Seas are rising as ice caps and glaciers melt

Low-lying islands in the Pacific may be the most obvious victims of rising sea levels, but the impact on California’s coastline will also be significant according to a new report by the National Research Council. The danger is primarily the result of melting ice sheets and glaciers, but an increase in the sheer volume of oceans as they warm also plays a role, as does the loss of gravitational pull on oceans by ice masses. As a result, sea water is increasingly free to distribute itself globally, pushing up levels worldwide.

The report underscores the impact of time and tide as ice caps melt. “Coastal communities need to understand these processes, what sea level rise indicates to them, and plan accordingly,” says Gary Griggs of the University of California Santa Cruz. Sea levels around the world have risen 7” in the last century, but the rate of acceleration has doubled over the past two decades when compared to the past 100 years. That’s significant news for California.

Sea levels are predicted to rise six inches by 2030 between Cape Mendocino and Mexico’s border, with a one-foot rise predicted by 2050 while seas along the California coast could run three feet higher by 2100. The impact won’t be as great along the Oregon and Washington coasts where tectonic plate activity is pushing the coast upward, but a different set of tectonics is sinking California by 1 to 2 millimeters a year, adding to its sea level rise.

The effect of increasingly frequent El Niño conditions will magnify sea level threats according to the report, increasing the possibility of flooding, coastal erosion and loss of wetlands. High tides, large waves and storm surges caused by large El Niño events can raise coastal sea levels 4 to 12 inches during winter months.

It’s particularly disturbing news for the San Francisco Bay area where coastline development has been built on fill easily impacted by water rising only a few feet. The NRC says San Francisco and Oakland airport runways could become flooded within the next few decades.

Armoring cliffs with rock and seawalls is the most common defense. Ten percent of the California coastline has now been armored, says Griggs, including 33 percent of the coastline in Ventura, Los Angeles, Orange, and San Diego counties. Still, it's a short-term solution complicated by a loss of beach sand. 28 dams and more than 150 debris basins in the watersheds of eight major rivers in southern California have impounded more than 4 million cubic meters of sand, starving the beaches of their natural protection.

The study underscores research conducted in 2009 which predicted significant impact to tourism, homes and businesses along Huntington, Newport, Laguna, Venice and Zuma beaches. The blue areas on this map show vulnerabilities in Marina Del Rey and Venice. The Pacific Institute study estimated that a 5-foot rise in sea levels by 2100 would affect 480,000 people who live in areas at risk, causing $100 billion in property damage. Today's updated research points to a 2-foot smaller sea rise, but one that’s still worrisome.