Clarifications and at least one correction are required about the pictures of the Upsala Glacier in Patagonia, Argentina, “from Al Gore’s An Inconvenient Truth (2006)”, on the first page of Bill McKibben’s “Warning on Warming” (NYRB, March 15, 2007).
At the top, the 1928 photograph of a vast flat glacier; at the bottom, the 2004 ice-free landscape as captured from a similar vantage point as the one 76 years earlier (at least two peaks are clearly distinguishable).
I was surprised indeed to see the New York Review of Books reproduce without much commentary and with a wrong caption a couple of photographs that may turn out to be exceedingly misleading.
First of all: the caption is wrong. Contrarily to the published text, it is _not true_ that by 2004, “most of the glacier had melted“.
Upsala Glacier still occupies well in excess of 850 sq km (330+ sq mi), an area vastly larger than the one covered by the photographs.
You can see pictures of Upsala taken from the Space Shuttle in January 2004 at the NASA website.
A discussion of the situation 2001-2004 is available on the same site.
If one could rely on photographs alone, those of Upsala could be the definitive, final, closing, incontrovertible evidence that something has warmed up during the XX century, at least at the location of the Upsala Glacier.
Pictures, however, are not everything, as any modern consumer must have learnt one way or another by now.
Do some little research about Upsala, in fact, and more than one doubt arises about the glacier’s changes having not been mostly caused by warming, global or local or otherwise.
They may be the result instead of the behavior of a large glacier when subjected to particular mechanical stresses.
See for example “Historic Fluctuations of Outlet Glaciers from the Patagonian Ice Fields” at the USGS web site.
That web site reports a picture from “Thinning and retreating of Glaciar Upsala, and an estimate of annual ablation changes in southern Patagonia“, by R. Naruse, P. Skvarca and Y. Takeuchi (Annals of Glaciology, Vol. 24, 1997).
In that paper, it is suggested that “considerable retreat due to calving may have resulted in reduction of longitudinal compressive stress exerted from bedrock rises and islands near the glacier front, causing a considerable decrease in the emergence flow.”
R. Naruse repeated similar considerations at the 2nd International Symposium on Arctic and Antarctic Issues, at Punta Arenas, Chile, in November 1998 (“Dynamic features of glaciers in Patagonia“).
More recently, in “Recent behavior of Glaciar Upsala, a fast-flowing calving glacier in Lago Argentino, southern Patagonia” (Annals of Glaciology, 36, 2003), P. Skvarca, B. Raup and H. De Angelis proposed again that “drastic glacier retreat in the last two decades” may be explained “partly due to the release of back stress when the glacier retreated beyond the islands in Brazo Upsala […] which acted as pinning points.”
You can also read an earlier paper by Mr Skvarca: “Significant Ice Retreat in the Region Patagonia – Antarctic Peninsula Observed by ERS SAR” (ESA ERS 1997 Workshop, 1997) by H. Rott, W. Rack, M. Stuefer and P. Skvarca:
“It cannot yet be assessed if the ice retreat in Patagonia […] indicates just regional changes of the atmospheric circulation patterns or can be assigned to global climatic change.”
Last but not least, Upsala is not the only glacier in Patagonia.
Surely if the dramatic retreat of Upsala were related to global warming, all the other glaciers would be retreating too? And yet that is clearly not the case.
Read “Recent Fluctuations and Damming of Glacier Perito Moreno, Patagonia” by H. Rott, M. Stuefer, T. Nagler and C. Riedl (ESA Envisat and ERS 2004 Symposium):
“The satellite data, in synergy with field measurements, confirm the stability of the [Perito Moreno] glacier, showing only minor front fluctuations and indicating an approximately balanced mass budget since many years.”
Furthermore, they report the Pio XI glacier as having experienced a “net advance of about 10 km […] from 1945 to 1995“.
Some revealing considerations should be made about Perito Moreno glacier indeed, the advancing glacier whose pictures have been used by Frank Capra in 1958 and by Al Gore in 2006 to demonstrate the retreat of glaciers due to global warming: but those will have to wait for a future article or letter.
For the time being, I am confident the above makes the main points clear:
(1) Most of the Upsala glacier has not melted.
(2) The Upsala glacier 1928-2004 pictures can only be seriously understood with an in-depth commentary of what is being shown, including “what lies beneath”.
And there are all the indications that the local characteristics of the terrain, rather than “Global Warming”, have had a major role in what has been happening.
Given the reputation of the New York Review of Books then, I will be expecting a prompt publication of this letter and of all the necessary explanations.
Keep up the good work