'Managed retreat'


Sea level rise is real, and it's coming to a coastal city near you. Research published last month from the University of Arizona finds that hundreds of coastal cities in the lower 48 will lose an average of 9 percent of their land area as climate change causes seas to rise about one meter by 2100. Released with the new paper is an interactive map showing potential extent of sea level rise on coastlines.

Another new study released this week, to be published by the American Geophysical Union, shows that accelerated melting of the Antarctic and Greenland ice sheets will drive sea level rise, over taking the contributions from melting land glaciers and ice caps. Thermal expansion of the ocean, caused as seawater swells with warmer temperatures, also contributes significantly to sea level rise.

At the current rate of greenhouse gas emissions, global temperatures are projected to be eight degrees Fahrenheit warmer by 2100, according to University of Arizona lead researcher Jeremy L. Weiss.

Projected sea level rise from one meter (dark red) to six meters (light orange) in California's Bay Area.

(Courtesy Weiss and Overpeck, 2011)

"That amount of warming will likely lock us into at least 4 to 6 meters of sea-level rise in subsequent centuries, because parts of the Greenland and Antarctic ice sheets will slowly melt away like a block of ice on the sidewalk in the summertime," Weiss said in a press release.

Even a one-meter rise in sea level would have major impacts on coastal cities in the U.S. and around the globe. Some forward-looking cities on the West Coast and elsewhere are getting ready for the flood. 

In Olympia, Wash., the city relocated its new city hall to higher ground and raised the foundation by a foot over concerns about rising seas. The city also relocated its primary drinking water source to wells on higher ground. Downtown Olympia sits between 1 foot and 3 feet above current high tide, while local sea level rise projections range from six to 50 inches by 2100.  Now the city is considering a sea wall to protect the fragile artificial fill on which downtown is built. See a map of potential impacts here.

"We tend to be fairly ambitious about (planning for sea level rise) because our vulnerability is high," said Andy Haub, engineering and planning supervisor for the City of Olympia.

Projected sea level rise from one meter (dark red) to six meters (light orange) in Tacoma, WA.

(Courtesy Weiss and Overpeck, 2011)

At Surfers Point in Ventura, Calif., the city is demolishing a bike path and large parking lot eroding into the sea and rebuilding 65 feet back from the beach, a $4.5 million "managed retreat" that could be a model for how coastal communities deal with progressively higher tides.

"The challenge is we have built most of our civilization within a few feet of sea level or right at the edge," Gary Griggs, a coastal geologist at UC Santa Cruz, told the LA Times. "It's either going to be managed or unmanaged, but it's going to be retreat."

California's populous Bay Area is also one of the most vulnerable to sea level rise on the West Coast. The San Francisco Bay Conservation and Development Commission is preparing for a 14-inch rise in seas by 2050 by proposing additional shoreline protection efforts, building flood-resilient and easily relocated buildings in at-risk areas, removing structures and including sea level rise estimates in the permitting process. Development in low-lying areas could also be limited and even pulled back. More maps of San Mateo [PDF] and Oakland [PDF] from the state's 2009 sea level rise impacts study give a alarming glimpse of what's coming.

Projected sea level rise from one meter (dark red) to six meters (light orange) in Southwest Alaska.

(Courtesy Weiss and Overpeck, 2011)

Further north, the coastal village of Newtok, Alaska, is in the process of relocating nine miles inland to escape erosion and flooding caused by melting permafrost and coastal ice shelves. Sea level rise will only exacerbate these problems for some 25 other coastal villages in need of relocation in the near future, according to the Government Accountability Office.

But the rising sea isn't an issue if the land is rising, too, as is the case in Juneau, Alaska. As the Mendenhall Glacier retreats inland -- another by-product of the changing climate -- the land is actually lifting up with the loss of that tremendous glacial weight, and it's rising at a rate faster than the sea.

Not all seaside communities are so lucky.

Nathan Rice is a HCN intern.

Images courtesy Weiss and Overpeck (2011) "Areas potentially impacted by sea level rise." Based on Climatic Change DOI 10.1007/s10584-011-0024-x. ESRI provided basemaps.