Linking key concepts to content
Feedback and coastal landscapes/cold environments.
[As we approach the exam season, students should prepare themselves for questions that link the key concepts of geography with the content areas they have studied. Here are two essay questions, and answers, that illustrate such links. Remember my word limit of 600 words - the maximum, in my view, for the time allocated.]
[You can read my post on Feedback here, published in January 2023:
Feedback - by David Redfern - A Level of Geography (substack.com) ]
To what extent can an understanding of feedback systems help with the management of one or more coastal landscapes that you have studied?
Coastal landscapes are open systems that are in a state of dynamic equilibrium. An example of this would be when the rate of sediment being added to a beach is the same as the amount leaving the beach resulting in the beach remaining the same size.
If any inputs or outputs change either because of environmental or human factors, then the system becomes unbalanced and will change. When an initial change within a system brings about further change in the same direction this is known as positive feedback. When a system returns to equilibrium following a change in the system this is known as negative feedback. It is negative feedback that allows systems to adjust to short term changes. For example, storms can remove huge quantities of beach material in a short time. After reverting to normal conditions, sediment is slowly shifted back to the beach by waves, so that equilibrium is restored, and the beach looks much the same as before the storm.
This general situation contrasts with the 5km long barrier beach at Porlock Bay, Somerset. This is the longest continuous shingle barrier system on the western coast of Britain. The cliffs to the west of Porlock were covered by head deposits, sediments formed under periglacial conditions composed of clay with a wide range of sizes of angular rock fragments. As sea levels rose following the melting of ice sheets at the end of the last glacial these head deposits were eroded from the cliffs and transported eastward by longshore drift. The rock fragments were deposited as a spit which gradually extended out across Porlock Bay. A storm beach composed of coarse shingle and pebbles developed as Atlantic storms hit the bay and hurled the pebbles above the reach of all but the highest waves. A freshwater lake developed inland of this beach.
However, the construction of groynes at Gore Point and sea walls at the back of the beach to protect the main road in the early 19th century, have interrupted and reduced the sediment supply entering the system from the west. Also, a lot of beach material is being lost because of both the steady movement of beach material east by longshore drift, and highly destructive storm waves. The reduction in volume of the ridge has resulted in increased instability. As a result of these positive feedback processes, management of this coastal landscape is now needed.
Prior to 1996, the response was to use beach replenishment techniques to move shingle from areas where there was still some accumulation to somewhere that was losing material. This had the effect of thinning the upper ridge along much of the beach. In 1996 a deep south westerly gale caused storm surge levels that were superimposed on the high tide to exceed the height of the barrier. Massive waves demolished the barrier crest. As the tide fell, the water rushing back out to sea opened a breach in the ridge which was so large that it was impossible for it to repair naturally. Since the 1996 breach, the coast has been managed by coastal adaptation where it has been allowed to develop naturally. For example, the former freshwater marsh behind the beach is now a saltmarsh.
The positive feedback mechanisms that have taken place here have resulted in some direct management such as beach replenishment, and some less direct management such allowing the saltmarsh to develop. Future changes to the inputs of the coastal system, such as sea level rise, are going to throw the system further out of balance with significant consequences for coastal managers. (596)
To what extent can an understanding of feedback systems help with the management of one or more cold environments that you have studied?
Cold environments are open systems that seek to be in a state of dynamic equilibrium. If any inputs or outputs change either because of environmental or human factors, then the system becomes unbalanced and will change. When an initial change within a system brings about further change in the same direction this is known as positive feedback. When a system returns to equilibrium following a change in the system, this is known as negative feedback.
A significant series of feedback mechanisms is now taking place in the Arctic zones of the world. The permafrost in northern Canada and Siberia is melting caused by warmer temperatures due to rising levels of CO2 in the atmosphere. Tundra plants in these areas are growing at increasing rates, resulting in more carbon uptake, a form of negative feedback. However, a lower albedo is created as previous white snowy surfaces are replaced with a darker plant-covered surface - resulting in warming. This warming releases even more latent CO2 from the decayed vegetation previously locked in the permafrost.
Permafrost covers about one-fifth of the northern hemisphere’s exposed land surface. The Arctic has gone through rapid warming, with temperatures increasing by 0.3C to 1C per decade since the 1980s. The melting of the permafrost poses a big threat to many buildings and infrastructure facilities located in these areas. Up to 50% of the infrastructure could be at high risk by 2050, prompting calls for urgent action from managers to mitigate the risks. It is estimated that there are 120,000 buildings, 40,000 kilometres of roads, and 9,500 kilometres of pipelines located in the permafrost in the northern hemisphere, a large part of which could be at risk.
In 2020, the warming of the permafrost caused one of Russia’s most severe environmental disasters. Over 20,000 tons of diesel spilled from storage tanks into nearby rivers and lakes in the Arctic north. The tanks sank into the ground because of the permafrost melting. Arctic coastal infrastructure has increased 15% since 2000, and ironically, about 70% of that growth comes from the fossil fuel industry - which keeps on expanding, emitting greenhouse gas emissions, and contributing to the climate change that’s causing the problems in the first place – another positive feedback mechanism.
A warming permafrost reduces its capacity to carry loads imposed by infrastructure. This is because the strength of the soil drops as the temperatures rise above the melting point of ice. Russia is particularly affected, as almost 65% of its land is underlain by permafrost. These areas are largely populated, increasing the risk of catastrophes. Over 60% of settlements and nearly 90% of the population in Arctic permafrost areas are in Russia. Life in North America would also be challenged, as 50% of the Canadian and 80% of the Alaskan land is underlain by permafrost.
However, costs could be minimised by acting now to prevent permafrost degradation on infrastructure. Heat removal techniques have been used in Russia and North America for decades, such as raised pipelines, convection embankments and heat drains, which can help cool the ground during the winter. Future construction projects should be based on an assessment of infrastructure risks and their management using such techniques.
Overall, there are complex and far-reaching impacts of climate change in the Arctic mainly driven by positive feedback mechanisms. Many people may think that colder regions would benefit from rising temperatures, but that’s not the case. The resultant changes make management of these environments ever more challenging. (576)