The Federal Interagency Sea Level Rise and Coastal Flood Hazard Scenarios and Tools Task Force, a joint task force of the National Ocean Council (NOC) and the U.S. Global Change Research Program (USGCRP), was charged with developing and disseminating future sea level rise and associated coastal flood hazard scenarios and tools for the entire United States, to support coastal preparedness planning and risk management processes.
Two key subtasks of the overall Task Force effort have been to (1) develop updated scenarios of global-mean sea level (GMSL), and (2) regionalize these global scenarios for the entire U.S. coastline, to serve as inputs into assessments of potential vulnerabilities and risks in the coastal environment, as well as key technical inputs into NCA4. In order to bound the set of GMSL rise scenarios for year 2100, the Task Force assessed the most up-to-date scientific literature on scientifically supported upper-end GMSL projections, including recent observational and modeling literature related to the potential for rapid ice melt in Greenland and Antarctica. These provide evidence to support a physically plausible upper-bound GMSL rise of 2.5 m by the year 2100, with an overall range of 0.3–2.5 m.
This GMSL range was discretized into 0.5-m increments into six GMSL rise scenarios (Low, Intermediate-Low, Intermediate, Intermediate-High, High and Extreme, which correspond to GMSL rise of 0.3 m, 0.5 m, 1.0 m, 1.5 m, 2.0 m and 2.5 m), which were then used as the basis for deriving relative sea level (RSL) rise on a 1-degree grid covering the coastlines of the U.S. mainland, Alaska, Hawaii, the Caribbean, and the Pacific island territories, as well as at the precise locations of available tide gauges along these coastlines. The RSL values account for key factors important at regional scales, including (1) shifts in oceanographic factors; (2) changes in the Earth’s gravitational field and rotation, and flexure of the crust and upper mantle, due to melting of land-based ice; and (3) vertical land movement (VLM; subsidence or uplift) due to glacial isostatic adjustment, sediment compaction, groundwater and fossil fuel withdrawals, and other non-climatic factors.
These global and regional/local scenario products are available for the period 2000–2100 at 10-year intervals and from 2100–2200 at a coarser temporal resolution (scenario values provided for 2120, 2150, and 2200).
| GMSL rise Scenario | RCP2.6 | RCP4.5 | RCP8.5 |
|---|---|---|---|
| Low (0.3m) | 94% | 98% | 100% |
| Intermediate-Low (0.5m) | 49% | 73% | 96% |
| Intermediate (1m) | 2% | 3% | 17% |
| Intermediate-High (1.5m) | 0.4% | 0.5% | 1.3% |
| High (2m) | 0.1% | 0.1% | 0.3% |
| Extreme (2.5m) | 0.05% | 0.05% | 0.1% |
Relative sea level (± the global-mean value) for each of the six global-mean sea level rise scenarios
