A person walks into the path of blowing sand on the crest of a dune in Chile's Atacama Desert. Photograph by Joel Sartore, National Geographic

By Ker Than for National Geographic News
October 18, 2010 Around the world, surface winds are slowing down, a new study says. Strangely enough, the alleged culprits aren’t new buildings but new trees. The easing breezes—if also detected higher up—could affect movements of air pollution but may not necessarily give the wind power industry a case of the doldrums, experts say. For the new study, published Sunday by the journal Nature Geoscience, scientists analyzed nearly 30 years’ worth of wind speed data collected from more than 800 land-based weather stations, mostly in the Northern Hemisphere, where long-term wind-data collection has been most reliable. The average annual surface wind speed in countries in mid-northern latitudes—including the United States, China, and Russia—had dropped by as much as 15 percent, from about 10.3 miles (17 kilometers) an hour to about 9 miles (14 kilometers) an hour, the study found. Wind speeds in the Southern Hemisphere are probably slowing too, the team speculates. Winds in different parts of the world are coupled, so average wind speed can’t decrease at one latitude but increase in another—a hypothesis perhaps underscored by Australian data also showing mysteriously slowing surface winds. If wind speeds higher in the air are also slowing down, that could affect the spread of atmospheric pollutants or even the dispersal of windblown seeds, said study leader Robert Vautard, a researcher at the Climate and Environment Science Laboratory in France. “We are not saying it’s a good or bad thing,” he added. “We are just observing it and trying to explain it.” … But reforestation can explain only about 60 percent of the wind speed reductions, the study says. Changes in air circulation due to global warming may be responsible for the rest, but more studies are needed to be sure, according to Vautard. “So far we only have pieces of the puzzle,” he added. “We have not completely attributed the phenomenon.” …

Winds Slowing Around the World, Study Suggests via Apocadocs