The most up to date climate projections available were used for this Plan based on ‘CMIP5’ global climate models, judged to perform well over Australia. Subsequent to the planning process, revised climate data has been made publicly available by CSIRO. Examination of this data makes no substantive changes to the results and recommended options.
The climate scenarios considered in the vulnerability assessment in terms of carbon emission projections based on the CMIP5 climate model results provided by CSIRO were:
Representative Concentration Pathways 4.5 - Moderate scenario (in terms of future carbon emissions)
Representative Concentration Pathways 8.5 - Extreme scenario (in terms of future carbon emissions)
Representative Concentration Pathways (RCPs) are four greenhouse gas concentration (not emissions) trajectories adopted by the IPCC for its fifth Assessment Report (AR5) in 2014. The pathways are used for climate modelling and research. They describe four possible climate futures, all of which are considered possible depending on the level of greenhouse gases emitted in the years to come. The RCPs are consistent with a wide range of possible changes in future anthropogenic (i.e. human) greenhouse gas (GHG) emissions. Emissions in RCP 4.5 peak around 2040, then decline. In RCP 8.5, emissions continue to rise throughout the 21st century (Commonwealth of Australia, 2013).
The results indicated that for the RCP 4.5 scenario there was predicted to be only moderate levels of impact on natural assets in East Gippsland until the 2090 time period. The RCP 8.5 scenario predicted a more significant response in East Gippsland for the 2050 and 2090 timeframes, indicating moderate to high impacts for some assets.
In consideration of the vulnerability assessment results, it was decided, for the purposes of this Plan, to use the RCP 8.5 emission scenario for the 2050 time period. This scenario was chosen because it provides a slightly longer planning horizon than the RCS (35 year compared with 20 years), and has been judged to provide a realistic view of possible impacts, for the most relevant climate factors, particularly changes in temperature and rainfall.
Planning also considered the potential impacts in the 2070 and 2090 time periods to help inform thinking about trajectories and potential longer-term impacts for less vulnerable assets.