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Sea level rise projection

There is strong evidence that global sea-levels gradually rose in the 20th century and will continue to rise at an increasing rate compared to a period of little change prior to 1870.

Sea-level is projected to rise at an even greater rate during this century. Global temperature increases are driving sea-level rise. As the global temperature increases, oceans warm and this causes the sea-level to rise because of thermal expansion of the oceans. This means the water expands as it warms. Increased melting of ice on land also contributes to sea-level rise. There is scientific consensus that global temperatures are rising because of emissions of greenhouse gases, such as carbon dioxide and methane, which result from human activities such as burning oil, coal and other fossil fuels.

The projected sea-level rise of 0.8 metres by the year 2100 adopted by the Queensland Government is based on climate modelling for probable scenarios of world development presented in the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report released in 2014 (AR5). See IPCC, 2014: Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. IPCC, Geneva, Switzerland, 151 pp.

The IPCC provides a complex set of sea-level rise projections based on possible future global greenhouse gas emissions scenarios. However, for planning purposes a single value or a single projection to describe future sea-level rise is needed, to allow this factor to be considered in decisions on future development and urban settlements.

The 0.8 metre sea-level rise value is based primarily on the median value of the RCP 8.5 greenhouse gas emission scenario which is ‘business as usual’ where the current rate in the growth of greenhouse gas emissions remains the same. It also considers the projected variation in the local sea-level rise rate of northern Australia. Uncertainty about how fast our climate will change, and by how much, compels us to take a precautionary approach because:

  • greenhouse gas emissions, global temperature and sea-level rise are currently tracking at, or above, the upper bounds of the IPCC projections consistent with the IPCC ‘business as usual’ scenario
  • current research indicates that IPCC projections are more likely to be an underestimation of sea-level rise than an overestimation, due to recently observed acceleration in land-based ice sheet melt, particularly in Greenland and also Antarctica
  • there is a long lag time between global temperature increases and resulting sea-level rise. Even if greenhouse gas emissions were stabilised within the next few decades, sea-levels would continue to rise for centuries after, due to the inertia of the system
  • The results of the Fifth Assessment Report are broadly consistent with that in the IPCC’s 2007 Fourth Assessment Report indicating that the world scientific community is approaching a stable future projection. A decision was made to continue the previous 0.8m sea-level rise planning value used in the Queensland Coastal Plan 2012 to maintain stability and certainty in the planning environment.