Climatide

This is the third story in our four-part series Cape Change: A Local Perspective on Global Warming.

• Cape Change: A local perspective on global warmingPart 3: Cape Cod’s shifting sandsDownload

NASA

The 'hook' or 'fist' of Provincetown is one of the few parts of Cape Cod that is growing.

The tiny village of Woods Hole is a mish-mash of million-dollar homes and renowned scientific institutions perched on the southern tip of Cape Cod. Much of the coast is clad in sea walls and jetties intended to hold the line against the forces of erosion. But they can’t stop the rising sea.

At a recent workshop hosted by Waquoit Bay National Estuarine Research Reserve, Greg Berman of Woods Hole Sea Grant showed off a three-dimensional animation of what a popular restaurant perched atop one of those seawalls might look like under various sea level rise scenarios.

“So here we are at normal high tide,” he said, walking attendees through the animation. “You can bump it up to one foot of sea level rise. Three feet sea level rise. And then six feet of sea level rise.”

Sea level around Cape Cod has already risen one foot in the past century, and that rate is increasing as global temperatures rise and melting of the world’s major ice sheets accelerates. Three feet of additional rise by 2100 is now considered a moderate to conservative estimate, and six feet is within the realm of possibility. At that point, the restaurant in the animation would be flooded at high tide. Add storm surge from a major storm, and the computer-generated water levels rise to absurd heights half-way up the first-story windows – a prospect that elicited nervous laughter from workshop attendees.

“So really is it worse getting flooded to here,” asked Berman. “Is that going to matter too much more?”

All joking aside, Berman says the animation should be taken with a grain of salt. For one thing, any building that filled with water at every high tide probably wouldn’t be left standing there. Still, the images do drive home the point that the Cape’s heavily developed coastlines are highly vulnerable to rising seas. But climate change and sea level rise are nothing new for Cape Cod.

“In geology, we’re always concerned about changes,” explains Graham Giese, co-founder of the Provincetown Center for Coastal Studies. “And things are always changing at all kinds of scales. And with Cape Cod geology, the Cape is a product of climate change.”

Cape Cod’s geological backbone is basically a pile of rocks and rubble carried here by a glacier during the last Ice Age, then left behind when a period of global warming forced that glacier into retreat around fifteen thousand years ago. As temperatures rose and glaciers everywhere melted, sea level rose hundreds of feet. Then, five or six thousand years ago, sea level rise slowed to a pace that approached stability.

At that point, the outer Cape looked more like a triangle than the narrow ‘arm’ so familiar today. The tip of the triangle would have been somewhere around High Head, in Truro. The ‘hook’ or ‘fist’ that is modern-day Provincetown didn’t even exist. And off to the southeast of the Cape, the highest parts of George’s Bank were still dry land.

“George’s Bank went underwater – we think, more or less – about six thousand years ago,” says Giese. “And that change was enough to initiate the Provincelands Hook building.”

With George’s Bank flooded, southeasterly waves began to pound the outer Cape pushing sand from the Atlantic-facing beaches north along the coast, where it began to pile up. To this day, Provincetown continues to grow at the expense of the beaches to its south. And that process is likely to accelerate as rising sea level exacerbates erosion. Provincetown’s growth is only possible because the beaches being eroded are part of Cape Cod National Seashore – what Mark Adams, a geographic information specialist with the National Seashore, calls “one of the few long stretches of coastline in the North Atlantic that’s unaltered, that’s not hardened, that doesn’t have a lot of structures on it.”

The lack of development means there are few homes or roads to worry about. It also means the beach is free to move naturally, maintaining the same shape and character as it shifts landward. That’s a distinct difference from many beaches on Cape Cod, which are disappearing as neighboring seawalls or jetties starve them of much-needed sand.

“So we’re in a fantastic position,” says Adams, “because we can watch it erode, we can measure it, we have this exciting laboratory for change here to see nature in action. And it’s not a crisis for us, in that sense.”

That’s a luxury shared by few other spots on Cape Cod or, for that matter, the east coast. And it hints at what many scientists say is the only permanent way to cope with rising seas – get out of the way, and let nature take its course.

More Cape Change stories:

• Warming, more acidic oceans threaten New England’s fisheries
• Mild winter highlights rift between climate scientists and the public