Positive Feedback Event?

Positive Feedback Event: Pine Island Glacier Retreat

In Antarctica the Pine Island Glacier is in a self-sustained retreat. This is based upon scientific observations from the British Antarctic Survey (BAS) who have been monitoring the West Antarctic ice glacier for several decades. An international team of scientists has shown that Pine Island Glacier, the largest single contributor to sea-level rise in Antarctica, has entered a period of irreversible, self-sustained retreat and is likely to increase its discharge into the ocean in comparison to the last decade. The Pine Island Glacier has receded around 10km over the last decade and contributes 25% of the total ice loss from West Antarctica. The glacier is contributing to sea level rise and will continue to do so based upon observations and computer simulation modelling. This article in Science magazine illustrate large variations in ocean heat available to melt the glacier from the adjacent bay. A seabed ridge prevents deeper melting and the prevailing climatic conditions will affect the retreat. Oceanic melting decreased by 50% between January 2010 and 2012, with ocean conditions in 2012 partly attributable to atmospheric forcing associated with a strong La Niña event. In such an event there is a fall in the ocean temperatures as part of short term climatic oscillations.

There are two scientific concepts at work here: one of a positive feedback loop and one of hysteresis. These will be considered in turn:
1. Hysteresis can be defined as a phenomenon exhibited by a system, in this case the glacier, in which the reaction of the system to changes is dependent upon its past reactions to change. Previous reaction of the Pine Island glacier is one of retreat due to warmer ocean currents and weather events (climate forcing perhaps). Past reactions have influenced the current recorded increased rate of retreat.
2. Positive feedback loops or events occur when changes in the system (the glacier here) result in the same type of change and that change increases. An example is the rate of glacial retreat gets faster due to the momentum of the changes that have gone before: in this case once the glacier is retreating and getting faster then the faster the rate of retreat becomes. The retreat is becoming “self-sustained”.

Like all research it is difficult to predict what will happen to the glacier. Given recent past changes and agreement in international computer models, there appears to be a strong likelihood of sea levels increasing from the Pine Island glacier as it disintegrates into the sea.

Island Series For 2014

During this year, this blog is to look at a number of islands and view them in terms of their unique geography and features. This is partially from a sustainability perspective but mainly from a geographical perspective. From a biogeography point of view there have been studies into islands in terms of their unique ecology from the 1960s. It was the work of MacArthur and Wilson with their 1967 publication “The Theory of Island Biogeography” that placed an emphasis upon the uniqueness of islands. This approach may see an island as a unique area of land: it does not have to be a physical island (surrounded by water) but could be an isolated area of upland habitat cut off by land at a lower elevation for example. The upland area with it’s unique species could be described as an “island” in this case.

The series begins with an island that is not conventionally an island, major flooding has turned one rural village into an island for several weeks. With poor weather continuing there is a chance that the village will remain an island for a longer period.

A New Island

The first in the series of islands is in fact, under normal conditions, not an island. Recent weather events have made an area of Somerset in South West England an island leaving an entire village of Muchelney cut off from the outside world. The only way in and out is by boat or tractor. Around a year ago the same village was cut off for several weeks as reported on this blog. The event was classed as a 1 in 100 year flood event, which in theory should not happen for another 100 years. Just over a year later there is more flooding that has resulted in the local council calling a state of emergency in the area affected. This OpenStreetMap view of the area has been mapped showing the flood area and the village of Muchelney cut off from the out side world.
Muchelney Flood Area: A new island is shown, the village is where the red marker is.

Historically Muchelney was an island on the Somerset Levels, an area of wet lowlands, until it was drained. In 1086 the village was recorded as Micelenie meaning, ironically, “the increasingly great island”. The current flooding has been caused by much rainfall and, perhaps, a continued “mismanagement” of watercourses? The locals argue that the rivers have ceased being dredged which has made the flooding worse than ever.


About mappedit

Geographical practitioner with an interest in climate change, open mapping, sustainability, the transition movement, transport and many other things.
This entry was posted in Climate Change, flood, Islands and tagged , , , , . Bookmark the permalink.

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