Creating Global Sea-level Scenarios
The SimCLIM 4.x for Desktop Sea-level Scenario Generator contains tabled year-by-year output, a simple global climate model, as forced by RCP greenhouse gas emission scenarios used by the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report. For each scenario, low, mid and high projections are provided for global-mean changes in temperature, sea level (thermal expansion only) and sea level (total, including ice melt). The corresponding values for atmospheric concentrations of carbon dioxide are also provided. To view these data, proceed as follows:
1] Click on the Site Sea Level Rise Scenario Generator in the main tool bar or right click in the main display and select the icon from the list displayed.
2] The following dialogue box will appear.
Proceed from the top of the dialogue box to complete the various attributes for your analysis:
1] Toggle to the local observed sea-level trend you are interested in:
Vertical land movement component only: Trend of relative sea-level that excludes climate-change-related components (eg. land subsidence or uplift). This trend will be added directly to your scenario.
Total trend: The total observed, undifferentiated trend of observed relative sea-level change which includes Greenhouse Gas-related effects. SimCLIM 4.x for Desktop will estimate the non-climate change component of the trend for you, and factor it into your scenario.
2] Enter a local trend value in mm/yr (this value has to be provided by the user based on off-line work) reflecting the output from Step 1.
Vertical land movement information can be quickly obtained from:
3] Select the normalized Global Circulation Model (GCM) pattern from the drop-down menu in the dialogue box. Select all for an ensemble or you can query individual GCMs.
4] Select an emission scenario (RCP), with which global-mean sea-level projections are associated.
Clcik and a map will appear.
5] Click on the map to identify the cell of interest (or enter longitude and latitude directly). IMPORTANT you need to click on the select arrow in the toolbar before clicking on a site in the dialogue box map that you wish to analyse.
6] Click Load Data.
For each emission scenario, three projections of estimated eustatic sea-level changes from 1990 to 2100 are provided, for three sets of sensitivity values. If one wishes to adjust these values in order to obtain relative sea-level changes that take into account long-term, non-greenhouse-gas-induced trends, take the additional steps:
7] Click . The program will now make three estimates of the recent greenhouse-gas-related trend component that are consistent with each of the low, mid and high model parameter sets. These estimates are then subtracted from the overall trend that you provided. The residual, non-climate-related trends which result are typically related to changes in land elevation from, for example, tectonic activity, land subsistence or isostatic readjustment. These local trends will be added to the three future projections following the methods outlined in the “Methods Guide” of the main SimCLIM manual.
There are many options for viewing the various outputs from the analysis. Click on for a tabular display of the variability across GCMs.
When viewing the spatial patterns it is important to understand the legend. The values in the legend reflect the scaling factor in relation to the global-mean sea-level change (pertaining to the thermal expansion component only). For example, if a cell value is 1.0, then the interpretation is that as the sea-level change in that location would be equal to the global-mean value. However, if the cell value is 0.5, then the sea-level change at that location would be half the global-mean value. Do not interpret these numbers as the actual change in sea level in meters.
The values highlighted in red above represent from left to right, the longitude (0 to 360 degrees) and the latitude (0 to 90 degrees for the northern hemisphere and 0 to -90 degrees for the southern hemisphere). The final number represents the actual scaling factor for that particular cell at the longitude and latitude depicted.
Results for a chosen cell can be depicted graphically as shown below by clicking on the tabular data.
The graphic display includes the longitude and latitude of the site, in blue across the top and by clicking on the ‘follow mouse’ box in the top right you can scroll around the graphic and get exact data for different years.
It is possible to run any number of scenarios using different GCM patterns and to compare them. Notice that the Y axis of the graphs is not standardised between different graphical depictions. Interpretation must therefore be carried out carefully when comparing different sea-level scenarios.
By right clicking on the tabular data a dialogue box, as shown below, is displayed.
These useful data transfer capabilities can facilitate comparisons of the effects of different CGM patterns and global emissions scenarios on changes in sea level.
Activity: Open the Sea Level Rise Scenario Generator and zoom into an area of your choice. Create some sea level rise scenarios and complete the following table. Use a High sensitivity in all your scenarios.
Do the same analysis but add some data to the following (for example -2.00 for local observed trend and then try 2.00):
Compare your results with those above.