Changes in global temperatures over a long term timescale result in changes in sea-level, mainly through thermal expansion of the ocean and the melting of land ice. Over the past 100 years the world has warmed by about 0.5°C (Climatic Research Unit, University of East Anglia). Due to increasing concentrations of carbon dioxide and other greenhouse gases in the atmosphere, the world will be a warmer place in the future. Predictions of the extent of sea level rise are varied but no matter what the level, the coastline of Cornwall will be affected.
Climate change causes sea levels to rise in two main ways. Water expands as it warms. As the globe warms up, so do the seas and as they expand the sea level rises. This is thought by scientists to be the most dominant factor in sea level change. The second most important factor is melting land ice. Water in glaciers has been trapped as ice for thousands of years and when the glaciers melt the water enters the sea and the sea level rises.
The Intergovernmental Panel on Climate Change (IPCC) published its Fourth Assessment in 2007. The main conclusions drawn were as follows.
1.Warming of the climate system is unequivocal.
2.Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic (human) greenhouse gas concentrations.
3.Anthropogenic warming and sea level rise will continue for centuries due to the timescales associated with climate processes and feedbacks, even if greenhouse gas concentrations were to be stabilized, although the likely amount of temperature and sea level rise varies greatly depending on the fossil fuel burning intensity of human activity during the next century.
4.The probability that this is caused by natural climatic processes alone is less than 5%.
World temperatures could rise by between 1.1 and 6.4 °C during the 21st century.
5.Sea levels will probably rise by 18 to 59 cm.
6.There is a confidence level of more than 90% that there will be more frequent warm spells, heat waves and heavy rainfall.
7.There is a confidence level of more than 66% that there will be an increase in droughts, tropical cyclones and extreme high tides.
8.Both past and future anthropogenic carbon dioxide emissions will continue to contribute to warming and sea level rise for more than a millennium.
9.Global atmospheric concentrations of carbon dioxide, methane, and nitrous oxide have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values over the past 650,000 years.
Some critics have contended that the IPCC reports tend to underestimate dangers, understate risks, and report only the "lowest common denominator" findings (McKibben, 2007). It may already be out of date and omits recent observations and factors contributing to global warming, such as the release of greenhouse gases from thawing tundra. Some other studies estimate that in 2100 sea levels could be 0.5–1.4 m above 1990 levels (http://news.bbc.co.uk/1/hi/sci/tech/6179409.stm).
The South West could see the highest sea level rise in Britain with a rise of between 20cm to 80cm by 2080. Mean sea level at Newlyn has risen 15cm since 1915 (NTSLF, Proudman Oceanographic Laboratory). Mean wave height has increased from 1.8m in 1962 to 2.3m today. The predicted changes in sea level are dramatic and are at their most extreme at the western tip of Cornwall. The National Trust believe managed retreat may be the only solution for some low lying areas e.g. Marazion. The UK Climate Change Impact Programme (UKCIP) predicts extreme sea levels (spring tides, storm surges etc.) will be experienced more often and storm frequency is expected to increase with over 50% more winter low pressure systems crossing the UK.
Taking all these factors into consideration sea level rise in Cornwall should be taken as a given and attention should turn to mitigating the effects and resulting impacts on the coastline. Such impacts may include increased coastal erosion, higher storm-surge flooding, more extensive coastal inundation, changes in surface water quality and groundwater characteristics, increased loss of property and coastal habitats, increased flood risk and potential loss of life, loss of cultural resources, impacts on agriculture and aquaculture through decline in soil and water quality, and loss of tourism, recreation and transportation. However appropriate management techniques are still being formulated and would appear to fall into two categories, coastal defence (hard engineering) or managed retreat (soft engineering).
Many countries (such as the Netherlands) have a single controlling authority for coastal management which can treat the coastal zone as a whole, with the foreshore, hinterland and offshore areas being parts of a single unit within which occur a complex series of interactions. This is not the case in the United Kingdom. Coastal defence in the UK is the responsibility of local authorities (in this case Cornwall County Council) with some support supplied by the Environment Agency (part of DEFRA). Although Cornwall County Council recognises the fact of sea level rise it does not seem to have any concrete plans to deal with it. This could be due to several factors but the overriding factors would seem to be the financial cost of mitigation, whether through hard or soft engineering, and the lack of central government guidance. Vulnerable areas have been identified but the management options are still being developed.
Sea Level Rise in Cornwall. (http://www.cornwall.gov.uk/index.cfm?articleid=11617)
Sea Level Rise in the Fal Estuary (http://www.cornwall.gov.uk/index.cfm?articleid=11617)
However, hard engineered coastal defences such as offshore breakwaters, seawalls and embankments might not be the only option.
