At some point in the climate adaptation planning process you might have to choose a sea level rise scenario(s). One(s) that incorporate global projections and local change rates. Most plans use a span of 100 years or time horizon of 2100 as the endpoint. Many researchers have published a range of sea level rise scenarios, including the The Intergovernmental Panel on Climate Change, which produces the international consensus report (2007 was the latest) that provides a range of global sea level change scenarios. It is from this range of scenarios that a community can determine which particular scenario(s) makes the most sense for their needs.
In some cases sea level change scenarios are used as planning targets, such as a 1 meter rise by the year 2100. The scenario chosen should be relevant to the timescale of decisions being made. Banks may prefer to use a 30 year time frame for housing projects since that is the lifetime for the average loan. Local officials would be wise to move beyond that if possible, as housing developments and infrastructure have a much longer life span, and sea level changes are expected to increase over time. This approach would require using increments of sea level change over a specified number of years, such as 0.18m to 0.30m by 2050, 0.30m to 0.58m by 2080 which is what the state of Connecticut is using for planning.
Whatever the approach, the selected sea level change increments should be derived from a reputable source and the vertical distance between increments supported by the vertical accuracy of the land elevation data, particularly if maps of sea level change will be produced. Failure to do this may result in uncertainty in the maps and resulting impact assessment.
0.3m – 0.6m are reasonable sea level change increments to apply in mapping projects that use most current lidar data collection specifications.
Some applications choose not to tie sea level rise increments to a specific time frame. Rather sea level rise increments are illustrated and the user can choose the time horizon. For example, a library of maps showing 0m – 2m feet of sea level rise can be linked to any sea level rise curve. The impact assessment is attached to whatever timing the user selects. This is the approach used in the Digital Coast SLR and Coastal Flooding Impacts Viewer.
The below figure shows 18 different sea level rise scenarios (based on various climate scenarios) in the literature (showing author). A quick comparison and averaging points to an average high scenario of 1.25m by 2100 and the average low scenario of 0.6m by 2100. This literature review was done to support development of sea level rises scenarios for the National Climate Assessment. What is interesting to note is that the original IPCC scenarios are now considered fairly conservative and the range among studies is quite large. Factoring in ice melt and non-linearity or not into these studies adds to their discrepancies.
……And these are just the Global projections. Relative or “local” changes in sea level are even more variable due to vertical land motion, locally realized contribution from global ocean mass and volume changes, changes in estuarine and shelf hydrodynamics, regional oceanographic circulation patterns, and hydrologic cycles (river flow). Rates will vary greatly along the U.S. coastline.
So do you want a conservative or liberal sea level rise scenario? Choose wisely. Unfortunately you will have to wait until 2100 to see if you were right.
For more details on sea level rise scenarios, visit these links.