Climate change

The flooded streets of Laks Entrance during the floods of July 2007

Over the medium to long term, climate change poses real and serious threats to our coast. During this century, it is likely the Victorian coastline will be impacted by sea level rise and increased frequency and severity of storm events leading to inundation and erosion. It is also predicted that higher temperatures will increase bushfire risk along the coast, and increased sea temperatures, changing sea currents and further acidification of the ocean will affect the marine environment.

The Intergovernmental Panel on Climate Change (IPCC) is the authoritative international scientific advisory body on human-induced climate change science. In the Fourth Assessment Report, (November 2007) the IPCC projected sea level rise of between 0.18-0.59 metres by 2090-2099 using a hierarchy of models plus additional ice sheet melt of 0.1-0.2 metres. however, the upper values of sea level rise (e.g. 0.59 metres) projected by the models were not considered to be upper bounds of possible sea level rise by 2099 (refer figure 4).

While there is uncertainty about the quantum of the sea level rise, the data provided in the IPCC report shows the sea level is rising and will continue to rise in the 21st century and in all likelihood beyond.

Recent observations (refer figure 5) show the observed sea levels from tide gauges and satellites are tracking near the upper bound of the IPCC 2001 projections since the start of the projections in 1990 (Rahmstorf et al. 2007).

On the basis of the IPCC report and until national benchmarks for coastal vulnerability are established, a policy of planning for sea level rise of not less than 0.8 metres by 2100 should be implemented. This policy should be generally applied for planning and risk management purposes. As new scientific data becomes available, the policy will be refined.

It is the combined effects of sea level rise, the impact of tides, storm surges, wave processes and local conditions such as topography, elevation and geology that will produce climate change impacts and risks in coastal areas. Figure 6 shows the impact of tides, storm surge and wave processes on sea level.

In this context, it is useful to recognise that sea level rise will create a spectrum of risk, with the highest likelihood of impacts in the lowest lying areas.

Managing and adapting to these impacts and risks will pose challenges in the short, medium and long-term, depending on the events that arise and the life of the buildings and infrastructure and other assets.

There are three adaptation options, protect, accommodate or retreat. Adaptation strategies should be precautionary, that is, planning for likely future circumstances even if full scientific certainty is not possible.

Figure 4: Projected sea-level rise for the 21st century: The projected range of global averaged sea-level rise from the IPCC 2001 Assessment Report (Church et al. 2001) for the period 1990 to 2100 is shown by the lines and shading. The central dark shading is an average of models for the range of Special Report on Emission Scenarios (SRES) greenhouse gas emission scenarios. The light shading is the range for all models and all SRES scenarios and the outer bold lines include an allowance for land-ice uncertainty. The updated AR4 IPCC projections of 2007 for the SRES scenarios (Meehl et al. 2007) are shown by the bars plotted at 2095. The magenta (lighter) bar is the range of model projections (90% confidence limits). Ocean thermal expansion and melting of glaciers and ice caps are the largest contribution to this range. The red bar is a potential but poorly quantified additional contribution from a dynamic response of the Greenland and Antarctic ice sheets to global warming. Note that the IPCC AR4 states that "larger values cannot be excluded, but understanding of these effects is too limited to assess their likelihood or provide a best estimate or an upper bound for sea-level rise." Source - figure and caption: CSIRO 2008a

Figure 5: Observations versus Projections: Recent observations show the observed sea levels from tide gauges (blue) and satellites (red) are tracking near the upper bound (black line) of the IPCC 2001 projections (grey shading and black lines) since the start of the projections in 1990 (Rahmstorf et al. 2007). This upper limit leads to a global-averaged sea-level rise by 2100 of 88 cm compared to 1990 values. These observations do not necessarily indicate that sea level will continue to track this upper limit - it may diverge above or below this upper limit. However, the ice sheet uncertainties referred to above are essentially one-sided - i.e. they could lead to a significantly larger sea-level rise than current projections but are unlikely to lead to a significantly smaller rise. Note also that greenhouse gas emissions are now tracking just above the highest of the Special Report on Emission Scenarios (SRES) emissions scenarios used in calculating these projections (GCP_CarbonBudget 2007, Raupach et al. 2007; Canadell et al. 2007). Source - figure and caption: CSIRO 2008b

Planning and management programs that can help vulnerable habitats to survive and improve the resilience of the coastal and marine environment are preferred. This means working with the scientific community to identify and encourage ongoing research and analysis to inform future planning and management. The potential climate change impacts for coastal areas are summarised in Table 2.

Source: Planning for climate change, National Sea Change Taskforce, 2008 (IPCC 2007a, Henessy et al. 2007, Voice et al. 2007)