Sea Level Rise in the Coastal Waters of Washington State


Mote, P.W., Petersen, A., Reeder, S., Shipman, H., Whitely Binder, L.C. 2008. Sea Level Rise in the Coastal Waters of Washington State. Report prepared by the Climate Impacts Group, Center for Science in the Earth System, Joint Institute for the Study of the Atmosphere and Oceans, University of Washington, Seattle, Washington and the Washington Department of Ecology, Lacey, Washington.


Local sea level rise (SLR) is produced by the combined effects of global sea level rise and local factors such as vertical land deformation (e.g., tectonic movement, isostatic rebound) and seasonal ocean elevation changes due to atmospheric circulation effects. In this document we review available projections of these factors for the coastal waters of Washington and provide low, medium, and high estimates of local SLR for 2050 and 2100. The fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) projects global SLR over the course of this century to be between 18 and 38 cm (7-15″) for their lowest emissions scenario, and between 26 and 59 cm (10-23″) for their highest emissions scenario. Based on the current science, our “medium” estimate of 21st century SLR in Washington is that in Puget Sound, local SLR will closely match global SLR. On the northwest Olympic Peninsula, very little relative SLR will be apparent due to rates of local tectonic uplift that currently exceed projected rates of global SLR. On the central and southern Washington coast, the number of continuous monitoring sites with sufficiently long data records is small, adding to the uncertainty of SLR estimates for this region. Available data points suggest, however, that uplift is occurring in this region, but at rates lower than that observed on the NW Olympic Peninsula.

The application of SLR estimates in decision making will depend on location, time frame, and risk tolerance. For decisions with long timelines and low risk tolerance, such as coastal development and public infrastructure, users should consider low-probability high-impact estimates that take into account, among other things, the potential for higher rates of SLR driven by recent observations of rapid ice loss in Greenland and Antarctica, which though observed were not factored into the IPCC’s latest global SLR estimates. Combining the IPCC high emissions scenario with 1) higher estimates of ice loss from Greenland and Antarctica, 2) seasonal changes in atmospheric circulation in the Pacific, and 3) vertical land deformation, a low-probability high-impact estimate of local SLR for the Puget Sound Basin is 55 cm (22″) by 2050 and 128 cm (50″) by 2100. Low-probability, high impact estimates are smaller for the central and southern Washington coast (45 cm [18″] by 2050 and 108 cm [43″] by 2100), and even lower for the NW Olympic Peninsula (35 cm [14″] by 2050 and 88 cm [35″] by 2100) due to tectonic uplift (see Table III). The authors intend to continue investigating the factors contributing to local SLR and will provide updates to this report.