Global Sea level Rise
Global sea level will rise between 0.2 m and 1.9 m by 2100 according to the Intergovernmental Panel on Climate Change (IPCC). Sea level rise is caused by a combination of processes including the melting of polar ice caps and glaciers, thermal expansion of ocean water, mining of groundwater aquifers, and, in places like Hawai‘i Island, subsidence of land masses (the island is slowly sinking). Estimates of sea level rise vary depending on the trajectory of global greenhouse gas emissions, and are based on different scenarios established by the IPCC. The more extreme values of sea level rise (1.9 m) reflect a future emissions scenario in which global population growth is coupled with continued intensive fossil fuel use. In all scenarios, rates of sea level rise are accelerating and will continue to accelerate in the future.
Geospatial predictions of coastal change under sea level rise typically pair current coastal elevation data and future sea level scenarios. These models tend to be conservative because they often do not incorporate future tectonic uplift or subsidence, high wave events, or shoreline erosion which will exacerbate coastal inundation and change, especially during large episodic events (e.g. storms or tsunamis). In some coastal areas, groundwater floating on top of denser, more saline water, may also exacerbate flooding as sea levels rise. In all sea level rise models, predictions should be viewed with the understanding that there is considerable regional and local uncertainty in the future propagation of storms and waves, vertical land movement, and variation in basin wide processes such as the El Niño Southern Oscillation and the Pacific Decadal Oscillation.
