"The number of dust storms is rising. What does that mean?"

"The American West is becoming an increasingly dusty place: So-called "dust emissions"—including giant dust storms reminiscent of the Dust Bowl era—have increased in the past 17 years, according to a new study.

Scientists understand only some of the reasons for the surge.

'About half of the changes [we see] are due to drought and high-wind events. We're seeing more of these larger storms that can move dust,' said Jason Neff, a geological scientist at the University of Colorado at Boulder and a co-author of the study. 'The other half [of dust storms we see remains] unexplained, but candidates include off-road vehicle use, oil and gas development, urban and rural development, and grazing.'

In the new study, published online in the journal Aeolian Research, Neff and his team calculated the amount of dust blowing across the United States by estimating the amount of calcium-containing dust particles colliding with water droplets in the atmosphere."

Ker Than reports for National Geographic News June 12, 2013. [2]