Every once in a while, I like to go for a run on the beach. One of my favorite spots to hit the sand is San Gregorio State Beach — it lies just across the Santa Cruz range, is invariably quiet early on weekday mornings and offers a good stretch of hard-packed sand along a southern route toward Pomponio State Beach.
At least, when the tide is out.
When I first started frequenting San Gregorio, I never worried about the position of the moon. Absent a storm surge, no matter whether the tide was low or high, I could comfortably make my way around all the cliffs and headlands. But after a few winter storms, I found this was no longer true: Fierce waves had reshaped the coastline, piling up wide beaches at some points, but leaving bare rock in others. Now, if I don’t time my runs right, I’ll find myself knee-deep in ocean backwash.
Although cross-checking with tide charts cuts back on my impulsive beach trips, I’ve found I really enjoy the ever-changing coastline. Unlike every other distance route I’ve carved out for myself here in California, the beach run holds something new for me every time.
Of course, most of us — particularly those who own property along the coastline — prefer a bit more stability in our lives. After all, it’s one thing to have an extra sand mound to sprint up, and another thing to have your house fall into the ocean.
That’s the worry of thousands of homeowners along both the East and West coasts of the United States.
California in particular is the poster child for coastal erosion drama. The sea cliffs that line the San Francisco peninsula have given way before; it’s not hard to find the remnants of foundations along coastal trails. The bluffs overlooking the shoreline are themselves marked by warnings to stay back from the disintegrating edge.
Elsewhere in the state, homeowners prefer an active response. One third of Southern California’s coastline has been backed by some human barrier, be it a carefully designed sea wall or a messy pile of concrete and boulders intended to buttress the coastal landscape.
But planting solid structures in front of a dynamic sea comes with consequences. The walls and boulders may hold their ground, but deflected water scours away sand and gravel with an even fiercer intensity than unobstructed waves. In the end, while the absolute line drawn by man may hold, the sand on the seaward side will disappear.
Those of us who don’t own clifftop dwellings — and occasionally enjoy the sandy beaches below them — would probably prefer to let nature take its course. Standing back would certainly save us the hundreds of millions of taxpayer dollars spent maintaining shorelines. And in a world arguably over-managed by human desires, it would be nice to leave something to Mother Nature.
Unfortunately, it’s not just personal property that’s on the line.
San Francisco knows this all too well as it looks west at a shrinking Ocean Beach. A major transportation artery and a major sewage line run a few meters inshore from the present-day mean high-tide line. The economic balance sheet gets a lot more complicated when you weigh the cost of relocating infrastructure against coastal reinforcements.
Add in sea level rise and you have an urban planner’s worst nightmare.
As humanity adds carbon dioxide to the atmosphere, we warm not only the air, but also the sea. Warmer water expands, and warmer ice melts. Together, these effects lead to a rise in sea level.
Conservative models project a half-meter (roughly twenty inches, or the height difference between Shaquille O’Neal and Muggsy Bogues) average increase in sea surface height by the end of the century. San Francisco is anticipating a 14-inch rise by 2050.
A couple of feet may not seem like much until you consider how many people are perched along the world’s coastlines. Six hundred million people face direct displacement by flooding; many more will lose food supplies as saltwater intrudes into low-lying soil. Add changing weather patterns and amped up storms to the mix, and whole cities could be inundated by storm surges.
In San Francisco — and around the country — we have the luxury of combating global change. Collectively, we can afford to build, bulldoze and bludgeon our shores into a semblance of stability. But I’m not so sure I’d like to live in that concrete fortress. Following the sand inland is much more my cup of tea.
Holly welcomes questions, comments, and running buddies at hollyvm “at” stanford “dot” edu.