The world is getting breezier, according to a new study, which found a slow but steady increase in top wind speeds across the oceans over the last 23 years.
Although global warming is a suspect, researchers can’t say for sure whether climate change is behind the growing gusts. The trend could simply be part of a natural and long-term cycle that pushes wind speeds both up and down over the course of many decades.
But if winds continue to pick up at the same rate, hurricanes could become far more damaging by the middle of the century. Among other implications, engineers would need to rethink they way they plan coastal and offshore structures.
“We may be observing an upward increase of something that, in the future, will go down again,” said Ian Young, a physical oceanographer at the Australian National University in Canberra. “However, the fact that we’re seeing this on a global basis in both the northern and the southern hemispheres suggests it may be a long-term trend rather than an oscillation. If we’re going to design things in the future, we may want to actually factor in oceanic waves going up.”
Winds over the oceans directly influence wave heights, and orbiting satellites use altimeters to regularly monitor both. Scientists are interested in these measurements because they affect the exchange of heat and gasses between water and sky. Winds also influence the frequency and strength of major storms.
Various studies have shown upward trends in wind speed over the last decade or two, but all of those projects have focused on limited parts of the world. Young and colleagues wanted a more global perspective.
The researchers gathered data from seven satellites taken between 1985 and 2008. Then, they used five independent statistical techniques to combine, calibrate and calculate the records. All five produced the same result.
Despite large seasonal variations, the mean wind speed over the oceans hasn’t changed much in the last two decades, the researchers report today in the journal Science. Speeds of the fastest winds, though, have risen by about half a percent each year, and heights of the biggest waves have risen by between a quarter and half a percent each year. Those trends have been strongest in the southern hemisphere.
Over time, these kinds of small and incremental rises add up. Off the coast of Southern Australia, for example, the tallest 1 percent of waves have risen from five to six meters (16 to 20 feet). The most extreme winds are now blowing 10 percent faster than they used to.
Ongoing changes in the most extreme conditions could have major consequences, said Mark Donelan, an oceanographer at the University of Miami in Florida. If winds continue to get gustier at the same rate over the next 50 years, for example, the destructive forces of Category 5 hurricanes would multiply.
“They’d go from knocking over 90 percent of the buildings to knocking over all the buildings,” Donelan said. “It’s hard to say how much more damage would be done. But it definitely wouldn’t be a good thing.”