Offshore wind speeds have increased during the past 20 years, but the implications for the wind power industry are unclear. Credit: flickr/~Bob~West~
If you think of climate science as a monumental edifice — a skyscraper, say, which represents a complete understanding of Earth’s climate system — then the building is still under construction. The foundations are solid, and so are most of the lower floors, but the upper levels are still being assembled brick by brick as new information about how the climate actually works is gathered, interpreted and fitted with what's already there.
But while some bricks slide right into place and push the structure toward completion, others — well, it’s not obvious how they fit, or whether they fit at all. And a new report appearing in the current issue of Science is still in the uncertain category. A team of researchers based in Australia has used satellite measurements over the past two decades to look for trends in wind speeds and wave heights in the world’s oceans, and concluded that both have increased — the winds more than the waves, and with the greatest increases for the most powerful winds and the highest waves.
So far so good. But what exactly does it mean? That's were things get more difficult, on all sorts of levels. Winds are a good thing, for example, if you want to build wind turbines in order to generate low-carbon electricity. Some studies have predicted that wind speeds could drop, on average, in a warming world, so this new result might seem to be a pleasant surprise.
Or not, says Cristina Archer, a climate scientist at California’s Chico State University who studies wind patterns and wind power. “It’s potentially good news,” she says, “but caution needs to be exerted for several reasons.”
First, she points out, the study focuses on wind speeds within 10 meters, or about 33 ft., above the ocean surface. But offshore wind turbines — the kind currently being considered for locations up and down the East Coast — are more like 80 or 100 meters high. “Are the winds at those heights increasing too?” she wonders. “If I were to make an educated guess, I’d bet they are.” But educated guesses sometimes turn out to be wrong.
Another potential problem: wind turbines have to shut down when wind speeds are too high, to avoid damage. So the fact that it’s extreme winds that are seeing the greatest increase isn’t the happiest news. Beyond that, the effect of stronger winds seems to be greater toward the centers of the oceans — the places, in other words, where wind turbines aren’t being built at this point.
The authors acknowledge, moreover, that they have no explanation for why winds and waves have gotten stronger. The study covers only 20 years or so because that's how long satellites have been looking globally at winds and waves; before that, scientists had to rely mostly on observations by ships, which are much spottier and more random. So the increase could be part of a long-term climate trend, or it could be a natural cycle. If it’s the latter, then oceanic winds might well weaken again over the next 20 years.
And we’re not done yet: a study published last year is only the most recent to suggest that winds over land — where most wind turbines are now located — have actually slowed down in the Northern Hemisphere during the past several decades. But that may not be climate-related either: the authors attribute much of the slowdown to an increase in “surface roughness” —which simply means more trees and other vegetation to catch and slow down near-surface winds.
Meanwhile, Iowa State University researcher Eugene Takle, co-author of an earlier studypointing to slowing winds in the U.S., told the Associated Press that higher winds over the oceans could lead to more evaporation. That could ultimately trigger more rain.
The bottom line here is that there’s no bottom line, not even a hint of one at this point. But that’s how science works: sometimes it’s not clear at first whether a new result will ultimately turn out to have any value at all. And sometimes, despite that initial lack of clarity, it turns out to be the first hint of something that ends up being truly important.