“There is no guarantee that hard defences work in the long term: they are often only a temporary solution. As sea levels rise and severe storms increase, it will become ever more difficult and expensive to build and maintain strong defences. They can also disfigure the coast and cause environmental harm by moving the problem to another location. We believe therefore that hard defences should only be used as a last resort.” (National Trust, 2005)
This illustrates the approach to managed retreat that is increasingly being adopted by NGO’s such as the National Trust, Royal Society for the Protection of Birds, Wildlife and Wetlands Trust etc. By working with nature instead of against it and managing the retreat from the advancing sea by creating space along the coastline such as salt marshes and sand dunes to act as natural sea defences, they believe that wildlife and habitats can be protected. At the same time these natural coastal defences would enhance the protection already provided to infrastructure and housing. The National Trust believes this is likely to be the most realistic and cost-effective approach over the long term.
The National Trust is Britain’s largest coastal landowner. With 1130 kilometres of coastline the Trust now owns nearly 10% of the coast of England, Wales and Northern Ireland. Of this they have identified 169 sites along some 608 kilometres (60%) of National Trust-owned coastline which could lose land by erosion. Nearly 10% of this loss could be between 100-200 metres inland and 5% more could be losses of over 200 metres inland. Of the sites identified, 126 (with land covering 4040 hectares) are currently at risk from tidal flooding with a further 33 low-lying sites at risk of combined tidal and river flooding within the next 100 years. Looking at these figures it can be seen that the National Trust’s response to sea level rise could have a significant impact on local and national government policy. Five key areas were identified. (Taken from Shifting Shores: Living with a Changing Coastline, 2005. The National Trust)
“1. Long-term planning is essential. To adapt effectively to sea-level rise and climate change we need to plan at least 50 to 100 years ahead. In many cases it will be necessary to relocate people, habitats and buildings and to do so cost-effectively requires early action. The future is inherently unpredictable, even more so with climate change and a dynamic coastal environment, so we need to allow flexibility in our management and planning.
2. Think and act in a wider context. The boundaries of the Trust’s coastal sites take no account of the real boundaries of the coastal cells in which coastal processes operate. In order to take a flexible and responsive approach to dealing with coastal change, we need to think and act in a much wider spatial context, managing our sites within freshwater catchments and coastal cells.
3. Work with nature not against it. Our experience has demonstrated that working with natural processes is the most sustainable approach. In some cases this will mean undoing past mistakes, taking out hard defences and letting the coast realign naturally. In others we will need to phase our approach, buying time with temporary solutions while finding space to allow natural defences to form.
4. Solutions need partnership. We cannot operate in isolation as the decisions we make nearly always impact beyond the immediate site. Tackling the problems facing our sites also requires action by others, especially neighbouring coastal owners and managers. Finding mutually beneficial solutions like large-scale realignment projects requires a strong partnership approach.
5. Involving the public is critical. Raising awareness of the impacts on our coastal sites is vital to winning public confidence. Any form of realignment of the coast can create uncertainty and even hostility. Building consensus and providing information takes time and effort, but is crucial to finding sustainable solutions.” (National Trust, 2005)
So what are the options for managing the effects of sea level rise on Cornwall’s coastline? Most of the major population centres are in the coastal zone – Falmouth, Penryn, Truro, Penzance, St. Ives, Newquay, Bude and St. Austell. They contain a large proportion of the urban population and housing in Cornwall as well as major infrastructure (e.g. Falmouth docks), centres of education and local government, cultural and historical areas, retail centres and areas of regeneration and development. Managed retreat from these locations would be prohibitively expensive, legally ambiguous and socially disruptive.
Most already have some form of hard coastal defence which could be added to and maintained with help from central government. As these would be major civil engineering projects they would provide employment and investment opportunities in a region of high unemployment.
At the same time the option of managed retreat and the creation of natural coastal defences could be instituted for the rest of Cornwall’s coastline. Areas such as the Fal estuary, with its salt marshes and St. Ives Bay, with a well established dune system are ideal for establishing the management systems required. These could then be applied to other areas of the coastline.
Although this would still require large expenditures, these would be cheaper than large scale hard engineering and have the added benefit of providing protection to wildlife and existing habitats and creating new habitats.By combining the two approaches to mitigating sea level rise a viable management system could be developed to maintain a sustainable economy and society in Cornwall. Whether the political will and financial resources to implement such a system exist is another question.
No comments:
Post a Comment