Climate Change = Slower Wind?

This summer scientists published the first study that comprehensively explored the effect of climate change on wind speeds in the U.S. The report was not encouraging. Three decades’ worth of data seemed to point to a future where global warming lowers wind speeds enough to handicap the nascent wind industry. But the real story, like so much in climate science, is far more complex.

The study of decreased wind speeds came from a team led by Sara Pryor, professor and chair of the atmospheric science program at Indiana University. It examined wind speed data from hundreds of locations across the U.S. The team attempted to correct for any change in instrument position (such as what would happen if an airport places its anemometer atop a new control tower) and calculated for each site the average annual wind speed. Pryor and her colleagues found that in most of the U.S. wind speeds appear to be waning, in many locations by more than 1 percent a year.

The decline has the potential to be especially pernicious because turbines are exponentially sensitive to changes in wind speed. If the wind blows just 15 percent faster, a turbine will produce 50 percent more power. Conversely, a drop in average wind speed will significantly reduce the power output. Most of the locations that showed the most prominent decreases in wind speeds are strung along a corridor stretching from Texas to the Great Lakes that is home to 60 percent of the nation’s installed wind power.

Yet the situation may not be as dire as the data imply. Direct observations of wind speeds are inherently problematic. Anemometers are far less accurate and consistent than thermometers, Pryor says. In addition, almost all the locations used in the study are close to fast-growing urban areas that can alter wind patterns in unpredictable ways. And unlike temperature measurements, which in some locations stretch back 150 years, relatively accurate and widespread wind measurements began only in the 1970s—hardly enough time to pluck a subtle trend out of noisy data.

Because direct measurements of wind speeds are so unruly, Pryor’s team also tracked indirect measurements. These come from surface temperature and pressure records as well as balloon and satellite surveys. Computers crunch the data to produce a rich series of atmospheric portraits—a way to measure wind speeds without measuring the wind. This “reanalysis” data showed no change. Says Pryor:

“If you have a mechanism causing your wind speeds to change”—global warming, for instance—“it should be evident in both the observations and in the reanalysis data.” If only one out of the two shows an effect, no one can say for sure what is going on.

Read more at Scientific American »