Wednesday, December 24, 2008

Are Waves Getting Bigger?

From Wired Science

By Alexis Madrigal December 19, 2008

Surfer

SAN FRANCISCO — The largest waves in the Pacific Northwest are getting higher by seven centimeters a year, posing an increasing threat to property close to the shore. And the strange part is: Scientists aren't sure why.

Oregon State researchers found that the danger to property from these larger extreme waves will outweigh the impacts of rising sea levels caused by global warming over the next several decades.

"Over a decadal scale, the increases in wave height ... have significant impacts on both erosion hazards and coastal flooding hazards and those currently exceed the influences of sea level rise," said Peter Ruggiero, "And they probably will over the next decade or two unless something drastic happens."

The world's oceans are in serious turmoil. Fisheries have collapsed across the globe and scientists predict that rising global temperatures — particularly nearer the poles — will melt the polar ice caps and cause sea levels to rise. Waves, however, are the bringers of this bad oceanic news onto human-inhabited shores and evidence that extreme wave heights are increasing in some regions has remained relatively under the radar.

"This is the first time I've seen a comparison between wave height and sea level," said Sultan Hameed, an atmospheric scientist at Stony Brook University, who organized the American Geophysical Union annual meeting session at which Ruggiero presented. "That was excellent analysis."

Unlike sea level, the current data suggests that wave heights are not increasing uniformly across the globe. However, many regions lack the right data to do proper analysis. Bigger wave heights off the coast of Oregon were first discovered just a few years ago by other OSU scientists. They had the advantage of working with the unique dataset created by the Pacific coast's longest-floating buoy; it's been gathering data on wave heights for over 30 years.

"This is high quality data and you didn't have enough data to do this kind of analysis until very recently," Ruggiero said.

Despite the clear wave-height increase in the data, particularly of the largest waves, Ruggiero and his colleagues still can't explain it.

"I don't think we do know exactly why wave heights are rising," Ruggiero said. "Some people have linked it to global warming and changes in the storm tracks. Others have linked it to dust from China. I don't have a great answer."

If it is linked with global climate change, rising sea levels could combine with increasingly big waves to wreak havoc on coastal areas around the middle-latitudes where the wave height effect seems to be strongest.

That's why it's become imperative to figure out what has driven the changes in the wave patterns along the northwest coast of North America over the last thirty years.

Hameed said that linking the wave height increases to wind velocity changes in the global climate could give the work international impact — particularly in places where detailed wave data isn't available. 

"Wind data are available over a much larger domain," he said.  "If you find coherence between changes in wind speed or direction and wave height, you can extend the analysis [to other areas]."

Image: dennis/Flickr. A surfer at Mavericks, where the waves are already plenty big.