climate alarmists to pronounce every new observation of melting glaciers as “unprecedented.” In a freak event that surprised scientists, nearly all of Greenland's massive ice sheet suddenly started melting during July, 2012. Three NASA satellites showed what the space agency called “unprecedented melting” of the ice sheet. While some ice usually melts during the summer, what was unusual was that the melting happened in a flash—starting on July 8 and lasting four days. “You literally had this wave of warm air wash over the Greenland ice sheet and melt it,” said NASA ice scientist Tom Wagner.
NASA satellites detected widespread melting in July 2012.
The ice melt area went from 40% of the ice sheet to 97% in four days, according to NASA. But this is not as dire as it would seem at first blush. The melting was only on the glacier's exposed surface, the thick underlying ice remained untouched. Previously, the most extensive melting seen by satellites was about 55%, but satellite observations have only been available during the past 30 years. Ice core records show that the last time such melting happened was in 1889, with earlier events occurring approximately every 150 years. Evidently, to climate scientists, “unprecedented” means “not recently” or “not in the researcher's life time.”
Now, instead of depending exclusively on data from the satellite age (roughly 1970 to present) a more accurate, longer view is available. A few historical photographs have transformed a simple three decade melting trend into a century long advance/retreat cycle, reinforcing earlier reports of glacial cycles in Greenland. Now imaging what would happen if a trove of photographs appeared from the Holocene Climate Maximum (~6,000 ya), when temperatures were much warmer than today.
Or take an even longer view and go back to the Eemian interglacial (~125,000 ya), when things were even hotter and sea levels even higher. All of the hype and hyperbole would melt away, as Greenland's glaciers have many times in the past and will again in the future. Sadly, no pictures from the ancient past can exist, but on the bright side, we now know there is nothing unprecedented about the melting observed in Greenland today.
Be safe, enjoy the interglacial and stay skeptical.