At several spots along California's stubbornly wild 24.8-mile Lost Coast National Recreation Trail, hikers consult tide tables to time their passage across narrow strips of cobbled beach where waves crash against rocky headlands for 18 or more hours a day. The strategizing is just one of the many ingredients–along with fresh bear tracks in the sand, photogenic sea stacks, and edge-of-the-world campsites–that make the coastal experience so intoxicating. But it could all become a memory in your lifetime.
Within the next century, coastal marshes, wetlands, and seaside trails across the Gulf Coast and up the eastern seaboard–from the Everglades (see page 79) to Assateague Island to Cape Cod–will be dramatically altered, if not submerged. The Lost Coast, Olympic's shoreline, and Vancouver Island's precipitous West Coast Trail will get pinched, too.
How will it happen? "People think of sea-level rise as a gradual, constant process, but it often occurs in fits and starts," says Hal Wanless, chairman of Miami University's Geological Sciences Department. From his research on reefs and sea level history, Wanless has concluded that ocean levels may remain stable for centuries, then suddenly jump 10, 20, even 30 feet within a 100-year span, or even decades, due to shifts in ocean currents and ice-shelf collapses.
"It happened often in prehistoric times, and it's no stretch at all to predict it again, particularly with the [global warming] effects we will see soon, like large increases in methane generated by thawing Arctic permafrost," Wanless says. "I've been studying sea level fluctuations since 1980. We're only now starting to realize that climate change is happening much faster than we expected back then, and the concept of linear, gradual change is inaccurate."
While beaches and low-lying wetlands are the most obvious at-risk spots, they're not the only ones. National seashores along the Atlantic are already seeing radical change. Assateague, a barrier island off the Maryland coast, has moved its visitor center inland three times. Along the Pacific, coastal trails will be squeezed between sea and bluff by even modest sea level rises. If the cliffs don't erode as fast as the sea rises, these paths, currently a mere foot or two above mean sea level, will rapidly vanish.
The U.S. Geological Survey has rated more than half of Olympic National Park's 65 miles of coastline as high-risk. Especially vulnerable are the hiker-friendly Rialto, Ruby, and Shi Shi Beaches. The USGS also identified the beaches on the west side of Point Reyes National Seashore and about half of the 250 miles of shoreline around Channel Islands National Park as highly sensitive.
"There are dramatic changes already happening," says Wanless, "and if we don't get our greenhouse emissions under control, our outlook for this next century will be very wet along our coasts."