As projections of the severity of climate change seem to become more dire by the day, planning for Seattle's seawall is like shooting at a moving target.

Two years ago the Intergovernmental Panel on Climate Change (IPCC) predicted that by 2100, global sea level will rise between 7 and 23 inches. But this past December, a new international study predicted a 2100 sea level rise (SLR) of 4.5 feet, concluding that "the current target for mitigation should be a maximum of 2 meters (6.6 feet)."  These new projections are higher because new data shows faster-than-anticipated rates of ice melt in Antarctica.

The most recent sea level rise projections for the Pacific Northwest can be found in a January 2008 paper published by the Climate Impacts Group at the University of Washington. The "medium" projection for 2100 SLR is 13 inches.

Concerns over the Seattle seawall and climate change are not new, but as of 2008, the new seawall was being designed to handle only an 11-inch SLR. Mayor Mike McGinn, through a spokesman, has said only that there “a lot of environmental factors that we have to take into account," and that sea level rise "will be one of them.” More recent designs, if they exist, have not yet been made public. But clearly, 11 inches isn't going to cut it.

Let's just say that ideally, we'd plan conservatively—for a SLR of six feet. Add to that the increasing frequency and intensity of storm surges that is expected as the planet warms, and you might as well kiss Harbor Island goodbye.

What would a seawall look like that could handle those conditions? Taller than what we have now, it's safe to assume. And assuming the wall has to be significantly higher than Alaskan Way, there will major impacts on the design of the waterfront street and open spaces.

Many hope that the city will a choose a seawall design that provides enhanced habitat for salmon and other sea life, and that also creates opportunities for people to touch the water. Both of these goals will be complicated by the magnitude of SLR that is now likely. For example, how much will be left of the beach at Olympic Sculpture Park (photo below) in 50 or 100 years?

Welcome to the reality of climate change. As Climate Impacts Group scientist Lara Whitely Binder put it, "There's always going to be a coastline. It's just a matter of where it is."



P.S. I can't stop myself from pointing out that in this related Times online piece, Benny Peiser, director of the Global Warming Policy Foundation is given an opportunity to express the contrary view, and—no lie—says this: "We look out of the window and it’s very cold. [So] it doesn’t seem to be warming."