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Scientists look at whether climate change is causing bigger ocean waves

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By Les Blumenthal
Saturday, December 11, 2010; 7:08 PM

It's one of the most treacherous stretches of water in the world, where 1 million cubic feet of water a second collides with 20- or 30-foot ocean swells over a four-mile stretch of shifting sand.

A small band of pilots braves often-dangerous conditions to guide ships across the Columbia River bar spanning Washington and Oregon.

The pilots who work the "Graveyard of the Pacific" have a deep respect for the relentless forces they face daily as they ride out to tankers, bulk carriers, car carriers, and cargo and passenger ships standing offshore. They commute in 72-foot self-righting boats that can roll over 360 degrees as winter gales and sometimes hurricane-force storms blast out of the North Pacific.

The pilots also confirm what marine scientists have just started talking about: Ocean waves are becoming bigger and more powerful, and climate change could be the cause.

"We've been talking about it for a couple of years now," said Captain Dan Jordan, who served in the merchant marine for 30 years before becoming a Columbia Bar pilot. "Mother Nature has an easy way of telling us who is in charge."

Using buoy data and models based on wind patterns, scientists say the waves off the coast of the Pacific Northwest and along the Atlantic seaboard from West Palm Beach, Fla., to Cape Hatteras, N.C., are steadily increasing in size. And, at least in the Northwest, the larger waves are considered more of a threat to coastal communities and beaches than the rise in sea level accompanying global warming.

Similar increases in wave height have been noticed in the North Atlantic off England.

Unclear is whether the number and height of "rogue" waves beyond the continental shelf have increased. The existence of such freak waves, which can reach 100 feet or more in height and can swamp a large ship in seconds, wasn't proved until 2004, when European satellites equipped with radar detected 10 of them during a three-week period. According to some estimates, two merchant ships a month disappear without a trace, thought to be victims of rogue waves.

"Obviously, this is an issue we are interested in," said Trevor Maynard of the emerging risk team at Lloyd's of London, which tracks global climate change developments. "We are seeing climate change fingerprints on a lot of events."

Increasing averages

Since the mid-1970s, buoy data show the height of the biggest waves off the Northwest coast has increased an average of about four inches a year, or about 10 feet total, according to Peter Ruggiero, an assistant geosciences professor at Oregon State University and the lead author of a study published recently in the journal Coastal Engineering.

Ruggiero and his colleagues also estimated how high a 100-year wave might be. These would be the largest waves expected to come along every 100 years. The estimate has increased 40 percent since the 1970s, from 33 feet to 46 feet. Some calculations estimate that a 100-year wave might be 55 feet high, taller than a five-story building.

"We are assuming the trends will increase in the future," Ruggiero said.


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