Jul 20 2012 -- Sep 20 2012 New Report Examines Sea Level Rise in the Northwest
Sea level rise and increased storminess will threaten structures in exposed areas. Photo courtesy of DOGAMI.A recently released report on sea level rise (SLR) by the National Research Council reviews the current state of the science and provides a more finely detailed projection of climate impacts to the Northwest coast than was previously available.
The report considers the significant roles of plate tectonics and regional ice melt. The study was commissioned by ten state agencies requesting updated projections for long-term planning efforts. According to the study, land north of Cape Mendocino, California is rising due to tectonic “uplift.” This includes over 1,000 miles of shoreline along northern California, Oregon, and Washington. The movement of the land caused by the collision of tectonic plates affects relative sea level rise more than had previously been accounted for.
Total vertical land movement from regional tectonic activity is estimate using GPS measurements. These measurements suggest that much of the coast is rising about 1.5-3mm per year north of Cape Mendocino, while the coast south of the Cape is sinking an average rate of about 1mm per year. These are regional rates that do not consider the small-scale tectonic differences at the state level.
For the coastal area north of Cape Mendocino, sea level is projected to change between -4 cm (-2 in) (sea-level fall) and +23 cm (9 in) by 2030, and -3 cm (-1 in) and +48 cm (19 in) by 2050 (decreasing northward). Areas south of the Cape are predicted to experience sea level rise closer to the predicted global rate of change of 8-23 cm (3-9 in) by 2030, relative to 2000 levels, 18-48 cm (7-19 in) by 2050, and 50–140 cm (20-55 in) by 2100.
Collapsing seawalls and bluff retreat will be a likely product of sea level rise. Photo courtesy of DOGAMI.Regional ice melt in Alaska and Greenland (influencing the coastline of Washington and Oregon) and Antarctica (influencing all three states) causes relative sea level rise. The net effect of melting ice and land movement is stated to be a reduction in relative sea level rise by 42 percent along the north coast (Neah Bay), 24 percent along the central coast (Eureka) and 14 percent along the south coast (Santa Barbara) for 1992-2008.
One significant caveat to the rate difference for the Pacific Northwest is the potential for an earthquake of magnitude 8 or greater. The result of this kind of massive tectonic shift would significantly increase the rate of sea level rise by as much as 1-2 meters (3-7 feet) as a result of subduction and significant drops in coastal elevation.
Global sea level rise is currently driven by two primary climatic phenomena: melting ice sheets, ice caps and glaciers; and the expansion of sea water as a result of increases in global temperatures. The potential impacts are magnified by increases in storm intensities that have also been predicted, and in fact are already taking place. According to the study, storms and sea-level rise are causing coastal beaches, dunes and cliffs to recede at rates that vary from centimeters a year, to several meters per year in severely affected areas.
Based on historical rates, erosion is expected to increase by 10-30 meters (30-100 feet) of retreat by 2100. Even without the predicted increases in storminess that play a key role in accelerating retreat, sea level rise will intensify storm surges and wave heights. The Pacific Northwest could see changes due to the predicted northward shift of North Pacific storm tracks. Concerns surround the destructive forces of increased wind intensities and wave heights that could be further exacerbated by strong El Nino influences that add high astronomical tides to the destructive mix.