Not a new phenomenon
“Dust deposition on mountain snow cover has occurred throughout much of recent history as demonstrated by annual dust layers in high elevation ice cores, increasing with prolonged or intense drought and land disturbance in source regions” (Painter et al., 2007).
“Like many arid environments, the drylands of the western United States have experienced widespread land-use change over the past two centuries, with rapid acceleration of agricultural and grazing activities following the westward expansion of the United States in the 1800s. Despite growing evidence of the impacts of land use on wind erosion of soils around the world, the history of human influences on atmospheric dust remains poorly documented. Records showing increased dust accumulation in Antarctic ice cores between the nineteenth and twentieth centuries, and evidence for changing chemistry of glacial dust during the twentieth century, suggest higher contemporary atmospheric mineral aerosol loads than during the pre-industrial period” (Neff et al., 2008).
Although not a new issue, it has gotten worse since records have been kept
“By studying sediment cores from high-elevation lakes in the San Juan Mountains, Jason Neff, a geological sciences professor at the University of Colorado at Boulder, has estimated that the amount of dust falling back to Earth now is up to five times as much as the amount before Europeans arrived. Dust deposition was even greater around the turn of the last century, before the government put restrictions on grazing” (Eilperin, 2009).
“In two alpine lakes, sediment accumulation rates over the past ~150 yr are more than five times greater than average accumulation rates over the past 5,000 yr, on the basis of radiogenic 210Pb and 14C dates” (Neff et al., 2008).
“…the period of increased sedimentation rate is contemporaneous with an intensification of western US land use, and particularly livestock grazing activities, that began in the early 1800s” (Neff et al., 2008).
““From about 1860 to 1900, the dust deposition rates shot up so high that we initially thought there was a mistake in our data,” said Neff. “But the evidence clearly shows the western U.S. had it’s own Dust Bowl beginning in the 1800s when the railroads went in and cattle and sheep were introduced into the rangelands”” (EurekAlert, 2008).
“While droughts can trigger erosion and increased dust deposition, western U.S. droughts during the past two centuries have been relatively mild compared to droughts over the past 2,000 years, Neff said. Instead, the increased dustiness in the West coincides with intensive land use, primarily grazing, according to radiocarbon dating and lead isotope analysis of soil cores retrieved from lakebeds, he said” (EurekAlert, 2008).
“The study also shows more than a five-fold increase in nutrients and minerals in the lakebed sediments during the last 150 years, said Neff. Increases in nitrogen, phosphorus, potassium, calcium and magnesium – byproducts of ranching, mining, and agricultural activity – have been shown to change water alkalinity, aquatic productivity and nutrient cycling” (EurekAlert, 2008).
“Overall, nearly 70% of the natural ecosystems of the western United States have been affected by livestock grazing, resulting in loss of soil stability and increases in wind erosion of soil. The extensive degradation of western US rangelands led to the Taylor Grazing Act of 1934, which imposed regulations and restrictions on grazing activities in these rangelands. At about this time the mass accumulation rates of the lake sediments begin a moderate decline, which persists through the second half of the twentieth century” (Neff et al., 2008).