This section discusses the importance of adapting to climate change and sea level rise in addition to the already complex and challenging task of managing the existing natural and human pressures on the coast.
Climate change and the rise and fall of sea levels are not new phenomena on this planet and, left alone, the coast's natural systems have great capacity to adapt and establish a new equilibrium. In undisturbed environments plant and animal communities can adjust and move with the changing shoreline, and in unpopulated and undeveloped areas these mechanisms can largely be left to proceed unaided. However, in more developed areas, existing private and public assets may not only hinder natural adaptation by causing 'coastal squeeze' (pressure on natural and cultural heritage values), but also require protection in their own right.
In the Coastal Works Manual it is recognised that, in Australia and other countries, artificial shoreline protection is a very costly business, it will impact on the aesthetic and ecological values of coasts, and all protective structures have a limited life span. Tasmania's relatively small population is unlikely to have the economic resources to protect any but the most important built assets and shorelines from erosion and inundation. To help reduce the future cost of shoreline protection, some underlying principles are suggested for managing climate change and sea level rise.
- Work in partnership with local communities and other stakeholders.
- Base decisions on good scientific knowledge - investing in appropriate studies can help avoid very costly and damaging mistakes.
- As far as possible, do not interfere with natural processes.
- Manage the coast's vegetation and habitats to enhance their natural resilience to change.
- Avoid locating new buildings and other infrastructure where there is any chance they might interfere with natural processes, and/or require protection within their expected life span.
- Where intervention is absolutely necessary, thoroughly assess any potential consequences for adjacent shorelines.
- Choose 'soft' reversible coastal protection options in preference to more permanent 'hard' structures.
- Recognise that any intervention to protect assets will almost certainly be costly, ongoing, and continue to increase in scale as sea level continues to rise.
These principles are largely self explanatory. In essence the advice is to plan well with good information and, where engineering or other works are proposed, take every measure to keep disturbance of the area to an absolute minimum (this may involve a review of the existing works culture). Consider whether the area or asset to be managed is defensible in the long term - in a growing number of places around the world it is being recognised that parts of the coast will have to be left to respond in their own way.
It is also important to recognise the value of no-regrets, low-regrets and win-win adaptation options when managing climate change risks:
- No-regrets : policies and decisions that will have immediate benefits under present-day climate conditions
- Low-regrets: low-cost policies, decisions and measures that have potentially large benefits over time
- Win-wins: policies, decisions and measures that help manage several coastal hazard or climate related risks at once, or bring other environmental and social benefits, e.g. preservation of natural character.
(Derived from: Coastal hazards and climate change: A guidance manual for local government in New Zealand
, Ministry for the Environment 2008)
Predicted Sea Level Rise and Climate Change Consequences
Over the coming century scientists expect the sea level to continue to rise, at times at an accelerated rate as has been observed over the last few decades. The Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC 2007) conservatively estimated a sea level rise of up to 79cm by 2100, however this figure did not allow for polar ice-sheet melting. Measurements since 2007, and improved understanding of ice-sheet responses, show that sea level rise of over 1.0m and as high as 1.5m is possible, and sea levels will continue to rise long after 2100. It is anticipated that these higher projections will be reflected in the next IPCC report, expected in 2014.
Most state governments in Australia roughly agree on the sea level rise benchmarks to use for future planning and management decisions. For example, for planning purposes New South Wales now assumes a sea level increase of 40cm above 1990 levels by 2050 and 90cm by 2100. Victoria has recommended working to a figure of 80cm by 2100, and Queensland is recommending the same 2100 value. It is likely that these benchmarks will be revised upwards following the release of the next IPCC report. There may be small discrepancies between exact figures but there is agreement that sea levels will rise considerably, the mean high and low water mark will increase and storm surges will reach further inland.
Many of Tasmania's coastal areas will be at risk from sea level rise and more severe storm surges associated with climate change, with impacts including increased coastal erosion and recession of erodible shorelines, inundation and flooding of low-lying areas, and coastal infrastructure. Coastal infrastructure in high-risk locations is likely to incur damage or require redesign or relocation.
For more information, see Chapter 2
, Climate Change and the Coast, Tasmanian Coastal Works Manual.