Climate Change in Washington - Sea Level Rise

Sea Level Rise

At Seattle, Washington, sea level is already rising by increments of 8 inches (200 mm) per century, and it is likely to rise another 19 inches (480 mm) by 2100. The four main factors that contribute to sea level rise (SLR) are:

• thermal expansion of the ocean
• melting of land-based ice
• local atmospheric circulation
• local tectonic movement

The report on Sea Level Rise in the Coastal Waters of Washington State summarized the possible sea level change for the Northwest Olympic Peninsula, Central and Southern Coast, and Puget Sound region and for each made estimates for very low, medium, and very high sea level change. For the year 2050, estimated Northwest Olympic Peninsula SLR ranged from -12 cm to 35 cm with negative SLR due to the predicted upward tectonic movement. Central and Southern Coast estimates ranged from 3 cm to 45 cm and Puget Sound was estimated at SLR of 8 cm to 55 cm. These values roughly double in all regions for the 2100 projections. Homes and businesses within reach of tidewater and low-lying agricultural areas in Washington are at high risk for flooding and current developers and anyone developing or buying property will likely take SLR into account before making an investment. Parts of Tacoma and Olympia are at higher risks than other cities like Seattle, since many areas in Tacoma and Olympia are built just a few feet above sea level. pg. 65. Current estimates project that Tacoma and surrounding areas could see sea levels rise from 5 to 16 inches (410 mm) by 2040. It is said that “shipping terminals, marinas, docks, and recreational facilities associated with coastal port districts are places where impacts will reach more deeply into the state’s economy through effects on commercial and recreational activities.” The cost of preparing for such rises is largely unknown, however, Seattle has five seawalls and plans for rebuilding of the Alaskan Way seawall may increase in cost by 5-10% based on projections for sea level rise. pg. 65.

Methods to protect shorelines are to build a seawall or to pump sand onto beaches to prevent erosion. Attempts at managing river flow for the direction of increased water levels is also a possible way to control SLR. When considering the cost to protect shorelines, it is difficult to calculate due to some shorelines being developed and others undeveloped. Agricultural factors and the potential lost of profit from SLR in that vector, is also difficult to predict and often unaccounted for. Potential development for housing is often excluded also. An estimate of potential national cost to protect land from SLR and considering such variability of land quality but excluding future value, is $270–475 billion for a one meter rise in Sea Level.