Saturday, January 17, 2009

Glaciers and the Little Ice Age

I suppose that many of us that are trying to do “due diligence” in looking at the scientific data that relates to the issues of climate change come to the table with different perspectives. In my case, as I explained earlier, my curiosity was wetted by the information that the Earth goes through cyclic periods of warming and cooling, the most recent of which have become known as The Medieval Warming Period, and the Little Ice Age. I am currently reading Jean Grove’s “Little Ice Ages-Ancient and Modern.” She was a Fellow and Director of Studies in Geography at Girton College, Cambridge, and, since her death in 2000, the book has been issued in a second updated edition, by Dick Grove, her husband. It is now in two volumes, and this will be about some of the information that lies in the first of these. It deals with glaciers, but glaciers grow from snow, and that snowfall has changed over the years.

As a fairly comprehensive text, it takes the history of many of the glaciers around the world back beyond their most recent past to discuss how they have advanced and retreated. Using evidence from, among other things, church records, it shows how farms that were prosperous in the MWP had been wiped out and over-run by the glacial advances of the LIA. And it shows, through copious references to the scientific literature in the field, the times and rates of these advances and retreats. Some of those who discuss this cycle have suggested that the MWP was a localized event in Europe, this text clearly shows that it was not, though I will talk about the MWP period more in a later post, and in this one concentrate on the event that is the most recent Bond event, as some now call these cyclic cold periods. It is interesting that in the fluctuating entry that covers the Bond event at Wikipedia the LIA comes and goes as a recognized Bond event (today it is gone).

Jared Diamond, in “Collapse – How Societies Decide to Collapse of Succeed,” wrote of the contrast between the native population of Greenland (I will call them the Thule, though there are debates on which group it was) and those descended from the families who came to Greenland with Erik the Red in around 982 AD. (He does not address that the Thule may, in turn have arrived in Greenland from Alaska by migrating across the North of Canada in the same time frame). Diamond concludes that the inability of the Vikings to adapt to the sea harvest as the weather got colder made it more difficult to sustain the conventional farming life in Greenland. However Grove points out that the advance of the glaciers to the sea changed the patterns of fish migration, so that the harvest may not have been there, at least in the form that they were used to – though if the fish were not there, then presumably the seals that feed on them would also have migrated, and the Thule also, so that only the farmers, tied to the land would be left starving). However Grove also quotes Arneborg who examined the bone collagen of some of the settlers, which indicated that the Norse diet changed from 20% sea food in the eleventh century to 80% in the fourteenth, so perhaps it was just the climate change that marked the beginning of the LIA in that time frame that was the real cause of the disappearance of the Norse.

Being tied to the land in the peculiarities of society of the time had considerable disadvantage as the glaciers advanced. The cold winds around the glacier were not good for crops. Grove quotes from a court of inquiry report of 1742
It was apparent that it was the nearness of the glacier which is the cause of crop failure on this farm, for in the fields where the crops were now in ear, the ears on the side towards the glacier from the west were quite brown, and on the other side green, though some ears were not even in bud because the cold and the strong cold winds which the glacier exhales freezes it away in one night’s still weather.
With the winter snowfalls and short cold summers the glaciers, in this case the Bersetbreen branch of the Jostedalsbreen glacier in Norway, advanced through arable farmed land over the period from 1680 to 1745. After reaching a peak advance in 1748 it has since retreated some 4.5 km according to Erikstad.

And it is in this advance and retreat of the glaciers, whether in Greenland, Norway, Switzerland The Pyrenees, the Urals, The Caucasus, Tibet and the Himalaya, Mexico, Ecuador, Africa or South America that the bulk of the text is devoted. The dates of glacial advance, the point of maximum range and then the consequent retreats are documented and discussed. The book goes into considerable detail, where it is available, documenting both glacier behavior, and the effects that the extensions of the glacier had on the surrounding inhabited areas. This effect was particularly severe in Europe coinciding as it did, with the onset of the Black Death. And while glaciers grow and shrink in part due to changes in precipitation, she documents, for example, the changes in Snowfall in Scotland during the LIA, as illustrative of the changing patterns that predominated.

Grove cites others who show that the LIA was pervasive outside of just the glacial fields. For example Thompson, who considered that 1490 marked in the beginning of the LIA in the Northern Andes, with the long-term Holocene cooling culminating in the seventeenth and eighteenth centuries.

In Chile the Ada Glacier advanced until some time after 1858, but by 1882 was in retreat, and has been retreating since. Similarly in Argentina by 1895 Hauthol was reporting on the glacier in the Atuel valley wrote that
the glaciers clearly indicate not only that until a short time ago they were of much greater extent but also that they are now losing volume and retreating at a great rate.
Between 1914 and 1937 Groeber reported that the glacier had retreated 3.2 km.

The Patagonian Icefields include the San Rafael and San Quentin glaciers which have been studied more intensely than others. Both have been in general retreat for most of the last century, after reaching a maximum LIA extent in around 1876. The San Rafael has oscillated over a distance of 10 km. Since the glaciers have had floating tongues which is more prone to precipitation as a means of control, rather than temperature, these oscillations may not be climate controlled. Moving further south into the Southern Patagonian Icefield
In the early part of the twentieth century the easter outlet glaciers of the Southern Patagonian Icefield retreated rapidly from extended postions reached in the mid to late nineteenth century, leaving clear trim lines in the vegetation (Lliboutry, Clapperton).

A short review of a book that has references to supporting scientific papers in virtually every paragraph and which covers the field with the depth and detail that this does can do very little justice to it. The book, however, clearly shows that the LIA was a global event, and that it brought glaciers forward around the world. Further it shows that the globe began recovering from the depths of the LIA in the 1800’s and glaciers have been retreating from their maximum extent for most of the twentieth century. This predates the increases in carbon dioxide so that glacial retreat, in and of itself, cannot be used as evidence of CO2 impact on climate. The variations that occur in advance and retreat speeds and directions, even between glaciers that are quite close show that there can be over-riding other parameters that are more influential than temperature change, although when there is a general trend for glaciers to grow through the LIA from minimal positions before it, and then to retreat similarly generally after the peak of the LIA conforms to its presence.

Other evidence can be used to surmise the temperatures before the LIA arrived, Grove cites grain being grown in Greenland and Iceland, in areas where farms have not yet been able to be re-established. She cites orange growth in the Tang and Deng counties of Xichuan (which cannot grow them at present) as late as1264 to mark the beginning of the LIA, with the MWP ending somewhat later in Tibet, though there is some discrepancy in the data from different ice cores from that country.

On an editorial note I would have added the references cited, unfortunately they are in the second volume, and I don’t have that one yet.

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