Dust increase chokes US west:

In the 1930s, fierce dust storms created by drought conditions and farming techniques that led to soil erosion swept the prairies of the western US, causing widespread ecological calamity. But this so-called ‘Dust Bowl’ period was just a small example of a huge increase in dustiness in the US west in the past 150 years due to human activities such as settlement,farming and livestock grazing,scientists said.Starting from about 1860 to 1900,the dust deposit rates surged at least fivefold over previous levels-coinciding with a upswing in human activities that kicked up dust into the atmosphere, scientific dating techniques showed. The researchers said droughts in the past 150 years were not sufficient to explain the dust level increase because there had been worse droughts prior to that period.