Storm Warnings | EcoCenter: Oceans | Smithsonian

Storm Warnings

Is global warming to blame for the intensity of recent Atlantic hurricanes? While experts debate that question, they agree that more devastating tempests are headed our way.

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Plunging through a stand of poison ivy, Jeffrey Donnelly wades into Oyster Pond and begins assembling a crude raft. He and two colleagues lash a piece of plywood on top of two aluminum canoes and push off, paddling their makeshift catamaran toward a fringe of scrub bordering this brackish pond in Woods Hole, Massachusetts. Donnelly whips out a hand-held GPS receiver and takes a reading. "This is the place," he says. After setting out a web of anchors, the team settles into hours of monotonous labor. They push long pipes through nearly 25 feet of tea-colored water into thick layers of sediment below. The moans of foghorns drift in from Vineyard Sound, and mist rises and falls like a scrim.

"One, two, three!" Donnelly brings up a five-foot-long core of sediment encased in transparent plastic. "Look!" he whoops, pointing to a thick deposit of yellowish sand bracketed by black-brown pond muck. "That’s a hurricane!"

Donnelly, a geologist and paleoclimatologist at the Woods Hole Oceanographic Institution, has been prowling the lakes and marshes that dot the New England coastline for nearly a decade, assembling a record of hurricanes going back hundreds of years. The record takes the form of sand washed inland by monstrous storm surges.

What Donnelly is staring at now may be the gritty calling card of the Great New England Hurricane of 1938, which lifted up a dome of water 20 feet high as it slashed its way from Long Island to Cape Cod with Katrina-class force, leaving at least 680 people dead and tens of thousands homeless. Or perhaps the sand is from the Great Colonial Hurricane of 1635, which ravaged the fledgling Plymouth and Massachusetts Bay colonies, or the Great September Gale of 1815, which put Providence, Rhode Island, under more than ten feet of water.

Hurricanes that intense may not threaten Northeastern states as often as they do Louisiana, Florida or the Carolinas, but they aren't as rare as the people living along the coastline from Virginia to Maine might like to think. The sediment cores Donnelly has collected indicate that devastating hurricanes have slammed into the Northeastern seaboard at least nine times in the past seven centuries.

Understanding hurricane history takes on new urgency in the wake of the worst hurricane season on record. In 2005, the Atlantic basin produced more tropical storms, 28, and more full-blown hurricanes, 15, than any year in at least the past half century. Last year, memorable for its four major hurricanes, could also lay claim to three of the six strongest storms on record. And as bad as it was, the 2005 season was just an exclamation point in a decade-long hurricane onslaught, which will end—well, scientists can't agree on when, or even whether, it will end.

That's because late last year, around the time Hurricane Katrina stormed ashore in Mississippi, climate scientists were engaged in an urgent debate. According to one group, the increasing intensity of Atlantic storms comes from a natural climate cycle that causes sea surface temperatures to rise and fall every 20 to 40 years. According to another group, it comes from human emissions of carbon dioxide and other greenhouse gases. (So far, no one has linked the number of hurricanes to global warming.) In the first scenario, the fever in the Atlantic might not break for another decade or more; in the second, it might last for the rest of this century and beyond.

Evidence from sediment cores collected by Donnelly and others hints that long before industrial activity began pumping the air full of heat-trapping gases, particularly carbon dioxide, naturally occurring climate shifts influenced hurricane activity, either by changing wind patterns that steer hurricanes toward or away from land, or by altering the frequency and intensity of the storms themselves. Cores collected by Louisiana State University geographer Kam-biu Liu from four Gulf Coast lakes and marshes, for example, show that major hurricanes struck that region three to five times more often between 3,500 and 1,000 years ago than in the ten centuries since. Donnelly, for his part, has pieced together a similar record in Vieques, Puerto Rico; there, the active hurricane pattern starts 2,500 years ago and ends 1,500 years later. But, Donnelly cautions, these are just a few scattered jigsaw pieces. "We have to collect a lot more pieces in order to put the puzzle together." And that is why he’s out in the middle of Oyster Pond, coring his way through time.

I am to meet Donnelly the next morning at his lab. As a strong thunderstorm rolls through, Donnelly pedals in on a mountain bike looking like a sopping wet Power Ranger. Inside a cavernous room, chockablock with tools, the first core is standing on end, giving the slurry in the topmost foot or so a chance to settle. On the floor lie two long cores in aluminum pipes.

Using a hacksaw, Donnelly cuts the cores into shorter lengths, then uses a table saw to slice them in half lengthwise. Water puddles onto the floor, and we smell rotten eggs—hydrogen sulfide produced by microbes that live within the pond's deep, dark pockets of organic debris. Donnelly opens one of the cores, and I can see a sequence of sandy strips, the spoor of ancient hurricanes.

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